DinoGoss

The Debate: Newt Gingrich vs. Jack Horner

2012-01-22T05:33:00.000-08:00

This is something I had completely missed until my wife found it linked to on a political blog a few weeks ago. Filmed in 1998, it's a pretty awesome hour-long video of a debate held between paleontologist Jack Horner and then-Speaker of the House Newt Gingrich. The topic: "Were Tyrannosaurus rex active hunters or pure scavengers?" What else?

The debate is actually a follow-up to a previous forum Gingrich did with Horner, both as fundraisers for the Museum of the Rockies. Gingrich, it seems, is an avid armchair paleontologist.

It looks like C-SPAN doesn't let you embed videos, so here's a link to the full debate: http://www.c-spanvideo.org/program/111009-1

What's fascinating about this debate is how it illustrates almost point-by-point a lot of issues I've seen cropping up online lately about the nature of scientific hypotheses, and in particular Horner's approach to them. As some of you may know, Horner recently backpedaled on the whole tyrannosaurs-as-pure-scavengers hypothesis, saying that, from the start, it was merely an attempt to illustrate how the scientific process is supposed to work as opposed to how it often goes in paleo. (Horner explicitly renounced the pure scavenger theory in, among other places, an October 2009 interview on the outstanding Skeptics Guide to the Universe podcast).

Watching this debate unfold, two things surprised me more than I thought they would. First, wow, Gingrich really did his research for this! He comes fully prepared with several examples and analogues to modern ecosystems, many of the same arguments I've seen used in forum debates on this topic, including the fact that there are few if any pure scavengers among modern animals, that hyenas will often take live prey, that vultures can get away with it due to their ability to fly over enormous areas in search of carcasses, etc. Newt knows his stuff, and handily pummels Jack in the debate (though Horner appears to be acting as sort of a gracious host, lobbing him a lot of softballs and overall "letting" Gingrich win.)

The second thing, though, is in Horner's closing arguments. Gingrich easily beats Horner by throwing out analogy after analogy, employing simple logic to demonstrate why his hypothesis "T. rex were not pure scavengers" is superior. But Horner points out, in a way, that it doesn't matter. Debates are antithetical to science. Empirical science is in no way about who has the better argument. It's about who has a more rigorous, testable and ultimately falsifiable hypothesis and can support it with more data, not better analogies.

I have been a T. rex as predators booster since I was 6. But after watching this debate, it is clear to me that Horner has always had a better, more scientific hypothesis and overall approach to the science of paleontology. He is correct that the default assumption has always been that T. rex were active hunters. But at the end of the day, assumptions are not science, and it's a little bit appalling that this assumption has been made an implicit basis of so many statement published in peer-reviewed scientific papers without question. You can never, ever disprove the hypothesis that T. rex were active hunters without a time machine, because it's logically impossible to prove a negative. That's why in science, if we have a positive statement as our hypothesis, it's often necessary to take the null hypothesis (the opposite statement to the one we are testing) and attempt to disprove that in an attempt to support the actual hypothesis. Like string theory, T. rex-as-hunters is an idea that makes logical sense on paper but is unfalsifiable, and therefore not science--just educated speculation.

However, Horner's hypothesis can and has been disproved. We now have evidence of healed-over T. rex bite wounds that show that at least occasionally, they bit living prey species. Does this prove T. rex were active hunters? Not necessarily, but it's a major piece of data against Horner's scavenging hypothesis, and that is actually the strength of Horner's position--that it can be tested and shown to be wrong. In science, it's not always better to be right than it is to be rigorous.

So while he may have won the debate, Gingrich was right for the wrong reasons, while his opponent Horner was wrong for the right reasons.

Bruhathkayosaurus is Dead. Again.

2011-12-21T11:38:00.000-08:00

Above: Working sketches for a speculative B. matleyi reconstruction by Steve O'Connor. Click here for Steve's final drawing.

I don't know how common this knowledge is, but this is the first I've heard of it so humor me while I mourn the possibility of ever re-assessing the intriguingly large sauropod specimen known as Bruthathkayosaurus matleyi.

B. matleyi was known from fragmentary remains of the pelvis and limb bones found in the Tiruchirappalli district of Tamil Nadu, India. It was first described by Yadagiri and Ayyasami in 1989 as species of giant allosauroid. This classification was widely doubted online, but little follow-up work was ever done. The initial description is widely regarded as exceedingly poor in quality and not much can be discerned about the specimen due to poorly detailed drawings and insufficient text. Tom Holtz has even stated that "the hypothesis that this is no more than petrified wood has not been falsified yet to my satisfaction." However, Mickey Mortimer later noted that the tree trunk hypothesis "is questionable given the non-cylindrical bones preserved such as the ilium. Additionally, Chatterjee has personally examined the fossils, and while he has a bad record of misidentifying taxa, I give him enough credit to not confuse a tree for a limb bone."

Sankar Chatterjee did indeed apparently examine the material and told George Olshevsky and Tracy Ford that he believed it to be a titanosaur, as reported in 1999 here.

Holtz responded to these appeals by noting that "not all units are the Dinosaur Park or the Djadokhta. In some preservation is really, really, really crappy. You might get all sorts of authigenic growth on the fossils, or alteration of the original material. In outcrops like that, it isn't out of the question to be fooled into thinking bone is wood and vice versa, especially from simple surficial appearances. This is why a section of the fossil would help resolve if it is bone or wood." So, there's that. We'll now never be able to take that section.

While B. matleyi was a near-mythical celebrity among "semi-apocryphal gigapods", its legend loomed larger than (published) reality. While most online sources (such as the DML posts quoted above) had long since agreed that the specimen was probably a gigantic sauropod and not a gigantic carnosaur, no actual published reference to the species as a sauropod existed until five years ago (Krause et al. 2006).

And what a sauropod it was, maybe! Obviously with such a paltry footprint on the scientific literature, reliable size estimates for such a poorly described specimen are hard to come by. Luckily, some researchers have done the best they could with the available data and determined that, if B. matleyi was indeed a titanosaur with similar proportions to say, Argentinosaurus, it would have been very large indeed. Matt Wedel over at SV-POW has estimated the size of this animal in life at 139 tons. Mickey Mortimer has estimated its length at up to 34 meters. That would position it as one of the largest species of land animals ever, second only to Amphicoelias fragillimus, possibly.

And now, it appears that B. matleyi has suffered the same fate as its atlantosauroid rival for the record. In the comments at another SV-POW post about semi-apocryphal gigapods, Wedel reports that the type and only specimen of B. matleyi was at some point washed away in a flood.
UPDATE: Thanks to Fabrizio in the comments pointing out a source closer to the horse's mouth. Artist "palaeozoologist" at DeviantArt posted an apparent personal correspondance from Kumar Ayyasami last January, in which he reported that the specimen was lost in heavy rains several years ago. (There's some more discussion of the specimen and the author's publication record here, including the suggestion that Dr. Ayyasami may now be deceased--that is, if you can get past the inexplicable Ali G speak). So it sounds like not only was the specimen poorly described, but nobody had bothered to actually collect it from the field site in the ~15 years since its discovery, and it was (predictably and inevitably) lost to erosion.

Any hope of verifying the stupefying claims about this species' size now seem to be lost. And unlike A. fragilimus, which was described and well-illustrated by a mostly reputable source with no obvious errors, the poor state of the B. matleyi description will forever doom this creature to the realm of dubious claims. After all, given the poor state of the description, it seems possible that a simple scale bar error or other mix-up could have tainted the data, and therefore all of our size estimates.

So here's to Bruthathkayosaurus matleyi, a beast (or possibly, a tree?) that died 70 million years ago, raised its spectral head (or crown?) again for one tantalizing moment and then, like Hitchcock's Ornithichnites, sunk back beneath the earth before we could really learn anything about it.

Waddle, _Achillobator_, Waddle!

2011-12-05T07:56:00.001-08:00

"I've hunted most things that can hunt you, but the way these things move..."
"Fast for a biped?"
"Cheetah speed. Fifty, sixty miles an hour if they ever got out into the open, and they're astonishing jumpers."

This quote from the original Jurassic Park film did much to cement the image of dromaeosaurids, the raptor* dinosaurs, in the public consciousness as fleet-footed hyper predators. Despite being nearly 20 years old, this portrayal has by and large remained unchanged in popular culture, with raptors often stock monsters with near-supernatural murderous abilities in everything from tongue-in-cheek xkcd comics to (I hope) tongue-in-cheek made for SyFy movies.

*Yes, I'm going to commit a cardinal sin and refer to dromies as "raptors". "Raptor" in ornithology refers to most predatory birds, even those that hunt on the ground (the Raptor Research Foundation considers Secretarybirds to be raptors). Since dromaeosaurids were both predatory and birds under any sane definition of the word, there should be no problem referring to them as an extinct group of raptors.

But were raptors really particularly fast? Bipedal running speed in digitigrade animals (that is, those that walk on their toes like birds rather than their ankles like humans) is usually roughly determined by the ratio of the lower leg bones (the tibia/tibiotarsus) to the upper foot bones (the metatarsus). The longer the upper foot is in length compared to the lower leg, the faster an animal could run. Therefore, we would expect the fastest theropod dinosaurs to be those with the longest metatarsi relative to tibiae.

A prime example of a theropod specialized for running very very quickly are the parvicursorines. This specialized group of alvarezsaurids (strange theropodan insectivores with stout, powerful arms each bearing one very large claw) has among the longest lower leg to upper leg ratio of any Mesozoic dinosaur group. Looking at the statistics compiled by Mickey Mortimer at The Theropod Database (a phenomenal resource I turn to so often I really should just make it my browser's home page), the type specimen of Parvicursor remotus (see leg diagram here) has a femur 52.6 mm long, a tibiotarsus about 75.6 mm long, and a metatarsus 58 mm long. The functional lower leg is 113 mm long, well over twice the length of the upper leg. More importantly, the lower leg and upper foot bones were fairly close to being equal in length. This animal was clearly a speed demon.

How does this compare to raptors? If, as Jurassic Park claimed, raptors were exceptionally fast, we would expect them to have similarly long lower legs. The terrifyingly human-sized raptors in JP were a Hollywood invention, but we do know of raptor species slightly smaller and slightly larger than they were.

On the smaller side were the famous Deinonychus antirrhopus. According to TTD, the femora of one relatively complete specimen measured 248 mm, with a tibia 324 mm long, and a metatarsus 151 mm long. Again, the total lower leg length is nearly double the upper leg. But the upper foot bones were only half as long as the lower leg bones.

The "fast raptor" meme was started by John Ostrom himself, when he first described Deinonychus in 1969. This was merely speculation on his part, as the hind limb was not completely known in the first specimens. Ostrom actually changed his opinion in later papers, finding that the femur was shorter than he'd initially thought, and that the foot bones were surprisingly short compared to other dinosaurs. Not only was Deinonychus not particularly fast, it probably could not have been nearly as fast as most other small theropods, including modern flightless birds, let alone cheetahs.

Another very popular type of raptors are advanced giant dromaeosaurines (Utahraptor and Achillobator). I recently found myself revising an older drawing of an Achillobator giganticus, which were, as mentioned above, only slightly larger than the Jurassic Park raptors. Many young dinosaur fans are very attached to these species in part because they're much larger than most other raptors, and because they had a slightly anthropomorphized novel written about them by Bob Bakker shortly after JP was released (Raptor Red). As a result, these big birds have a cachet in the collective consciousness similar to the generally more famous Deinonychus and Velociraptor--that of super-fast, agile and intelligent predators.

However, when finishing up my revised drawing, I had to double check the proportions several times to make sure I wasn't screwing it up. To my amazement, the legs, particularly the lower legs and upper foot bones, looked almost laughably short. Again according to TTD, the femur of A. giganticus measures 505 mm long, the tibia 490 mm long, and the metatarsus a paltry 234 mm long--less than half the length of the tibia. Not only is the metatarsus much, much shorter than the tibia, the entire lower leg in only marginally longer than the femur! The first thing that struck me wen looking at my own reconstruction was that this looked like the dromaeosaurid equivalent of Majungasaurus, those abilisaurids with the ludicrously short legs (which, coincidentally like Achillobator, have been suggested to be made up of chimeric specimens). It is also reminiscint of another stout-legged dromaeosaurid species, Balaur bondoc. While Balaur have been suggested to be possibly herbivorous due to these strange proportions, partial jaws and some teeth of Achillobator confirm that they were carnivores. But with legs like those, it's hard to imagine these creatures behaved the way the public imagines raptors to have done, chasing down fast moving prey. Frankly, it's hard to imagine Achillobator doing much beyond waddling across Nemegtian lake shores hunting turtles in epic slow-motion chases.

For the record, no described specimen of Utahraptor preserves both a femur, a tibia, and a metatarsus, so it's impossible to say whether or not they had the same squat proportions (unless somebody has some more detailed information on the numerous undescribed specimens in the BYU collections). For now, it would be safe to assume that they, too, would have been a laughing stock if they were caught trying to run.

Ok, but why would predatory animals have such stubby legs? There is a lot of evidence that dromaeosaurids were specialized for hunting big game, often animals larger than themselves. Deinonychus are infamous for their association with large ornithopods Tenontosaurus tilletti, and while evidence suggests they mainly targeted juveniles (Forster 1984), these were still much larger in terms of weight than even adult Deinonychus. Velociraptor are known to have grappled with the larger Protoceratops, and even a rumored specimen of a Microraptor apparently preserves evidence that they tackled prey larger than themselves. The short legs, especially the short foot bones, seem to be linked with the function of the large sickle-claw, making lack of speed a trade-off for improved ability to grapple and kill large game. Dinosaurs like Tenontosaurus and Protoceratops probably weren't particularly fast-moving themselves, making this sacrifice in speed worthwhile for the chance to down a massive animal that could provide a whole lot of food.

In the end, while the raptor chase scenes in Jurassic Park remain some of the most exciting parts of the movie, they require a significant amount of disbelief to be suspended; after all, it would be more realistic but slightly less suspenseful if Laura Dern had been able to evade the raptors in the power bunker by simply breaking into a light jog.

An Alternate History for "Archaeoraptor"

2011-11-20T14:30:00.000-08:00

For those who didn't figure it out, yesterday's mystery bird teaser was a bit of a trick question. In fact, the bird, which I restored on a lark when working on other species, never existed at all. It was, in fact, a restoration of the famous fossil chimera, "Archaeoraptor liaoningensis". Two commentors did get it half right, guessing Yanornis, though the long tail would make that identification impossible (as euornithines, Yanornis had short tails with retractable fans of feathers). You'll notice I modified the image a bit since yesterday: Mickey Mortimer pointed out that Yanornis were not fully toothed, and while the premaxilla had teeth, there is a small edentulous anterior portion which may have supported small beaks.

Despite being the most famous fossil forgery to come out of China, the "Archaeoraptor" debacle really is a success story for the peer review process. You can read a summary of the history of the specimen here. The upshot is that several researchers were suspicious of the chimeric specimen to begin with, and though they rather dubiously chose to submit it for publication anyway, their paper was subsequently rejected by two major journals, Nature and Science, before unfortunately being reported on without review in National Geographic magazine.

In fact, it's not surprising that so many researchers were suspicious of the specimen's validity to begin with. At it combines the skull, body and wings of a Yanornis martini (a songlingornithid euornithine) and the tail of a Microraptor zhaoianus (a microraptorian dromaeosaurid), the "Archaeoraptor" specimen would have been a very odd anomaly had it been real, given our knowledge of bird evolution (even in 1999, when it was first revealed to the public). Note that many news reports have stated that the hind limbs of the composite specimen also come from a Microraptor or even a third, unidentified type of bird, Zhao et al. (2002) noted that they also come from a Yanornis martini. Anyway, I broke out Professor Farnsworth's What-If Machine to try to suss out how our current understanding of bird evolution would be different if the composite nature of the original "Archaeoraptor" specimen had never been discovered.

Intuitively, it seems like a bird with the long tail of a dromaeosaurid combined with the advanced wing configuration and well-developed breastbone of an euornithine doesn't make much sense and would have eventually caused a rather extraordinary rearrangement of the bird family tree. To test this idea, I employed the services of phylogeneticist extraordinaire Mickey Mortimer, who had coincidentally just finished coding Yanornis martini and entering it into a combined Theropod Working Group matrix. Mickey very helpfully humored my request and combined the relevant anatomy Yanornis and Microraptor into a single taxon, and plugged the result into a theropod phylogeny which included only other taxa known in 1999.

I'll let Mickey explain the analysis in more detail:

"Okay, so what I've done is taken my Theropod Working Group analysis and restricted it to taxa described by 1999 (when "Archaeoraptor" was supposed to be described) and coded by the TWG [Theropod Working group - Ed.] by 2005. I've also limited it to those characters taken from the first TWG analysis (Norell et al., 2001), since I already posted those results on my blog (http://theropoddatabase.blogspot.com/2011/06/theropod-working-group-matrix-recoded.html) and Scott understandably doesn't want more of the Lori results being distributed before publication [Click here for the scoop on Lori, Scott Hartman's unpublished Morrison troodontid -Ed.]. So data-wise, this is equivalent to results I've already posted and with the exception of new specimens of old taxa (like the new Caudipteryx specimens in Zhou et al., 2000), which would be far too tedious to correct for, is representative of our knowledge in 1999. "Archaeoraptor" is represented by the Yanornis codings mixed with Microraptor tail codings. Many of those Yanornis codings are from specimens besides the Archaeovolans holotype, but I'm not going to take the time to go through and see exactly which characters can be coded from only that specimen. In total, 11 codings were changed between Yanornis and "Archaeoraptor". The entire matrix is 51 taxa and 210 characters."

The result of Mickey's analysis was that "Archaeoraptor" ended up as the sister taxon to Confuciusornis, but with some caveats. First, no other pygostylians (the group uniting Confuciusornis and modern birds)were included, because Confuciusornis is the only pre-1999 taxon coded by the TWG. A complete test of "Archaeoraptor"'s 1999 relationships would require the addition of taxa like Patagopteryx, Songlingornis (which is a potential close relative of Yanornis), Cathayornis, Iberomesornis, etc. Because the only plesiomorphic character of "Archaeoraptor" relative to Yanornis and other euornithines proper are the "longer tail, elongate distal caudal prezygapophyses and rectangular proximal caudal centra", "Archaeoraptor" looks, for 1999 standards, like what we might have expected the sister taxon of Pygostylia to be like. Nevertheless, because the bulk of the specimen is so derived, Mickey reckons the presence of the long tail might not pull it away from euornithines even if other basal pygostylians were included (the long tail would then have to be considered a bizarre reversal).

Mickey also tested a few alternate hypotheses to see how much support they would get. Perhaps the obvious conclusion for a scientists faced with an oddity like "Archaeoraptor" would be that it is probably a sister group to Pygostylia as mentioned above, or somehow intermediate between dromaeosaurids and pygostylians. Mickey tested this by forcing "Archaeoraptor", Confuciusornis, and dromaeosaurs to clade together, which resulted in only three extra steps: this would have been considered a pretty sound hypothesis given the small pygostylian sample. Interestingly, this arrangement would also have resulted in unenlagiines as basal eumaniraptorans and put Archaeopteryx in Troodontidae. Removing "Archaeoraptor" from the mix decreased the likelihood of a Dromaeosauridae+Pygostylia clade by five steps, which Mickey notes is still "plausible" but certainly less likely, and shows that "Archaeoraptor" would have created the kind of link between dromies and more advanced birds touted by the original NatGeo article.

This leads me to speculate that "Archaeoraptor" may have provided "evidence" for the modular evolution of pygostylians directly from some traditional dromaeosaurs. Modular evolution refers to cases where major traits of a descendant group appear in a taxon which simultaneously retains major "primitive" or plesiomorphic traits of the ancestors taxa. One famous fossil example of this phenomenon is Darwinopterus modularis, which is a long-tailed pterosaur with a generally primitive, "rhamphorhynchoid" body plan, but which has a characteristically pterodactyloid-type skull. Had "Archaeoraptor" been accepted as real, we may now have believed that characteristic euornithine traits evolved first in the skull, forelimbs and torso of taxa which possessed otherwise dromaeosaurid tails (this is almost the exact opposite of how we view bird evolution today, with tail shortening coming very soon after the split between dromaeosaurs and pygostylians). As Mickey found, without more discoveries of basal pygostylian and ornithothoracine birds, our cladograms may have rendered dromaeosauridae paraphyletic with respect to modern birds.

Ok, but how would all this stand up over the years after 1999, with more and better specimens of basal birds from a variety of lineages? From Mickey:

"Here's where I'd expect the inclusion of more pygostylians to have an effect though, since right now with only Confuciusornis, "Archaeoraptor" is effectively the most basal pygostylian. But if we had an omnivoropterygid, an enantiornithine, and other ornithuromorphs in there, Yanornis' birdy characters would nest it with those and make its dromaeosaurid-like tail a reversal."

So, the discovery of more and better basal bird specimens may have been enough for "Archaeoraptor" to be regarded more and more as a curious side-branch of the avian family tree, less and less relevent to bird evolution as a whole: a euornithine with some rather inexplicable reversals. This would be similar to the way the relevance of the Piltdown Man to human evolution was exponentially reduced by numerous valid specimens before it was finally found to be a hoax.

It wouldn't be DinoGoss without a discussion of taxonomical minutiae, and this is a question that has popped up on the net several times before: if "Archaeoraptor liaoningensis" included the holotype specimen of Microraptor zhaoianus, why isn't the former an objective senior synonym (that is, a name that is synonymous by virtue of being based on the exact same specimen, not a different specimen later assigned to an already named species) of the later?

The crux of the argument is that the original National Geographic article that released the "Archaeoraptor" name did not satisfy the criterion for publication set forth by the International Code of Zoological Nomenclature (ICZN).The article, "Feathers for T. rex", was written by Christopher Sloan for the November 1999 issue of the magazine. While Sloan did technically coin the name "Archaeoraptor liaoningensis" by publishing it in a widely-distributed magazine (and the ICZN does not mandate that names can only be created in peer-reviewed journals), he did not make it clear that he was intending to formally erect a new taxon (usually done by specifying ("new genus and species", "gen. et sp. nov.", or some variation). Furthermore, he explicitly referred to the fact that a formal description of the species was forthcoming. Most observers have interpreted this as falling short of the ICZN requirements for naming taxa, and I don't know of any good reason to disagree.

A more complicated factor is that, among the subsequent publications on the chimeric fossil, some authors did try to formally name the taxon and designate a lectotype (when a type specimen is found to actually represent two or more individuals, a lectotype must be chosen from among them to officially bear the name that originally applied to the lot). Noted BANDit Storrs Olson published an article in a 2000 issue of the Backbone newsletter of the US National Museum of Natural History in which he attempted to remove the tainted name from his own area of study, fossil birds. This is before many BANDits (the "birds are not dinosaurs" crowd) collectively reversed their positions and decided that dromaeosaurs ARE fossil birds after all, thus becoming MANIACs ("maniraptorans are not in actuality coelurosaurs"). Olson therefore designated the tail specimen as the lectotype. This would seemingly make "Archaeoraptor" the official senior synonym of Microraptor.

Not so fast. Olson did not actually describe the specimen or convey intent to coin the name. Like Sloan, he referred the creation of the name to other authors (in this case, Sloan himself, in the mistaken belief that Sloan's article DID coin the name). So Olson effectively specified that the nomen nudum "Archaoraptor" should refer to the tail, but failed to officially create the name, let alone specify its lectotype.

And that is why "Archaeoraptor liaoningensis" remains a nomen nudum; at least, just until some cheeky bastard decides to formally attach the name to something for reals. Technically, nomina nuda are still up for grabs nomenclature-wise...

Who's That Birdie?

2011-11-19T11:01:00.001-08:00

Because I initially got the inspiration for tomorrow's big post while working on the new restoration above, I thought I'd post it alone first as a teaser. First to correctly guess the species gets a shout-out!

"Behold the Tyrannosaurus and his rival, the Triceratops!" Scientific Grammar for the 21st Century

2011-11-11T06:26:00.001-08:00

A gorilla is a type of primate. The gorilla is a primate. Gorilla is a primate. Gorilla gorilla is a primate. Hominidae is a group of primates. We use such oddly varying ways of talking about taxa. Image by Pierre Fidenci, licensed.

Recently, an illustration of an Allosaurus was selected as an upcoming picture of the day at Wikipedia. Before going live, the POTD folks asked the article editors to suggest improvements to the caption they had written (based on the text already in the Allosaurus article, which is a featured article at Wikipedia and thus thoroughly checked for errors). Here is the original caption written by the POTD editors:

"An artist's rendition of the gape of an Allosaurus species of dinosaur, based on the research of paleontologist Robert T. Bakker. Allosaurus was an active predator of large animals, and had the ability to open its jaws extremely wide. Studies suggest that it used its skull like a hatchet against prey, attacking open-mouthed, slashing flesh with its teeth, and tearing it away without splintering bones."

The obvious error there is that it describes Allosaurus as a "species of dinosaur" when it is in fact a genus. So, just change the first sentence to "An artist's rendition of the dinosaur genus Allosaurus" and it's fixed, right? Pretty much any science writer or paleontologist you talk to would say yes. The following was proposed as a correction:

"An artist's rendition of the dinosaur genus, Allosaurus, with it's jaws open fully, based on the research of paleontologist Robert T. Bakker. Allosaurus was an active predator of large animals, and probably had the ability to open its jaws extremely wide. Studies suggest that it used its skull like a hatchet against prey, attacking open-mouthed, slashing flesh with its teeth, and tearing it away without splintering bones."

But isn't there a problem with referring to a genus in the singular that way? Though many dinosaur genera are monotypic, a "genus" is still technically a group of animals, no different from a "family" or an "order." Let's re-write the same caption, but replace Allosaurus with Allosauridae:

"An artist's rendition of the dinosaur family, Allosauridae, with it's jaws open fully, based on the research of paleontologist Robert T. Bakker. Allosauridae was an active predator of large animals, and probably had the ability to open its jaws extremely wide. Studies suggest that it used its skull like a hatchet against prey, attacking open-mouthed, slashing flesh with its teeth, and tearing it away without splintering bones."

This caption obviously makes little grammatical sense, because we intuitively recognize that the family Allosauridae is collective (despite the fact that, like the genus Allosaurus, it is usually thought to contain only one species). But the genus Allosaurus is also collective, and for that matter, the species Allosaurus fragillis is a collection of populations and individuals.

But these strange constructions are nearly universal in science writing, including (especially) formal science writing. In a way, this is a bit of an archaism. Think of the archaic-sounding phrasing in some old children's books, like "Tyrannosaurus: he was the king of the dinosaurs! His mortal enemy was Triceratops." Referring to an entire genus as a "he" ties into the anthropomorphic "roles" we assign dinosaurs ("Tyrannosaurus: he's a bad guy. Triceratops: he's a good guy). Mark Witton has previously written about this effect here. Similarly, referring to genera or even species in the singular places them in the same league as Godzilla: single, towering, fantastical monsters, rather than categories of normal animals.

Referring to an animal as "the this" or "the that" is a another archaism."The Tyrannosaurus was the dominant predator of his time." "The gorilla is the largest living primate." This is more correct than some of the other examples, but also strikes me as stodgy and archaic. Here's a quote from a 1985 paper: "The gorilla is more closely related to man than the chimpanzee is". Wouldn't "gorillas are more closely related to humans than chimpanzees are" seem more suited to the 21st (or even 20th) Century?

But Tyrannosaurus is not that animals' name. It's the name of that animals' genus, the group which contains it.That animal is "a" Tyrannosaurus, it is not the genus Tyrannosaurus itself. Alternately, it is "a tyrannosaur", but it is not simply "tyrannosaur." Using lowercase "common names" is one easy solution, but one that can create a different kind of confusion. Is a "tyrannosaur" a Tyrannosaurus or any tyrannosaurid? Is Daspletosaurus a genus of tyrannosaur? This isn't a perfect example because there's no group named "Tyrannosauria", at least not yet. But think of how we use "dinosaur" instead of "dinosaurian", when it could just as easily be referring to the genus Dinosaurus. One solution would be to use such common names the way we do for living animals: common name followed by clarification. "This is a picture of a tyrannosaur (Tyrannosaurus rex)." "That is a picture of a tyrannosaur (Daspletosaurus torosus)."

Here's my take on the example caption, using a more precise way of conveying the same ideas:

"An artist's rendition of an Allosaurus fragilis with it's jaws open fully, based on the research of paleontologist Robert T. Bakker. Allosaurus were active predators of large animals, and probably had the ability to open their jaws extremely wide. Studies suggest that they used their skulls like hatchets against prey, attacking open-mouthed, slashing flesh with their teeth, and tearing it away without splintering bones."

"An" Allosaurus fragilis: it is an image depicting a member of that species, not an image of the "species" itself. Allosaurus "were" active predators, pleural, because Allosaurus is a grouping of dinosaurs. In my opinion, these slight changes in phrasing give a much more naturalistic feel to the description. It's clear that we're talking about a type of animal in the real world, not enumerating the abilities of an individual Pokemon character.

Isn't it time we put some more thought into how we write about taxa? I think we should be trying to frame dinosaurs as parts of nature, not exceptions to it. Would it be helpful to change the way we talk about taxa, or is the existing method too entrenched and well-understood by those who will obviously know what you're talking about to bother?

Release the -- Nah. Forget It.

2011-10-10T06:45:00.000-07:00

Above: Shonisaurus, favorite paintbrush of giant mythological cephalopods.

In a move that should surprise no one, media outlets have picked up and are running with possibly the stupidest, most blatantly ridiculous scientific "discovery" since the Cambrian mini-men.

Let's break this down. There is a bonebed consisting mainly of Shonisaurus vertebrae which are interpreted as having been deposited in deep water. In some odd twist of fate, the disarticulated vertebral columns of these elongate giant ichthyosaurs were (somehow!) fossilized in long rows. A reasonable person would look at this and think, "it's almost as if vertebrae are stacked in rows inside the body or something."

An unreasonable person, like paleontologist(?) Mark McMenamin, would look at this and think "A sentient giant squid arranged these vertebrae like that in order to create a self portrait of its tentacles!"

I'm sorry you had to subject your brain to that hypothesis.

How such a travesty of logic made it into the abstracts of the 2011 GSA Annual Meeting in Minneapolis, I don't know, but if the scientific publication process works at all, it will not make it through peer review in a real journal. But, of course, that won't stop the media from credulously reporting every word as "new science" because, hey, everybody likes a good "Release the Kraken!" headline.

Most disappointing is that even Science Daily, usually pretty good with the science reporting, ran this story without even a hint of skepticism. Not even a single quote from another scientist to say "um yeah, in case you didn't read what you just wrote, this is obvious BS." For shame.

Feathers ARE Color

2011-09-16T16:35:00.000-07:00

A lot of my posts lately have been dedicated to color in prehistoric feathers (primer here). As a paleontographer, it's hard not to get excited about finding new ways to more accurately and naturally depict long-gone animals, and I know a lot of you reading this feel the same way. It can also be frustrating knowing the basic color palate we're dealing with, but having specific data from only a handful of species to draw inspiration from. I've already seen, not surprisingly, a few illustrations of Microraptor, Xiaotingia, etc. that basically mimic Anchiornis down to the spangles. We're so conditioned to follow phylogenetic bracketing that it's tempting to use what little info we have, and extrapolate it to close (and even not so close) relatives. This can apply to larger feather patterns as well; as I mentioned in this post, it's fine to extrapolate Microraptor-style feathering to Velociraptor, but it's not the ONLY way to do it, nor is it even necessarily the most plausible for a creature of such different size and ecosystem, as many online critics of Dinosaur Revolution would have you believe ;)

With that in mind, I want to start with a disclaimer: this kind of info only gets you so far. I'm not setting out to write the inerrant Bible of paleoart in these types of posts. Yes, all the evidence we have of dromaeosaurs shows full, lush feathering equivalent to small modern birds. But then again, we're dealing with small prehistoric birds here. Yes, we can interpret feather coloration and use inferences from modern birds and biochemistry to say what colors are likely and which are unlikely; but we can't always identify structural color in fossils, and we have yet to identify carotenoids, and many small dinosaurs we think of as "carnivorous" might well have trended more toward omnivory, insectivory, etc., or other unforeseeable pathways to those tasty, tasty bright yellow pigments.

Ok, preamble out of the way, the point of this post is to provide a general way I've used, and others can use, to try to make somewhat educated guesses about coloration in prehistoric birds which have not yet been analyzed for color pattern.

A few people pointed out to me when this recent paper by Wogelius et al. came out, in which the research team was able to identify color patterns in some Mesozoic birds using chemical markers rather than direct observation of melanosomes, that their reconstruction of Confuciusornis based on these findings was pretty similar to the restoration I'd done a while earlier.

Above: Restoration of Confuciusornis by Richard Hartley, from the press release. Below: My own earlier restoration of C. sanctus.

The two are pretty similar in the broad pattern: dark head, body, and coverts, white or light-colored wings with more black on the secondaries than the primaries. Now, so far this is only one data point, so I don't want to draw too many conclusions. But I was not simply guessing when I restored C. sanctus that way back in 2009.

The trick is to understand what you're looking at when you see a fossil feather. These are often referred to as 'impressions', but often the impressions are only part of the story, or even completely absent from the fossil. The breakthrough that led Vinther , Prum and others to figure out how to suss out feather color, was in realizing what fossil feathers are made of.

As Prum summarized on the Skeptics Guide to the Universe podcast a few years back, traditional wisdom held that the dark, 'carbonized' looking fossil feathers were the result of bacteria. Now, some old-school feather impressions, like those from Solnhoffen and the Santana formation, do contain nice, deep, actual impressions. These look very different from the stuff you find in the Jehol (compare the fossil feathers of the Berlin Archaeopteryx with the holotype of Microraptor gui). But most fossil feather,s including the famous single-feather holotype of Archaeopteryx and most Jehol stuff, are dark stains in the rock. Under the microscope, these looked to early researchers to be made up of fossil bacteria which had eaten away the feather keratin during decomposition.

Above: Photograph of an unsubscribed Anchiornis specimen by Robert Clark, from National Geographic, showing clear color patterns matching those predicted by Vinther et. al.

What Prum, Vinther, etc. showed in recent years is that this is flat-out wrong. Those granules are not bacteria--they're melanin! When you look at a fossil feather, most of the time, you're looking directly at the color pattern of the feather itself, the keratin and everything else having long since disappeared. This is especially apparent in very well-preserved fossils; for example, the beautifully preserved new Anchiornis specimen above is essentially proof of Vinther's hypothesis, which had previously been based on more obscured differences in shade. This is where my method of eyeballing it falls flat--I'd never have gotten the correct pattern from the specimen Vinther was looking at without really close physical examination. You need really nice specimens for it to conceivably work, or you have to Dave-Peters the heck out of low-res images trying to spot differences in contrast on the feathers.

Luckily, Confuciusornis was a safe bet, because so many specimens are known, and you can start to see patterns emerge. Many of the best specimens tend to have a very dark halo of feathers around the body and arms, with the wing feathers very faint, even sometimes difficult to see at all. Knowing that dark feathers means dense melanin = dark coloration, and light color = lack of melanin = light color, it was easy to come up with a good guesstimate of the life coloration. This was first inspired by Longrich's work on Sinosauropteryx, showing that the apparent bands in the tail were due to color patterning, which was later supported by published studies.

Obviously this is not a foolproof method. But it's a good place to start for artists who may want to add a little evidence-based thinking to their reconstructions, even if the evidence itself is wide open to interpretation. At the very least, if a good specimen has obvious areas of light and dark, I'd personally restore that pattern in a life illustration. It may end up being wrong, but it's better than pure speculation.

All Aboard!

2011-08-29T11:11:00.000-07:00

Readers of this blog will definitely be familiar with all the standard complaints about dinosaur documentaries these days. Even old classics like Walking With Dinosaurs were heavily criticized by paleontology enthusiasts at the time for being too heavy on drama and too light on science. As a paleoartist, I love shows that attempt to reconstruct prehistoric life in a natural way, and all the necessary speculation that entails. But people are justified in pointing out that this doesn't exactly do wonders for public understanding of science.

Sure, shows like WWD or even more sensationalist 'monster movie' type programs like Jurassic Fight Club create plenty of interest in paleontology and foster enthusiasm in young paleo fans, who can certainly be forgiven for being into the 'cool factor' and less into the hard science, which may well come with time. But these documentaries also blur the line between science, educated speculation, and pure fantasy. Use of talking head segments helps, but without weaving the science behind the entertainment into the body of the program, many people simply disregard it.

Worse, producers have a tendency to edit the token scientist sound bites in a way which fosters stereotypes of scientific authority - talking heads are shown explaining that "yes, what you just saw is true" rather than explaining how we know this stuff in the first place, which is where the actual science is. Science is a process, not a set of facts spouted off by guys sitting in labs. Most dinosaur documentaries pay lip service to science as an excuse to sell entertainment, plain and simple.

There is one very surprising exception: By far, the best dinosaur show produced in the last ten years in terms of actual science content is a cartoon aimed a preschoolers.

Produced by Craig Bartlett with the Jim Henson Company for PBS and first airing in 2009, Dinosaur Train has now clocked in 40 episodes over two seasons. The aim of the series is to present science to young children in a way that is accessible and entertaining, and in that DT succeeds where pretty much every other dinosaur TV show in the past has failed.

Each episode features two separate stories, all following the adventures of a Pteranodon family (included their adopted sibling, Buddy the T. rex, which is, based on the opening credits sequence, apparently the first recorded instance of nest parasitism in a non-avian theropod). The adventures consist of daily rides on the Dinosaur Train, a Doc Brown-esque vehicle which is capable of travelling to any time or place in the Mesozoic era (even under water in later episodes). Right off the bat, this provides ample opportunity to teach kids the basic (yet still occasionally missed or messed up in other media) idea that dinosaurs were often separated from each other by huge spans of time. I particularly liked the clever bit in one episode where the kids go to visit the one of the first dinosaurs, Eoraptor; reaching the end of the track somewhere in the Late Triassic, they have to get out and transfer to an old-style push-handle rail cart to go the rest of the way!

The geographic separation of different dinosaurs is also emphasized, and in another cute touch dinosaurs are often given accents based on their country of origin. This theme of, essentially, biostratigraphy was the subject of an entire episode in which the Pteranodons attend a block party with their immediate neighbors (the ones featured on the show in their home time, before getting on the train). The neighbors include a Styracosaurus, Lambeosaurus, Daspletosaurus, a Euoplocephalus and Hesperornis. Savvy readers will probably recognize this as the Dinosaur Park Formation fauna, and while Pteranodon itself is the only one out of place there by a few million years, it's impressive to see a kid show try to get this kind of detail right while teaching a more basic lesson (that every member of a community has a role or niche).

It's also funny to watch how the later plays out in the middle of an anthropomorphic, cartoon universe. On one hand, it's refreshing to the large theropods treated as characters who are friendly with the herbivores and not background monsters like in Disney's Dinosaur. On the other, this fact makes it even funnier/weirder in episodes that discuss the defensive tactics of some herbivores; for example, a group of stegosaurs have to group up and fend off a comically insane-acting, marauding allosaur. This kind of kid's-TV-paradox becomes even more acute in the episodes on marine fauna. I have to hand it to the producers for featuring such obscure critters as ancient fish and ammonites as characters, but it's also disconcerting in that almost every episode features the pteranodonts devouring heaps of these same fish! A bit like the Simpsons episode with Homer in an "Under the Sea" musical number gobbling down horrified anthropomorphic sea cucumbers? The producers do a good job keeping this kind of thing segregated, and I doubt the target audience would ever notice the inconsistency.

The best thing about the format of Dinosaur Train is that nearly every episode highlights and explains the scientific process in a really very deft and simple way that I think small children can understand, or at least in a way that gets them thinking scientifically at an early age. Buddy, the main T. rex character, is a very curious type who is always bugging the smart, train-conducting Troodon to answer questions his explorations raise. In case the show made it too charming and understandable to notice what's going on here, these are the first two steps of the scientific method--Buddy explores the word and forms questions based on what he sees. With the help of the conductor, the kids then do some research for background information on the topic, and then--get this--the kids explain to each other (and the audience) what a hypothesis is: "an idea you can test!"

I don't want to sound condescending, but I've met adult science enthusiasts who seemingly have not yet grasped how science really works. Many casual dinosaur fans seem to think they need to find an idea and defend it to the death. Dinosaur Train teaches children that they should think about the world around them, then ask questions. They should think of possible answers to their questions, and then try to prove themselves wrong! This is done so brilliantly it's almost sad to realize how easy it is to teach scientific thinking to people, most of whom have no idea what science is or how it operates, let alone to little kids.

My favorite example of the show's handling of the scientific process is in the episode where the kids travel to Jurassic Germany to visit an Archaeopteryx. The conductor explains to them that Archaeopteryx is the first bird, and Buddy develops an hypothesis: if she is a bird, he reasons, she can fly and lives in a nest, like other the birds he's seen in his own time period. The conductor knowingly encourages him to test his hypothesis by talking to the Archaeopteryx. To Buddy's surprise, despite the fact that she is a "bird", and has wings, she does not have a nest and can't fly! Instead, the Archaeopteryx demonstrates how she can use her wings to run up a tree (first instance of WAIR portrayed in a dinosaur show?) and then can glide down after insects. Buddy's hypothesis was disproved, but he learned some even more interesting things by testing it. If only this kind of message could somehow be applied to standard, "adult" dinosaur shows.

If the show itself doesn't amply demonstrate scientific concepts to children, each episode is followed by an epilogue featuring paleontologist Scott Sampson (who also has a blog, The Whirlpool of Life) explaining the main points again and giving some additional facts (some aspects of the show that rely heavily on anthropomorphism are sometimes hilariously shot down by a debbie-downer type stickler who pops out and says, for example, "Fact: Troodons did NOT play hockey!" followed by a chorus of disappointed kids).

To follow in the stickler's footsteps (would it be Dinogoss if I didn't?), I did see some missed opportunities in the premise of the show. It's impossible and silly to criticize a cartoon for accuracy ("Daffy Duck does NOT fold his wings correctly!"), but paleo fans will no doubt notice some glaring ones in the main cast. The Troodon are conspicuously lacking in feathers, and the Pteranodon appear to have bat-like wings (a condition not shared by other pteorsaurs in the show). This is a little baffling as the science consultants must have a very big hand in the production--most aspects of each episode, from colorful, feathered Velociraptor to Styracosaurus using their spikes for display rather than combat, are obviously based on the kind of up to the minute research only people active in the paleo community could provide.

I'm betting that the main cast were designed and set in place before the consultants effectively took over--some later episodes show that the conductor is feathered, his feathers are just under is hat. His catch-phrase is the rather belabored "Bless my scales and feathers!", probably modified at the behest of Sampson or another consultant taken aback by a Troodon, of all species, exclaiming "Bless my scales!" The family life of the pteranodonts rings false not for blatant inaccuracy, but for the fact that it's just the kind of interesting facts the bulk of the episodes would fall over themselves to include--the sexual dimorphism that could have been present between mom and dad, the fact that the eggs were likely buried rather than laid in a bird-like nest, etc. But none of this really takes away from the core value of the show as a tool for teaching science.

For paleo fans, there seem to be some 'inside joke' type moments as well. Buddy was elated in one episode to be inducted into the "Theropod Club" . The club basically consists of a bunch of theropods getting together and patting themselves on the back for being by far the coolest dinosaurs - to the consternation of his friends. Nick Gardner could sympathize! Even here, though, the educational message is clear; it not only teaches kids what a theropod is, but often makes a point to explain why birds are also considered to be members. Buddy, apparently a budding comparative anatomist, is also prone to getting really excited over "comparing features", to the point that in at least one episode, when the kids were suggesting games to play during a long train ride, his suggestion to compare features with other dino passengers was met with groans and eye-rolls (maybe the pterosaur kids are more in the geological school--they do like to collect rocks, and at least one entire episode has been dedicated to geology rather than dinosaurs themselves).

At any rate, this is in my opinion the best science show made for young kids, at least those still too young for Bill Nye, and I'd encourage any dinosaur fans to check it out. Despite the target age range, it's fun to see how the new discoveries we follow on a day to day basis are being communicated effectively to the next generation.

Old Names for Old Bones

2011-08-13T08:52:00.000-07:00

Before writing up a big review post for tomorrow, I thought I'd address a request I've gotten a few times, most recently over on my deviantArt page. I've written a few times about old/disused names that have fallen out of fashion in paleontology with little reason (or for reasons that can't really be supported by evidence). In fact, a lot of these 'quaint' or 'old-fashioned' sounding names should really be considered just as valid today as when they were coined.

Now, keep in mind that at least in cases of priority for family-level names, it has been argued that anything goes, because researchers are not necessarily using these names as 'families' under the ICZN but identical clade names that fall under no governing code. In my opinion this is a bit of a cop-out, and a bit hypocritical when espoused by people who would otherwise argue that nomenclature needs to do its best to reduce confusion. I agree with some PhyloCode proponents that, for this reason, endings like -idae should be avoided in clade names at all costs, or at least, those names should be defined in such a way that they roughly correspond to their traditional family name homonyms.

There has been a general tendency in the past few decades to somewhat arbitrarily replace names based on fragmentary taxa with those based on more complete (or simply more famous) taxa. This, again IMO, ultimately negatively impacts stability of nomenclature, despite the fact that many of these 'replacement' names have since come into such common use, coinciding with widespread use of the Internet, that changing them back now gives a false impression of instability. Luckily, some more recent research is beginning to correct a few of these mistakes of recent history. Megalosauroidea (a name based on a fragmentary taxon) had long been replaced by Spinosauroidea (a name based on a different but more apomorphic fragmentary taxon) in the literature, but several recent papers by Benson and colleagues have argued fairly successfully for a reversal of this trend and a return to valid priority.

In a way, it's a shame that the PhyloCode will not give priority to the original author of a name, but rather to the author of its definition, essentially enshrining unjustified replacement names like Coelophysidae in favor of older names like Podokesauridae, robbing the original authors of their rightful credit. It would upset temporary stability (or rather, reverse prior results of instability) but ultimately make more sense to automatically give preference to the older names and their authors, even if they aren't converted to clades immediately when PC goes into effect.

Anyway, here I'll give a brief rundown of some disused names that should still by all rights be considered valid senior synonyms of other names. I'll also throw in a few genera that may have a claim to seniority over more widely used, better known names. Note that this later bit is a completely separate issue--seniority for family-level names is straightforward. At the genus or species level, as I've argued before, often names are ignored as unofficial "nomina dubia". Nomen dubium refers to a name based on a specimen which lacks key apomorphies and cannot be distinguished from two or more similar specimens. However, in many cases I believe stratigraphy itself should be taken into account. If a bone fragment is obviously from a allosaurid theropod, and current evidence only supports the presence of one other such theropod in its stratigraphic level, parsimony dictates they should be considered the same taxon. If and when evidence is found to support the presence of multiple allosaurids in that formation, then and only then can non-diagnostic allosaurid remains be declared nomina dubia.

One more note on nomina dubia: the ICZN does not support the existence of this concept (and as far as I know, neither does the PhyloCode). According to the ICZN, if a type specimen is found to be non-diagnostic relative to more complete specimens, the name should not be ignored--rather, one of those more complete specimens should become the neotype of the oldest available name. So, for example, Deinodon (see below) should not simply be ignored as non-diagnostic relative to Gorgosaurus and Daspletosaurus and then ignored; rather, scientists should have arbitrarily chosen one of those two specimens to become the neotype, removing the validly published name from poor material and leaving the poor material nameless. This is, of course, almost never done, especially among paleontologists, where making sure your name is the one that sticks has historically been a higher priority than eliminating nomenclatural clutter (whether or not scientists who name scrappy material have more of a right to their names to persist than those who describe complete specimens is another story).

Okay, enough of an intro. Here are some old names, and quick examinations of whether or not they should be resurrected:

Families:
Podokesauridae (Huene 1916) is perhaps the classic example of a valid taxon name abandoned for no good reason. In use up until the early 1990s, the name was suddenly changed to Coelophysidae (Nopcsa, 1928) when Holtz and Sereno began to fist include this group in phylogenetic analyses. As far as I know no justification for this was ever given, but I don't have these initial papers to check. At any rate, the type specimen of Podokesaurus has been distinguished from Coelophysis by researchers going back to Colbert in the 1950s, so it is by definition not even a nomen dubium. There is therefore no justification to ignore this name in favor of Coelophysidae/Coelophysoidea etc.

Metriacanthosauridae (Paul 1988) is another case like Podokesauridae where a perfectly valid name based on diagnostic material was arbitrarily replaced by its junior synonym, Sinraptoridae (Currie & Zhao 1994) among most researchers. Nobody doubts the diagnosibility of Metriacanthosaurus as far as I know, and as discussed, this doesn't matter anyway.

Megalosauroidea (Huxley 1869), as discussed above, is a senior synonym of Spinosauroidea (Stromer 1915). Again, Spinosauroidea gained broad acceptance in the early '90s, but several recent papers have been effective in reversing this baffling trend to arbitrarily ignore a widely used name with a history almost as long as dinosaur paleontology itself.

Omnivoropterygidae (Czerkas & Ji 2002) is another case where a once-ignored name is starting to gain traction again in favor of its junior synonym Sapeornithidae (Zhou & Zhang 2006). Both Greg Paul and Tom Holtz have used the correct name in recent popular works, though Sapeornithidae still crops up in the technical literature. This name is an even better illustration of the Czerkas problem. People who favor the junior Epidendrosaurus over Czerkas' senior Scansoriopteryx can at least fall back on the online vs. print publication excuse (though the ICZN is clear and unequivocal on the matter). In the case of this family name (neither have yet been defined as clades), Czerkas' name has 4 years of priority and is still ignored. Let's not beat around the bush--people disagree with Czerkas' conclusions and don't like the way he has (validly if unpopularly) published many of his taxa, and they express this distaste by ignoring his taxonomy. The ICZN has no provision to replace names created by unpopular scientists.

Ornithodesmidae (Hooley 1913) has priority over the better-known Dromaeosauridae (Matthew & Brown 1922). The scrappy type specimen of Ornithodesmus, though initially (correctly) identified as a primitive bird, was soon confused with the much better remains of the pterosaur now known as Istiodactylus. Hooley named Ornithodesmidae as a family of pterosaurs, but it became a theropod family when Ornithodesmus was again recognized as a maniraptoran in 1993. Naish & Martill (2007), as well as Makovicky & Norell (1995), and Mortimer (online) have shown that Ornithodesmus falls into the same family as Dromaeosaurus. So, unless Dromaeosauridae is re-defined to include only Dromaeosaurus and a few closely related taxa (~current Dromaeosaurinae) or trated as a synonymous but differently goverened clade (under the future PhyloCode), Ornithodesmidae has clear priority of name under the ICZN.

Atlantosauridae (Marsh 1877) has clear priority of name over the more well known Diplodocidae (Marsh 1884), and Hay (1902) argued that it has priority over Amphicoelidae (Cope 1877). Atlantosaurus is almost certainly a synonym or close relative of Apatosaurus, and while it may be a real nomen dubium in relation to the various species of contemporary atlantosaurine (=apatosaurine) sauropods, it is definitely a member of this group, and thus higher taxon names should be used accordingly. Even if a taxon is a nomen dubium, there is no reason to change higher taxa names based on it if it can be confidently classified at the 'family' level (as is the case with Ceratopsidae). Again, Atlantosauridae has not yet been defined as a clade, so if Diplodocidae is defined first under parallel systems such as PhyloCode, a situation will arise where Atlantosauridae is valid under one code but not the other--Diplodocidae will be a valid name but for a clade, not a family. Olshevsky (1991) incorrectly labelled Atlantosauridae a nomen oblitum (forgotten name). The ICZN states that to be a nomen oblitum, a name must not be treated as valid in the scientific literature after 1899. However, Atlantosauridae was in use in papers by Steel (1970) and Nowinsky (1971) well into the late 20th Century.

Deinodontidae (Cope 1866) is a slightly more complicated case than the above. It was in clear, widespread use through the mid 20th Century (as in Maleev 1955) and almost always treated as the senior synonym of Tyrannosauridae (Osborn 1905). However, Russel (1970) argued that Deinodontidae be abandoned, because he considered the type specimens of Deinodon (isolated teeth) not diagnostic, rendering the name a nomen dubium. However, the teeth are clearly diagnostic at the family level and possibly even genus and species, as they must have come from either Daspletosaurus or (more likely) Gorgosaurus, and the rocks those dinosaurs come from are well enough sampled to rule out the presence of a third large tyrannosaur species unless such compelling evidence is found. Similarly, it is questionable whether or not the pertinant ICZN rules allow for abandoning a name due to a dubious type genus. Even if this is the case, it is only followed sporadically in the literature, and many family names remain in use that are based on dubious type material, including Hadrosauridae, Ceratopsidae, and Troodontidae (the latter is also based exclusively on teeth of questionable diagnosability at the genus and species levels). Olshevsky (1991) recognized this, but argued that the name is still invalid because Cope initially spelled it Dinodontidae, and the name Deinodontidae was an emended spelling not published until 1914, after Tyrannosauridae. He concluded that therefore Deinodontidae (with an e) is a junior synonym and Dinodontidae (no e) is a nomen oblitum. However, Olshevsky's argument is incorrect because the ICZN clearly mandates that any family names based on misspellings or unjustified spelling changes of their type genus (Cope spelled the name Dinodon) can and must be emended by any subsequent revisor, and that this does not change the original authorship or date of the name (ICZN Article 35.4.1). Also, note that even if Deinodontidae and Deinodontoidea are ignored, several studies have found Coelurus fragilis to be a "tyrannosauroid", and so the next available name for that group after Deinodontoidea is Coeluroidea (Marsh 1881).

Trachodontinae (Lydekker 1888) may have priority over Lambeosaurinae (Parks 1923). As discussed below, the Trachodon holotype teeth may be diagnosible to subfamily level, as some researchers have suggested that they belong to a 'lambeosaurine' rather than a 'hadrosaurine/saurolophine'. If this is the case, even if Trachodon is itself a real nomen dubium (which it probably is), the family name would still carry priority.

Titanosauridae (Lydekker 1885) is, despite being based on a possible nomen dubium, a valid taxon name. However, this situation is complicated for a new reason: the 'family' has proven so large that most researchers now divide it up into several families. If multiple families of titanosaur are used, Titanosauridae itself (but not Titanosauroidea) must be restricted to its dubious type species. This is analogous to the Ornithodesmidae situation described above: if 'dromaeosaurids' were divvied up into several families (Microraptoridae, Velociraptoridae, Saurornitholestidae, Dromaeosauridae), then Ornithodesmidae would still be valid but monotypic, and probably (rightly) fall out of use again.

Hylaeosauridae (Nopcsa 1902) is a senior synonym of Polacanthidae (Weiland 1911), but this is another situation where a name is only valid under certain classifications. Some older classifications placed the group as separate from Ankylosauridae and Nodosauridae, or as a subfamily of either (as Polacanthinae). In these cases, Hylaeosauridae/inae has priority. However, some new studies show the 'polacanthines' the be nested within nodosaurs, and to be possibly paraphyletic. Nodosauridae (Marsh 1890) has priority over both Polacanthidae and Hylaeosauridae, so both names are sunk either way.

This last one isn't a dinosaur group, but is quite an odd situation. As it turns out, Pterodactyloidea (Meyer 1830) has, according to the principal of coordination, priority over the widely-used pterosaur group Ctenochasmatoidea (Nopcsa 1928). Note that this is a different taxon than Pterodactyloidea (Pleininger 1901), traditionally labeled as a suborder. But... they have the same name. This isn't technically a problem because the later Pterodactyloidea, named as a group above the rank of superfamily, is outside any governing code, and practically, nobody uses the superfamily Pterodactyloidea (or Rhamphorhynchoidea, for that matter). But those have priority over other names, which makes them more valid than the suborder name, which can easily be replaced with a new name the way Segnosauria was replaced with Therizinosauria (neither of them governed by the ICZN, so anarchy applies).

Genera and species:
Deinodon horridus (Leidy, 1866) currently appears to be a real nomen dubium, as it is based on deinodontid teeth from the Judith River Formation. I say currently because its status depends on the currently messy taxonomy and stratigraphy of the various specimens/species assigned to Daspletosaurus. Daspletosaurus is not present in the Judith River formation sensu stricto, and is generally known from younger deposits than the chronologically-overlapping albertosaurine species Gorgosaurus libratus. However, specimens that may or may not be Daspletosaurus are known from such a wide temporal and geographic range that it's possible these teeth could belong to it (or a similar tyrannosaurine) instad of Gorgosaurus. Additionally, if it ever is demonstrated to be possible to distinguish between albertosaurine and tyrannosaurine teeth, Deinodon can and should be ressurected to replace one of these two genera. Note that Matthew & Brown 1922 considered both G. libratus and Albertosaurus sarcophagus to fall within the genus Deinodon--this is dependent on subjective lumping vs. splitting (if libratus and sarcophagus are placed in the same genus, and Deinodon=Gorgosaurus, Albertosaurus is also a junior synonym of Deinodon), and ignores the possibility that Daspletosaurus represents the true skeleton of Deinodon. For now, Deinodon must be considered a nomen dubium.

Trachodon mirabilis (Leidy 1856) was named for isolated teeth of a hadrosaur (and some mixed in from a ceratopsian), Also from the Judith River formation. As mentioned above, they may be diagnosable to the level of Lambeosaurinae (=Trachodontinae?). I'm not knowledgable enough about hadrosaurs to know if this species might be currently valid based on stratigraphy. As far as I'm aware, no definite remains of named lambeosaurines are known from the Judith River formation, though this spans a great deal of time and in places overlaps with the Oldman and Dinosaur Park formations of Canada, which contain numerous lambeosaurs at different and better-studied stratigraphic levels. If anybody knows approximately which portion of the Oldman/Dinosaur Park group this part of the Judith River corresponds with, we might be able to find an answer.

Antrodemus (Leidy 1870) has long been recognized as a possible synonym of Allosaurus (Marsh 1877). In fact, I remember making a note 'alos known as Antrodemus' in one of my dinosaur books in the '80s (sticklerism arises early!). As Mickey Mortimer points out on the Theropod Database, Chure (2000) noted that the species of Allosaurus Antrodemus comes from can't be determined, but Chure doesn't consider it a synonym of Allosaurus because it comes from an unknown quarry. I would agree with this, as long as there are multiple genera of allosaurids recognized in the Morrison (i.e. Saurophaganax). If, however, one were to synonymize Saurophaganax and Allosaurus, the name for this genus must then become Antrodemus, no matter how many diagnosable species it contains (Antrodemus valens, the species, would still be a nomen dubium).

I'm sure there are other dinosaurs that could be added to this list, and I may try to do a 'part 2' someday. I've discussed the situations about the Lancian forms Manospondylus, Agathaumas, and Thespesius before.

Stay tuned for something a little less arcane, nitpicky, sticklerish, and taxonomical. The next post will be (gasp!) an unabashedly positive review of possibly the best dinosaur show ever to make it to air.

Know When To Fold 'Em

2011-05-30T05:15:00.000-07:00

Above: Maximum wrist folding for the theropods studied by Sullivan et al. 2010. Not to scale.

(Cross-posted from Art Evolved)

To continue talking about aspects of maniraptoran anatomy that can be a bit vaguely defined in the minds of paleoartists, I'm going to write a bit on the issue of wrist folding. As most of you will know, a major characteristic of maniraptorans is the semi-lunate carpal, the half-moon shaped bone in the wrist that allows the blade of the hand (metacarpal 3) to fold backward toward the forearm (ulna). While this is common knowledge among paleo buffs and artists, what seems to be less understood is exactly how tightly the hand (and in aviremigians, the wing) could actually fold up. I myself have never been too clear on the issue, and there don't seem to be many papers addressing this. But in the last few years, a few papers have come along that can help shed light on the subject. The first was Senter 2006, which studied the full range of motion in the forelimbs of two dromaeosaurs, Deinonychus and Bambiraptor. The second was Sullivan et al. 2010, which examined the range of motion in the wrist of several species representing each major group of non-avialan maniraptorans.

Both papers, however, present geometric data that can come across as a bit inaccessible for your average artist, so I'm going to try to break down their conclusions for those of us who are more visual thinkers. The Sullivan paper, in particular, discusses the degree to which the wrist could fold, but doesn't necessarily provide diagrams or even final angle between the metacarpals and ulna for each species that could be used as a simple reference. I've done my best to translate their findings into the image at the top of this post, using modified skeletal diagrams by Scott Hartman and Jaime Headden.

Above: Anatomy of a maximally folded wing of the Wild Turkey Meleagris gallopavo, modified from Sullivan et al. 2010

The degree of wrist folding is controlled by two wrist bones. The cuneiform, on the inside where the wrist meets the bottom of the distal ulna, provides an inner limit. The cuneiform blocks the hand from actually touching the ulna. The radiale, on the outside of the fold, forms the surface which the wrist cannot fold beyond. This is basically a little process anchored to the tip of the radius where the top part of the hand articulates. The hand can obviously not fold beyond the angle of the radiale, or the animal would dislocate its wrist. Therefore, the angle the articular surface of the radiale forms with the ulna is used as the key factor in determining maximum wrist folding by Sullivan et al. Again, see my interpretation at the top for how their results likely translate into life position.

The results show that in almost all maniraptorans, the wrist could not be folded to the same degree as modern birds (for comparison, see the photo of the turkey wing above, which is at its own maximum folding point). Note that in actual, functional angle of folding in the turkey is 57 degrees between MCII (where the feathers attach) and the ulna. To see how this translates into a live animal, here's a photo of wild turkeys nicely showing the way the feathers fold (photo by D. Gordon E. Robertson, from Wikipedia, licensed):

The wrist is located about where the coverts form the point of a triangle, following the line formed by the border of the the brown secondary (ulna) feathers and white banded primary (metacarpus) feathers. Note that with the wrist folded at a 57 degree interior angle, the feathers (especially the secondaries, which help cover the primaries when folded) are basically stacked one on top of the other with little to no fanning out at the tips. This is because the feathers also have some ability to move at their bases, and can themselves fold relative to their anchor bones through muscle and ligament action.

Looking at the aviremigians in the diagram up top, it is apparent that their wrists could not fold tightly enough to fold the wing feathers to the same degree as a modern turkey. Small deinonychosaurs like Sinovenator and Bambiraptor could achieve close to a 100 degree angle (see image of Bambiraptor wing folding above, from Senter 2006), but larger ones like Deinonychus seem to have lost some of that folding ability, presumably for increased use of the forelimbs in predation. Indeed, if Deinonychus retained long remiges, they would hardly have been able to fold at all, and would have been permanently fanned out (not that this would have gotten in the way of grabbing prey, as Senter pointed out). This lack of ability to tightly fold the wrists may have posed a significant problem for those species with very long remiges, like Microraptor gui. Dave Hone, who was a co-author of the Sullivan paper, discussed alternative ways they could have kept their remiges free of the ground at his blog last year.

In pygostylians, the degree of wrist folding began to approach that found in modern birds. Eoconfuciusornis, for example, could fold its wing to about the same degree as a turkey. Where it gets weird is in the oviraptorosaurs. As I mentioned in my post on the Ashdown maniraptoran, oviraptorosaurs (at least the small basal ones like Caudipteryx) seem to have been capable of folding their wings far beyond what is possible for even many modern birds. It's unclear why this is so, especially as the remiges of Caudipteryx, while clearly for display, are not exactly very long compared to the body. Certainly its wings were much smaller than those of paravians, which would have presumably had more need to fold them up. I've seen this mentioned as possible evidence in support of the hypothesis that oviraptorosaurs are in fact avialans, and that the extreme folding of the wrist was inherited from flying ancestors, though I can't think of where. Sullivan et al. do note that more than folding up the remiges to keep them safe from wear and tear, wing folding is an important part of the avian flight stroke, and it makes sense that it would have become more developed in flying forms.

Anyway, we've only got a handful of specimens that have been specifically studied in regards to the degree of wrist folding, and there may well be exceptions in each maniraptoran group, where certain lineages independently evolved a greater or lesser degree of wrist folding from their ancestors as seems to have happened in therizinosaurs, where the derived Alxasaurus can fold its wrist more than the basal Falcarius, and deinonychosaurs, where the relatively derived Deinonychus can fold its wrist less than the more basal Bambiraptor. So this guide shouldn't be considered as a set of hard and fast rules, but rather a starting point for artists who want to make their restorations as plausible as possible.

Finally, a few days ago I posted a teaser for this post challenging people to determine what aspect of the above Deinonychus illustration was incorrect. By now it should be clear that the wrist is folded too far back. Appropriately enough, the first one to nail it was the artist, Nobu Tamura, himself! Commenter A.G. came close, speculating that it was due to the orientation of the glenoid, but that has more to do with the range of motion of the upper arm and how far it could extend into a bird-like flapping position, rather than the way the wing folds up. Good job guys!

References

* Senter, P. (2006). "Comparison of Forelimb Function Between Deinonychus And Bambiraptor (Theropoda: Dromaeosauridae)". Journal of Vertebrate Paleontology, 26(4): 897–906.
* Sullivan, C., Hone, D.W.E., Xu, X. and Zhang, F. (2010). "The asymmetry of the carpal joint and the evolution of wing folding in maniraptoran theropod dinosaurs." Proceedings of the Royal Society B, 277(1690): 2027–2033.

The Ashdown Maniraptoran

2011-05-25T12:16:00.000-07:00

As you may have heard by now, Darren Naish and Steve Sweetman have described an incredibly small, yet apparently adult, cervical vertebra of a maniraptoran dinosaur from the Wadhurst Clay Formation. My first reaction upon seeing pictures of this nice little water-polished bone was "that is effing adorable," followed by "I need to restore this despite the fact that we can have no clue what it looked like." So I did, and the result is shown above (and on my deviantArt page). Let me emphasize again: this is a *highly speculative* restoration of the so-called Ashdown maniraptoran. Darren did a great job of discussing the new paper at TetZoo, so I won't go into details here.

While it is entirely speculative, based as it is on a single bone, it is possible to make some educated guesses about life appearance. Naish and Sweetman note several characteristics of the vertebra that are similar to oviraptorosaurs. However, it is from the early Valenginian age, about 140 million years ago. This is nearly 20 million years earlier than the oldest known definitive oviraptorosaurs, Caudipteryx and Protarchaeopterx. So, I essentially restored this as a very small protarchaeopterygid-grade animal, hence the short tail and tightly-folding wing feathers (oviraptorids could fold their wings more tightly than even many early birds).

There is also some influence from scansoripterygids, given its small size (and as a slight nod to GSP's interpretation of Epidexipteryx hui as a basal oviraptorosaur). Naish and Sweetman point out that the large neural canal of the vertebra is a characteristic of Avialae, but that it may also be a more general size-related character. The scansor influence is found mainly in the shape of the skull and the large procumbant teeth, but those these are the characteristics which are shared by early oviraptorosaurs anyway, and so allow extra wiggle room should it turn out to be closer to avialans. I made the legs quite long compared to the ratio seen in its larger possible relatives, and made the foot fairly large (to better emphasize the diminutive size). The longer legs would, I reckon, help escape hungry mammals, lizards, and whatever else was preying on tiny maniraptors.

Finally, the coloration is fairly drab and cryptic (inspired by small modern birds that spend time hiding in undergrowth) and I chose yellow hues to indicate a bit of an omnivorous diet.

So, while it's impossible to accurately depict an animal based on a single bone which we have trouble even assigning to any specific clade, using some knowledge of basal maniraptoran lineages (it is almost certainly a fairly basal member of whichever clade it belongs to, given its early age), we can make some pretty reasonable (I hope!) guesses.

References:
* Naish, D., and Sweetman, S.C. (2011). "A tiny maniraptoran dinosaur in the Lower Cretaceous Hastings Group: evidence from a new vertebrate-bearing locality in south-east England." Cretaceous Research, 32: 464-471.

Giants & Other Early Reptiles Online

2011-05-19T05:56:00.000-07:00

When your average modern dino fan hears the name "David Peters", they probably think of lepidosaurian pterosaurs, archosaurian mammals, invisible babies and the most extreme examples of paleontological pareidolia since Chonosuke Okamura. But to the surprise of some commenters , Peters was, for a while, a somewhat prolific and outstanding paleoartist. I have long credited his two early 'gallery' style books with being one of my main early influences. These books more than anything except maybe Phil Tippet's Prehistoric Beast fostered my interest in paleontology as a kid and kept it going, giving me ample figures to copy... I mean... giving me plenty of references to use in my first attempts at palaeontography. Looking back through them I reckon those influences are still very much with me. Each page even functions as a scale chart, which must not have made too much of an impression on my developing mind.

For those also looking to be inspired by some 'old school' but still fairly accurate (especially in Gallery which features a Deinonychus so bird-like it blew my 12 year old mind) or at least interesting renditions of prehistoric animals, I recently discovered both of these gallery-style books are available as free PDFs from Peters' art site (often overlooked in favor of his more, um, eccentric science and phylogeny site). You can download both Giants of Land, Sea & Air Past & Present and A Gallery of Dinosaurs & Other Early Reptiles here.

And speaking of Prehistoric Beast... hell yeah.

Tyrannosaur Tooth Count

2011-05-17T11:53:00.000-07:00

Making the rounds right now in the media is a story about a newly described, well-preserved baby Tarbosaurus bataar that helps shed some light on the way tyrannosaurs grow, as well as touches on lingering controversies. Plenty of other blogs have already covered this, so here's a link to the backstory from Brian Switek at Dinosaur Tracking.

Interestingly, the baby Tarb has 15 teeth in the lower jaw, the same number as adult T. bataar. There has been controversy over whether or not tyrannosaurs reduced their number of teeth as they grew, particularly when it comes to the controversial taxon Nanotyrannus lancensis. Nano is known from two specimens (one is nicknamed "Jane") that, depending who you talk to, might really be simply juvenile specimens of the contemporary Tyrannosaurus rex. The differences cited to separate the two boil down to differences in the braincase (certain braincase changes were demonstrated in the new juvenile Tarbosaurus as well), and the number of teeth. Adult T. rex are usually said to have only about 12 teeth in the dentary, while specimens of N. lancensis have a whopping 17. The new juvenile Tarb suggests that in at least some tyrannosaurs, the tooth count is not drastically reduced during growth from juvenile to adult. However, as the authors caution, this same pattern may not necessarily hold true for other tyrannosaurs, even very close relatives.

And, the same pattern does not hold true for the very closely related T. rex. Also making the blog rounds these last few days has been this video of Jack Horner's talk at TEDx in Vancouver (thanks to David Orr at Love in the Time of Chasmosaurs for posting the video link!).

Here Horner gives the basics of his theory that dinosaurs are oversplit, not in the subjective taxonomic sense, but in the more objective biological sense that specimens that could be shown to belong to one species actually represent juveniles of other species. You've all heard the details before, but towards the end he shows a slide (reproduced above) that is pretty damning to the crowd who support the validity of N. lancensis. In fact, adult specimens of T. rex show a very wide ranging tooth count, and it even appears to correspond with relative size (and presumably growth stage. If anything, the number of teeth seen in N. lancensis specimens are only one or two teeth outside the range of variation for T. rex proper, a minor variant that can almost certainly be attributed to ontogeny, and not some cryptic species of giant tyrannosaur lurking in the Lancian faunas that has so far only been identified by two juvenile specimens, while the very common T. rex is known from no juveniles at all.

Anybody know the tooth count for the "Tinker" specimen, currently held in a private collection?

Confuciusornis: Bird-o-Dactyl

2011-05-16T12:09:00.000-07:00

There's been a lot of debate about Confuciusornis lately. Could it fly? If so, how? And how well? It probably wasn't doing anything like a modern bird does. Studies of its feather strength suggest it couldn't do more than glide (or could it?). But studies of its forelimb and shoulder girdle show it couldn't lift its arm much above the horizontal plane, making flapping pretty much impossible. Unless that huge, fenestrated deltopectoral crest gave it a rather unique flight stroke that only minimally involved the humerus.

Or, maybe this was a small theropod with enormous, high-aspect ratio wings larger than those of any other early bird, with asymmetrical feathers, puny feet and short legs ill suited for running and a small, barely reversed hallux ill suited for climbing, which couldn't flap and could barely glide with its thin feather shafts, yet is consistently found preserved as enormous flocks at the bottom of deep lake deposits. In which case the giant wings would be for display, obviously, to hopefully impress a predator so much that they decline to eat the poor bird which has no means of escape or defense other than to flee into the depths of the water like a 1960s brontosaur, only to remember that it also can't swim. No wonder they're extinct! Anyway... I hope much, much more study (and some wind tunnel tests) will eventually help untangle this mystery. For now, I was struck by something a little more frivolous. Working on a lateral view of Confuciusornis sanctus, checking and re-checking papers to make sure proportions are right, it started to look unmistakably like the profile of a... rhamphorhynchid pterosaur? Between this, and basal paravians with expanded, diamond-shaped vanes on the tips of their tails, in terms of general body plan there are some curious similarities (convergences?) between the first gliding/flying birds and primitive, long-tailed, high-aspect ratio-winged pterosaurs. My PhyloPic style silhouette version above.

Restoring _Hesperornis_

2011-05-03T03:18:00.001-07:00

Wow, lots of great responses to Monday's challenge! Some of you came very close to the particular aspect of the anatomy I was thinking of, though nobody got the specifics. However, many of you brought up additional issues with the reconstruction so I'll address some of those observations below before I get to the real answer.

1. Trish brought up the Coot-like lobed feet. While not the major fix I had in mind, this is also something I had already changed in the new version. The toes of Hesperornis are extremely similar to Grebes in terms of their anatomy, so while no soft tissue impressions of the toes exist for this group, it is almost certain that the toes were lobed rather than webbed (as in Loons and many other diving birds). I had initially based my illustration on this model, which restores the toe lobes divided into somewhat Coot-like segments. However, given the similarity to Grebes, it's probably a safer bet to go with a Grebe-like foot, with non-segmented, asymmetrical lobes (that is, like the flight feathers of birds, the 'vane' of each lobe would be small on the outside edge of the toe but broad on the inside edge). As this was still a work in progress when I began the revisions, I didn't yet add to the podotheca (foot skin covering) with its distinct scutes, but skin impressions from Parahesperornis show that they were present and, again, fairly Grebe-like in appearance.

Above: The feet of Hesperornis probably looked very similar to those of this Grebe.

2. Nobu Tamura pointed out that I bungled my interpretation of the leg integument. Good catch! In my own defense the text of Williston 1896 (which described skin and feather impressions in a specimen now referred to Parahesperornis) isn't exactly clear on the issue and the figure doesn't help much. Williston wrote: "I count twenty-six [metatarsal scutes] on the slab, and to the back part of the bone, while impressions of the feathers will be seen on the opposite side. These feathers were evidently long, reaching nearly to the phalangeal articulation". I remembered this as saying that the feathers essentially cover the tarsometatarsus and that the scutes were present close to the phalanges, but re-reading it sounds more like the MTs were only partially covered in long feathers (on the proximal part of the bone?) while the scutes were present across the distal part. The feathers were long enough to reach the toes, forming some very odd 'bellbottoms' around the scaly part of the metatarsus. I've tried to make this more clear in the new version.

3. Several people suggested that the wings are too prominent/visible, and honestly I'm not sure about this one. I don't know of any research on forelimb musculature that could suggest whether they were external or internal to the body wall, or whether or not they'd be useful in steering or something. I suppose we artists have license to go either way on this one right now, but as you can see I've de-emphasized them in the new version. The old one began to strike me as too Penguin-like, suggesting (even subconsciously) a role in propulsion that was probably not there in life.

4. Marco Tedesco wondered if the orange feathers on the head were incorrect. I have previously blogged about the likelihood of certain feather colors based on diet and structure. However, I don't think Hesperornis would have had much trouble sinking its teeth into some carotenoids to deepen the chestnut hue possible through melanin alone into a richer orange. We know that many cephalopods (including, apparently, some ammonites with preserved pigment) contain deep red carotenoid pigmentation, as do many fish, both of which may have been parts of hesperornithine diet. And in fact, these are colors found in modern Penguins. While on the subject of color, I chose to give Hesperornis a distinct, Penguin-like counter-shaded pattern. It seems to me that counter-shading gets apparently stronger in several independent lineages of diving birds, with more specialized diving forms (Penguins, Loons, Auks) wearing similar black/white colors (at least among breeding males) while less specialized forms (ducks, etc.) are counter-shaded with more subtle earth tones. Hesperornithines are probably the most specialized diving birds of all time (Zinoviev 2010) so it made sense to me to give them generally Penguin or Auk-like coloration.

Ok, now on to the "real" answer. Several people got this pretty close. It does indeed involve the hindlimb anatomy, including the position of the femur, the degree of sprawl in the legs and, ultimately, the life posture and ability to move around on land.

Several online sources have stated that Hesperornis was unable to walk, and must have instead slid around on its belly when on land. As I hinted in the last post, the Web site for the BBC show Sea Monsters (and possibly the show itself which I haven't seen) flat out states that they couldn't walk. But as we all know, TV documentaries are not exactly reliable sources. I tried and (initially) failed to find any support for this in the literature, aside from Marsh's own speculation in his famous Odontornithes monograph: "It may be fairly questioned whether it could even be said to walk on land, although some movement on shore was of course a necessity."

Two pieces of information can be combined to give the answer, the second of which also strongly impacts any life restoration, on land or swimming/diving. First, while the feet of hesperornithines are extremely Grebe-like, the rest of the hind limb anatomy is very similar to that of Loons (Reynaud 2005). Like Loons, hesperornithines had very long tibiotarsi, very short femora, and a high-angle hip socket with a very limited range of motion. Essentially, this means that the upper legs of Hesperornis were locked into a sprawl, which would have made standing upright very awkward. Loons rarely walk upright, and in fact I can't find any images online of such behavior. Loons also will push themselves along on their bellies, "flopping and dragging" as one site describes it (image above from birdinginformation.com)

Now, while the femur was basically immobile, it still had a role in contributing propulsive forces, as demonstrated by the arrangement of muscle attachments, which allowed it to conduct strong backward force through the leg. This is quite a feat because, (finally the answer to the challenge!) as in Loons, the entire, laterally projecting femur, the knee joint, and most, if not all of the tibiotarsus, was likely encased inside the body wall! Yes, according to some recent research (Zinoviev 2010), "the tibiotarsus...was held close to the body and was probably enclosed in the thickly feathered skin of the body wall". So images like mine, and the one below by Nobu Tamura (from Wikimedia Commons, CC licensed) showing free legs are wrong.

Like Loons (image of Common Loon above by Matthew Studebaker, from his photo blog), the feet stick out laterally from the very rear end of the animal near the tail, and it is the feet, rather than the leg as a whole, that provide most of the thrust and control (though, again, even the internalized leg musculature contributes to this).

So, congrats you those who noticed something wonky with the hind limbs! In all, hesperornithines were essentially super-Loons with Grebe feet, though their unique specializations for diving exceeded nearly all modern divers, making them possibly the most truly aquatic dinosaurs that have ever lived.

One last thing: quilong suspected something off with the posture of the neck. As he points out, highly specialized diving birds tend to have advanced ligament systems to keep the neck positioned during dives, and it tends to be streamlined into the body, often in a tight s-curve. This is correct, and my image is a bit misleading as it's meant to depict a hesperorn swimming at the surface with its neck at full extension to reach above the water, like an Anhinga (or indeed, a swimming Loon, which tend to swim almost completely submerged except the top of the back, the head, and the neck). While diving, the long neck would almost certainly be held in a position closer to the body so as not to be subject to forces that would bend it every which way. Whether or not hesperorns did have advanced ligament systems in the neck to help with this, I don't know, but given their extremely derived morphology it wouldn't surprise me.

References:
* Johnsgard, P. (1987). "Diving Birds of North America: 2 Comparative Distributions and Structural Adaptation. " Papers in the Biological Sciences.

* Reynaud, F.N. (2005). "Functional morphology of the hindlimbs of Hesperornis regalis: A comparison with modern diving birds." Geological Society of America, 37(7): 133A.

* Zinoviev, A. (2010). "Notes on the hindlimb myology and syndesmology of the Mesozoic toothed bird Hesperornis regalis (Aves: Hesperornithiformes)." Journal of Systematic Paleontology, 9(1): 65-84.

I'm Doing It Wrong: More on _Hesperornis_

2011-05-02T10:23:00.000-07:00

Following the last post on beak anatomy in toothed birds like Hesperornis regalis, I have been coming across some confusion online about another aspect of this ancient diving bird's anatomy. This factoid shows up in a lot of sources (including the official web site for a certain CGI-based TV show) but never, it seems, with a solid reference. I have been trying to dig into this issue myself and am finding out some interesting new info on the anatomy of this bird, to the point that one of my in-progress drawings had to be halted and revised. More on this in an upcoming post, but for now, see if you can figure out what's wrong with this picture:

You're Doing It Wrong: Birds With Teeth

2011-04-20T05:59:00.000-07:00

Above: If only Charlie from Always Sunny could visit the Mesozoic.

My previous post on beaked theropods left one thing a little too ambiguous for my taste. We know that many non-avian theropods had beaks, but we also know that, famously, many of these also possessed teeth. An issue I've often come across in palaeontography is how exactly to restore this. Should the teeth erupt directly from the beak? Were they segregated to different portions of the jaw? Did the beak edge overlap an inset tooth row? This is an issue which I've rarely seen discussed online, let alone in the literature, so hopefully this post can be a starting point to suss things out. Because it's one of the most famous examples and one that's been frequently discussed in the lit, I'll focus specifically on Hesperonris regais here.

Look at almost any life restoration of Hesperornis, and it will show a keratinous beak covering the entire extent of the upper and lower jaws. I say "almost" only hypothetically, because I've literally never seen a hersperornithine drawn any other way (please link me one if you can). Here's a link to a google Image search for Hesperornis, and every reconstruction is the same. Some, like the beautiful painting above (by artist Larry Felder), clearly show teeth erupting directly from the tomia (edge) of a continuous keratin beak. As discussed last time, the continuous appearance of this beak is likely incorrect in itself, since non-avian birds probably all had 'compound rhamphotheca' made up of several distinct plates that are often visible in life.

Above is bit of anatomy lingo to make this discussion easier. The rhamphotheca ("beak") is usually divided (and literally divided, in the case of compound beaks) into several segments or regions. The figure is figure 5 from Heironymus & Witmer, 2010.

Now, for comparison, here are two views of the skull of Hesperornis regalis. On top is a ventral view of the skull showing the premaxilla and maxilla, from Elzanowski 1991. The bottom is a right lateral view of the skull taken from Heilman, 1926.

A few things to note here. The dentary teeth continue almost all the way to the tip of the jaw, though the very tip (and small predentary that was probably present) were toothless. In the ventral view of the upper jaw, you can see indentations where the lower teeth would have locked into the premaxilla. If there was a hard beak present, it would have been pitted to accommodate the dentary teeth (these are labelled dp, dental pits, in the top figure above). However, you can also see that the indentations are inset to the jaw a bit. The edges of the upper jaw slightly overhung the lower jaw, which would have allowed for the tomia, if it was there, to not come into contact with the lower teeth, causing wear any time the mouth closed.

The back of the jaws are a different story. As you can see in the lateral view, upper teeth are present only in the maxilla, not the premaxilla, and therefore restricted to the very back of the mouth. This can also be seen in the 'dental grooves' (dg) in the ventral view of the skull.

According to Heironymus & Witmer 2010, in both Ichthyornis and Hesperornis, the premaxillary nail and mandibular nail were the most heavily keratinized part of the beak. This is where the beak would have been most solid, like a normal bird bill. The same authors note that the simple presence of teeth in the maxilla and dentary of these species probably means that they lacked the latericorn and ramicorn parts of the beak entirely, and that the presence of cornfield rhamphotheca on the edges of the jaws may be unique to modern birds. However, as I noted above, the premaxilla in Hesperornis is also toothless and provides area for a tomia of some kind to be present. This would have been somewhat softer tissue, like the more pliable bills of ducks and geese. Further support for the presence of a beak on the premaxilla comes from the presence of a rhamphothecal groove on the dorsal part in front of the naris (visible but unlabeled in the figure above).

So how far did the beak extend? Heironymus & Witmer found that the latericorn almost always extends to the back of the subnarial bar in birds. This is a process of the premaxilla that extends back to separate the naris from the maxilla. Basically, this means that the beak will very rarely, if ever, extend onto the maxilla itself. As you can see in the lateral figure above, the maxilla in Hesperornis even compensates for this limitation by extending a bit forward underneath the subnarial bar to extend the tooth row anteriorly a bit past the possible full extent of the beak.

So, based on the evidence above, Hesperornis probably had a beak like the recon I whipped up below. The toothless, pointed tips would have been solid, normal beak, while the rest would have been more like stiffened skin grading into normal skin and feathers toward the back of the skull. At no point would the teeth have occupied the same physical space as the rhamphotheca. Basically, the rhamphotheca never seems to have housed tooth sockets. The beak and the teeth were segregated to different parts of the jaws. In short, no Mesozoic birds had "teeth in their beaks" as is often stated and depicted in art, but rather had both beaks and teeth, in different parts of the skull, and presumably serving different roles in food capture and processing.

References:

-Elzanowski, A. (1991). "New observations on the skull of Hesperornis with reconstructions of the bony palate and otic region." Postilla, 207: 1-20.

-Heironymus, T.L. and Witmer, L.M. (2010). "Homology and evolution of avian compound rhamphothecae." The Auk, 127(3): 590-604. PDF link

April fools! A bit late but who's counting?

2011-04-06T13:48:00.001-07:00

UPDATE!

This is a late-arriving April Fools joke. Got me!

Archaeocursor. The bahariasaurid (yes, new family) with feathers. Commence head explosions.

Paul C. Sereno, Oliver Rauhut, Xing Xu, Wang, Y., Zhu, T., Gao, X. & Gong, D. (2011). "Basalmost theropod with filamentous integumentary structures and new clade of basal 'carnivorous' dinosaurs". Kirtlandia 37: 82-113.

I haven't seen any discussion of this, save that it's been added to Wikipedia. Apparently from the Tiaojishan formation, the same beds that have yielded Anchiornis and Tianyulong. Also, note the scare quotes around "carnivorous." Could their proximity to Limusaurus mean bahariasaurids are partially or wholly herbivorous? Just idle speculation for now. More if/when I get my hands on this paper.

You're Doing It Wrong: Dinosaur Tails

2011-02-21T15:41:00.001-08:00

A new post by W. Scott Persons over at the Art Evolved blog is an excellent overview of why most artists, even the pros, have been getting dinosaur tails completely wrong since the Dinosaur Renaissance. It makes me feel a little better to know I was in the company of Mark Hallett and other titans of paleoart when I'd simply make up cool-looking tail musculature in my older drawings with no regard for anatomy...

You can read the post here.

Heat, Feathers, and Half-Arsed Velociraptor

2011-02-14T15:45:00.001-08:00

Above: Comparison of common Velociraptor reconstructions by artist Tomozaurus, used with permission.

A month or so ago, this diagram (also shown above) produced by an artist known as Tomozaurus stirred up a good deal of debate over at DinoForum. Tom was trying to illustrate common misconceptions about the most likely life appearance of dromaeosaurids. By now, everyone (including the birds-are-not-dinosaurs crowd) agree that dromaeosaurids were fully feathered and pretty bird-like. Whether or not to consider them actual birds is a matter of semantics at this point. But, among dino-fans weaned on their depictions in pop-culture, there seem to be a lot of heated reactions to depicting them as too bird-like. Many will admit that they had feathers, but stop short at reconstructing them in a really bird-like manner, preferring a short, cat-like pelt that allows the graceful and well-known contours of the skeleton to show through in life. But compare any bird skeleton to a live specimen, even those with "simple" feathers like chicks or kiwi, and you'll immediately see that this is the wrong way to go. Even most feathered theropod fossils show a feather covering that does not hug the body contours, but like modern birds, consists of a lot of poofy, long feathers (especially at the breast and neck) that would make them look very "bulky."

The debate about the above image concerned how well these principles should apply to larger dino-birds like Velociraptor. Velociraptor is perhaps the worst offender in this area due to its enormous popularity: it has a very well-ingrained image in the popular consciousness that, in all likelihood, doesn't match how it would have appeared in life. But just how likely is any reconstruction?

The fact is, we don't know very much at all about the feathering in Velociraptor. At least one specimen preserves quill knobs on the ulnae where large secondary feathers must have attached, so we know for a fact that it had wings. But what about the body feathers? Tom's picture supposes that we would do best to reconstruct the remaining feathers based on related (but much smaller) species in which the full compliment of feathers has been preserved; things like Microraptor, Anchironis, Archaeopteryx, and the unnamed species nicknamed "Dave". Based on these, Tom gave his "correct" Velociraptor a full set of long primary feathers (present in Micro and Archie but much shorter in Dave and Anchi), a feather crown (present in Micro and Anchi but not Dave and Archie), flight feathers on the hind legs (present in Micro, Anchi and Dave but not Archie, though the last does have "bell bottoms" of long, non-planar pennaceous feathers down to the ankles), and feathers covering the face and most of the snout (present in all but possibly Archie). Last, he restored the body contour feathers as pennaceous rather than downy. This is the most problematic, present (apparently) in Anchiornis but not in the others (Archaeopteryx has pennaceous feathers over the hips but this appears to be a single or paired feather tracts (pterylae), and the rest of the body is covered in plumulaceous feathers or simple protofeathers).

In contrast, Tom presents two "incorrect" versions: the Greyhound/Lizard (which is so obviously wrong there's not much else to say about it) and the "Half-Arse." The later is interesting because while it deviates considerably from the inferences drawn based on its relatives, there's nothing obviously inaccurate about it, or at least implausible. The drawing seems to be identical to the Velociraptor computer models used in the TV show Dinosaur Planet: feathered, but barely so, with a short, mammal-like pelt hugging the contours of the body, a large crown for display, and many featherless areas of the body.

Defenders (or at least devils advocates) for this reconstruction pointed out that it doesn't deviate too wildly from larger, flightless modern birds. Ostriches (Struthio camelus) are famously stripped-down of feathers, more so than many people think (see image above, showing the naked underside of the wings and featherless torso). However, ostirches are also quite a bit larger than Velociraptor, and smaller ground birds from the same environment like the Secretary Bird (Sagittarius sepentarius) lack extensive naked patches. On the other hand, Rhea (Rhea spp.), which are similar to Velociraptor in weight, do have naked patches on their underwings, though not as extensive as ostirches (see image below).

So, while I still think the rather short body feathers would be a little far-fetched (longer ones would be better for thermoregulation--if overheating is the issue, the feathers would probably simply be lost entirely, which is not the case in modern birds that lose feathers only on extremities), the Half-Arse version doesn't seem all that bad.

But there's more that needs to be taken into account. A great post at Tetrapod Zoology today touches on some aspects of featherless patches on birds and its effects on thermoregulation. A bit counter-intuitively, a heavy feather coat can actually help keep birds cool--they're general insulators, not simply heat-trappers, like a thermos. In the post, Darren Naish discusses male wild turkeys, which famously have bare heads with brightly colored, outlandish soft tissue structures for display. This actually puts the male birds at a disadvantage, because all that bare skin causes the males to be more prone to overheating, requiring them to spend more time cooling in the shade than females. Like the tail of a peafowl, the naked heads of turkeys are a sexual display structure that puts the birds at a disadvantage when it comes to survival. Granted, this is only the example of one bird. I don't know how this might apply to, say, ostriches. Ostriches, like Velociraptor, inhabit a hot, arid environment. Indications suggest that Velociraptor lived in an even more desert-like setting, dominated by barren dune fields, making it a solidly desert bird. Would the extensive bare patches of the Half-Arse be beneficial in this setting, or would they tend to drastically overheat the animal under an unrelenting desert sun with few sources of shade?

Above: Photo of a Greater Rhea (Rhea americana) by Ramon Moller Jansen. This species is about the same size as an adult Velociraptor mongoliensis, but live in more lush environments with some tall shade plants.

According to Willmer, Stone & Johnson (2000), many ratites use similar strategies to regulate their body temperature and prevent overheating. Ratites such as the Rhea store their heat while active, and only actively attempt to shed it while at rest. This is achieved through strategies such as panting, drooping the wings (allowing air to conduct heat from the sparsely feathered underwings while at the same time shading them), and raising or lowering the sparse feathers of the back (known as ptilo-erection). It's interesting to note that in Archaeopteryx, the back is the only region of the body that has pennaceous feathers, better for trapping or shedding heat. With all of these adaptations, ostriches rarely have to seek shade, even when it's available (Levy et al., 1990). So while feather-loss in modern birds is an important strategy for those living in hot, arid climates, note that the pattern of loss is not random or extensive, but rather strategic, allowing for maximum thermal regulation.

If I were to speculate, I'd make an educated guess that bare patches in Velociraptor must have been limited to the legs, flanks and underwings for these reasons. Those areas could be shaded simply by the animals own body and cooled easily as needed. The head and neck would have been most prone to overheating. The animal could only shade these by adapting a Mei long style sheltered posture with the head tucked under the wing and body feathers (but only if a hefty body covering was present, not a form-fitting pelt). One question I can't seem to find an answer to is how ostriches cope with direct sun to their nearly bare heads and necks--the problem faced by male turkeys. My wild guess would be that the heads of turkeys are highly decorated with thickened skin, presumably a better insulator than the plain skin of an ostrich, which would allow more loss of heat to the air. Or maybe they bury their heads in the sand to keep cool... (I kid, I kid!). If anybody knows of any studies or physiological issues that would cause this to be a problem for one and not the other, please leave a comment!

References:
* Levy, A., Perelman, B., Grevenbroek, M.V., Creveld, C.V., Agbaria, R. and Yagil, R. (1990). "Effect of water restriction on renal function in ostriches (Struthio camelus)." Avian Pathology, 19: 385-393.
* Willmer, P., Stone, G. and Johnston, I.A. (2000). Environmental Physiology of Animals. Wiley-Blackwell, Science. 644 pp.

Scientific Anachronism and why Biostratigraphy Matters

2011-01-26T15:54:00.000-08:00

Image: Stegosaurus confronts Tyrannosaurus, from Walt Disney's Fantasia. Such anachronistic views of paleontology could never form the basis of peer-reviewed literature, could they?

A new study (Carbone, Turvey &Bielby, 2011) suggests T. rex could not have been a pure scavenger.

Yeah, I know. This is already the universally accepted position of modern paleontologists. Of course T. rex scavenged if it could, but there is ample reason to think (and ample fossil support backing this up) that it hunted as well. Even the originator of the scavenging thoery, Jack Horner, has basically admitted that he only came up with it as a way to get young people to think critically about their own preconceptions (obviously, he has never met any young paleontology fans. I'd have given up that strategy after I witnessed my first T. rex vs. Spinosaurus debate).

However, as Denver Fowler pointed out on the DML today, drawing an obvious conclusion is the least of the paper's problems.

I recently participated in at least two paleoart discussion threads in which really awesome artists showed off some mind-blowingly fantastic paintings depicting the Jehol biota. I know first hand that both artists are completely on the ball and know their stuff. But both made common errors in the often neglected field of biostratigraphy.

In one, a Sinornithosaurus watches as two Microraptor glide down from the trees. These are two similar animals from around the same time and place. However, there is no evidence that they ever met. All known fossils of Microraptor come from the Jiufotang formation, dated to 120 million years ago, plus or minus 700k years. The youngest Sinornithosaurus fossils are from the upper Yixian formation, dated to around 122 million years ago. The timespan and environment are grossly similar, but 2 million years is still a long time in a world where most dinosaur species, if not genera, don't span more than a couple million years (and the ones that do are probably egregiously over-lumped, like Iguanodon).

Another painting portrayed a Yixian formation scene with Yixian ornithopods and Yixian insects being fed on by Jeholopterus, a pterosaur which lived in the Daohugou biota, in beds dating to at least 150 million years ago, a full 25 million years before the Yixian faunas existed. The error here was probably based on a confused history of dating the formations (old sources placed the Yixian in the late Jurassic), and many sources, both professional and popular, which tended to conflate the various Chinese feather-preserving formations into one amorphous pseudo-fauna.

Artistic depictions throwing together prehistoric animals from disparate times are obviously nothing new. Walt Disney Pictures has done this at least twice, first and most famously in Fantasia (Stegosaurus meets T. rex meets Pteranodon), and later and more flagrantly in Dinosaur (I can't think of any two animals in that movie that were actually contemporaries, and many didn't even live together on the same continent).

This is somewhat excusable when it's done for the sake of art (as long as that art isn't passed off as being scientifically rigorous). But this kind of disregard for, or generalization of, biostratigraphy can creep into science and completely foul up your results.

In Carbone et al. 2011, the authors attempt to calculate the amount of potential carcasses that would have been available to scavenging Tyrannosaurus rex in its environment to make their case. Their lists of T. rex contemporaries are reproduced in part below:

Species and body masses of carnivorous non-avian theropod dinosaurs of Late Cretaceous North America
Dromaeosaurus albertensis
Richardoestesia gilmorei
Richardoestesia isosceles
Saurornitholestes
Velociraptor sp.
Troodon formosus
Chirostenotes elegans
Chirostenotes pergracilis
Nanotyrannus lancensis
Albertosaurus sarcophagus
Tyrannosaurus rex

Species and body masses of herbivorous dinosaurs of Late Cretaceous North America
Parksosaurus warreni
Prenocephale edmontonensis
Ornithomimus velox
Struthiomimus sp.
Thescelosaurus garbanii
Thescelosaurus neglectus
Leptoceratops gracilis
Montanoceratops sp.
Pachycephalosaurus wyomingensis
Edmontosaurus annectens
Edmontosaurus regalis
Edmontosaurus saskatchewanensis
Lambeosaurus sp.
Parasaurolophus walkeri
Edmontonia rugosidens
Ankylosaurus magniventris
Triceratops horridus
Alamosaurus sanjuanensi

The authors state, "our species list is treated as representing a consistent sympatric faunal unit across this region for the purposes of analysis." But they absolutely don't represent that.

If you have even a little bit of a handle on Late Cretaceous biostratigraphy, or the paleoecology of T. rex, you may notice a few problems with these lists. Namely, the fact that they are complete messes, incorporating erroneous or outdated taxonomic assignments or over-generalizations of the geologic column.

This kind of data crunching would require taxa to be broken down on an environment-by-environment basis. That is, in order to be meaningful, all included taxa have to be demonstrated to be contemporaries. Most of the taxa in those lists were not, or can't be said to have been with any confidence.

To be fair, some of the mistakes are due to very new research, some of which has only appeared in abstracts or mentioned briefly in papers. For example, while Edmontosaurus regalis is widely reported from the late Maastrichtian Hell Creek and Lance formations, this is mainly by default, skeletons that are not identifiable to the species level. Ongoing stratigraphic and taxonomic work by Nicolas Campione has shown that E. regalis was actually not a contemporary of E. annectens, and specimens assignable to that species are only known from lower strata. The validity of E. saskatchewanensis, which is from the same stratographic level as T. rex, is pretty dubious. E. annectens is its likely synonym.

Parasaurolophus is known exclusively from the Campanian-age Dinosaur Park Formation, over five million years before the earliest known T. rex fossils. Same goes for Lambeosaurus. While the former was tentatively identified in the Hell Creek by Sullivan & Williamson (1999), this was based on very fragmentary remains that almost certainly belong to Edmontosaurus instead. Montanaceratops is from the St. Mary River Formation, dated to the early Maastrictian and also pre-dating T. rex.

Some cases are even more nuanced. Alamosaurus did coexist with T. rex, but not with many of the other listed species. Current indications are that the southern part of North America during the late Maastrichtian supported a different fauna from the north, comprised many of species which are related to, but distinct from, their northern counterparts. Alamosaurs, for example, did not coexist with Triceratops, but Ojoceratops (assuming they're distinct). It didn't coexist with Torosaurus latus (which the authors apparently lump with Triceratops), but with "Torosaurus" utahensis. Indications are that these beds are a bit earlier than the late Maastrichtian as well, so while Alamosaurus lived alongside Edmontosaurus, it was E. regalis rather than E. annectens.

The carnivores don't fare much better. Most are tooth taxa, like Troodon (another Dinosaur Park critter from the Campanian). While "Troodon" teeth are known from the same beds as T. rex, they're almost certainly not Troodon formosus. The same goes for Dromaeosaurus. However, these are taxonomic issues, not biostratigraphic ones, and don't really affect species count--whatever we name them, there were at least one troodontid and at least two dromaeosaurids present (though the authors erroneously list both Velociraptor and Saurornitholestes, based on the same specimens, first referred to the former and then the later, both incorreclty). Not so for the inexplicable inclusion of Albertosaurus. I can figure out where these other misplaced species came from, but I don't know of any albertosaur remains having been reported from Lancian-age deposits. Anybody? Either way, it's almost certainly an error (as is making Nanotyrannus a distinct taxon, but that's another story).

So you can see why failing to understand which dinosaurs lived together, specifically, can have major implications for actual science. This kind of paper also illustrates why it's a bad idea to keep non-diagnostic genera around as nomina dubia and not sink them into their better known, probably-synonymous counterparts or simply designate neotypes from the good material. These authors avoided pitfalls like including Thescelosaurus infernalis (=T. sp.), Manospondylus gigas (=Tyrannosaurus rex), Aublysodon molnari (=Tyrannosaurus rex), Thespesius occidentalis (=Edmontosaurus annectens), Trachodon mirabilis (=Edmontosaurus annectens), or Agathaumas sylvestris (=Triceratops horridus), but those taxa aren't doing science any favors by cluttering the playing field.

Here's my preliminary attempt to clean up their faunal lists, based on a Lancian-age, northern ecosystem: (updated thanks to additional information provided by Mickey Mortimer in the comments. note that I'm following the authors in not including avialans)
Dromaeosaurinae sp.
Zapsalis abradens
Richardoestesia gilmorei
Richardoestesia isosceles
Troodontidae indet. spp. (multiple species)

Pectinodon bakkeri

Paronychodon sp.

Avimimidae sp.
Chirostenotes elegans

Chirostenotes? sp.
Tyrannosaurus rex (=Manospondylus gigas)
Struthiomimus sedens

Ornithomimus velox

Ornithomimidae sp. (="Orcomimus")

Dromeiceiomimus sp.

Alvarezsauridae sp.

Therizinosauridae sp.
Thescelosaurus garbanii
Thescelosaurus neglectus
Leptoceratops gracilis
Pachycephalosaurus wyomingensis
Edmontosaurus annectens (=Thespesius occidentalis)
Edmontonia schlessmani (=Denversaurus schlessmani)
Ankylosaurus magniventris
Torosaurus latus?
Triceratops horridus (=Agathaumas sylvestrus?)

References:
* Campione, N.E. (2009). "Cranial variation in Edmontosaurus (Hadrosauridae) from the Late Cretaceous of North America." North American Paleontological Convention (NAPC 2009): Abstracts, p. 95a.

Brilliant New Anchiornis, the Bone Wars, and More

2011-01-20T16:57:00.001-08:00

A few quick news items while I finish up a post exploring the extent and structure of beaks in theropods...

"Dinosaur Wars" on PBS's American Experience
I haven't had a chance to check out this new PBS special on the Bone Wars (darn you, unreliable internet connection!) but the whole thing can be seen here.

"Dinomorphosis" on National Geographic's Naked Science
Airing next week, this special explores current knowledge of feathered dinosaurs. You can see the trailer here (not bad, aside from the rampant bunny hands and baffling statement that all feathered dinosaurs were carnivorous), and a related article from the magazine with photo gallery.

Be sure to check out the image of an undescribed Anchiornis specimen in the photo gallery. The preservation is utterly phenomenal, and even the previously-described color pattern is visible to the naked eye.

Also exciting is a new paper on sexual dimorphism and reproduction in the pterosaur Darwinopterus. Check out the great article summarizing the findings at New Scientist, and this skimpier Discovery article highlighting an awesome new restoration of male and female specimens by Mark Witton.

Theropods That Fit the Bill

2011-01-16T21:31:00.000-08:00

[Image: Skull of a gull compared to a living specimen. The apparent differences in the extent of the beak are caused by the presence of different kinds of rhamphotheca.]

One aspect of Mesozoic birds and other theropods that doesn't get discussed much are their bills. Beaks or beak-like structures (generally, rhamphotheca) have a wide but extremely spotty distribution among Mesozoic theropods, and numerous theropod groups seem to have evolved them independently of one another.

Perhaps the most basal known theropod that likely bore a beak (assuming we can safely exclude the skull material attributed to the infamous "first bird" Protoavis) is Limusaurus inextricabilis from the Oxfordian, about 160 million years ago. Though it belonged to the otherwise toothy clade Ceratosauria, Limusaurus was completely toothless. To be precise, most theropods have teeth in the three major sections of their jaws: the premaxilla at the front of the skull, the maxilla behind it, and the dentary, or lower jaw. Ornithischian dinosaurs had an additional bone, the predentary, at the tip of the lower jaw that was always toothless, indicating that almost all ornithischians probably bore a beak, at least on the lower jaw (and ceratopsians added an additional, pre-premaxilla: the rostral). Limusaurus lacked teeth in the premaxilla, maxilla, and dentary, so it was completely toothless and, therefore, it is assumed to have been beaked.

[Image: Skull reconstruction of Limusaurus, posted by Dave Hone at his Archosaur Musings blog.]

As far as I know, Limusaurus is the only non-coelurosaurian theropod that bore a beak. Generally, this fits well with the idea that non-coelurosaurian theropods were hypercarnivorous flesh eaters with little variation in their diets. However, as a number of recent papers by Lindsay Zanno and colleagues has shown, coelurosaurs started playing around with omnivory and herbivory, and as a consequence, many lineages cast off some or all the sharp teeth that characterized their ancestors.

[Image: Skull reconstruction of Pelecanimimus by Ville Sinkkonen]

The first coelurosaur lineage to start shedding their teeth permanently were the ornithomimosaurs. This group is well-known for their toothlessness, and evidence from specimens with preserved keratin sheaths on the jaws (Norell et al, 2001) show definitively that they bore keratinous beaks on both the upper and lower jaws, at least in advanced species. As expected, the most primitive ornithomimosaurs still retained teeth. Pelecanimimus polydon, as its name implies, had teeth in the premaxilla, maxilla and dentary. The next most advanced ornithomimosaur, Harpymimus, is the first example among theropods of the "half beak." While its upper jaw was toothless and likely beaked, it retained teeth in the lower jaw. I'll come back to the implications of these "half beaks" further down. The most basal ornithomimosaur wich lacked teeth completely seems to be Garudimimus, though the status of Beishanlong is unknown.

After the ornithomimosaurs, beaks are found in therizinosaurs. Again, early forms like Falcarius had a full compliment of teeth, but in laker ones like Beipiaosaurus, the teeth became restricted to the middle of the jaws, leaving room for a beak in the front, similar to ornithischians. Next, oviraptorosaurs seem to have developed beaks fairly early in their evolution. While Incisivosaurus had teeth in both jaws (though restricted to the tips), Caudipteryx had only a few teeth in the premaxilla, another example of a "half beak" where a toothless lower jaw is matched with a toothy upper jaw. While the several possible intermediate forms lack skulls, both caenagnathids and oviraptorids proper had fully toothless jaws, so presumably they were fully beaked by the time they diverged.

Next up were the deinonychosaurs, and while some seem to have dabbled in omnivory, they were mainly carnivorous, and none seem to have developed beaks. Greg Paul is infamous for restoring them with cornified tissue or "proto beaks" at the tips of their jaws adjacent to teeth, but there isn't much evidence to support this idea as far as I know. However, many deinonychosaurs which preserve feathers show a (usually small) portion near the tip of the snout that is unfeathered. This featherless snout tip is also seen in some toothed, presumably beakless enantiornithines. It's possible this could be evidence of "rhamphotheca" in its loosest sense--the very lightly cornifies, flexible bill skin found toward the back of the beaks in some modern birds, where the horn-like, kerationous portion thins out into normal skin. More on these flexi-bills down the page.

[Image: My own simplified cladogram of Aviremigia showing some notable occurrences of beaked and half-beaked and beak-free birds. Excuse the quality in close-up, some of these were yoinked from works in progress.]

Around the base of Avialae, the occurrence of half-beaks seems to explode. Almost all known basal, non-pygostylian avialans lack teeth in the upper jaw (e.g. Jeholornis, Yandangornis) or lower jaw (omnivoropterygids) and, possibly, both (Jixiangornis preserves no teeth and may have been full-beaked, but the skull is badly crushed, and crushing has been known to obscure the tiny teeth that should be present in other basal avialan specimens). This trend appears to culminate with the confuciusornithids, which are not only toothless but have sharply pointed jaws that, in some very rare specimens, preserve the actual keratin of the beak. These impressions show that even in these fully beaked birds, the rhamphotheca was thin and delicate and probably not as heavily mineralized as in modern birds.

The next bit is rather odd given the trends seen at the base of avialae. In most basal ornithothoraces (the group that includes enantiornithines and ornithuromorphs), the jaws are fully toothed, with no evidence for beaks. It's tempting to think that this could unite the enantiornithines with the toothy, beakless deinonychosaurs and Archaeopteryx in a "Sauriurae" to the exclusion of the beaked birds. However, given the numerous times beaks have evolved independently in vertebrates, it's not unthinkable that each of the half-beak examples above arose independently of one another (or, that some reversal occurred at the base of ornithothoraces to return birds to a state of fully-toothed maws). Either way, while many enantiornithines preserve jaw material, only a few exhibit the kind of toothlessness at the front of the jaws that could imply a beak. These include the half-beaked Alethoalaornis (with a toothless dentary but toothed premaxilla), the fully-beaked Gobipteryx, and the half-beaked Boluochia. Boluochia had teeth in the dentary but none in the upper jaw and, in fat, had a strongly hooked premaxilla similar to the hooked beaks of modern raptors. Enantiornithine relationships are too unresolved to be able to tell if these beaked birds all form a natural group, or if beaks evolved multiple times among enantiornithes, but given their diversity it's a safe bet that many different lineages came up with their own particular feeding solutions.

[Image: The compound rhamphotheca of an albatross is visible as distinct sutures, and is also found in some non-avian birds. Image from the RSPB.]

As expected based on the enantiornithine record, most primitive ornithuromorphs (the fan-tailed birds, including Aves) either lakced beaks or exhibited a half-beaked configuration. While Hongshanornis was originally reported to have a beak, Jingmai O'Connor and colleagues later showed that it had tooth sockets preserved in the upper and possibly lower jaws (same goes for the related Longicrusavis). The earliest fully-beaked ornithuromorph is also one of the most primitive, however: Archaeorhynchus lacked teeth and had a flattened, Spoonbill-like beak. The songlingornithids (such as Yixianornis), and the later hesperornithines and Ichthyornis all had a therizinosaur-like configuration, with toothless premaxilla (and even predentary-like bones in the hesperornithines) with toothy maxilla and dentaries. Evidence from bone texture shows that likely had keratinous beaks at the tips of their jaws, and either feathery toothed jaws or pliable, skin-like rhamphotheca further back. Since both major lineages of avians lack teeth, it's likely their common ancestor was also fully beaked, so teeth must have been lost for good in the bird lineage shortly after Ichthyornis diverged. Interestingly, studies of ichthyornithines and hesperornithine bone structure shows that they likely had "compound rhamphotheca", and this may have been the ancestral condition for modern birds (Heironymous & Witmer, 2010). While the quintessential bird beak is made up of a single keratin sheet covering the jaw, in species with compound beaks, the keratin is arranged in discrete plates on the jaws. This can best be seen in some modern seabirds like the Albatross.

Unfortunately, in interesting taxa like Hollanda, Gansus, and Patagopteryx, the condition is unknown. However, we can use parsimony and phylogenetic bracketing to try and come to a reasonable guess. Most studies find these three to be ornithuromorphs more primitive than the hesperornithines and Ichthyornis. Given the condition in Ichthyornis, it's most likely that Archaeorhynchus evolved its toothless beak independently of more advanced birds, most of which have toothed upper and lower jaws with beaked tips in the grade between Archaeorhynchus and Aves. While the three intermediate birds may well have lost some or all of their teeth independently again, it's probably more parsimonious to assume that like hesperornithids, hongshanornithids and songlingornithids, they were either fully toothed or had beaks restricted to the tips of the jaws.

[Image: Cassowary chick by Michael Thirnbeck, from Flickr. Note the horny beak only covers the tip of the bill, leaving the nostril surrounded by more skin-like tissue. Thanks to meidamon over at DinoForum for finding this and other pictures illustrating beak anatomy.]

So, to rephrase an old fallacy, what use is half a beak? Many Mesozoic coelurosaurs had teeth only on the upper or lower jaw, and most researchers have assumed that edentulous = beaked (see for example Zanno et al., 2009). But "beaks" are more complex than simple sheathes of keratin covering toothless parts of the jaw. As anatomist Larry Witmer has explained (in print as well as on the DML), rhamphotheca can consist of everything from solid, hard keratin (which, obviously, is a bit antithetical to tooth growth and replacement) to softer, pliable, barely mineralized tissue. For example, it's a general rule of thumb that the keratin rhamphotheca never completely encloses the external nares, meaning the nostrils of a bird are never encased in keratin. This is most obvious in species that have a cere, a prominent fleshy part of the posterior rhamphotheca found in pigeons, parrots and hawks, among other birds. But in many other birds (especially aquatic forms like ducks and gulls), the nostrils do appear to erupt from mid-bill. What's going on?

[Image: Duck skull by ~Oryx gazella~, from Flickr. Note that only the tip is fully keratinized.]

Basically, the "beak" of a duck (and many other birds) is only really solid towards the tip. The broad bill of a duck is, laterally, fairly soft, and made of rhamphotheca that is only lightly mineralized. Essentially, it's mostly toughened skin (this is why ducks and other anseriforms are particularly prone to bill injuries). In the kiwi, the nostrils don't just erupt from the "beak", they occur at the very tip. Again, the bill of a kiwi is not highly keratinized, but rather made up of soft, pliable integument full of sensory organs (Martin et al., 2007).

So, our mysterious half-beaked birds may have had some cere-like tissue covering the upper portion of the toothed bill, while the lower portion contained more keratinized rhamphotheca. Perhaps the upper jaw had a small keratinized tip wedged between the front teeth, as seen in toothed pterosaurs like Rhamphorhynchus and Pterodactylus. Or maybe the half-beaks of some of these birds contained little to no keratin at all. As the kiwi shows, it's not always necessary for all food-aquisition behaviors to have a beak or teeth.

Hopefully, this rough guide can also serve as a reference for artists, many of whom are a bit over-eager to add a beak to anything that is called a "bird." While a wide range of rhamphotheca like structures may have been present on Mesozoic birds, it wasn't necessarily present on all of them, and many probably looked a bit strange compared to the simple, smooth yellow bills of modern birds.

References
* Heironymous, L. and Witmer, L.M. (2010). "Homology and Evolution of Avian Compound Rhamphothecae." The Auk, 127(3): 590-604. doi: 10.1525/auk.2010.09122
doi: 10.1525/auk.2010.09122
* Martin, G.R., Wilson, K.-J., Wild, J.M., Parsons, S., Kubke, M.F., et al. (2007). "Kiwi Forego Vision in the Guidance of Their Nocturnal Activities." PLoS ONE, 2(2): e198. doi: 10.1371/journal.pone.0000198
* Zanno, L.E., Gillette, D.D., Albright, L.B., and Titus, A.L. (2009). "A new North American therizinosaurid and the role of herbivory in 'predatory' dinosaur evolution." Proceedings of the Royal Society B, 276(1672): 3505–3511. doi: 10.1098/rspb.2009.1029.

Tearing Up Pteranodon

2010-12-14T19:54:00.000-08:00

Above: Male (foreground) and female Geosternbergia sternbergi, mounted casts at the Royal Ontario Museum. Photo by Kenn Chaplin, licensed.

On the PteroGoss front, I just came across a new paper that doesn't seem to have received much press online yet. A new paper by A.W. Kellner has appeared online concerning the taxonomy of the small but well-known pterosaur family Pteranodontidae. The abstract can be found here.

This paper is interesting in that it attempts to reverse some of the trends of the past few decades concerning pterosaur diversity, in some cases (in others it's merely a re-calibration of the old genericometer). Kellner erects two new species and ressurects a genus, Geosternbergia.

I first encountered Pteranodon sternbergi in Dave Peters' awesome picture book A Gallery of Dinosaurs and other Ancient Reptiles (which also probably instilled my OCD towards drawing scale diagrams). It took my young mind a while to register that this huge, tall/broad crested pterosaur belonged to the same genus as the familiar, backward-pointing-crested Pteranodon lonciceps that flew beside it. I have to admit that I though P. sternbergi just looked... cooler. In this kind of side-by-side comparison, they really don't looks like they belong to the same genus. But as always, genera are subjective things, and nobody doubted that P. longiceps and P. sternbergi were each others closest relatives (they even overlapped in time and geologic range).

P. sternbergi was first described by Harksen in 1966 as a species of Pteranodon, based on a skull which differed from other species by its tall, vertical crest. In 1972, Miller placed it rather arbitrarily in its own subgenus, as Pteranodon (Sternbergia) sternbergi. The name Sternbergia turned out to be pre-occupied (as far as I know, subgenenus names compete with genera for priority). Miller amended the name to Geosternbergia in 1978.

However, this designation fell out of favor by the 1990s, when Chris Bennett published a couple of hefty reviews of Pteranodon from the Niobrara and related formations in Kansas. Bennett stramlined Pteranodon taxonomy, taking the several species that had been considered valid up to that time and showing that much of the variation was likely due to age and/or sexual dimorphism. For example, Bennett re-affirmed the idea that some small-crested Pteranodon specimens represent females (and some juveniles) of the same species as the longer-crested adult males. With this variation in mind, he suggested that all Pteranodon specimens could fit into two species: P. lonciceps and P. sternbergi. Because differences between species are limited almost entirely to the skull and crest (though Kellner 2010 suggests that some consistent differences may be found in the skeleton with further study), Bennett had to rely mainly on stratigraphic position to decide which species a specimen belonged to. While the two did overlap in time, it was only for a very brief period, so even though skulls are very rare compared to skeletons, a specimen from the lower Niobrara could be confidently referred P. sternbergi, while one from higher in the formation probably came from P. longiceps. (Image at left: illustration of various Pteranodon skulls by Matt Martyniuk, licensed).

One problem with this method, which Kellner points out in his new paper, is that many specimens (especially those recovered back during the days of Cope and Marsh) lack information about their provenence detailed enough to allow such an assignment. Bennett himself simply referred these to Pteranodon sp., but if Kellner's new work holds up, they'd need to be assigned even more broadly, only to indeterminate Pteranodontidae.

That's because Kellner has re-assessed the variation within the traditional grouping known as Pteranodon, and found some specimens that seem to represent new species among them. For me, the most interesting is Dawndraco kanzai, or "Kanza Dawn dragon" named for Dawn, apparently an Iroquois sky goddess, not the English word. The type and so far only specimen is UALVP 24238, a really interesting nearly complete skull and skeleton usually attributed to P. sternbergi (as in Bennett, 1994). Aside from being one of the most complete (former) Pteranodon specimens, it has always struck me as very, very odd. One of the primary reasons for making this a new species it its upper jaw. In most Pteranodon skulls (though none are as complete as you may assume based on its ubiquity in paleoart), the jaws can be seen to curve upward toward the tip and taper off into a needle-sharp projection at the tip. In the Dawndraco holotype, the preserved portion of the jaws are extremely long relative to the rest of the skull, but show no signs of tapering. In fact, the top and bottom margins of the upper jaw form essentially completely parallel lines up until the break. Letting your imagination fill in the rest, this must represent either a phenomenally long-billed animal, or one with a very unusual fat, somewhat flattened tip. The bone within this tall, long bill looks like a loose, honeycomb mesh of very thin struts. Taken together, this does seem like it probably comes from something fairly different than Pteranodon proper. (Image at right: Skull of Dawndraco, from Kellner 2010. Scale bar = 500mm).

The next new species is Geosternbergia maysei. Kellner considers Geosternbergia a distinct genus based on its unique skull characteristics, but again, there is currently no analysis to suggest that it is any more or less closely related to Pteranodon than anything else, so it remains a subjective decision (though it would be interesting to see someone perform an analysis using all of Kellner's species and Nyctosaurus). Anyway, G. maysei is named for a partial skull (KUVP 27821) from the South Dakota Sharon Springs formation. It was a large individual that Bennett previously referred to P. longiceps. However, Kellner notes that the crest is inclined further upward than it should be for that species, and that the premaxilla is arranged differently in forming part of the crest. It also appears to have a larger nasoantorbital fenestra, and a lower and larger temporal fenestra, than in G. sternbergi.

How well either of these identifications remains to be seen. I'm more inclined to be convinced by Dawndraco than G. maysei, simply because the very strange bill of the former seems harder to explain by age or gender variation. Kellner has also tended to be the 'leader' of one 'camp' when it comes to pterosaur taxonomy, usually opposed to Dave Unwin -- see their drastically different recent taxonomies of the ornithocheirids, for example. It will be interesting to see not only if these new species are accepted, but by whom.

While on the subject of new pterosaurs, two new species have also just been reported from the mid-Jurassic Tiojishan formation, some with soft tissue: Kunpengopterus sinensis and Darwinopterus linglongtaensis seem to add support for a monophyletic group of Tiaojishan pterosaurs somewhat intermediate between pterodactyloids and "rhamphorhynchoids", the Wukongopteridae. If I have time to read the paper more closely I'll try to follow up with a full post on these guys.

References:
Kellner, A.W.A. (2010. "Comments on the Pteranodontidae (Pterosauria, Pterodactyloidea)
with the description of two new species." Anais da Academia Brasileira de Ciências, 82(4): 1063-1084. doi: 10.1590/S0001-37652010000400025.