Skeletal Drawing

Hey, a trailer with "my" dinosaurs

2013-05-01T09:54:00.001-07:00

I know, it's not exactly an earth-shaking post on anatomy or reconstructing prehistoric life, but as I mop up some of the duties that have taken me away from blogging the last few months I thought I'd share this trailer, which shows off some of what took time away from blogging last year at this time:

I know that some will object to the anthropomorphization of the dinosaurs' actions, but actually a ton of time was spent on trying to develop less mammalian behaviors and expressions that would still read to an audience. In the end not all of them worked out, but the realities of such a project are that no movies with this sort of budget will get made if they people fronting the cash think audiences won't be able to relate to it.

Anyhow, I think the anatomy will be some of the best ever seen on the silver screen. The compositing and color in one or two of the shots don't look as good as say the Jurassic Park movies, but with a final release not coming until holidays in 2013 I seriously doubt the entire film has been through final color grading, so I wouldn't let that bother you.

What do you guys think?

P.S. I was only one of the anatomy designers - Mark Witton was the other major designer that I know of (that is, created anatomical creature design illustrations as well as consulted), although there was an impressive assortment other paleontologists consulting on the project. After the 2D design was done the talented David Krentz added greatly to the character designs while transferring our work into the realm of three dimensions. Even after models are made a project like this depends on an army of incredibly talented artists, including those who paint the models, the technical directors and riggers who make it so those static models can move, and the animators who bring them to life. The finished look also strongly depends on the texture and render artists, including shader development, digital lighting, and the people who composite and color grade the finished imagery. I only use the term "my" to illustrate enthusiasm for having played a role, not to imply that the role was more than a cog in a large and very talented army of people who worked on the project.

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Massive changes incoming to diplodocid sauropod stance

2013-04-01T09:05:00.001-07:00

I know it's been a while since I posted anything, and luckily I have a backlog of content to share in the coming weeks, but I'm so excited about this project that I felt I had to post this, if for no other reason than as a warning to artists out there that are thinking about restoring sauropods in the near future.

In particular diplodocoids - think "therizinosaur" and you'll be on the right track. I can't say too much until the paper clears embargo later this week, but all of the oddities we see in diplodocoids will make a lot more sense, including the massive upcurve in the tail. It also nicely links Taylor et al's work on neck posture with Emily Giffin's older work on reduced forelimb innervation in Apatosaurus.

More as soon as the journal will allow it!

Edit: Well it's April 2nd, and I'm going to have a post on this prank up in the next day or two, but in case you are landing on this page from an external source I wanted to clarify that it was indeed an April Fool's prank.

Ornithomimus had wings...as an adult

2012-10-25T12:22:00.003-07:00

Just a quick note, because today we got one of the cooler new papers on dinosaurs to have been published in quite a while, describing not one but three specimens of Ornithomimus with feathers.

And not only are there three specimens, but they are of different ages, and it turns out the feathers change as Ornithimimus grows up. In particular, the adults seem to have large wings with branching feathers on them, while the juveniles are covered only with the dinofuzz that we have become familiar with in the Chinese dinosaurs we have come to know and love.

This also pulls protowings further down the family tree - prior to this we only had definite wings in those wacky oviraptorids, deinonychosaurs (the various "raptor" dinosaurs), and those critters on the main bird line.

So for those of you who illustrate the fleet-footed ornithomimids, you may need to alter some of the images. It also brings up some interesting questions regarding what the feather condition is in alverasaurs (which may have been ant-eaters) and the bizarre therizinosaurs. Specimens of the basal therizinosaur Beipiaosaurus have been found covered in dinofuzz and non-branching plumes, but not with true branching feathers, so it was assumed that the origin of wing-like structures must have happened closer to birds. Now it appears that was wrong, and we will have to try and figure out whether therizinosaurs lost them at some point during their evolution, or if perhaps the Beipiaosaurus specimen might have been too young to have developed them.

There will also be questions about what those feathers were doing in such animals, which clearly did not fly or live in trees (and equally clearly did not evolve from flying or tree-dwelling ancestors); alas that will have to be another post. In the mean time, there are a couple other fun implications to consider from this paper:

1) The Ornithomimus specimens are from fluvial deposits; for those non-geologists out there all you need to know is that most dinosaur deposits around the world are fluvial, so this discover means we will have a lot more museums taking a closer look at their specimens, rather than assuming that feathers can't be preserve outside of a few special depositional settings. In other words, there are going to be a lot more discoveries in the coming years now that more people know what to look for.

2) Along those lines, not all of the feathered dinosaurs are from China anymore. Having been to China and seen many of the specimens personally this never was a big deal to me, but for the couple of stragglers that simply didn't want to believe in feathered dinosaurs, this should end any sort of conspiracy theory.

3) Looking at the already-decided debate about whether birds are dinosaurs, I can't really say that this is the final nail in the coffin - realistically all of the nails were pounded into that coffin years ago. But this discovery makes sure there is a large concrete memorial placed on top of the coffin preventing it from ever being dug up again, and for those of you who lived through the original birds are dinosaurs wars that has to be comforting.

If you have any thoughts or questions be sure to leave them below. And for the paleoartists out there, go forth and illustrated winged adult ornithomimids. Here is a skeletal to get you started:

Zelenitsky, D., Therrien, F., Erickson, G., DeBuhr, C., Kobayashi, Y., Eberth, D., Hadfield, F. 2012. Feathered non-avian dinosaurs from North American provide insight into wing origins. Science. 338, 510-514

Terrible Claw!

2012-06-25T08:06:00.000-07:00

I haven't been posting much lately, so I thought I'd at least put up this skeletal I finished over the weekend...

It's Deinonychus antirrhopus, the quintessential "bird-like" dinosaur that John Ostrom discovered in the 1960s. More than any other discovery. it is responsible for sparking the Dinosaur Renaissance of the 1960s and '70s. Bob Bakker's illustration of Deinonychus for Ostrom's monograph is probably the single most famous piece of paleo art ever produced (although it looks awfully cold in its featherless nudity!).

Deinonychus was my favorite dinosaur for a lengthy portion of my childhood, so it was a lot of fun working on this skeletal - the closest thing that technical illustration has to a stroll down memory lane (for me at least).

There are a couple of unpublished specimens floating around, but this skeletal is based almost entirely on the Yale Peabody Museum and AMNH specimens that compromised Ostrom's original papers. Happily there is enough overlap that I don't anticipate any large changes.

The two biggest questions I see are how retroverted the pubis is - I did not restore the pelvis with the more extreme Velociraptor-like backsweep seen in some reconstructions, but until an articulated pelvis is published we won't know the exact angle. Also, I'm not entirely sure whether the curve on the ventral margin of the jugal of YPM 5210 is natural, or due to being a bit squished.

Hopefully new specimens will clear those points up soon. The good news is those are fairly minor changes to make if necessary. In the mean time, I'm off to work on more skeletals, as well as preparing for my upcoming course on advanced creature design, which is now officially open to registration.

I'm teaching an online course on anatomy

2012-06-18T06:41:00.002-07:00

So it turns out I haven't vanished (and actually have a lot of new content to share) but I've been swamped working on several projects of late. One of them I'd like to share, for those of you who really like dinosaurs but actually have different job aspirations:

I'll be teaching a course for Visualarium, one of the leading educational resources for visual effects artists (and artists in training) that use Pixologic ZBrush. The class is Advanced Creature Anatomy, and rather than being on dinosaurs (although you'll see some of them!) it centers on learning enough comparative anatomy from living and extinct animals to develop your own mental toolkit of concepts you can apply when to design more plausible speculative anatomy for fictional creature design.

I'll do my best to keep it fun, so if ZBrush and 3D art is your thing, I invite you to check it out; we'll be conducting a free webinar this Thursday so people can get a taste of what the course will be like.

Yup, the OK Apatosaurus is freakin' huge!

2012-04-27T21:24:00.001-07:00

How big did Apatosaurus get? Well, that gray silhouette that is being dwarfed in terms of bulk there is Supersaurus vivianae. So yeah, that's one big honk'in sauropod...

The genesis of this post comes courtesy of a Matt Wedel post over at the excellent SV-POW! blog, where he was taking a look at the size of the partial Apatosaurus specimen preserved in Oklahoma, specimen OMNH 1670. Matt took a measuring tape to the OMNH specimen himself, and it measures up at a whopping 135 cm (for those of you who don't know the metric system, 135 centimeters is equal to one really big vertebra...).

But Matt really caught my attention when he stated:

...so the big Oklahoma Apatosaurus was probably in Supersaurus territory, mass-wise, and may have rivaled some of the big titanosaurs.

A younger me carving a pedal ungal. Look at
that hair - what a hippy!

Supersaurus is an animal near and dear to my heart - it's an animal I've literally shed blood over. Yes really. In addition to working with my coauthors on a description of the second specimen of Supersaurus and a reassessment of diplodocid phylogeny, we also had to produce a full mount of the animal under exceedingly tight time constraints. As with many small museums this meant we all had to pitch in, and that included learning how to sculpt missing bones. Near the very end of the project, while getting by on little more than 2 hours of sleep and coffee doses that would kill a small horse, I had a very small boo-boo with a carving knife (see photographic evidence at right). No stitches were necessary, and thankfully no sauropods where injured in the process.

The end result of our work was a mount that received top billing in a temporary exhibit in Japan in summer 2006. While the estimated length of 34 meters and mass estimate of 36-40 tonnes is smaller than some of the more sensational numbers that have been floated in popular books (and of course the internet), we suggested in our paper that many of those estimates were, shall we say... extravagant. Supersaurus appears to be close to the longest animal whose length can be reliably estimated (read: not counting Amphiceolias fragilimus), though it was lighter than the giant titanosaurs.

Given my personal stake here I wasn't about to take Matt's vicious maligning of Supersaurus on faith. But - and this is the darnedest thing about science - the facts are on his side. After scaling the fourth dorsal of Apatosaurus louisae up to the appropriate size, it turns out that the thing definitely is bulkier than Supersaurus. And if you try it with the other species of Apatosaurus (to whit: A. ajax and A. excelsus), it turns out just as bad - or worse in the case of A. ajax, who seems to have a proportionately shorter D4, which in turn leads to a larger animal when it's scaled to 135 cm.

Of course Supersaurus still looks to be longer by a fair amount, in large part due to the highly elongate neck. But when it comes to moving the dial on a scale, it's clear that Apatosaurus is just more sauropod than Supersaurus. Oh well Jimbo, we'll always have Japan...

Fishing at Dawn

2012-04-08T21:40:00.001-07:00

Unenlagia comahuensis looking for fish at dawn.

What can I say, it's been over a year since I tried my hand at something more artistic than a muscle or skeletal reconstruction. I did the sketch over a year ago, and had it ready to go (it's a digital painting in Photoshop), so I decided to give it a crack and it fell into place a lot faster than I'd expected (most of the time was spent painting water detail).

I've reconstructed Unenlagia as somewhat less ecologically specialized than it's relatives Buitreraptor and Austroraptor, but fishing none-the-less. I don't really have a lot more to say about it - we'll get back to more hard core skeletal stuff soon, I promise! If you have any questions about the process I used I'll do my best to answer in the comments section.

I.O.Yutyrannus

2012-04-05T20:24:00.003-07:00

Hey, it's not every day that a completely fuzzy, nearly 30-foot long meat-eating dinosaur is described, now is it? I'm afraid my current schedule won't allow for a full skeletal of this critter for several more weeks, so consider the skull a down payment.

First, I should say that I'm not going to retread much of the excellent writing that has already been done on Yutyrannus. If you'd like more in depth coverage, I highly recommend David Hone's excellent write-up on his blog Archosaur Musings. For more coverage and some reasons to question whether Yutyrannus is a actually a tyrannosauroid, check out Darren Naish's coverage on his Scientific American TetZoo blog. I'd also be remiss to not mention Brian Switek's article over at the Smithsonian website.

Photograph by Roberto Appiani

What I will cover are some of the difficulties I've already observed in restoring Yutyrannus. The reconstruction above is based on one of the beautifully preserved skulls (there are 3!); like everything else found in the Yixian Formation, the specimens have been squashed flat. Relatively robust bones like a femur hold up fairly well, but skulls really don't. They tend to be highly three-dimensional in shape, and are made out of relatively thin elements. In particular, on theropod skulls the top and rear of the skull tend to fold upward as the head undergoes the pancake treatment of diagenesis.

Small dinosaurs with larger eyes and brains (like the juvenile Scipionyx above seen at right) exaggerate the problem even more, and unsuspecting artists can restore the skulls as having huge domes over the eyes if they don't know better. In Yutyrannus I suspect we are seeing something similar, which probably exaggerates the apparent size of the nasals (especially as you move closer to the eyes), as well as the top of the skull at the back.

If you check out the beautiful photograph of the head of juvenile specimen ELDM V1001 in David Hone's blog (the same one I've restored above), you can probably see what I'm getting at.

The skull restoration at the beginning of this article takes those things into account, attempting to return a 3-dimensional shape to the steam-rolled remains of the skull (by the way, the mandible is largely a place holder for now, the surangular is actually a fairly different shape). Below I've included a comparison of the the skull with and without those "corrections". Because there are three skulls, and because they have likely been subject to distortion from somewhat different angles, I should be able to double check this with greater precision once I get around to doing the full skeletal.

For those of you investing the time to study the comparison image, the top one is the restored version, while the bottom one treats the outline more literally. In both cases I've re-articulated the lacrimal (the bone in front of the eye) with the jugal (the bone underneath the orbit). In both cases the lower jaw is (as mentioned above) just a generic placeholder that is the correct size, but doesn't take the information from other specimens into account.

That's all the time I have to put into a new skeletal on my own whim for the moment. Until I get a chance to do the whole thing enjoy this Yutyrannus I.O.U.

When journalists attack!

2012-04-03T11:16:00.001-07:00

As recently reported on several apparently legitimate news sources, a new interpretation of dinosaur biology has been proposed that is "so revolutionary it stands the whole world of palaeontology on its head." What is this landmark new idea that has set paleontologists agog? It's being termed the "Aquatic Dinosaur" hypothesis, and as the name implies it suggests that the Charles Knight painting you see above isn't out of date, it was just ahead of its time. And not just for sauropods, but all large dinosaurs.

If something smells fishy to you, it's not just the swamp water; something is very wrong here...

First, to be clear, there is no such controversy, or even an idea that you need to take seriously. To be sure, some guy wrote an article in Laboratory News, so I've listed the evidence below in a handy tabulated format:

Literally, no data was provided in the article. The author makes references to "calculations" that were run, but they never make it into print. The article is mostly long-winded hyperbole, filled with such gems as "Dinosaurs look more convincing in water, and the physics stands up more soundly."

So the author's main point appears to be "See??! They look better in the water, so it must be true! Also, I have some secret calculations I won't bother to share with you support my aesthetic preference!" The fact that it was in the April edition might give us pause to wonder if this isn't a big joke, but alas there are reasons to suspect otherwise (see below).

Two general claims seem to permeate the article, that dinosaurs were just really big so water would help, and that dinosaur footprints aren't as deep as you'd expect from such big animals. Of course how deep a footprint sinks is only partially related to the mass of an animal. The surface area of the foot must be taken into account, as smaller feet concentrate the weight while large feet spread it out. That's why a woman in high heels can dent substrates that elephants won't. And of course the substrate itself matters - no animals leave tracks on concrete, while people easily get bogged down in viscous mud.

The "they're just so big" meme, is painfully wrong; there's an entire literature of biomechanics that shows that dinosaur limbs are strong enough to support terrestrial locomotion. And of course dinosaurs lack the aquatic features seen in animals such as hippos or crocodiles, which actually spend most of their time in water. Running your mouth off (err, running your text editor off?) without even bothering to read the literature is one of those "the stupid, it hurts!" sorts of moments.

From xkcd

Ok, enough ragging on "professor" Ford; he's either a crank or a practical joker (perhaps those aren't mutually exclusive?), but he's not the first person to have a loony idea and not support it with any evidence. Heck, the internet is littered with such people.

The real problem here is that his personal speculation somehow got reported as news by the mainstream press. First, if this isn't an April Fools prank, it calls the editorial judgement of Laboratory News into serious question (and if it IS somehow a prank, why was it allowed to be spread pre- and post-April 1st to other media outlets?). Amusingly, on page 17 of the same issue of Laboratory News there is an article lamenting the state of science reporting in the news (seriously, I couldn't make this stuff up if I tried).

If you or your lab has a subscriptions to Lab News, I'd seriously consider making inquiries, or simply dropping it. If they allow this sort of thing to happen, how can you trust the rest of their articles?

More importantly, why on Earth was this story picked up and repeated by serious news outlets? Does BBC Radio 4 do any sort of review at all before they put someone on the air? Have journalistic standards sunk that low at the British Broadcasting Company? A quick listen to the audio shows the show starting out as mildly skeptical, but concluding by comparing Ford to Galileo freakin' Galilei!

W. T. F.?!!

Galileo, you may recall, did actual science and was being silenced by non-scientists due to the (presumed) theological implications of his findings. Mr. Ford (who the BBC charitably refers to as a "cell biologist" despite being more of a media gadfly and author of popular books and articles, not a publishing scientist) is not doing science - he in fact seems intent on ignoring science at all costs - and was simply being refuted by an actual, you know, paleontologist. Yet they whipped out the Galileo reference!

Which honestly begs the question of whether anyone should bother listening to BBC Radio 4. To be fair, actual paleontology has been covered on Radio 4 and it seems to otherwise have solid programming, but the BBC should move swiftly to clear this up if they don't want a permanent stain on their credibility.

Most of the web and print articles are based on the BBC interview, but that doesn't exonerate them; not a single one of them bothered to inquire as to whether there was any real science here, and when they did contact paleontologists, they presented it as another "side" in a debate, rather than the debunking of junk Science.

Regular readers have already seen that sources like Scientific American can get even basic anatomical facts wrong, but this goes well beyond an incorrect fact in an otherwise solid story; it's misleading through and through. In a follow up article the Telegraph directly compares the aquatic dinosaur nonsense with actual research, in the process repeatedly mutilating the concept of a scientific theory.

This stuff really matters. We live in a world where huge swaths of people don't understand basic scientific concepts, and this sort of nonsense just makes it harder to teach. Worse, listeners that were sympathetic to the reporting will become disillusioned when they find out the reality of the situation, possibly making them view all science more cynically (or simply avoiding science altogether).

We deserve better science reporting than this. The BBC and everyone else who carried this story should be ashamed.

------------------------------------

Note on the possibility of an April Fools prank:

Several people (myself included) have raised the question of whether this could be an elaborate prank. While I sincerely hope so, it turns out that Mr. Ford has a history of publishing similarly speculative and unfounded ideas, including an idea a previous article in Laboratory News on human and canid evolution. The continued media promotion of the aquatic dinosaur story after April 1st, and a somewhat disturbing "how to spring rhetorical questions on paleontologists" guide on Ford's website cast significant aspersion on the possibility of this being a joke.

It's worth noting, however, that the above criticisms of science reporting in the media do not change even if it is a prank, as the news media has clearly been duped one way or another, and could easily have discovered it with a modicum of research prior to reporting it.

Carnotaurus - delving into self-parody?

2012-03-29T09:03:00.001-07:00

This is Carnotaurus sastrei, a theropod that seems to be little more than a mouth with a set of legs to carry it around. Carnotaurus belongs to an aberrant group of theropods called abelisaurs, which dominated much of the southern hemisphere during the Cretaceous. While all abelisaurs appear odd to our tetanuran-biased eyes, it seems like Carnotaurus is striving for weirdness as a means to its own end; as if it were making some sort of meta-commentary on abelisaur diversity.

I should take a moment to make a public service announcement: I apologize for my absence from blogging and other social media that last several weeks - I've been producing more than a few new skeletals (on a schedule), so time has become a scarce resource. On the upshot, several of the new skeletals address blog-worthy topics, so I'm going to produce some shorter posts that examine them.

One of the questions raised in the comments of a previous post involved the hyoid bones - the bones that support several muscles, including in dinosaurs the tongue musculature. Being long, slender bones that don't directly articulate to other bones, hyoids are often not found (and other times are probably not collected or m-identified). Even when they are found, their lack of a direct connection to other bones makes restoring them problematic. In Carnotaurus this wasn't a problem, as they were found in direct association with the underside of the mandible, apparently in their life position. The fact that extensive skin impressions were found with Carnotaurus reinforces the likelihood that the soft tissue holding the hyoid in place had not been disturbed.

In the skeletal above you can see part of the hyoid sticking out from under the bottom-rear part of the jaw. Part of the hyoid is obscured, but there's not much I can do about that. Having the hyoid is actually pretty useful - the trachea and esophagus have to pass through it (or above it), so having a properly positioned hyoid constrains the throat tissue.

Carnotaurus is also striking due to its advanced arm reduction - in side view the arms almost disappear, as they don't even extend past the stomach. What on Earth could such arms be used for? Hold on to that thought, as I'm not ready to go public with my thoughts on that just yet. But it sure reinforces the "legs carrying a head" image.

Finally, for those of you paleo-artists out there considering Carnotaurus as your next paleo-subject, I wanted to point out something not obvious in side view: Carnotaurus is really flat on top. The transverse processes on the tail actually stick up in a V-shape that reaches just about to the level of the neural spine. Persons & Currie recently described how this impacts the tail muscles (TL;DR version is the tail is very wide at the base, and quite flat on top).

From Person's & Currie

The back and neck also have osteological structures that raise up to, or above the level of the neural spine. So most of the animal should be restored as having a remarkably flat top. Given how narrow the head is, this must have produced a really strange life appearance.

A final note on the skeletal itself: while Carnotaurus is a wonderfully complete specimen, the lower legs and much of the tail is missing, so those elements were restored after its close cousin Aucasaurus.

The evolution of (my) Acrocanthosaurus

2012-01-28T19:10:00.000-08:00

With Spinosaurus temporarily out of the way, we're going to take a closer look at Acrocanthosaurus. This series is going to include a post on what we know and don't know about Acrocanthosaurus, how to restore the skeletal in multiple views, and how to restore the muscles. At the end of that series I'll also comment on some areas of soft-tissue variation that artists should keep in mind when they envision "their" Acrocanthosaurus.

First though, I wanted to take a moment to look at how my own reconstruction of Acrocanthosaurus has changed over the last decade. With any luck some of my earlier errors in methodology might help others who want to do skeletals. Also I hope to provide some insight to how I update skeletals over time, and the importance of revising your work as new data is published.

Join me after the break for an in depth look at the evolution of (my skeletal reconstruction) of Acrocanthosaurus...

Although Acrocanthosaurus is hardly the best known theropod, it provides more than its share of challenges when attempting to reconstruct it. In my case, I attempted the original skeletals during what I'd call a methodological nexus - it was one of the first skeletals I attempted within an entirely digital environment, and to some degree the initial reconstruction suffered as a result. I had developed many techniques when I executed skeletals in pen and ink, and most of those translated fairly well during the years (roughly 2000-2004) when I used a hybrid method of digital and ink work. Alas, attempting to work entirely inside a computer forced me to rediscover how to accomplish the same things inside of Photoshop, and as a result the first couple of attempts were actually a step backward in some ways. Luckily I stuck with it, and the results are now far better then anything I accomplished in the "analog" world.

In the beginning...

Acrocanthosaurus itself is not a new dinosaur. It was described in 1950, and it was noted at the time that the specimen was a carnosaur with enlarged neural spines on the back. What really brought Acrocanthosaurus to my attention, however, was the reconstruction of NCSM 14345, the "Fran" specimen, which was prepared, molded, and mounted by Black Hills in the 1990s. One of those specimens became part of a travelling display that I contributed to, and I was inspired by the fully restored mount, as well as my ability to take lots of photographs of the mount.

Alas, that was in the "olden days" when cameras captured light on sheets impregnated with silver nitrate rather than CCDs, and I never did scan in those photos. I still had them in 2003, but they appear to be one of many casualties of moving around frequently.

I was also attending the University of Wyoming, and their Geology library had supplied valuable gifts: descriptions of Acrocanthosaurus specimens by Jerry Harris (1998), and Currie & Carpenter (2000). Armed with proto-pdfs (read: xeroxed copies), lots of photos, and an abundance of enthusiasm I sat down to create my first all-digital skeletal reconstruction.

The tomb of the unknown skeletal...

Directly above, what you don't see is my first Acrocanthosaurus skeletal. I'm not being shy, I just didn't back up the original very carefully, and eventually the hard drive it was on suffered a systemic failure. Cloud storage was a pie-in-the-sky dream at the time, so I've lost several "original" skeletal files during the course of computer failures over the years. Luckily I've been anal retentive enough to keep current versions of skeletal files on multiple hard drives, so I haven't totally lost a reconstruction (at least, not a digital one).

What I can say is that in many ways my first attempt was an unmitigated failure. For starters, I didn't actually have the papers I mentioned above in their entirety. I'd read them in Laramie, but at the end of the semester I only photocopied the parts I thought I'd need (hey, it took time and money to copy texts in those days!). And of course the photocopies didn't always do justice to the original figures.

Instead I had to rely strongly on the photographs I had taken of the Fran mount. Even that was fraught with uncertainty, as I hadn't been able to take orthographic photos of the mount. Also, there were errors in the fully restored mount, but without all of the text from Currie & Carpenter I didn't always recall what was restored and what was cast from original bone. The results were predictably poor.

You don't have to take my word for it though. I posted that first attempt to the Dinosaur Mailing List in early July of 2003. Jaimie Headden and Waylon Rowley made quick and (deservedly) pointed replies. I had missed several characteristic parts of the tail and neck vertebrae, and a bunch of other minor details had simply been missed.

What happened? For one thing I really didn't have enough data on hand. But more importantly, I was distracted by having to solve the technical problems of a new medium. Digital skeletal reconstructions have many advantages, but at the time they were lost on me as I struggled to figure out how to simply do the things I'd taken for granted in the "analog world".

The Acro strikes back

With a bit of work, I quickly produced the skeletal above, which addressed some of the basics. It wasn't a horrible attempt - it accurately captures almost all of the proportions, and many of the changes since have been either due to newer research getting published, or on changing interpretations in soft tissue reconstruction.

One thing mistake in this earlier version is that the neural spines were too tall - I had based their height on the mount of the Fran specimen, but it turned out that neural spines were not complete in that specimen (at least not the ones in the back, sacrum, or the front part of the tail). A review of other specimens ruled out such a grandiose neural spine height, and that also has implications for paleoartists wondering how to illustrate the back.

Two important papers were published on Acrocanthosaurus after that early skeletal. One was on the forearm, which showed that the arm couldn't actually reach as far forward as I'd illustrated it (and also clarified details of the size and shape of all the elements). Another paper was published in the last year that updated our understanding of the skull of Acrocanthosaurus. When I was asked if I could supply the skeletal to an upcoming book, it was clear that I had to revamp the skeletal before sending it along...

Back to the future

Which brings us back to my current skeletal. In addition to the new skull and arm data, the newfangled Acrocanthosaur naturally sports my new skeletal pose. So how crazy different is it? In some ways it's pretty similar - the overall dimensions really didn't change, and that's a good thing. A bunch of more subtle soft-tissue changes took place (at least some of which will get to star in their own post in the future), but a couple of obvious ones involve the tail and the neck.

The tail in the newer one has a heavier base, reflecting the research by Persons and Currie on tyrannosaur tails that I wrote about last year. The tail also is a bit less bouncy. The current skeletal is moving at a more sedate pace, and its tail is no longer bouncing along like a dropped garden hose. The neural spines on the tail have also been updated, with the spines on the front of the tail (near the hips) shorter to reflect other specimens, and the ones in the middle a bit taller, again based on other specimens.

Looking at the neck, the silhouette is no longer shrink-wrapped as tightly to the skeleton. I will probably address the "why" part of that in a later post, but suffice it to say that the newer Acro would have an easier time wolfing down large pieces of meat it tore off a carcass.

A final set of changes were made in the pectoral girdle (the shoulder region). I added a furcula which, while not found in Acrocanthosaurus, now appear to be a primitive feature found in all theropods. Additionally, I used to illustrate a large cartilaginous presternum that split the coracoids apart (you can see it poking out the bottom and front of the chest area on the older skeletal).

Reflecting the articulated chest regions of other non-maniraptoran theropods, I changed it to a smaller presternum, that would have ended sooner and allowed the coracoids to almost contact one another along the midline. This slightly changes the outline in side view, but in front or top view has the effect of narrowing the front of the torso across the shoulders. Now if only someone would produce multiple-angle skeletals of Acrocanthosaurus to show this off...

...tune in next week, for the exciting "surprise" reveal!

Dawn Thief

2012-01-24T09:53:00.000-08:00

A quick post (and a new skeletal) today, while I apply a bit more polish to the Acrocanthosaurus series. To satisfy all of your skeletal-drawing-based-amusement needs I give you Eoraptor lunensis, one of the most primitive dinosaurs yet discovered.

How primitive? So primitive that we can't actually answer that question with any certainty right now. Eoraptor is one of those taxa that bounces around a lot in different studies. When it was originally describe, it was thought to be one of the most primitive theropods known. Other studies suggested it might be more primitive than the split between theropods and sauropods. Recently, some have even found it to be on the line leading to sauropods!

All three positions have shown up in recent studies, so for now at least the answer is "we're not sure". Why all the trouble figuring out who is Eoraptor's closest relative? Basically what it boils down to is that Eoraptor is so primitive that this is what the common ancestor of theropods and sauropodomorphs would look like. No matter where Eoraptor ends up on the dinosaur family tree, the difference between it and animals at the other position will be very small indeed.

If you compare Eoraptor to Panphagia (which I examined in this post), which is a well-supported basal sauropodomorph, you can see just how similar the two are. The problem is sort of like being handed photographs of all of the Kennedy's when they were two years old and being asked which one was closest in age to JFK - there's a correct answer, but it's awfully hard to tell from the information you have.

As for the skeletal reconstruction, Eoraptor didn't present nearly as many challenges as some other taxa do. For one, it's know from fairly complete remains. It would have been nice to have a more detail description of the animal in print (the original papers leave something to be desired along those lines), but luckily the specimen is available in detailed orthographic photos, which do a nice job of supplementing the published data.

That's all for now!

The Great Skeletal Repose of 2011: A Retrospective

2012-01-20T22:27:00.000-08:00

Well, it's 2012, so the Great Skeletal Repose of 2011 must officially come to an end. Most of the bipedal skeletals in my collection have been reposed much like this Velociraptor. I had plenty of things to say, and we saw some great discussion by guest writers, but when it comes right down to it, the issue feels incomplete without some sort of summary as to how I got here, and what's left to do. So let's take a quick look at where things stand now...

To some degree, the walking pose shown above was selected by acclimation. When I started to show off different types of poses, by far the most popular was the walking pose you see above. And I want this pose to be one that other scientific illustrators can feel free to adopt, so widespread can only enhance that proposition. But it wasn't just a popularity contest - there are several practical reasons why this walking pose became the winner:

The Good

1) Utility - Greg Paul of course will continue to use his pose, and a number of previously published skeletals by other authors (including all of mine up until last year) had adopted the same pose. By selecting the walking pose the retracted left leg remains unchanged, allowing for a easy comparison of the proportions. This was probably the biggest factor.

2) Functional Aesthetics - The old pose of animals sprinting along at a lively clip tended to impose a specific hypothesis of activity on the animals. While in some cases dashing along may have been quite likely, it still required that a research who wanted to use the skeletals to swallow that hypothesis, whether they agreed with it or not. With Velociraptor that wasn't unlikely, but with larger theropods it became needlessly controversial, and with graviportal taxa like therizinosaurs the results could be laughable.

3) Laziness - I prefer "efficient" over "lazy", but no matter what label you place on it, this pose required a minimal amount of alteration to my existing skeletals. And the stark reality is that when you have to repose hundreds of technical illustrations that time adds up. Quickly. Of course this reason would not have been sufficient if it weren't for the more important points 1 & 2, but it sure was a nice bonus.

Does that mean I'm thrilled with the outcome?

Yes and no. Since I'm starting with a blank slate, it would have been fun to come up with something truly distinctive. Yet the allure of the new wasn't worth sacrificing how useful the skeletals were for comparative purposes. Also, thanks to lots (and lots) of time spent pondering the issue, and to the extra stimulus provided by Mike Habib and Jon Conway's excellent guest posts, I've come to some unsettling questions that are still unresolved.

The Bad

1) Whither goest utility? - As I wrote way back in the halcyon days of...spring 2011, after I announced that I would relinquish the old pose and select a new one I got many requests that I refrain from this. Almost all of them were concerned with losing the ability to easily contrast my skeletals to others after the repose. I was (and am) sympathetic to that plight, and selected a pose that minimized the "damage".

Yet I also had a disconcerting realization: Both Greg Paul and myself had been varying the pose of the forelimbs for years and no one ever bothered to complain about the loss of utility. Sometimes we've both illustrated maniraptorans with the arms flexed into their folded-wing pose, sometimes not. Less advanced theropods obviously never adopted such a pose, so their arms often hang listlessly. My tyrannosaurs went from a similar "hanging out" pose to one that reflected the work done by Lipkin and Carpenter. Why was the issue never broached? Are forelimbs less important for comparative purposes than hind limbs? Or do we naturally gravitate towards the larger structure because of how our visual cortex's work? I don't know, but I'm unsatisfied by the discrepancy.

2) Is variety the spice of life? - Jon Conway also brought up a good point in his guest article, that there isn't a single pose that best serves every need. This is certainly true, and while I still feel that within groups making poses similar is useful, I also have to admit that in some ways the job has just begun.

3) That job has just begun - Oh yeah, and another thing. Turns out there are quadrupedal dinosaurs too. Who'd have thunk it, eh? Despite the obvious and objective superiority of theropods, prosauropods, and basal ornithiscians, there's still a lot of four-footed critters in my skeletal collection, and I'm going to have to come up with a pose for them as well. Two actually, since the graviportal species will need a pose that is different from the quadrupeds with flexed limbs. Ah well, that just means that 2012 will also need to have a Great Skeletal Repose as well.

An end and a beginning

So we've come full circle. I've adopted a pose for the bipedal dinosaurs, but still have to come up with (two!) new poses for quadrupeds. I still am very much interested in soliciting outside opinions on the subject, but I also want the blog to move back to posts about anatomy and reconstruction, rather than a continuing series of posts on the technical issues behind selecting a pose. So expect to see the occasional progress report on the quadrupeds, but don't expect it to dominate space on the blog this year.

If you have a strong opinion on the subject, don't hesitate to email me (or use that Gchat thing). In the mean time, I really do have a series of upcoming posts on Acrocanthosaurus and Spinosaurus anatomy, as well as the trials and tribulations of reconstructing skeletals in multiple views.

Stick around, won't you? 2012 should be an interesting year.

Just say no to SOPA and PIPA

2012-01-18T08:26:00.000-08:00

I've generally refrained from talking about subjects not directly related to paleontology and scientific illustration, but since our ability to have these conversations are now under attack, I've decided to make an exception today and add to the chorus of people opposing SOPA and PIPA.

Both are bills that are intended to protect intellectual property - and given what I do and how I make a living, believe me when I say that protecting intellectual property is an important subject to me. But the bills go (much) too far in crippling online commerce, removing the job of oversight away from the public eye (inviting the censorship of unpopular views, rather than illegal activity), and are unlikely to be effective in combating piracy.

In short, this bill was written by people who don't understand the internet, and are throwing lots of money and influence at Congress is part of a desperate wish to try and turn back the clock to before the web was available. It won't stop those who are breaking the law. It will legalize tools for government agencies to censor parts of the web. It would slow or stop the economic growth of online companies, including the ones that make blogging possible (both companies like Google's Blogger and WordPress, and also many companies that support paid bloggers with advertising).

Also, I wanted to point out that this is a bipartisan issue: members of both U.S. parties acted to delay the vote on SOPA in the House of Representatives, and members of both parties are threatening to bring PIPA to a vote in the Senate quickly before more opposition appears. And this will impact U.S. citizens (and the international community) regardless of party affiliation.

If you want to learn more about the legislation you can read about it here.

To find a representatives to contact, head over to Wikipedia's main page, or to sign a petition go here.

We'll get back to dinosaurs tomorrow!

Revisiting the Fisher King

2012-01-11T11:04:00.000-08:00

I know, I know, my last post promised a series on reconstructing Acrocanthosaurus in multiple views - bear with me, as this is actually part of that series. Remember that both animals have stuff sticking up on their backs, so I want to be able to compare and contrast those elongated neural spines...and how those differences should impact reconstructions of the animals. But to do that I had to update this skeletal, as new information had rendered the older one no longer tenable.

Besides, Spinosaurus is cool! For one, it's the only dinosaur in the Jurassic Park series to tangle with a T. rex and emerge victorious (no matter how unlikely that outcome was). It's probably the longest theropod we know of, and may have been the heaviest as well. Yet counter-intuitively it shows specialization for piscivory (fish-eating)...maybe in JP3 the spinosaur mistook the T. rex for a really large lung-fish?

Tongue firmly out of cheek now, Spinosaurus has lit up imaginations partially due to its size, but also because there was so much you had to imagine to try and reconstruct the animal. Until the last decade or two it was sort of a theropod Rorschach test where you could project any sort of oversized monster theropod onto its scant (and now lost) remains. This brings a thrilling "Sherlock Holmes" quality when trying to imagine the living animal, but for most of the last century serious attempts to reconstruct Spinosaurus have been more frustrating than titillating.

Darren Naish has an excellent write up of the history (and tragedy) of of the type specimen of Spinosaurus, which I won't duplicate here. The long and short of it is that WWII claimed the fossils as another victim of the conflict. The already-meager remains lost, paleontologists were stuck with the original description and some somewhat uninspired sketches as the only link to the past.

A series of fortunate events occurred in the latter half of the 20th century that allowed for a more accurate interpretation of Spinosaurus to emerge. For one, other spinosaurids were found. Baryonyx from the U.K., and Nigerian Suchomimus, started to paint a more complete picture of what these animals were like. They had bizarrely long snouts that seemed to resemble a gharial as much as a traditional theropod. Suchomimus even had a smaller version of the enlarged neural spines on the back:

The amusingly-named Irritator from South America further clarified the relationships and anatomy of spinosaurids. But the real breakthrough was the re-discovery of several photographic plates of the original material. While Spinosaurus wasn't the most complete specimen, having photographs at least made it possible to ensure that what was found is incorporated accurately into a reconstruction.

Among other details, the image also shows what had been the basis of attempts to restore the shape of the elongate sail or hump on the back: Stromer's original interpretation for the position of the elongated neural spines. In particular, notice that the tallest one is set directly in front of the sacrum here, while the only associated tail vertebra (at the far left of the picture) has a very short spine. That has lead most people to infer that the spine started quickly after the neck, grew to ridiculous heights over the pelvis, and then quickly dropped off again. Indeed, this is the interpretation that I used in my first attempt, and has been widely seen in such disparate and reputable scientific endeavors as Jurassic Park 3, the Carnegie Collection of "museum quality replicas", and Greg Paul's reconstruction in his Princeton Field Guide to Dinosaurs.

And they're in excellent company (whereby I arbitrarily define myself as "excellent company"). I had been concerned with Stromer's original interpretation for the placement of the tallest neural spinse - no vertebral body (centrum) was preserved, but the change in the angle of the spine seemed pretty extreme compared to the previous dorsals, especially right in front of the sacrum. My solution was to assume it was a sacral neural spine. This largely preserved the traditional appearance of the "sail", but provided a bit of breathing room for the change in orientation.

Luckily for us, Andre Cau and Jamie Headden were busy mulling over this specific issue, and came to a much more likely conclusion, that the backward-oriented neural spine was actually an anterior caudal. Looking at a host of dinosaurs with elongate neural spines, they noted that in general you never seen backward-canted spines in front of the hips, you always see them after it. There is a bit more detail to the argument (which I encourage you to read on their blogs), but in essence they make a very compelling case.

And so it was back to the virtual drawing board. I made some other corrections from my previous attempt - there had been some scaling issues with the neck vertebrae that had given my reconstruction a thinner Baryonyx-like profile in the neck. Also, it appears that the necks of these animal don't have as much of the traditional theropod S-curve, so that was changed as well (although I still don't buy the extreme hang-dog look that Greg Paul has started to restore his spinosaurs with). The results are a stockier animal, with a more elongate sail (or hump):

Looking at the rigorous reconstruction, it's clear that there's still quite a bit of uncertainty in the skeleton, although not all of the missing parts are created equal. Much of the pelvic girdle is known from Irritator, as is the back of the skull. Also, some unpublished specimens shed light on this, even if they aren't documented well enough to be official parts of the reconstruction. Still, there's a bit of ambiguity about the exact limb proportions, the length of the tail, and the exact shape of the sail.

Speaking of which, how should those tall neural spines be restored by artists doing life reconstructions? Is it a sail, was it supporting a hump of tissue like a bison, or was it simply a muscular ridge? We'll get back to that subject in a bit, after looking at Acrocanthosaurus.

Until then, best wishes to one and all for a wonderful 2012!

Happy Holidays!

2011-12-24T21:27:00.000-08:00

Happy holidays to one and all. We'll talk about that Acro skeletal and multi-view reconstructions in the New Year. Until then, be safe and enjoy the holiday season!

Please (properly) label your scale bars: Exhibit A

2011-12-20T18:15:00.000-08:00

As many of you know, I spend a lot of my time doing skeletal drawings. Not everyone does them, but I don't think I demand any special considerations in the papers I use as reference. Many of the critiques about measuring your dinosaur posted over at SVPOW are similar to what I think when I read a paper. Anyhow, in terms of typos making a scale bar useless, I think this next image speaks for itself:

That is all.

(If you're having trouble seeing what I'm talking about, read the image caption carefully)

Falcarius: bizarre sickle-cutter

2011-11-18T15:40:00.001-08:00

The truly strange looking animal above is Falcarius utahensis. It's an early, omnivorous member of the theropod clade known as therizinosaurs. Not only does it look weird, it's also a bit different from other skeletals you may have seen on the web. Join me after the break for a bit of a discussion about Falcarius, and the challenges I faced with this reconstruction.

I should warn you, this won't be a tutorial on how I make my skeletal reconstructions. That would certainly be a fun series, but it would require quite a lot of time to do properly, so for now it'll have to wait. But there are still several points worthy of discussion.

First off, the animal was discovered in a bone bed of disarticulated individuals. The good news is that most of the individual elements are known, but the down side is the bones aren't all from the same sized animals. That means that cross-scaling is needed to restore the skeleton, but even that presents a challenge; the usual method of cross-scaling involves double-checking the results against the proportions of close relatives. Alas, in this case the fossil record for the base of the therizinosaur family tree isn't well known, and what is known makes it clear that Falcarius has very different proportions than it's closest known relative: Beipiaosaurus.

When the original description of Falcarius was published in 2005, it came with the skeletal drawing at left. Obviously I don't agree with those proportions now, but at the time it had been done when fewer bones had been excavated, prepared, and described in detail, so Greg Paul had to try and scale them based on a smaller amount of material to compare with.

In fact, given the difficulty of restoring the proportions I intentionally avoided doing a Falcarius skeletal reconstruction for several years. I might have avoided it all together, but towards the end of my tenure at the WDC we mounted a cast of Falcarius that Gaston Design produced. Working on that skeleton I was able to not only measure and photograph all of the elements, but spend time looking at how the individual elements were matched up. Some parts of the cast's vertebral column are from different sized individuals (an unavoidable consequence of trying to piece together a skeleton from several different individuals). In other cases, vertebrae I had assumed to be from different sized animals were in fact crushed.

In addition to the hands-on data, Lindsay Zanno had been hard at work publishing more detailed information on Falcarius (this is actually notable, as not all researchers are as timely with getting more detailed descriptions of a new animal into print).

As the information piled up I felt that a skeletal was possible to be done. I still didn't tackle it though, as there were plenty of "low-hanging fruit" skeletals that could be done from less-challenging animals.

As luck would have it, I ended up being asked to produce a skeletal of Falcarius for a display in the new Utah Museum of Natural History building (side note: the new UMNH building just opened, and houses one of the most impressive natural history displays in North America, go see it!).

Since I was working with the UMNH, I got valuable input from several of the researchers who worked on the specimens. They were able to provide additional information - I won't go into the nitty-gritty of it (although you may if you would like), but I wanted to point out that the end result was quite a surprise to me. And little is more satisfying than when you are really surprised at the end of a skeletal reconstruction.

Resulting skeletal in hand, you can compare it to the most recent studies of the therizinosaur family tree, as well as the excellent research being done by Lindsay Zanno and Peter Makovicky on the origin of plant-eating in theropod dinosaurs, and Falcarius starts to tell an interesting tail about the order in which therizinosaur traits appeared.

Falcarius appears to already be specialized for browsing for high forage. Given the lack of an enlarged gut for fermentation it probably preferred to seek out higher-quality plant matter, like fruiting bodies or seeds. The partially upright stance appears concurrently with a widening of the passage through the pelvis (not visible in side view) allowing move guts into that area, causing the center of gravity to sit further back despite the elongation of the neck.

The large hand claws (from which the authors derived the name "sickle-cutter") may have allowed Falcarius to pick up small prey, but they also may have served as defense for a fairly slow animal with small teeth. The first toe is low and long enough to start interacting with the ground, perhaps to provide balance and stability when browsing high. All of these features would be carried to extremes in advanced therizinosaurs, but they seem to already be playing the same (albeit incipient) functional roles in Falcarius.

So with Falcarius we have an animal that at first glance appears inexplicably strange, but when viewed through the lens of where it was coming from (long-bodied small-headed meat eaters) and where it ends up (the upright, pot-bellied therizinosaurs) the combination of traits start to make a lot of sense.

Isn't science grand?

References:

Kirkland, J. I., Zanno, L. E., Sampson, S. D., Clark, J. M. & DeBlieux, D. D., 2005. A primitive therizinosauroid dinosaur from the Early Cretaceous of Utah. Nature, v435, pp 84-87.

Zanno, L. E. 2006. The pectoral girdle and forelimb of the primitive therizinosauroid Falcarius utahensis (Theropoda, Maniraptora): Analyzing evolutionary trends withing Therizinosauroidea. Journal of Vertebrate Paleontology, v26 n3, pp 636-650.

Zanno, L. E. 2010. Osteology of Falcarius utahensis (Dinosauria: Theropoda): characterizing the anatomy of basal therizinosaurs. Zoological Journal of the Linnean Society. v158, pp 196-230.

Zanno, L. E. & Makovicky, P. J., 2011. Herbivorous ecomorphology and specialization patterns in theropod dinosaur evolution. Proceedings of the National Academy of Sciences. v108 m1, pp 232-237.

Gauging stance in "wide-gauge" sauropods

2011-11-11T12:08:00.001-08:00

In 1999 Jeff Wilson and Matt Carrano published an excellent paper addressing the phenomena of "wide-gauge" sauropod trackways. For years researchers had been working to explain why sauropod trackways seemed to come in two very different flavors - some of them were very closely spaced...so much so that they would actually overlap on the midline of the track. Other sauropod tracks seemed to show animals walking with their feet spread much further apart.

What were paleontologists to make of this?

One explanation was that the trackways were made by the same type of sauropods that were engaging in different behaviors. In other words, perhaps sometimes a sauropod would walk with its legs close in, while at other times it would use a wide-gauge stance.

Wilson & Carrano proposed that instead the trackways were made by sauropods with different skeletal adaptations. They mustered quite a few lines of evidence, but perhaps the best was that there was a group of sauropods - titanosaurs - that in fact had a much wider pelvis than other sauropods. The paper created a framework for later workers to use when attempting to correlate track makers with fossilized trackways, and is generally a towering success.

But I did want to take issue with one figure of the paper - one that pops up repeatedly at SVP. It is figure 5, demonstrating their interpretation of hing leg stance:

That's Camarasaurus on the left and Opisthocoelicaudia on the right. The clever reader may have already surmised from the title of this post that I think the animal on the right has its legs spread too far apart. But I have a larger issue: both animals have their legs spread much too far apart.

Remember that narrow-gauged trackways actually have their feet fall so close together that they frequently overlap along the midline. There's no way even sauropod "A" could make those tracks in the stance as figured. And this is why I'm bringing this up, because animals generally don't walk around with their legs acting as perfectly vertical beams. If you spend time watching large animals walk away from you, you'd see something like this:

Elephant image from here, rhino image from here.

People also move like this, with our vertical limbs generally sloping in toward the midline when we walk or run. There are probably several reasons for this (including mechanical efficiency) but for our purposes here let's just setting on the fact that it happens. Large, straight-limbed graviportal animals tend to walk with the limbs angled inward, not down (and certainly not angled out).

And the trackways also demonstrate this. If you place place sauropods over the actual trackways in question, you end up with a stance more like this:

In this case I've put a diplodocid (Supersaurus) on the left, while the animal on the right is scaled to the pelvic dimensions of Opisthocoelicaudia as seen in the original paper. Both animals have the hind legs mostly vertical but gently sloping inward.

This is not to say that sauropods never adopted a pose with their legs spread out a bit; Wilson & Carrano point out that titanosaurs have adaptations that may have allowed them to evert their hind limbs more effectively. They suggest that titanosaurs may have done so when rearing up, or during other activities that require greater stability.

I don't take issue with that, and those sorts of differences in the legs and pelvis may make it possible to tease out further behavioral differences between sauropod groups. But when walking around in their day to day lives both the footprints and modern analogs make a strong case that the limbs should be vertical, and if anything sloping in towards the midline rather than spread away from it.

Reference:

Wilson, J. A, & Carrano, M. T. 1999. Titanosaurs and the origin of "wide-gauge" trackways: a biomechanical and systematic perspective on sauropod locomotion. Paleobiology, 25(2), pp. 252-267.

Um hey, Scientific American? Bird knees bend the same way as everyone else.

2011-09-30T21:08:00.000-07:00

Ok, time for a quick anatomy lesson: Despite what you may have heard, bird knees do not bend backward. Nor, in fact, do the knees of any tetrapod perform this trick. Given the role of the knee in locomotion, it's not even clear how such a reversal could evolve after the initial "knee bend" direction was settled upon several hundred million years ago.

Why bring the anatomical equivalent of a fairy tale? Well, it's a fairly common misconception. So common, in fact, that it was recently enshrined by none other than Scientific American. So let's see if we can clear this up after the break:

Really, it's not.

It's a surprisingly common mistake. When looking at living birds many people fail to realize that part of the leg is hidden on a bird; the upper leg barely moves, and along with the knee it is actually buried up under the feathers of the wing and body. Birds also have quite long ankles, leaving their ankle joints in roughly the position we'd expect the knees to be on a human. Like this:

The key here is that people are plantigrade animals, while all theropods (including birds) are digitigrade. That means that human ankles are flat on the ground, and in our case our knees are roughly in the middle of our legs. In birds and other digitigrade animals (most dinosaurs and many mammals, like dogs, deer, and horses) it's only the toes that contact the ground. The ankle joint is well up off the ground, and the knee is is actually in the upper 1/3rd of the leg. And in birds the thigh is actually even a smaller part of the leg, and as mentioned above is also mostly hidden under feathers. Here's a look comparing the same leg portions of a human (in two poses), a dog, and an extinct bird:

Presbyornis Copyright Scott Hartman, other skeletals modified after Charles Knight.

In the diagram the thigh bones (femora) are all colored red, the shin bones and proximal ankle bones are colored blue, the "foot bones" (the distal tarsals and the metatarsals) are green, and the individual toe bones are yellow. Notice that the femur of the Presbyornis is small and very high, and the knee (the joint between the red and blue bones) is up where it would be hidden by the body and wings. But please also notice...the knee is bending the same way as ours. And the same way as everything else that has a spine and walks on land.

Which brings us back to the article posted by Scientific American. I don't want to go too far with "gotcha" blogging; Scientific American is generally one of the more accurate popularizers of science on the web and in print. I took a look the other pieces published by the author, and she seems like a solid reporter that just happens to have made a mistake. Journalists don't get science degrees (and even if they did that would only be one subject), so this should not be construed as an attack.

But at the same time, this is a serious error. It's like reporting that September has 32 days in it, or that the Red Sox clinched a playoff spot this week. Only worse, as it's perpetuating a myth that gets passed around as "common knowledge". I attempted to bring this to the attention of the relevant parties shortly after it was reported, both on Google+, where SciAm blog editor Bora Zivkovic has been making effective use of the new social network, and the author's Twitter account (which is frequently used). Despite near real-time feedback, days have gone by with no correction.

Making a mistake is understandable, but failing to correct it is not. Scientific American has written hundreds of articles on the state of science education, and has often been an effective advocate for ways to improve it. But the authority they derive comes from their attention to scientific detail, so I hope we will now see a quick correction without further delay.

Talos: A troodontid with a leg up on the competition

2011-09-20T12:58:00.000-07:00

It's my pleasure to introduce the newest member of the troodontid family: Talos sampsoni. Named for paleontologist Scott Samspon, Talos was described by Lindsay Zanno and others in the wonderful open source journal Plos ONE. Talos is the first troodontid to be named from the Kaiparowits Formation of Utah, making it about 76 million years old. Cross-sections of the long bones suggest that the animal was between four and six years old, and while it hadn't stopped growing, it appeared to be reaching reproductive age at a smaller size than it's close relative Troodon. Of note is that the specimen had a bone in its second toe that was injured and partially healed. Since it appears to have been injured from violent trauma, it's consistent with with the idea that the "switchblade" toe was used in a way that could result in such an injury (presumably either attack or defense). Also, since the rest of the foot shows no indication of the sort of limping or other adjustments you see from a prolonged foot injury, it also reinforces the idea that troodontids walked with the second toe off the ground (as shown above).

I was producing the above skeletal reconstruction for the Utah Museum of Natural History, who has constructed a new building filled with exciting displays that will open this Fall. It should be a state of the art exhibit that everyone should go see if they get the chance. Dr. Zanno was working on describing Talos at the time, so I worked with her to incorporate the data into the skeletal. There is quite a bit of troodontid material from the Kaiparowits, but only a fraction of it can be confidently assigned to Talos at this time. Restricting ourselves to the type specimen looks something like this:

You could be forgiven if your first reaction is "that's not very complete!". But I was thrilled. Why? It's hard to remember sometimes, since Troodon is illustrated frequently, but the published material that Troodon is usually based on is really scrappy. Here is a quick and dirty example of what was published in Dale Russell's 1969 paper:

To create the reconstruction (then called Stenonychosaurus) of Troodon that inspired him to create his infamous dinosauroid sculpture, Dale Russell had to combine all of the material from the Asian taxa Saurornithoides (as seen below) just to create a usable composite:

That made the size of the head and pelvis more clear, and provided more back and tail vertebrae to scale from, but look at how "dotted" the outlines of the limbs are - there still wasn't a good guide for scaling the limbs of any of these advanced troodontids. A few unpublished specimens are out there, but none of those provided definitive limb proportions. Talos finally does that.

So in addition to the interesting conclusions on biogeography, ontogeny, and mode of life, Talos should be exciting to illustrators because it provides the first definitive glimpse of the limb proportions of advanced troodontids. They aren't radically different from the proportions Dale Russell speculated on in the 1960s (although the forelimbs are shorter than some people have speculated since then), but the good news is that we now know for sure. In fact at this point the only serious unknown is the neck, although there are plenty of more basal troodonts to base that on.

Running around like an Ornitholestes with it's head cut off!

2011-09-15T12:52:00.000-07:00

If you watched Episode II of Dinosaur Revolution, you may have laughed at this Ornitholetes, who I'll refer to as Ichabod. This may seem like an odd scene to pick for a scientific discussion, but I think it actually has something useful to teach. Also, I'm partially responsible. I should be clear, the story idea was not mine (that's above my pay grade), but it's something that was run by me, and I did not try to shoot it down (and still wouldn't).

Why? I think it's reasonable.

No wait, let me explain: I'll grant you that there isn't much in the professional literature on the subject on the subject of "headless running" in animals, but from some criticisms I've read I think people maybe thinking about this the wrong way (i.e., wondering about the distribution of "headless-running" in birds like the behavior it's an advanced condition).

Vertebrates as a group have one of the more centralized nervous systems among animals (with some arthropods and especially some cephalopods as the other contestants in the "flexibility over redundancy sweepstakes"), but tetrapod nervous system evolution in general is a story of progressive centralization that (so far) culminates in mammals. Even in humans, with our gobs of ridiculously calorie-hungry centralized gray matter, we still have autonomous reactions that don't require the brain to be involved (as anyone knows who's burned themselves and jerked their hand away before they felt the pain). That said, we have gone a long way down the path of nervous system centralization, and if you cut a mammal's head off you may get some twitching but it won't run around; our limbs literally cannot coordinate themselves without the brain's involvement (although morbidly it does appear that the head itself retains some coordination afterwards, if medieval reports are true that heads react for up to a 15 seconds after a beheading).

This degree of centralization is the derived condition, not the primitive one. So it seems unlikely that chickens are special here, except in as much as they more frequently get clean beheadings in the presence of human observers than most other birds (a quick Google search shows that turkey's exhibit this as well). This should be true of lizards, crocs, etc too (diapsids as a whole). So with enough experimental trials I'd fully expect an Ornnitholestes to do a good headless chicken impression. Now, I'll grant you that this would require a pretty clean bite on the allosaur's part, and the odds of observing it in the wild would not be very high. But the sequence was devised as be a surprising bit of humor in a scenario that was possible, not probable.

Given those parameters it seems reasonable enough to me.

Dinosaur Revolution Episodes III & IV on tonight on Discovery Science

2011-09-13T11:54:00.000-07:00

Just a quick note, for those looking forward to the last two episodes. They will be showing tonight on Discovery Science at 9 and 10pm (check local listings).

Reign of the Dinosaur Revolution

2011-09-08T14:46:00.000-07:00

One of the projects I've worked on the last two years was Dinosaur Revolution - although for most of that time it had the working name "Reign of the Dinosaurs" - which is still how I think of it in my head. I'm sure I'll get over it.

Two of the episodes aired this last Sunday(September 4th) and the last two air ~~this Sunday (Sep 11th)~~. (Note! The airing of episodes III & IV have been postponed, as Discovery felt that the show wasn't appropriate for September 11th. Thanks to Tom Holtz for point that out!) I'm sure there will be other showings. Anatomically-speaking, the dinosaurs will be the best to yet reach the screen (although there will be a few recent discoveries that couldn't get worked in on time). The artists working to create these dinosaurs were about as good as it gets when you need to combine talent and knowledge of dinosaurs into one package. The "story" in the episodes is more ambitious, attempting to hook viewers with no narration (although some minimal narration did get added late in production). How well it works for you is probably a matter of opinion, although I enjoyed it. Regardless, the show is well worth your time.

The reason I bring this up is over my long association with the project I've developed a new appreciation for how difficult it is to get anything on TV, let along maintain a specific scientific or artistic vision. That might actually make for a good post or two. But first I want to open this up for discussion.

So, who saw it, and what did you think? Some of you commented on Google+ - feel free to cut and paste your response over here if you want (or else come up with something even snazzier to say). I'll talk more about the experience, and the challenges, in the days to come.

Mike Habib's Great Flying Skeletals: Perspectives from Pterosaurs

2011-08-11T18:09:00.000-07:00

Today we get the second guest post on pterosaurs. In addition to his extensive background in biomechanics, Mike has started a blog with Justin Hall on biomechanics - you should check it out. Now, one with the main programming...

Great Flying Skeletals: Perspectives from Pterosaurs

Scott has graciously invited me to do a little guest post from the perspective of a biomechanist. While Skeletal Drawing focuses primarily on dinosaurs, I am going to depart a bit on this occasion and use pterosaurs to highlight some of the biomechanics issues that can occur with skeletal poses.

The Case of Running Pterosaurs
Many of you have probably seen pterosaurs reconstructed in the popular standard pose (particularly preferred by Greg Paul) where they are in mid-sprint, like so:

From here. Copyright Gregory S. Paul.

It's an impressive pose for a flying animal. A lot of people really like the look, and it lines up nicely with the same pose in birds, to which pterosaurs are often compared. There's just one (big) problem with it: pterosaurs probably never sprinted around on their hindlimbs like the reconstructions show.

In the case of pterosaurs, the "standard running pose" is typically presented as a launch pose. However, in the late 90's, Jim Cunningham made a strong case for quadrupedal launching in Quetzalcoatlus at a series of presentations for both engineers and biologists. In 2008, I published a manuscript on a sizable comparative study I ran on bone structural strength estimates in the forelimb and hindlimb, which demonstrated that most pterosaurs probably launched quadrupedally rather than bipedally.

Now, I know you're thinking "Oh c'mon, Mike, you just don't like those bipedal running pterosaurs because they conflict with your personal results. You're biased!" I may be biased in some sense, but actually, that's not the problem. I would not mind bipedal, sprinting pterosaurs if another study had used different data to support the idea. But the reality is that no analysis has ever produced support for bipedal launching in pterosaurs. In fact, so far as I am aware, my paper was the first attempt at testing between the two modes of launch. There have not been a great number of biomechanical analyses run on pterosaurs, but there were a handful back in the 1970's and again in the early 2000's. A few of these considered their performance during takeoff, and the authors all assumed a bipedal launch mechanism, as in birds. The key word there is assumed - those studies asked the question "if pterosaurs launched like birds, then how would it work out?", but they never actually tested if a bipedal run was likely. I think the first lesson here is this:

Don't reconstruct skeletal images in poses the animal was not known to reach, unless you are specifically trying to argue the plausibility in conjunction with the pose, with appropriate empirical data present.

Most viewers of a skeletal reconstruction will assume that the animal could (and did) the action shown by the skeletal pose. More discriminating viewers may consider the issue more thoroughly, but either way this gets in the way of the point of a typical reconstruction.

A typical skeletal is supposed to show off the anatomy. If the paper you are illustrating happens to be arguing for a specific dynamic action, then it makes sense to show the animal in that pose. If there is a dynamic pose that others have shown to be plausible, then that's fine, too - but not as a standard pose, because there will nearly always be some animal that you come across later that can't do it. Nearly all terrestrial vertebrates can manage a slow walk, but only some can sprint - so choosing sprinting as your standard is risky. Inevitably, something is going to end up sprinting in your illustrations that never did so in life.

We can make an animal do anything we want in an illustration. Scott made an Allosaurus do a handstand. We could make Quetzalcoatlus launch by vaulting on its beak. These extreme examples are obvious, but less extreme cases can be difficult to detect. The ability to render a good illustration is powerful, because it can make the action or anatomy suggested by the image seem plausible, even if it's completely false or fabricated. If you're an illustrator, use your powers wisely.

Where Does that Wing Go?

One really tricky issue with pterosaurs is the wings - we don't know for certain where the wings attached in most species, and even if we pick a particular attachment point, there are a range of potential resulting wing shapes (if you want to read more about this issue, check out the section on flight over at pterosaur.net).

From David Hone's blog.

Of course, the soft tissue extent need not affect a skeletal reconstruction, but the typical methodology for skeletal illustrations is to include a black body outline. Usually this can made relatively conservative and follow typical muscle contours for vertebrates, but there is still a certain amount of conjecture there. When there is a major soft tissue structure involved, like the wing of a pterosaur, this can get very tricky. Any wing profile you show will be taken much the same as a pose: the viewer will assume you are explicitly supporting that particular wing shape.

One way to get around this issue is to leave off the wing membrane. A simple black muscle contour can be drawn around the wing spar and then the wing itself can be left out. This is, from my perspective, probably the best option if one is trying to simply show pterosaur skeletal anatomy in a neutral manner. However, if your illustration is for wide audience, then be forewarned that you will probably need to make a note that the wing is left out somewhere in the caption, or else non-specialists will be very confused.

This same problem can arise with other taxa, of course, especially swimmers - flukes and fins tend to be largely soft tissue, and sometimes there is no exact match to a bony contour (look at the tails of cetaceans, for example). In those cases, leaving off the fin or fluke might be especially confusing, so some sort of estimate might be required - but again, there is a danger of extrapolation. I do not know what the best option in that case would be, though half-tone might be an option for showing speculative components.

Up and Away?

The last major challenge for pterosaur skeletal illustration is probably choosing whether to show them flying or walking. As already discussed, bipedal sprinting is not likely, but pterosaurs certainly walked around (quadrupedally, as it turns out, based on the trackways), so one could easily show them walking, which would tend to match other skeletal reconstructions and work well for the standardization aspect. However, it can be difficult to show off pterosaur anatomy well with a walking pose, because the folded wing gets in the way. Some illustrators may also prefer to remind the viewer that the reconstructed critter was a flying animal. As such, there are some good arguments for a flying pose. As a biomechanist, I tend to be happy seeing either or both options, but this does bring one final consideration for skeletal standardization, which is that any given illustrator will inevitably need multiple standards. You can't really show a mosasaur walking, for example. As such, it may be that a separate standard is needed for each major mode of locomotion - flyers, swimmers, and walkers, as it were.

There are additional concerns that could be raised for pterosaurs, and for biomechanics interests, but those three general issues (plausible posing, soft tissue suggestion, and multi-modal animals) are some of the factors that speak most quickly to biomechanists like myself. Happy reading! Thanks again to Scott for the guest slot.

--Mike Habib