Paleoexhibit

2012 in Paleontology

2013-01-01T17:25:00.000-08:00

It’s time for a retrospective of year 2012 in the paleontological field. Many species were described that year and apart from a few obvious ones, it was quite difficult to decide what should make up the top ten stories. After multiple hesitations, here is my pick (not in particular order of importance):

1.- The Kelheim theropod unveiled in 2011 received its official scientific name as Sciurumimus albersdoerferi. More surprisingly, it turns out to be a Megalosauroid, making it the theropod the most distantly related to birds to show direct evidence of feathers.

Reference: O. W. M. Rauhut, C. Foth, H. Tischlinger and M. A. Norell. 2012. Exceptionally preserved juvenile megalosauroid theropod dinosaur with filamentous integument from the Late Jurassic of Germany. Proceedings of the National Academy of Sciences 29:11746-11751.

2.- At 9 meter in length, Yutyrannus huali is the largest dinosaur showcasing direct evidence of feathers. Yutyrannus is also a tyrannosauroid, moving the at least partial feather coverage idea for Tyrannosaurus rex, from good probability to almost certainty.

Reference: X. Xu, K. Wang, K. Zhang, Q. Ma, L. Xing, C. Sullivan, D. Hu, S. Cheng, and S. Wang. 2012. A gigantic feathered dinosaur from the Lower Cretaceous of China. Nature 484:92-95

3.- Echinoderms (starfish, urchins, sea lilies, etc…) are unique among animals in having a body with a fivefold symmetry. We know from embryology that they must have evolved from bilateral ancestors. The fossil record finally confirmed this with the discovery of Ctenoimbricata spinosa, a sea floor spiny animal which proved to be an early echinoderm with bilateral symmetry.

Reference: S. Zamora, I. A. Rahman, and A. B. Smith. 2012. Plated Cambrian Bilaterians Reveal the Earliest Stages of Echinoderm Evolution. PLoS ONE 7(6):e38296:1-e38296:11.

4.- Microraptor, the four-winged dinosaur that already made the headlines last year when it was discovered to feed on birds, reveals its true colors: the study of fossil pigments indicates it had the plumage of a crow: metallic black.

Reference: Q. Li. 2012. Reconstruction of Microraptor and the Evolution of Iridescent Plumage. Science 335: 1215-1219.

5.- Evidence of feathers was also found in the North American ostrich-mimic dinosaur Ornithomimus edmontonicus. While the body was covered with downy feathers, the arms in the adults had wing feathers, suggesting that mating display was the initial purpose of those, not flight.

Reference: D. K. Zelenitsky, F. Therrien, G. M. Erickson, C. L. Debuhr, Y. Kobayashi, D. A. Eberth, F. Hadfield, 2012. Feathered Non-Avian Dinosaurs from North America Provide Insight into Wing Origins. Science 338 (6106): 510.

6.- Mosasaurs form a group of highly specialized predators from the Late Cretaceous period, related to modern day monitor lizards and perfectly adapted for swimming. The fossil of Pannoniasaurus inexpectatus is the first evidence that these predominantly marine creatures have also conquered freshwater.

Reference: L. Makádi, M. W. Caldwell, and A. Osi. 2012. The first freshwater mosasauroid (Upper Cretaceous, Hungary) and a new clade of basal mosasauroids. PLoS ONE 7(12):e51781.

7.- Nyasasaurus parringtoni known from very fragmentary remains might have been the earliest representative of the dinosaur clade.

Reference: S. J. Nesbitt, P. M. Barrett, S. Werning, C. A. Sidor, and A. J. Charig. 2013. The oldest dinosaur? A Middle Triassic dinosauriform from Tanzania. Biology Letters 9(1):1-5.

8.- A morphometric study of archosaur skulls indicate that birds have the skull of baby dinosaurs. Our avian friends may have therefore evolved from neotenic dinosaurs retaining their juvenile characteristics through adulthood.

Reference: Bhullar, B., Marugán-Lobón, J., Racimo, F., Bever, G., Rowe, T., Norell, M., & Abzhanov, A. 2012. Birds have paedomorphic dinosaur skulls. Nature, 487, 223-226.

9.- A new phylogenetic analysis of the enigmatic Miocene creature known as Necrolestes patagonensis indicates that it was a survivor of an ancient lineage of primitive mammals thought to have disappeared at the end of the Cretaceous: the Meridiolestids.

Reference: G. W. Rougier, J. R. Wible, R. M. D. Beck and S. Apesteguía. 2012. The Miocene mammal Necrolestes demonstrates the survival of a Mesozoic nontherian lineage into the late Cenozoic of South America. Proceedings of the National Academy of Sciences of the United States of America 109 (49): 20053–20058.

10.- The Cetotheriids are a family of baleen whales that appeared during the Late Oligocene and thought to be extinct since the Late Pliocene. Not anymore: a new phylogenetic analysis indicates that the living Pygmy Right Whale (Caperea marginata) is in fact a modern surviving representative of this family.

Reference: R. E. Fordyce and F. G. Marx. 2013. The pygmy right whale Caperea marginata: the last of the cetotheres. Proceedings of the Royal Society B: Biological Sciences 280 (1753): 20122645.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)

Humble beginnings for the mighty diapsids: the Araeoscelids and Orovenator

2012-12-02T12:46:00.001-08:00

The amniotes (those initially four-legged creatures that produce "amniotic eggs", i.e. eggs adapted for land life) are traditionally divided into a few branches depending on some key characteristics of their skull, and the diapsids appear to be the most successful of all these branches. Virtually all living vertebrates that we commonly name "reptiles" are diapsids: crocs, lizards, snakes, the whole lot of them... Diapsids also include the birds by way of their forebears, the dinosaurs. In contrast, mammals and their ancestors belong to the synapsid branch of the amniotes. The distinction between diapsid and synapsid lays in the number of holes (scientist called those "fenestrae" which means windows) in the skull just behind the eye socket. Diapsids typically have two, the supratemporal (or upper temporal) fenestra on top and the infratemporal (or lower temporal) fenestra below. Synapsids only have one, the bottom infratemporal fenestra, simply called temporal fenestra. Both diapsids and synapsids evolved from more primitive reptiles with no opening behind the eye: the anapsids. The distinction between the different type of skulls are depicted in Figure 1.

Fig 1.- Different type of skulls among reptiles. Top left: anapsid skull of Procolophon trigonoceps (after Romer, 1956) top right: diapsid skull of Petrolacosaurus kansensis (after Reisz, 1981), bottom: synapsid skull of Eothyris parkeri (after Reisz et al., 2009).

The distinction seems simple enough but only reflects the primitive initial condition. Evolution indeed loves playing tricks. The same way that we know that dolphins are really mammals and not some strange air-breathing fish, scientists figured that everybody's favorite marine mesozoic reptiles, the plesiosaurs and ichthyosaurs, are really diapsids in disguise. Their skulls only have one opening behind the eye socket, the supratemporal fenestra, a condition which is called 'euryapsid'. The euryapsids used to be considered as a fourth branch of reptiles, but carefull examinations of the fossils show they evolved from diapsid ancestors and that the loss of the infratemporal fenestra is only a secondary characteristics. More tricky are the turtles. These do not have any opening behind the eye which classified them as "anapsids". However, nowadays, it seems quite firmly established that they too are highly modified diapsid reptiles, although it took scientists quite a while to figure this one out. Now look a the highly modified skulls of birds and snakes: you will have hard time recognizing any of the original temporal openings in them, but since their ancestors were diapsid reptiles, by way of basic phylogeny law (you shall belong to the same clade as your ancestors, ... i.e the monophyly principle), they too are diapsid reptiles.

That being said, the diapsids then really are the most successful group of amniotes with some 18,000 species, including birds, alive today (compared to the 5700 species of mammals representing the only survivors of the synapsid branch). But what is their origin? They probably evolved during the Late Pennsylvanian from a group of anapsid ancestors to which such lizard-like creatures as Paleothyris and Hylonomus belong to. But this is not at all very clear because of the scarcity of the fossil record. The first true diapsids are a family of small superficially lizard-like creatures called Araeoscelidia, to which Petrolacosaurus and Araeoscelis are the best known representatives. The fossil record of the Araeoscelids extends from the Late Carboniferous to the Early Permian.

Fig 2.- a reconstruction of Petrolacosaurus kansensis.

The most ancient known diapsid is Petrolacosaurus kansensis from the Late Pennsylvanian (the North American 'Missourian' stage which corresponds to the ICS Kasimovian stage, ~305 MYA) of Kansas. The generic name means "rock lake reptile" in reference to the "Rock Lake Shale" in which the type specimen (a nearly complete hind limb) was found. Although originally described in 1945 as a pelycosaur (thus a synapsid), it was not until 1977 after new specimens including the skull with its two characteristic openings, were thoroughly described, that it was realized to be the earliest known diapsid, raising the little critter from relative obscurity to paleontological stardom. In a world dominated by giant arthropods and fearful amphibians, Petrolacosaurus was indeed relatively small, measuring probably about 70 to 80 cm in length, accounting for the long tail.

Fig 3.- Reconstruction of Spinoaequalis schultzei.

Also from the Late Pennsylvanian of Kansas but a bit later (from the Calhouns Shale formation dated to the North American 'Virgilian' stage roughly corresponding to the ICS Gzhelian, ~ 300 MYA), comes Spinoaequalis schultzei. This early diapsid is a bit smaller (30 cm) and is only tentatively placed among the araeoascelids. The interesting note about this critter is the tail: the tall and equal size neural and haemal spines of the caudal vertebra (thus the generic name) which gives the distinct tall and laterally compressed shape to the tail is viewed as an adaptation for swimming, a good indication that Spinoaequalis was an aquatic animal. This is supported by the fact that its fossil was discovered in freshwater deposits among remains of spiny sharks (acanthodians) and other fully aquatic animals. However, the long and slender limbs, are those of a terrestrial animal, an indication that it wasn't fully aquatic. In any case, this makes Spinoaequalis the first amniote to have ever returned to water since their epic conquest of the dry lands.

Fig 4.- Skulls of Araeoscelis gracilis (after Reisz et al., 1984).

Araeoscelis dates from the Early Permian and was originally described in 1910 as a lizard. It has the same body plan than Petrolacosaurus but the skull was more massive with strong teeth, ideal for crushing the heavy exoskeleton protecting some of the arthropods of that time. Araeoscelis was about the same size too, with an estimated length of 70-80 cm accounting for the unknown tail. As a probable adaptation of its specialized diet, the lower temporal fenestra has closed making the skull more robust. Araeoscelis, has therefore this 'euryapsid' condition that will be common to the large marine predators of the Mesozoic. Two species have been described, A. gracilis from the Arroyo Formation of Texas (Kungurian age, ~275 MYA), known from several fairly complete specimens, and A. casei from the Admiral Formation of Texas (Artinskian age, ~285 MYA), known from at least seven individuals. The two are virtually indistinguishable and the separation into distinct species seems only to be justified by their difference in age, A. casei being from slightly (~ 10 millions years) older rocks than A. gracilis.

Fig 5.- Reconstruction of Araeoscelis gracilis.

The other Araeoscelids are poorly known and all date from the Early Permian. The 70 cm long Dictybolos tener from the Wellington formation of Oklahoma (~280 MYA) is known from isolated bones from numerous individuals. This one was presumably semi-aquatic and a fish eater. Zarcasaurus tanyderus from the Cutler Formation of New Mexico is known from a partial disarticulated skeleton. Characterized by its rather long neck vertebrae, it was a close relative of Araeoscelis. In Europe, the rather dubious Aphelosaurus lutevensis from the Tuilières formation of South Central France and first described in the 19th century, is another possible Araeoscelid, though it is hard to tell without any knowledge of a crucial piece of fossil information: the skull. Similarly, Kadaliosaurus priscus from the Rotliegend of Germany is only known from a postcranial skeleton and its classification among the araeoscelids is only tentative.

Fig 6.- Reconstructed skull of Orovenator mayorum (after Reisz et al., 2011).

Besides the Araeoscelids, there is one additional diapsid dating from the Early Permian, Orovenator mayorum discovered in one of the fissure fills of the Richards Spur locality of Oklahoma, and known from two partial crushed skulls. Orovenator has the distinction of being the earliest known and most primitive of the Neodiapsids, a clade that contains all the known diapsids except for the araeaoscelids. This was a small animal with an elongated skull half the length of those of Petrolacosaurus and Araeoscelis. The Richards Spur locality with its distinct Early Permian fauna of some 30 taxa of fully terrestrial vertebrates, is thought to originate from an upland ecosystem, which would only fossilized in very exceptional cases. This is in sharp contrast to the Araeoscelids which were all found in lowland swampy habitats, with better chances for fossilization. The hypothesis is therefore that the initial split of the early diapsids into the Araeoscelids and the Neodiapsids is the result of adaptation to two different habitats, with the Araeoscelids in the lowlands and the Neodiapsids in the uplands.

In conclusion, the early diapsids show a surprising degree of diversity with some forms that became at least partially aquatic (Spinoaequalis, Dictybolos) while others adapted to the harsher conditions of the uplands (Orovenator). There is also evidence of a quite specialized diet for some (Araeoscelis). However, the remains of these animals are quite rare and there is a rather long gap in the fossil record before we see them appear again in the Late Permian. Their number would not significantly increase before the Early Triassic. It is somewhat tempting to imagine that like the mammals of the Mesozoic dominated by the dinosaurs, the early diapsids lived in the relative shadow of the other reptiles for some 50 million years, when the world was dominated by larger synapsids, anapsids and amphibians and that it will take the massive Permian-Triassic extinction event to see the diapsids finally take the upper hand.

References:

Brinkman, D., Berman, D., & Eberth, D. (1984). A new araeoscelid reptile, Zarcasaurus tanyderus from the Cutler Formation (Lower Permian) of north-central New Mexico. New Mexico Geology, 34–39.

Debraga, M., & Reisz, R. (1995). A new diapsid reptile from the uppermost carboniferous (Stephanian) of Kansas. Palaeontology, 38(1), 199–212.

Lane, H. (1945). New mid-Pennsylvanian reptiles from Kansas. Transactions of the Kansas Academy of Science (1903-), 47(3), 381–390.

Olson, E. (1970). New and little known genera and species of vertebrates from the Lower Permian of Oklahoma. Fieldiana: Geology, 18(3), 359–434.

Reisz, R. R. (1977). Petrolacosaurus, the oldest known diapsid reptile. Science, 196(4294), 1091–3.

Reisz, R., Berman, D., & Scott, D. (1984). The anatomy and relationships of the Lower Permian reptile Araeoscelis. Journal of Vertebrate Paleontology, 4(1), 57–61.

Reisz, R. R., Modesto, S. P., & Scott, D. M. (2011). A new Early Permian reptile and its significance in early diapsid evolution. Proceedings. Biological sciences / The Royal Society, 278(1725), 3731–7.

Williston, S. (1910). New Permian reptiles: rhachitomous vertebrae. The Journal of Geology, 18(7), 585–600.

Williston, S. (1913). The skulls of Araeoscelis and Casea, Permian reptiles. The Journal of Geology, 21(8), 743–747.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)

The Lossiemouth Sandstone Formation of Scotland

2012-08-19T09:08:00.000-07:00

The yellowish sandstone of the Lossiemouth Sandstone Formation can be found on the coast near Elgin, in the Moray council area, north east of Scotland (Fig 1). Fossils were collected there in different quarries, around the town of Lossiemouth, at the end of the 19th and beginning of the 20th century, notably by the ardent collector William Taylor of Lhanbryde (1849-1921). The sand from the sandstone was probably carried by wind and deposited over a fluvial area, indicating that the location during the Late Triassic was a sand dune desert with narrow strips of lowland vegetation around rivers. The sandstone did not preserve any index fossil such as pollens, plants or invertebrates, and no radiometric dating could be performed, leading to some uncertainties on the exact age of the rocks. However, based on the correlation of the Lossiemouth vertebrate fauna with those of the Maleri Formation of India, the Santa Maria Formation of Brazil, the Ischigualasto Formation of Argentina, a Late Carnian age is generally attributed to the sandstone. The fauna is represented by eight taxa of reptiles, including six archosaurs.

Fig. 1.- Location of the Lossiemouth Sandstone Formation today (left) and during the Late Triassic (right).

Saltopus elginensis Huene, 1910 ("Elgin's hopping foot"), is known from a single badly preserved skeleton. The exact affinity of this small (60 cm long) bipedal predator has been debated for decades. It was at some point classified as an early theropod dinosaur but more recent analysis put it within the dinosauriformes but outside the Dinosauria clade as a sister taxon to them (It means Saltopus is not a dinosaur but one of its closest relatives). Since the skull in the fossil is missing, the diet of this animal is unknown.

Another interesting animal from the Carnian of Scotland is Scleromochlus taylori Woodward, 1907 ("Taylor's hard fulcrum") (Fig 2). This rather strange 1.8 m long creature looks a bit like a lizard on long slender legs. It was related or even has been considered ancestral to the pterosaurs, a group of archosaurs that will eventually conquer the air. Several skeletons of this animal are known.

Fig 2.- Reconstruction of Scleromochlus taylori.

The 4 meter long and probable top predator of its time, Ornithosuchus longidens ("long-toothed bird crocodile") (Huxley, 1877) (Fig. 3) belongs to another group of facultative bipedal carnivorous reptiles distantly related to crocodiles, the Ornithosuchians. They were equipped with sharp teeth and a row of bony scales (osteoderms) along their back and tail. Ornithosuchus was once thought to be ancestral to the theropod dinosaurs, but details of its skeletal anatomy such as the braincase and the configuration of the ankle show that it was a Crurotarsi like the Rauisuchians, the Aetosaurs, crocodiles and phytosaurs and not an Avemetatarsalia (Dinosaurs and Pterosaurs).

Fig. 3- Reconstruction of Ornithosuchus longidens.

Erpetosuchus granti Newton, 1894 ("Grant's Snake Crocodile") was a small (60 cm long) agile quadrupedal predator that might have hunted small lizards and amphibians (Fig 4). Erpetosuchus was the Lossiemouth fossil the most closely related to modern crocodiles and is known from at least four specimens. Considering the location of Scotland at that time (Fig 1), it is no surprise that an additional fossil referable to the same animal was discovered in the New Haven Formation of Connecticut, United States.

Fig. 4.- Reconstruction of Erpetosuchus granti.

Herbivores are represented by several groups of reptiles. The rhynchosaurs had stocky bodies with a broad skull and a powerful beak. They may have fed on tough vegetation, such as the seed ferns which were abundant at that time. In Europe, Rhynchosaurs were represented by the 1.3 meter long Hyperodapedon gordoni Huxley, 1859 ("Gordon's best pestle tooth") from Scotland (Fig. 5). It is known from at least 35 individuals, making it the most abundant vertebrate fossils of the formation. The fossils came into various sizes, reflecting ages, that can be grouped into two general types (morphotypes) possibly indicating sexual dimorphism. The genus Hyperodapedon had a worldwide distribution, with several species described from India, Brazil, Argentina. Zimbabwe, Madagascar, Tanzania and the United states. They had therefore been used to correlate different formations across the globe, serving as an "index" fossil.

Fig. -5. - A pair of Hyperodapedon gordoni.

Aetosaurs were heavily armored archosaurs, with a body covered with plate-like scutes (osteoderms) and spikes. These vegetarian animals were also distantly related to crocodiles and are now thought to have been fully terrestrial animals. The carnian representives in Europe include the genera Stagonolepis and Paratypothorax, with Stagonolepis robertsoni Agassiz, 1884 ("Robertson's pitted scale") being the Lossiemouth species (Fig. 6). It measured about 3 meters in length. The remains of Stagonolepis were originally mistaken for fish scales, thus the generic name.

Fig. 6.- Stagonolepis robertsoni.

Procolophonids were small lizard like creatures belonging to the ancient lineage of reptiles called Parareptilia. By the end of the Triassic they have adopted a vegetarian diet before being wiped out by extinction at the end of the period. Leptopleuron lacertinum Owen, 1851 ("Lizard slender ribs") is a typical procolophonid that measured about 30 cm in length (Fig 7). It might have lived in burrows. This little critter was the subject of a bitter rivalry between famed paleontologists Richard Owen and Gideon Mantell at the end of the 19th century, both wanting to be first to describe the animal. Mantell christened the fossil Telerpeton elginense but Owen was quicker to publish so the name he gave has priority according to the international rules of nomenclature.

Fig. 7.- Reconstruction of Leptopleuron lacertinum.

The rhynchocephalians (and more restrictively, the sphenodontians) were once a successful and diverse group of lizard-like mesozoic reptiles with both aquatic and terrestrial forms. The only modern surviving member of the rhynchocephalians is the tuatara (Sphenodon) from New Zealand, generally presented as a true "living fossil". The Lossiemouth sandstone has yielded the species Brachyrhinodon taylori Huene, 1910 ("Taylor's short nose teeth") (Fig. 8) which was very similar to the tuatara in shape, but smaller, measuring some 25 cm in length, and with probably a similar lifestyle. Both Leptopleuron and Brachyrhinodon are known from numerous specimens.

Fig -8.- Reconstruction of Brachyrhinodon taylori.

All artworks on this page are copyrighted to Nobu Tamura. Do not use without permission. Contact: nobu dot tamura at yahoo dot com.

References:

Benton, M. (1983). The Triassic reptile Hyperodapedon from Elgin: functional morphology and relationships. Phil. Trans. R. Soc. Lond. B, 302(1112), 605–718.

Benton, M. (1999). Scleromochlus taylori and the origin of dinosaurs and pterosaurs. Phil. Trans. R. Soc. Lond. B, 354, 1423–1446.

Benton, M., & Walker, A. (2002). Erpetosuchus, a crocodile-like basal archosaur from the Late Triassic of Elgin, Scotland. Zoological Journal of the Linnean Society, 136, 25–47.

Benton, M. J., & Walker, A. D. (2011). Saltopus, a dinosauriform from the Upper Triassic of Scotland. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 101(3-4), 285–299.

Fraser, N. C., & Benton, M. J. (1989). The Triassic reptiles Brachyrhinodon and Polysphenodon and the relationships of the sphenodontids. Zoological Journal of the Linnean Society, 96(4), 413–445.

Olsen, P. E., Sues, H.-D., & Norell, M. A. (2000). First record of Erpetosuchus (Reptilia: Archosauria) from the Late Triassic of North America. Journal of Vertebrate Paleontology, 20(4), 633–636.

Säilä, L. K. (2010). Osteology of Leptopleuron lacertinum Owen, a procolophonoid parareptile from the Upper Triassic of Scotland, with remarks on ontogeny, ecology and affinities. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 101(01), 1–25.

Spencer, P. (2000). The braincase structure of Leptopleuron lacertinum Owen (Parareptilia: Procolophonidae). Journal of Vertebrate Paleontology, 20(1), 21–30.

Walker, A. (1961). Triassic reptiles from the Elgin area: Stagonolepis, Dasygnathus and their allies. Phil. Trans. R. Soc. Lond. B, 244(709), 103–204.

Walker, A. (1964). Triassic reptiles from the Elgin area: Ornithosuchus and the origin of carnosaurs. Phil. Trans. R. Soc. Lond. B, 248(744), 53–134.

Watson, D. M. S. (1909). On some Reptilian Remains from the Trias of Lossiemouth (Elgin). Quarterly Journal of the Geological Society, 65(1-4), 440–440.

Woodward, a. S. (1907). On a New Dinosaurian Reptile (Scleromochlus Taylori, gen. et sp. nov.) from the Trias of Lossiemouth, Elgin. Quarterly Journal of the Geological Society, 63(1-4), 140–144.

Sciurumimus albersdoerferi: Is it a girl? Is it a boy? No, it’s a Megalosauroid…

2012-07-02T20:00:00.000-07:00

Remember the perfectly preserved complete articulated skeleton of a young dinosaur that was presented to the press last year? Well, the paper describing it has finally been published in the Proceedings of the National Academy of Science. ‘Otto’, also known as the Kelheim theropod, has now a proper scientific name, Sciurumimus albersdoerferi, the generic name meaning “Squirrel mimic” (in reference to its bushy tail) and the specific name honors Raimund Albersdörfer, who made the specimen available for study. The fossil was found near Painten, Bavaria (Germany) and dates from the upper Kimmeridgian. Besides the exquisite state of preservation of the fossil that shows evidence of proto-feathers covering at least part of the body, the importance of Sciurumimus stems from its phylogenetic position on the dinosaur evolutionary tree. It is a megalosauroid, sister taxon to the likes of Megalosaurus, Torvosaurus and Eustreptospondylus, therefore representing the most basal theropod showing direct evidence of feathers, and the most complete megalosauroid remain yet discovered. This raises the interesting possibility that feathers might be a common inherited trait to all theropods and even to all dinosaurs if indeed the feather-like structures found on Tianyulong (an heterodontosaur) and quills on the tail of Psittacosaurus (a Ceratopsian) are analogous structures.

References:

Oliver W. M. Rauhut, Christian Foth, Helmut Tischlinger, and Mark A. Norell (2012) Exceptionally preserved juvenile megalosauroid theropod dinosaur with filamentous integument from the Late Jurassic of Germany, PNAS, Advanced online publication.

Bicentenaria argentina, a new theropod dinosaur from Argentina

2012-06-28T00:33:00.000-07:00

Bicentenaria argentina, a new theropod dinosaur from Argentina

Argentina has commemorated the 200th anniversary of its May revolution that led to the country independence on May 25, 2010. Two years later, paleontologists from that country announced the discovery of a new dinosaur and named it after the event, perhaps because the remains were unearthed on that day. Bicentenaria argentina was unveiled to the public on Tuesday June 26, 2012 through a short press release with pictures of the mounted skeletons of two fighting individuals (from which my illustration is based on). It is a small theropod that measured about 2.5 meters in length. The paragraph quoted from an interview with lead paleontologist Fernando Novas simply says that Bicentenaria is part of a group of dinosaurs that contain tyrannosaurs and Velociraptor and a distant ancestor to birds. This hints that Bicentenaria is a coelurosaur. The pictures of the mounted skeletons do not tell how much of it is actually known, as people tend nowadays to reconstruct entire skeletons from rather incomplete material. The actual remains consist of some 130 bones from at least 3 adults and several juveniles. The mounts look like those of a generic small size theropod, which probably means that Bicentenaria was a rather basal coelurosaurian, neither a tyrannosauroid, nor a dromaeosaur. However, the press release says the fossil is 90 million year old, thus Late Cretaceous, which seems a bit of a young age for a basal coelurosaur. I could guess the remains were found in the Portezuelo Formation of Turonian age in the Rio Negro Province, which means that Bicentenaria was a contemporary of the fabled Megaraptor, the dromaeosaurs Neuquenraptor and Unenlagia, as well as the alverezsaur Patagonykus. But let’s wait for the formal publication of the description of this intriguing animal.

Correction: I was just told that Bicentenaria is from the Candeleros Formation of Cenomanian age, therefore a contemporary of Giganotosaurus and Buitreraptor.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)

Theropods of the British Isles Part III

2012-04-08T19:45:00.002-07:00

Fig 1.- Juratyrant langhami

Late Jurassic Theropods of the British Isles

From the Oxfordian stage (~ 158 MYA), Metriacanthosaurus parkeri (von Huene, 1923) is another obscure tetanuran theropod, known from vertebrae, pelvic and hindlimbs elements (OUM J.12144) found near Weymouth, Dorset in the Oxford Clay Formation. Originally thought to be a megalosaurid, there is a possibility that it actually belongs to a group called sinraptorid, better known by its Chinese representatives such as Sinraptor and Yangchuanosaurus. Metriacanthosaurus probably measured about 8 meters in length.

The Kimmeridge Clay Formation has yielded a few theropod remains: one incomplete tooth from Wiltshire referred to “Megalosaurus” insignis (Eudes-Delongchamps and Lennier vide Lennier, 1870) is from a indeterminate theropod. A tibia (OUM J13568) is possibly from a megalosaur or a tetanuran. Two pedal phalanges of Fleet, Dorset are from a tetanuran.

Fig 2.- Metriacanthosaurus parkeri may have been related to Sinraptor.

Tyrannosauroids are represented by Juratyrant langhami (Benson, 2008) from the Kimmeridge Clay of Tithonian age (~149 MYA). This one is known from a single partial skeleton including a pelvis, partial leg and vertebrae (OUMNH J.3311-1—J.3311-30) found in Dorset. Juratyrant is more closely related to the British Early Cretaceous Eotyrannus than to the North American Stokesosaurus to which the animal was originally referred. Juratyrant measured about 5 meters in length.

References:

R. B. J. Benson. 2008. New information on Stokesosaurus, a tyrannosauroid (Dinosauria: Theropoda) from North America and the United Kingdom. Journal of Vertebrate Paleontology 28(3):732-750

Brusatte, S.L. and Benson, R.B.J. (In press). "The systematics of Late Jurassic tyrannosauroids (Dinosauria: Theropoda) from Europe and North America." Acta Palaeontologica Polonica, (in press).

F. v. Huene. 1923. Carnivorous Saurischia in Europe since the Triassic. Bulletin of the Geological Society of America 34:449-458.

D. Naish and D. M. Martill. 2007. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: basal Dinosauria and Saurischia. Journal of the Geological Society, London 164:493-510.

Theropods of the British Isles Part II

2012-03-22T08:48:00.002-07:00

Middle Jurassic Theropods of the British Isles

The Middle Jurassic of England was dominated by Megalosaurids, a family of large primitive tetanuran theropods, now believed to be closely related to the fish-eating Spinosaurids, early representatives of groups that will thrive during the Cretaceous, the tyrannosauroids and the maniraptorans were also present.

Fig 1.- Duriavenator hesperis

The Aalenian-Bajocian stages: Magnosaurus and Duriavenator

The Inferior Oolite formation of Aalenian-Bajocian age (~ 172 MYA) has given a few fragmentary remains of a theropod named Magnosaurus nethercombensis (von Huene, 1923) (originally ‘Megalosaurus’ nethercombensis) and described from partial dentaries, vertebrae, partial ilium, pubis and hindlimb (OUM J12143) found in Nethercomb, Dorset. Various others bits from the same formation in southern England were also referred to this rather obscure tetanuran. The fossil of M. nethercombensis has recently been reevaluated (Benson, 2010) and established to be a valid taxon. This megalosaurid is the oldest known tetanuran.

From the Upper Inferior Oolite Formation of Bajocian age (~ 170 MYA) comes Duriavenator hesperis (Waldman, 1974) (originally Megalosaurus hesperis), known from cranial bones (BMNH R332) found near Sherbourne in Dorset. This is another megalosaurid.

Fig 2.- Megalosaurus bucklandii

The Bathonian stage: Megalosaurus and Proceratosaurus

The Bathonian age (~166 MYA) of the British Isles is represented by a handful of theropods. The most famous of them is Megalosaurus, a name coined by William Buckland in 1824 to describe various remains including a lower jaw, vertebrae and partial hindlimbs uncovered at the Stonesfield quarry (Taynton Limestone Formation) that he thought belonged to a giant lizard-like creature. As many of the names from the early days of paleontology, Megalosaurus became a formidable wastebasket taxon, given to an assortment of miscellaneous theropod bones found around the world. Nowadays, only one species, Megalosaurus bucklandii Mantell, 1827 is considered valid and corresponds to the original material described by Buckland. Megalosaurus was a large 9 meter long theropod that was probably the top land predator of its time.

Cruxicheiros newmanorum Benson & Bradley, 2010 from the Chipping Norton Limestone Formation of lower Bathonian age, is based on scant materials, including a partial right femur (WARMS G15770) and other bits found on the same location near Little Crompton, Warwickshire. This one was a basal tetanuran of some sort. A single damaged vertebra found in the same formation but now lost, was named Streptospondylus cuvieri Owen, 1842.

Iliosuchus incognitus von Huene, 1932 from the Taynton Limestone Formation (Bathonian) of Stonesfield, Oxfordshire is known from three small ilia (BMNH R83, OUM J29780 and OUM J28971) found alongside remains of Megalosaurus. It is unclear what it was, either a small megalosaurid or the earliest known tyrannosauroid as some have suggested. A fragmentary small tibia found in the same formation was referred to Iliosuchus as well.

Fig 3.- Proceratosaurus bradleyi

Proceratosaurus bradleyi (Woodward, 1910) from the Great Oolite Group (White Limestone Formation) of Minchinhampon, Gloucestershire (Bathonian) is known from a partial skull exhibiting a nasal horn (which was possibly part of a larger crest), thus the name. This is an early tyrannosauroid, a member of this group of coelurosaurs, which will culminate into the North American Tyrannosaurus rex at the end of the Cretaceous period. Proceratosaurus perhaps measured about 3 meters in length.

From the Forest Marble Formation of Bathonian age, famous for its fossils of the sauropod Cetiosaurus, some troodont-like and dromaeosaur-like teeth have been unearthed, making it the earliest occurrence of this group in the fossil record (Evans & Milner, 1994).

The Callovian stage: Eustreptospondylus

Later in the Middle Jurassic (Callovian stage, ~163 MYA), lived another Megalosaurid named Eustreptospondylus oxoniensis Walker, 1964. This one is known from a partial skull (OUM J13558) and a partial skeleton from a juvenile individual found in Wolvercote, Oxfordshire, at the bottom of the Oxford Clay Formation. This rather obscure species was popularized in one episode of the BBC Series “walking with dinosaurs”. It probably measured something like 5 m in length.

References:

R. B. J. Benson. 2008. A redescription of 'Megalosaurus' hesperis (Dinosauria, Theropoda) from the Inferior Oolite (Bajocian, Middle Jurassic) of Dorset, United Kingdom. Zootaxa 1931:57-67

R. B. J. Benson, 2010, The osteology of Magnosaurus nethercombensis (Dinosauria, Theropoda) from the Bajocian (Middle Jurassic) of the United Kingdom and a re examination of the oldest records of tetanurans, Journal of Systematic Palaeontology, 8(1): 131-146.

S. E. Evans and A. R. Milner. 1994. Middle Jurassic microvertebrate assemblages from the British Isles. In the Shadow of the Dinosaurs: Early Mesozoic Tetrapods, N. C. Fraser and H.-D. Sues (eds.), Cambridge University Press 303-321

F. von Huene, F. 1923. Carnivorous Saurischia in Europe since the Triassic. Bulletin of the Geological Society of America 34:449-458.

D. Naish and D. M. Martill. 2007. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: basal Dinosauria and Saurischia. Journal of the Geological Society, London 164:493-510.

R. Sadleir, P. M. Barrett, and H. P. Powell. 2008. The anatomy and systematics of Eustreptospondylus oxoniensis, a theropod dinosaur from the Middle Jurassic of Oxfordshire, England. Monograph of the Palaeontographical Society, London 160(627):1-82

M. Waldman. 1974. Megalosaurids from the Bajocian (Middle Jurassic) of Dorset. Palaeontology 17(2):325-339.

A. D. Walker. 1964. Triassic reptiles from the Elgin area: Ornithosuchus and the origin of carnosaurs. Philosophical Transactions of the Royal Society of London, Series B, Biological Sciences 248:53-134

Theropods of the British Isles Part I

2012-02-29T09:08:00.002-08:00

The bipedal theropods represent the most diverse group of dinosaurs including all the meat-eating ones as well as some omnivorous and herbivorous forms. Primitive theropods include the coelophysoids (small, slender and lightly built dinosaurs that thrived worldwide during the Late Triassic, and for which the best known representative is the North American Coelophysis), the ceratosaurs (including forms such as Ceratosaurus and Carnotaurus) and the tetanurans. The last group contains the vast majority of the theropods and its members are characterized among other things by a rigid tail and the total loss of the fourth and fifth digits in their hands. Megalosaurs (i.e. Megalosaurus) are early tetanurans while Spinosaurs (i.e. Spinosaurus and co) are possibly related to them. Later tetanurans are the allosauroids (large predators such as Allosaurus and Carcharodontosaurus) and the coelurosaurians, which in turn include the tyrannosauroids (such as Tyrannosaurus), the ornithomimosaurs (the ostrich-mimic forms such as Struthiomimus and Ornithomimus) and the maniraptorans. The maniraptorans with their modified wrist and generally large hands are represented by the birds (where the hands became wings) and all their closest relatives, such as the oviraptosaurs (Oviraptor and co), the deinonychosaurs (Velociraptor and co).

Fig 1.- Small coelophysoids lived during the Late Triassic in Great Britain.

Late Triassic Theropods

During the Upper Carnian (~ 220 MYA) of Scotland lived Saltopus elginensis Huene 1910, known from a poorly preserved partial skeleton including dorsal, sacral and caudal vertebrae and fragments of fore and hind limbs (BMNH R3915) found in the Lossiemouth Sandstone Formation, near Elgin, Morayshire. The exact affinities of the animal have been debated. It was either a primitive theropod or a more ancestral dinosauriform.

Theropods were definitely present during the Late Triassic period in the British Isles as proven by the discovery of fragments in the fissure fills of southern Wales. A pelvis, femur and dorsal vertebrae (BMNH PV RU P77/1 and RUP 76/1) from Pant-y-ffynon, Wales of Norian age (~210 MYA), were possibly from a coelophysoid.

The dubious ‘Zanclodon’ cambrensis Newton, 1899 of Rhaetian age (~200 MYA) is known from the mold of a large left dentary with teeth (BGS 6532/BMNH R2912) from Glamorganshire, Wales (Lilstock Fm). This one might be another coelophysoid.

Fig 2.- Larger coelophysoid such as Sarcosaurus roamed the Early Jurassic of England.

Early Jurassic Theropods

In the early Jurassic, coelophysoids are represented by the shadowy Sarcosaurus. The type species, Sarcosaurus woodi Andrews, 1921 is known from a partial pelvis, femur and vertebra (BMNH 4840/1) from Leicestershire (Lias Fm) of Early Sinemurian age (which probably is actually of earlier Late Rhaetian or Hettangian age, ~198-200 MYA). A second species, Sarcosaurus andrewsi Huene, 1932 (= Magnosaurus woodwardi) is based on a partial right tibia (BMNH R3542), originally reported by Woodward in 1908 from Warwickshire of Hettangian age (~198 MYA). Sarcosaurus was a quite large coelophysoid with an estimated length of about 3.5 m.

From the Sinemurian (~192 MYA) Upper Broadford Beds Formation of the Isle of Skye (Scotland) came an incomplete right tibia (NMS.G.1994.10.1), interpreted as belonging to a small theropod, probably another coelophysoid (Benton et al., 1995).

A partial hindlimb from Charmouth, Dorset (BMNH 39496) that was described by Owen (1861) alongside remains of the ornithischian Scelidosaurus harrisonii was reported from the Lower Lias (Hettangian-Sinemurian). This one was found to be comparable to a megalosaur and would therefore be an early member of this group of large theropods that will dominate the Middle Jurassic period.

Finally, a tooth (BMNH 41352) from the Lias group of Lyme Regis, named ‘Megalosaurus’ lydekkeri von Huene, 1926 (= Magnosaurus lydekkeri), is from an indeterminate theropod.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)

References:

C. W. Andrews. 1921. On some remains of a theropodous dinosaur from the Lower Lias of Barrow-on-Soar. Annals and Magazine of Natural History, series 9 8:570-576

M.J. Benton, D.M. Martill & M.A. Taylor, 1995. The first Lower Jurassic dinosaur from Scotland: limb bone of a ceratosaur theropod from Skye. Scottish Journal of Geology, 31, 177–182.

F. v. Huene. 1910. Ein primitiver Dinosaurier aus der mittleren Trias von Elgin [A primitive dinosaur from the Middle Trias of Elgin]. Geologie und Paläontologie Abhandlungen (n.s.) 8(6):317-322.

D. Naish and D. M. Martill. 2007. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: basal Dinosauria and Saurischia. Journal of the Geological Society, London 164:493-510.

O. W. M. Rauhut and A. Hungerbühler. 2000. A review of European Triassic theropods. GAIA 15:75-88.

Sauropods of the British Isles Part III

2012-02-18T08:36:00.000-08:00

Fig 1.- Rebbachisaurids were present on the Isle of Wight during the Early Cretaceous.

Sauropods from the Early Cretaceous (part II)

The Wessex Formation of the Isle of Wight

The Wessex formation on the Isle of Wight of Barremian age (~ 127 MYA) has a number of sauropod remains, all very fragmentary but enough to point to a high degree of diversity for this group in the British Isles during the Early Cretaceous.

The presence of Diplodocids is scarce if ever they were present at all. A chevron has been described by Alan Charig (1980) as belonging to a diplodocid, but the identification has since then been disputed. The presence of Rebbachisaurids, on the other hand, is well attested and is represented by isolated bones, including a characteristic scapula [= shoulder blade] (MIWG 6544), tail vertebra (MIWG 5384) and possibly teeth. From these scant remains, it appears that the unnamed British representative of this group is most closely related to the Spanish Demandasaurus and the African Nigersaurus (see my previous post about it).

Brachiosaurids were also certainly there and remains are represented by ‘Pleurocoelus’ valdensis Lydekker, 1889, based on teeth, dorsal and caudal vertebra found near Cuckfield, East Sussex, Hastings beds and on the Isle of Wight. Usually considered to be dubious, Pleurocoelus valdensis is, according to Ruiz-Omeñaca & Canudo (2005), a perfectly valid taxon that was also present in the Iberian Peninsula. Other possible brachiosaurid remains include ‘Ornithopsis’ eucamerotus Hulke, 1882, based on a set of pelvis bones (BMNH R97), an unnamed taxon evidenced by a single large cervical vertebra (MIWG 7306) that might have belonged to the largest dinosaur of Europe (Naish et al., 2004), and Eucamerotus foxi Blows, 1995, described from a neural arch (BMNH R2522), two dorsals (BMNH R89-90) and another dorsal from a juvenile specimen (BMNH R2524). Oplosaurus armatus Gervais, 1852, is based on a large tooth (BMNH R964) that may belong to a brachiosaurid, but more recent analysis indicated it is more probably from a camarasaurid (Canudo et al., 2002). Chondrosteosaurus gigas Owen, 1876 is known from two neck vertebrae (BMNH 46869 & BMNH 46870) and is probably a basal titanosauriform, although we cannot say if it is a camarasaurid or a brachiosaurid.

Fig 2.- The specialized Titanosaurs were the dominant group of sauropods at the end of the Early Cretaceous.

The most evolved group of sauropods, the titanosaurs, is represented by Iuticosaurus valdensis LeLoeuff et al., 1993, known from 2 tail vertebrae (BMNH R146a & BMNH 151).

Finally, two dubious taxa are indeterminate sauropods: the Isle of Wight ‘Ornithopsis’ hulkei dorsal vertebra (BMNH R28632) was renamed Bothriospondylus elongatus by Owen in 1875 and ‘Ornithopsis’ eucamerotus by Hulke in 1882. Chondrosteosaurus magnus Owen, 1876 is based on a single partial vertebra (BMNH R98).

The Lower and Upper Greensand

The Lower Greensand Group of Aptian age (~120 MYA) delivered a pelvis and associated sacrum (BMNH R12713) from Luccombe Chine, Isle of Wight of a titanosauriform of some sort (Stroh, 1949, Blows, 1995). Also from the Lower Greensand came Dinodocus mackesoni Owen, 1884, based on a humerus (BMNH 14695) from Hythe, Kent. Possibly another indeterminate titanosauriform.

The Upper Greensand formation (Albian-Cenomanian age, ~112 MYA) in southeastern England bears a few sauropod remains, which are the youngest in the British Isles and all belong to titanosaurs. “Titanosaurus” lydekkeri Huene, 1929 (= Iuticosaurus lydekkeri), based on a vertebra (BMNH 32390) found on the Isle of Wight, was synonymized with Macrurosaurus semnus by McIntosh, 1990, but generally considered a nomen dubium. Macrurosaurus semnus Seeley, 1876 is based on a set of 25 caudal vertebrae (SM B55630) and 15 more various bits found in Cambridgeshire and of Cenomanian age, and is an indeterminate titanosaur.

This concludes our tour of the sauropods of the British Isles.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)

References:

W. T. Blows. 1995. The Early Cretaceous brachiosaurid dinosaurs Ornithopsis and Eucamerotus from the Isle of Wight, England. Palaeontology 38(1):187-197

W. T. Blows. 1998. A review of Lower and Middle Cretaceous dinosaurs of England. In S. G. Lucas, J. I. Kirkland, and J. W. Estep (eds.), Lower and Middle Cretaceous Terrestrial Ecosystems, New Mexico Museum of Natural History and Science Bulletin 14:29-38

J. Le Loeuff, E. Buffetaut, M. Martin, V. Martin, and H. Tong. 1993. Découverte d'Hadrosauridae (Dinosauria, Ornithischia) dans le Maastrichtian des Corbières (Aude, France) [Discovery of Hadrosauridae (Dinosauria, Ornithischia) in the Maastrichtian of Corbières (Aude, France)]. Comptes Rendus de l'Academie des Sciences, Paris, Série II 316:1023-1029

R. Lydekker. 1889. Note on some points in the nomenclature of fossil reptiles and amphibians, with preliminary notices of two new species. Geological Magazine, decade 3 6:325-326

R. Lydekker. 1893. On a sauropodous dinosaurian vertebra from the Wealden of Hastings. Quarterly Journal of the Geological Society of London 49:276-280

J. S. McIntosh. 1990. Sauropoda. In D. B. Weishampel, H. Osmólska, and P. Dodson (eds.), The Dinosauria. University of California Press, Berkeley 345-401

A. G. Melville. 1849. Notes on the vertebral column of the Iguanodon. Philosophical Transactions of the Royal Society of London 139:285-300.

D. Naish, D.M. Martill, D. Cooper & K.A. Stevens, 2004. Europe’s largest dinosaur? A giant brachiosaurid cervical vertebra from the Wessex Formation (Early Cretaceous) of southern England. Cretaceous Research, 25, 787–795.

D. Naish and D. M. Martill. 2007. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: basal Dinosauria and Saurischia. Journal of the Geological Society, London 164:493-510

R. Owen. 1876. Monograph on the fossil Reptilia of the Wealden and Purbeck formations. Supplement no. VII. Crocodilia (Poikilopleuron) and Dinosauria? (Chondrosteosaurus). [Wealden.]. The Palaeontographical Society, London 1876:1-7

J. I. Ruiz-Omeñaca and J. I. Canudo. 2005. "Pleurocoelus" valdensis Lydekker 1889 (Saurischia, Sauropoda) en el Cretácico Inferior (Barremiense) de la Península Ibérica ["Pleurocoelus" valdensis Lydekker 1889 (Saurischia, Sauropoda) in the Lower Cretaceous (Barremian) of the Iberian Peninsula]. Geogaceta 38:43-45

H. G. Seeley. 1870. On Ornithopsis, a gigantic animal of the pterodactyle kind from the Wealden. Annals and Magazine of Natural History, series 4 5:279-283.

H. G. Seeley. 1876. On Macrurosaurus semnus (Seeley), a long tailed animal with procoelous vertebrae from the Cambridge Upper Greensand, preserved in the Woodwardian Museum of the University of Cambridge. Quarterly Journal of the Geological Society of London 32:440-444

M. P. Taylor and D. Naish. 2007. An unusual new neosauropod dinosaur from the Lower Cretaceous Hastings Beds Group of East Sussex, England. Palaeontology 50(6):1547-1564.

Sauropods of the British Isles Part II

2012-02-09T09:02:00.000-08:00

Fig 1.- A hypothetical reconstruction of Pelorosaurus conybeari.

Sauropods from the Early Cretaceous (I)

The Hastings Beds

The Hastings Beds in East Sussex, of Berriasian-Valanginian age (~140 MYA), bore a number of fragmentary sauropod remains. A set of tail vertebrae and chevrons (BMNH R2544–2555) found near Cuckfield, East Sussex, were originally described alongside some iguanodont remains by Richard Owen as Cetiosaurus brevis (Owen, 1842). Alexander Melville, noting Owen’s mistake, renamed the sauropod vertebrae Cetiosaurus conybeari (Melville, 1849). A year later, Gideon Mantell realizing that they belong to a animal quite distinct from Cetiosaurus, changed the name into Pelorosaurus conybeari (Mantell, 1850), and added to the description, a humerus (BMNH 28626) found a few meters away from the original vertebrae material. This succession of attribution changes resulted in a taxonomical nightmare for the later generation scientists. Technically, the name C. brevis has indeed seniority over Pelorosaurus conybeari and should be considered to be the valid name. However, with the invalidation of C. medius (see Part I), C. brevis would also be the type species of the genus Cetiosaurus, making its use for the Middle Jurassic C. oxoniensis, which turned out to be a very different animal quite problematic (As far as I know, the petition to ICZN to make C. oxoniensis the type species of Cetiosaurus is still pending) . As for the general aspect of what Pelorosaurus may have looked like, all that can be said from the scant remains is that it was a brachiosaurid and would probably resemble to a smaller version of the North American Late Jurassic Brachiosaurus, with a possible size of some 15 meters in length.

Not much can be said about the three other named sauropods of the Hastings Beds. ‘Pelorosaurus’ becklesi Mantell, 1852 (= Morosaurus becklesii Marsh, 1889) based on a humerus (BMNH R1868), ulna, radius and skin impressions, probably belong to a different animal than Pelorosaurus conybeari. It may also be a brachiosaurid unless it is a more advanced titanosaur. ‘Ornithopsis’ hulkei Seeley, 1870 is based on two dorsal vertebrae, one from East Sussex (BMNH R2239), the other from the Isle of Wight Wessex Formation (BMNH R28632), and originally thought to belong to a pterosaur (thus the genus name which means “bird likeness”). Owen (1876), however, split the two findings, naming the East Sussex vertebrae Bothriospondylus magnus, then Chondrosteosaurus magnus. The remains have no distinct characteristics apart the fact that they belong to a sauropod of some sort so the name should be considered dubious. Xenoposeidon proneneukos Taylor & Naish, 2007 is based on a single partial back vertebra (BMNH R2095). Xenoposeidon’s vertebra is so unique that its affinities within the Sauropods are quite uncertain.

Next will be the sauropods from the Wessex Formation.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)

References:

G. A. Mantell. 1850. On the Pelorosaurus; an undescribed gigantic terrestrial reptile, whose remains are associated with those of Iguanodon and other saurians in the strata of the Tilgate Forest, in Sussex. Philosophical Transactions of the Royal Society of London 140(16):379-390.

A. G. Melville. 1849. Notes on the vertebral column of the Iguanodon. Philosophical Transactions of the Royal Society of London 139:285-300.

D. Naish and D. M. Martill. 2007. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: basal Dinosauria and Saurischia. Journal of the Geological Society, London 164:493-510.

R. Owen. 1876. Monograph on the fossil Reptilia of the Wealden and Purbeck formations. Supplement no. VII. Crocodilia (Poikilopleuron) and Dinosauria? (Chondrosteosaurus). [Wealden.]. The Palaeontographical Society, London 1876:1-7.

H. G. Seeley. 1870. On Ornithopsis, a gigantic animal of the pterodactyle kind from the Wealden. Annals and Magazine of Natural History, series 4 5:279-283.

M. P. Taylor and D. Naish. 2007. An unusual new neosauropod dinosaur from the Lower Cretaceous Hastings Beds Group of East Sussex, England. Palaeontology 50(6):1547-1564.

Sauropods of the British Isles I

2012-01-29T19:06:00.000-08:00

Fig 1.- Reconstruction of Cetiosaurus oxoniensis.

Sauropods, the long-necked, long-tailed giant herbivorous dinosaurs, are better known in popular imagination by their North American representatives, Diplodocus and Brachiosaurus. Sauropods are divided into a number of families and groups that can be distinguished from details of their skeletal anatomy and teeth. Among the most primitive families, the Melanosaurids were only recently (Yates, 2007) recognized as early sauropods instead of being placed within more basal sauropodomorphs. Cetiosaurids are an ill-defined group of primitive sauropods built around the British Cetiosaurus and perhaps including other members such as the Chinese club-tailed Shunosaurus. The Turiasaurs form a recently erected clad (Royo-Torres et al., 2006) of gigantic sauropods so far restricted to southernwestern Europe. The Diplodocoids regroup three distinct families, the highly specialized rebbachisaurids, the relatively short-necked, tall-spined dicraeosaurids and the long and slender diplodocids. The Macronarians are characterized by their erect neck posture and comparatively large nasal opening (nostrils) on their head. They are subdivided into the camarasaurids (primitive macronarians), brachiosaurids and titanosaurs, the last two families including the largest and heaviest creatures that ever walked the earth.

Numerous remains of sauropods were found in the British Isles, but the vast majority of the named genera and species are based on very scant material with no unique characteristics making them nomina dubia (dubious names). However, they can generally be diagnosed at higher group levels, showing that the British Isles were once home to a diverse fauna of sauropods that include the earliest members of such groups as the Diplodocoidea and Rebbachisauridae. Let’s meet them in stratigraphical chronological order (please note that the list of fossils mentioned is in no way exhaustive)...

We already met in a previous post, Camelotia borealis from the Westbury Formation of Late Triassic Rhaetian age, which was possibly an early sauropod, unless it is a large representative of something more basal.

Sauropods from the Middle Jurassic

The first definite British sauropod remain comes from the Middle Jurassic Aalenian stage (~175 MYA). It consists of a partial left pubis and ischium (BMNH R9472) of the Northampton Sands Formation, from Harleston, Northamptonshire (Reid, 1984). This unnamed taxon was possibly a brachiosaurid or a titanosaur making it either way the earliest recorded macronarian in the world.

Fig 2.- Britain has some remains belonging to the earliest known macronarian.

Next come large collection of bones from the Forest Marble Formation of Bathonian age (~165 MYA). The most famous fossil of this formation is the primitive sauropod Cetiosaurus (“whale lizard”). Cetiosaurus is one of the earliest dinosaurs to receive a name and, as it happened to many genera described in the early days of paleontology, it became a so-called wastebasket taxon, with up to 13 species described in the British Isles alone, ranging temporally from the Middle Jurassic to the Early Cretaceous. In a general revision of the genus, Upchurch and Martin (2003) finally recognized the only Cetiosaurus oxoniensis Phillips, 1871 from the Forest Marble as a valid species. Cetiosaurus is known from various postcranial elements coming from different places in Oxfordshire (OUM J13605-13613, 13615-13616, 13619-13688, 13899), Northamptonshire and Gloucestershire. A partial skeleton from the slightly older Bajocian (~ 170 MYA) Rutland Formation of Rutland (LCM G468.1968) is also being assigned to C. oxoniensis, as well as a partial braincase (OUM J13596) and a tooth (OUM J13597) found at the same location than the Oxfordshire Blechington specimen. This large, perhaps 20 meters long sauropod exhibits a number of primitive features in the structure of their vertebrae. Due to the fragmentary nature of the remains, many aspects of this animal, such as the skull, are almost totally unknown, despite it being the best-known sauropod of Great Britain.

Cetiosaurus medius Owen, 1842 known from 11 caudal centra (OUM J13693–13703) and other various bits found in Oxfordshire, Gloucestershire, Buckinghamshire, is non-diagnostic. Since C. medius is generally considered as the type species of Cetiosaurus, its invalidation would render the naming of C. oxoniensis problematic. A petition has therefore been filed to ICZN to make C. oxoniensis the new type species for the genus. Cardiodon rugulosus described by Owen in 1844, out of a single, now lost, tooth unearthed near Bradford-on-Avon, Wiltshire, may be the same animal than Cetiosaurus, but it was also been proposed to be a Turiasaur.

Two other distinct taxa are known from the Forest Marble Formation: one is ‘Cetiosaurus’ glymptonensis Phillips, 1871 (= Cetiosauriscus glymptonensis (Phillips, 1871) McIntosh, 1990) described from a series of 9 caudal vertebrae (OUM J13750-13758) found in Glympton, Oxfordshire. It was possibly a diplodocoid, making it the earliest known member of this group in the world. However, due to the lack of unique characters, C. glymptonensis is generally considered to be a nomen dubium (Barrett et al., 2003). The as dubious Bothriospondylus robustus Owen, 1875 = Marmarospondylus robustus) from Bradford-on-Avon, Wiltshire, is known from a single dorsal vertebra (BMNH R22428) and might be a macronarian.

Another possible macronarian has been described from the similar age Kilmaluag Formation (late Bathonian) of Strathaird, Isle of Skye, Western Scotland: it is a tooth (NMS G 2004.31.1), one of the very rare dinosaurian remains found in Scotland. This fossil is distinctly different from both Cetiosaurus and Cardiodon (Barrett, 2006).

From the Lower Callovian age (~163 MYA) Kellaways formation, comes ‘Ornithopsis’ leedsi Hulke, 1887, known from vertebrae, ribs and pelvic fragments (BMNH R1984-1988), found near Peterborough, Cambridgeshire. This was probably a Brachiosaurid. The name Ornithopsis originally refers to the undeterminate O. hulkei from the Early Cretaceous (see part II), which would mean that O. leedsi probably requires a new generic name.

Fig 3.- other remains from britain are from the earliest known diplodocoid.

In the overlying Oxford Clay Formation (Middle Callovian – Early Oxfordian age, ~161 MYA), other materials from Peterborough, including a series of vertebrae (BMNH R.3078) were confusingly also referred to ‘Ornithopsis’ leedsi by Woodward in 1905. But Charig concluded in 1980 that the bones belong to a quite different animal, a diplodocid, and give them the name ‘Cetiosauriscus’ stewarti.

Sauropods from the Late Jurassic

From the Kimmeridge Clay Formation of Kimmeridgian age (~153 MYA), comes Duriatitan humerocristatus (Lydekker, 1888) (Initially named 'Cetiosaurus' humerocristatus) based on a gracile left humerous (BMNH R44635) from Weymouth, Dorset (Hulke, 1874). It was determined to belong to a Titanosauriform (Barrett et al., 2010). The dubious ‘Ornithopsis’ manseli (Lydekker, 1888) (= ‘Ischysaurus’ manseli ), based on a partial humerus ((BMNH 41626), also from Dorset, may belong to the same animal. The same can be said of Bothriospondylus suffosus Owen, 1875 from Wiltshire, known from dorsal and sacral vertebrae (BMNH R44592-5: 4).

Some non-diagnostic vertebrae, limb elements and dermal scutes found near Stretham, Cambridgeshire (BMNH 32498-99) were described as Gigantosaurus megalonyx Seeley, 1869 and belong to a sauropod of some sort. Also from the Kimmeridgian, ‘Cetiosaurus’ longus Owen, 1842 based on a single dorsal and caudal centra (OUM J13617) from the Portland Stone Formation at Garsington, Oxfordshire, is an indeterminate sauropod.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)

References:

P. M. Barrett. 2006. A sauropod dinosaur tooth from the Middle Jurassic of Skye, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 97:25-29

P. M. Barrett, R. B. J. Benson, and P. Upchurch. 2010. Dinosaurs of Dorset: Part II, the sauropod dinosaurs (Saurischia, Sauropoda) with additional comments of the theropods. Proceedings of the Dorset Natural History and Archaeological Society 131:113-126

A. J. Charig. 1980. A diplodocid sauropod from the Lower Cretaceous of England. In L. L. Jacobs (ed.), Aspects of Vertebrate History: Essays in Honor of Edwin Harris Colbert. Museum of Northern Arizona Press, Flagstaff 231-244

J. W. Hulke. 1874. Note on a very large saurian limb-bone adapted for progression upon land, from the Kimmeridge Clay of Weymouth, Dorset. Quarterly Journal of the Geological Society of London 30:16-17

D. Naish and D. M. Martill. 2007. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: basal Dinosauria and Saurischia. Journal of the Geological Society, London 164:493-510

R. Owen. 1841. Description of a portion of the skeleton of the Cetiosaurus, a gigantic extinct saurian reptile occurring in the Oolitic formations of different portions of England. Proceedings of the Geological Society of London 3, part 2(80):457-462

R. Owen. 1875. Monographs on the fossil Reptilia of the Mesozoic formations. Part II. (Genera Bothriospondylus, Cetiosaurus, Omosaurus). The Palaeontographical Society, London 1875:15-93

M. D. Jones. 1970. Cetiosaurus oxoniensis, Phillips J. A middle Jurassic sauropod from Rutland, England. Leicester Literary and Philosophical Society 64:144-150

J. Phillips. 1871. Geology of Oxford and the Valley of the Thames. Clarendon Press, Oxford 1-523.

P. M. Upchurch and J. Martin. 2003. The anatomy and taxonomy of Cetiosaurus (Saurischia, Sauropoda) from the Middle Jurassic of England. Journal of Vertebrate Paleontology 23(1):208-231.

Spinops: my very own personal paleoart portfolio

2012-01-29T17:13:00.000-08:00

Once upon a while, scientists came with really catchy dinosaur names. Examples of cool generic nomina include Dracorex (the “dragon king”), Raptorex (the “king thief”), Cryptoraptor (the “hidden thief”), Brontosaurus (the “thunder lizard”) and Diabloceratops (the “devil horn face”). Shame that some of those critters turn out to be invalid and too bad scientific names cannot be recycled! Others are just plain awful. For (at least) English speakers, there are real tongue twisters such as Bruhatkayosaurus (fortunately this one might just be a hoax [great post from Matt Martyniuk]), Futalognkosaurus (do I even get the spelling right?), Krzyzanowskisaurus, Naashoibitosaurus.

Among the recently allocated names, Spinops is one of the best I came across: it is short, easy to remember and combines those of two of the most iconic dinosaurs, Spinosaurus and Triceratops. Good reasons to use it for my new paleoart portfolio website, before somebody else get the same idea…

I’ve just started, and so far it has only some 140 images in it as I have to go through all my folders and hard drives to check what I've done since 2007. The nice thing about this online portfolio is that it is wholly searchable (type for instance “plesiosaur” if you want to see these only), and illustrations can be arranged by group or production date. Have a look…

Late Triassic Dinosaurs of the British Isles

2012-01-08T17:39:00.000-08:00

Fig 1.- Thecodontosaurus antiquus.

The British Late Triassic land vertebrate fauna is essentially known from disarticulated bones found in various Mesozoic fissure fills of underlying Lower Carboniferous limestone in England and Wales. The fauna include the very first British dinosaurs of Rhaetian age (~ 200 MYA), living alongside a variety of reptiles including sphenodontians, running crocs of the sphenosuchian group (such as Terrestrisuchus gracilis), trilophosaurs (such as Variodens inopinatus), and gliding lizards such as Kuhneosaurus. Dinosaurs were not the dominant group that will rule the land during the Jurassic and Cretaceous periods, constituting only about 10% of the vertebrate fauna found in those fissure fills. One archosaurian form, named Agnostiphys cromhallensis from the Cromhall Quarry in Avon, has clearly some dinosaurian characteristics. It was described in 2002 by N.C. Fraser and co-workers based on a left ilium, left maxilla, a right humerus, a pair of astragalus and an isolated tooth. The validity of the taxon is disputed as the different parts may come from different animals (thus making the original description a chimera) and the remains are too scant to decide if it was an archosaur closely related to dinosaurs or a true primitive dinosaur, possibly a herrerasaur.

Sauropodomorphs from Rhaetian fissure fills: Thecodontosaurus, Asylosaurus, Pantydraco

The other dinosaurian remains of the Rhaetian fissure fillings all belong to basal sauropodomorphs, the group of saurischian dinosaurs which will eventually lead to the Jurassic and Cretaceous long-necked herbivorous giants called Sauropods to which the North American Brachiosaurus, Diplodocus and Apatosaurus are the most popular members. From a locality known as Durdham Down, Clifton, near Bristol in England, hundreds of bones have been excavated in the 1830s and originally described by Riley and Stutchbury as three separate taxa: Thecodontosaurus antiquus based on a right dentary with 21 teeth, Paleosaurus cylindricon (Now Paleosauriscus cylindicon) and P. platyodon (now Rileyasuchus platyodon), the latter two, each based on a single tooth. The other bones were subsequently distributed by Owen (1842), Huxley (1870) and Marsh (1892) among the three taxa. Huxley (1870) was the first to recognize the dinosaurian nature of the remains. The different disarticulated bits had subsequently quite diverging and complicated systematic histories, some being referred to a phytosaur (i.e. Rileya), others to theropods and ornithosuchians. Sadly, a portion of the materials, including the holotype dentary of Thecodontosaurus, was destroyed during the WWII bombing of Bristol. Recent efforts try to put order in the systematic mess accumulated over more than a century, but opinions went from attributing all the Durdham Down dinosaurian bones to the single species of basal sauropodomorph, Thecodontosaurus antiquus (Benton et al., 2000) with different morphotypes representing sexual dimorphism, to reserving the generic name to the original jaw and its neotype only (Galton, 2005). In his last magisterial review, Pete Galton (2007) examined all the surviving materials of Durdham Down (including the mislabeled bones which were for a while thought to come from Australia, leading Seeley to described them in 1861 as a new species, Agrosaurus macgillivray, which would have been the earliest known dino from down under) and illustrations made of materials lost during the war. He concluded that the Durdham Down collection is a mixture originating from a handful of species: Thecodontosaurus antiquus, to which the jaw and gracile bones were attributed, a new erected taxon, Asylosaurus yalensis for the only significant articulated skeletal part (an almost complete forearm and associated dorsal vertebrae and ribs), and a few number of unnamed basal sauropodomorphs, including a possible anchisaur. New materials of Thecodontosaurus have been discovered in fissure fill at Tytherington Quarry, Avon, in 1975 are are being prepared and awaiting formal description. Compared to the later huge sauropods, Thecodontosaurus was a rather small dinosaur measuring no longer than 2.5 meters in length that was probably bipedal. His leaf shaped teeth indicated that it was a herbivore.

Fig 2.- Pantydraco caducus.

From the more or less contemporary fissures fill of Panty-ffynnon Quarry in South-Western Wales, came several partial skeletons including an almost complete skull and associated partial skeleton of the unfortunately named Pantydraco caducus. The remains are from a juvenile basal sauropodomorph. Like Thecodontosaurus, Pantydraco was a bipedal herbivore, measuring probably no more than 2 meters in length.

Fig 3.- Camelotia borealis.

The large Late Triassic sauropodomorph, Camelotia

All the sauropodomorphs from the rhaetian fissure fills were rather small in size and gracile in appearance, but a larger animal announcing the heavy sauropods from the Jurassic, existed at that time, as proven by a partial disarticulated skeleton found in sedimentary beds at the base of the Westbury formation at Wedmore Hill, Somerset. The animal was named Camelotia borealis, after the legendary castle of King Arthur. Remains of Camelotia are so fragmentary that it is hard to derive its affinities but it might have been related to the quadrupedal Melanosaurus, unless it was a very primitive sauropod. Camelotia is estimated to have measured about 10 meters in length.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)

References:

Benton M.J. , Juul, L., Storrs, G.W. & Galton, P. M. 2000. Anatomy and systematics of the prosauropod dinosaur Thecodontosaurus antiquus from the Upper Triassic of Southwest England. Journal of Vertebrate Paleontology 20: 77–108.

Fraser, N. C., K. Padian, G. M. Walkden, & A.L.M. Davis , 2002. Basal dinosauriform remains from Britain and the diagnosis of the Dinosauria. Palaeontology , 45 (1): 79-95.

Galton. P. M. 2005. Basal sauropodomorph dinosaur taxa Thecodontosaurus Riley & Stutchbury, 1836, T. antiquus Morris, 1843 and T. caducus Yates, 2003: their status re: humeral morphs from the 1834 fissure fill (Upper Triassic) in Clifton, Bristol, UK. Journal of Vertebrate Paleontology 25(3, suppl.):61A

Galton, P. M. 2007. Notes on the remains of archosaurian reptiles, mostly basal sauropodomorph dinosaurs, from the 1834 fissure fill (Rhaetian, Upper Triassic) at Clifton in Bristol, southwest England. Revue de Paléobiologie 26(2):505-591.

Galton, P. M., Yates, A. M. and Kermack, D. M. 2007. Pantydraco n. gen. for Thecodontosaurus caducus Yates, 2003, a basal sauropodomorph dinosaur from the Upper Triassic or Lower Jurassic of South Wales, UK. Neues Jahrbuch für Geologie und Paläontologie Abhandlungen 243(1):119-125.

Naish, D. and Martill., D. M. 2007. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: basal Dinosauria and Saurischia. Journal of the Geological Society, London 164:493-510

Yates. A.M. 2003. A new species of the primitive dinosaur Thecodontosaurus (Saurischia: Sauropodomorpha) and its implications for the systematics of early dinosaurs. Journal of Systematic Palaeontology 1(1):1-42.

R.I.P. Dan Varner (April 19, 1949 - January 1, 2012)

2012-01-04T20:01:00.000-08:00

Mosasaurus by Dan Varner.

I did not have the privilege to know Dan Varner and did not know until very recently, shame on me, that he was the man behind the beautiful paintings illustrating the “Oceans of Kansas” website. I sadly learned that he passed away on January 1st, 2012 after a prolonged battle with illness; a tremendous loss for the entire paleoart community…

From all the amazing Mesozoic marine life depictions he created during his too short a career, this one is a personal favorite. Mosasaurs were after all closely related to the modern monitor lizards, so it makes perfect sense to give them a similar tongue! The underwater light effect is eye-catching and the three transfixed ammonites watching the marine lizard swimming by gives to the entire scene a unique sense of cephalopodian apprehension... simply beautiful!

It’s hardly my place, I think, for me, an amateur nobody, to give a fitting eulogy to such a great artist so I am simply directing you to the ‘in memoriam’ sections I came across on the web, starting with the “Oceans of Kansas” website, followed by tributes from paleo-illustrators Jaime Headden (check his Globidens), Matt van Roojien, David Maas and from the Art Evolved Crew.

Ankylosaurs of the British Isles

2012-01-02T11:42:00.000-08:00

Fig 1.- Hyleosaurus armatus.

The Ankylosaurs form a group of heavily armored ornithischian dinosaurs best known by its North American cretaceous representatives, Ankylosaurus and Euoplocephalus. Ankylosaurs and Stegosaurs together form the Thyreophorans characterized by a body covered with an armor consisting of scutes, spikes and plates, that are highly derived osteoderms (ossified scales commonly found in various groups of vertebrates such as the crocodilians).

The Ankylosaurs are divided into two or three families. The Nodosaurids have a narrow skull, a club-less tail and large spikes while the Ankylosaurids have a distinct bony club at the end of their tails and a wider body. In addition, some authors detach some Nodosaurids, into a third family, the more lightly built Polacanthids.

Scelidosaurus harrisonii from the Early Jurassic of Dorset, is an early thyreophoran close to the ancestral stock of both stegosaurs and ankylosaurs. There is however a large gap in the fossil record between the first definite ankylosaur in the United Kingdom and Scelidosaurus. Jurassic ankylosaur remains are so fragmentary that not much definite can be said about them.

In the Middle Jurassic (Bajocian, 170 MYA), an incomplete radius and ulna (forearm bones) from the Isle of Skye in Scotland, described by Clark in 2001, possibly belongs to an ankylosaur, unless it is a stegosaur.

A bit younger (Middle Jurassic, Callovian, 163 MYA), Sarcolestes leedsi is known from an incomplete lower jaw from the Oxford Clay Formation in Cambridgeshire. Three osteoderms recovered from the same formation have been attributed to it (Galton, 1994). It was originally thought to be a theropod (thus its name meaning “flesh robber”), before being classified as a stegosaur, then an ankylosaur of some sort.

From the Late Jurassic period (Oxfordian, 160 MYA), a right femur found in the Ampthill Clay Formation of Cambridgeshire was named Cryptosaurus eumerus and first attributed to an ornithopod, until Peter Galton placed it among the ankylosaurs (1983). A maxilla of the same age named Priodontognathus phillipsi was found in Yorkshire. This also was first attributed to an ornithopod before Galton classified it as a nodosaurid ankylosaur (1980).

Better ankylosaur material appears in the Early Cretaceous with Hylaeosaurus and Polacanthus. Hylaeosaurus armatus is one of the original three animals (the others being Iguanodon and Megalosaurus) used by Sir Richard Owen to define the then new group he called Dinosauria in 1842. This 6 meter long polacanthid nodosaur is known from the Turnbridge Wells Sand Formation (Grinstead Clay member) of Valanginian age (~138 MYA) and its remains have been discovered in West Sussex. The holotype found in the Tilgate Forest area by Gideon Mantell in 1832 consists of the anterior portion of an articulated skeleton including a small portion of the skull. A second specimen from Bolney was partially destroyed by workers before Mantell could salvage a few bits including a left scapula, a fragment of the right scapula and a left tibia. A third specimen found by Mantell in 1827 from the Tilgate Forest quarry consists of an incomplete caudal series with armor (originally named H. oweni). From Mantell’s Bolney material combined with remains found in the Isle of Wight, Nopsca erected the new genus and species Polacanthoides ponderosus in 1928. Today, the Bolney material is attributed to Hylaeosaurus armatus while the Isle of Wight material is considered to belong to Polacanthus foxii, making Polacanthoides an invalid name. Hylaeosaurus is still a quite obscure animal despite being one of the earliest described dinosaurs. It was probably closely related to Polacanthus.

Fig 2.- Polacanthus foxii.

Polacanthus foxii, which was for some times being considered to be the same animal as Hylaeosaurus, is nowadays generally thought to be distinct. Stratigraphically, it is slightly younger, appearing only in the Wessex and Vectis Formations of the Isle of Wight of Upper Barremian age (~ 125 MYA). The generic name appears first in a anonymous field note from 1865 attributing the paternity of the name to Richard Owen. The holotype collected by the reverend William Fox consists of the rear end of the animal. A second specimen described by W. T. Blows in 1979 consists of neck vertebrae and anterior armor. A third specimen is currently in private ownership. A portion of a pelvis and some dermal armor, originally named Polacanthus becklesi by Hennig in 1924 is now considered to belong to P. foxii. Many other various bits attributed to P. foxii have been found including the now lost Isle of Wight parts used to define Polacanthoides ponderosus described above and the single spine named Vectensia by Delair, 1982. Polacanthus foxii was a 4-5 meter long nodosaur, serving as the type to the polacanthid family.

Blows has erected a second species of Polacanthus, P. rudgwickensis, in 1996 out of a partial skeleton from the mainland found near Rudgwick, Sussex. This species appears to be slightly larger and more robust than P. foxii but its validity has been disputed.

Fig 3.- Anoplosaurus curtonotus.

From the mainland Upper Greensand Formation of Albian age (~110 MYA), a number of fragments were attributed to ankylosaurs and named into several genera including Anoplosaurus, Acanthopholis, Eucercosaurus, Syngonosaurus and Macrurosaurus and a plethora of species. All of them, save perhaps Anoplosaurus curtonotus are dubious in the sense that from such fragmentary remains there are no unique characters to define each of the species. Anoplosaurus curtonotus has been described from various fragments from a juvenile individual and probably belong to a nodosaurid of some sort. The second species, A. major is probably chimeric. The genus Acanthopholis was often illustrated in dinosaur books but all the 7-9 species described, including the type A. horrida, were determined to be dubious by a review by Pereda-Superbiola and Barrett (1999).

This concludes our tour of the British Isles Ornithischians. Now to the Saurischians.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com).

References:

Blows, W. T. 1982. A preliminary account of a new specimen of Polacanthus foxi (Ankylosauria, Reptilia) from the Wealden of the Isle of Wight. Proceedings of the Isle of Wight Natural History and Archaeological Society 1980 pt. 5(7):303-306.

Clark, N.D.L. 2001. A thyreophoran dinosaur from the early Bajocian (Middle Jurassic) of the Isle of Skye, Scotland. Scottish Journal of Geology, 37, 19–26.

Fox. W. 1866. On a new Wealden saurian named Polacanthus. Report of the British Association for the Advancement of Science, Birmingham 1865:56.

Fox. W.1866. Another new Wealden reptile. Geological Magazine 3:383.

Galton, P.M. 1980. Priodontognathus phillipsii (Seeley), an ankylosaurian dinosaur from the Upper Jurassic (or possibly Lower Cretaceous) of England. Neues Jahrbuch für Geologie und Paläontologie Monatshefte 1980(8):477-489.

Galton, P.M. 1983. Armored dinosaurs (Ornithischia: Ankylosauria) from the Middle and Upper Jurassic of Europe, Palaeontographica Abteilung A 182(1-3): 1-25.

Galton, P. M. 1994. Dermal scutes of Sarcolestes, an ankylosaurian dinosaur from the Middle Jurassic of England. Neues Jahrbuch für Geologie und Paläontologie Monatshefte 1994(12):726-732

Naish, D.; and Martill, D. M. 2008. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: Ornithischia. Journal of the Geological Society, London 165 (3): 613–623.

Pereda-Suberbiola, J. 1993. Hylaeosaurus, Polacanthus, and the systematics and stratigraphy of Wealden armoured dinosaurs. Geological Magazine, 130, 767-781.

Pereda-Suberbiola, J. 1994. Polacanthus (Ornithischia, Ankylosauria), a transatlantic armoured dinosaur from the Early Cretaceous of Europe and North America. Palaeontographica Abteilung A 232(4-6):133-159.

Pereda-Suberbiola, J. & Barrett. P.M., 1999. A systematic review of ankylosaurian dinosaur remains from the Albian-Cenomanian of England, Special Papers in Palaeontology, 60: 177-208.

2011 in Paleontology

2011-12-31T08:52:00.000-08:00

Fig 1.- A selection of species described in 2011.

It’s time for a retrospective of year 2011 in the paleontological field. Besides the description and discovery of new species, here is my pick of the top stories that marked the year:

150th anniversary of the description of Archaeopteryx

2011 is a fitting anniversary year for Archaeopteryx with the unveiling of the 11th specimen, the ICZN decision to make the London skeleton the new type for the genus (originally based on a single feather). The systematic position of the transitional fossil is still uncertain with two papers challenging its place at the base of the avialian tree while another puts it back on. An attempt has also been made to reconstruct the color of the London holotype feather.

Fig. 2.- Archaeopteryx.

References:
R. Carney, J. Vinther, M. Shawkey, L. d’Alba & J. Ackermann. 2011. Black Feather Color in Archaeopteryx. 2011 Society of Vertebrate Paleontology Annual Meeting Abstracts, p 84.

Michael S. Y. Lee & Trevor H. Worthy. 2011. Likelihood reinstates Archaeopteryx as a primitve bird. Biology letters. Published online before print.

Darren Naish, Gareth Dyke, Andrea Cau, François Escuillié and Pascal Godefroit. 2011. A gigantic bird from the Upper Cretaceous of Central Asia. Biology Letters. Published online before print. Electronic supplementary info.

Xing Xu, Hailu You, Kai Du and Fenglu Han. 2011. An Archaeopteryx-like theropod from China and the origin of Avialae. Nature 475: 465–470.

ICZN. 2011. OPINION 2283 (Case 3390) Archaeopteryx lithographica von Meyer, 1861 (Aves): conservation of usage by designation of a neotype. Bulletin of Zoological Nomenclature 68 (3): 230–233.

Fig 3.- Polycotylus giving live birth.

Plesiosaur viviparity

The discovery of a fossil plesiosaur (Polycotylus) with a well-developed fetus in its womb strongly suggests that these marine reptiles were giving live birth.

Reference: O'Keefe, F.R.; and Chiappe, L.M. 2011. Viviparity and K-selected life history in a Mesozoic marine plesiosaur (Reptilia, Sauropterygia). Science 333 (6044): 870–873.

Fig 4.- Velociraptor captured with an IR camera.

Theropods were nocturnal

The analysis of scleral rings of many extinct taxa suggests that most theropods and some pterosaurs hunted at nights whereas the herbivorous dinosaurs were mostly diurnal.

Reference: Schmitz, L. and Motani R. 2011. Nocturnality in dinosaurs inferred from scleral ring and orbit morphology. Science 332, 705.

Fig 5.- Microraptor.

Microraptor ate birds

We already knew that the four-winged dromaeosaur Microraptor was eating small mammals but a new gut content study of one specimen of this dinosaur shows that it also fed on birds.

Reference: O’Connor, Zhou & Xu. 2011. Additional specimen of Microraptor provides unique evidence of dinosaurs preying on birds. PNAS.

Fig 6.- Deinonychus.

A new model for Deinonychus predatory behavior

Deinonychus might have use its powerful claws to pinned down its prey in a manner similar to modern day eagles.

References: Fowler, D. W.; Freedman, E. A.; Scannella, J. B.; Kambic, R. E. 2011. The Predatory Ecology of Deinonychus and the Origin of Flapping in Birds. PLoS ONE 6 (12): e28964.

Fig 7.- Eodromaeus.

Eodromaeus murphi, the earliest theropod?

This little critter might be the earliest and most primitive theropod to date, if indeed Eoraptor is reclassified as a basal sauropodomorph.

Reference: R. N. Martinez, P. C. Sereno, O. A. Alcober, C. E. Colombi, P. R. Renne, I. P. Montañez, and B. S. Currie. 2011. A basal dinosaur from the dawn of the dinosaur era in southwestern Pangaea. Science 331(6014):206-210.

Fig 8.- Camarasaurus herd.

Teeth gave proof of Camarasaurus seasonal migration

… and apparently they traveled quite a long distance in search of food. The technique of teeth analysis for isotopic content shows lots of promise for understanding behavior of creatures long gone.

Reference: H. C. Fricke, J.Hencecroth, M.E. Hoerner. 2011. Lowland–upland migration of sauropod dinosaurs during the Late Jurassic epoch. Nature. Advanced online publication.

Fig 9.- Diania.

Diania, the “walking cactus”

The Lower Cambrian Diania cactiformis is the first fossil of lobopod with jointed legs, and therefore a possible missing link to the Arthropods.

Reference: Jianni Liu, Michael Steiner, Jason A. Dunlop, Helmut Keupp, Degan Shu, Qiang Ou, Jian Han, Zhifei Zhang & Xingliang Zhang. 2011. An armoured Cambrian lobopodian from China with arthropod-like appendages. Nature. 470, 526–530.

Fig 10.- Juramaia.

Juramaia sinensis, the first eutherian

Juramaia from the Middle Jurassic of Liaoning, China, dislodged Eomaia from the Early Cretaceous as the first known placental mammal.

Reference: Z.-X. Luo, C.-X. Yuan, Q.-J. Meng and Q. Ji. 2011. A Jurassic eutherian mammal and divergence of marsupials and placentals. Nature 476:442-445.

Fig 11.- Shastasaurus.

Shastasaurus may have been a suction feeder

The giant ichthyosaurs of the Late Triassic might indeed have been specialized feeder that preyed on squids.

Reference: Sander PM, Chen X, Cheng L, Wang X (2011) Short-Snouted Toothless Ichthyosaur from China Suggests Late Triassic Diversification of Suction Feeding Ichthyosaurs. PLoS ONE 6(5): e19480.

Fig 12.- Cryptolacerta.

Cryptolacerta hassiaca, the most primitive worm lizard

The modern amphisbaenians are burrowing limbless creatures that superficially resemble earthworms, but Cryptolacerta confirm their link to lizards.

Reference: Müller J., Hipsley C.A., Head J.J., Kardjilov N., Hilger A., Wuttke M. & reisz R.R. 2011. Eocene lizard from Germany reveals amphisbaenian origins. Nature 473, 364-367.

Fig 13.- The Triassic Kraken.

The Artsy Kraken

And finally, 2011 was marked by one outrageous claim about giant cephalopods playing with giant ichthyosaur bones.

Happy New Year 2012, Folks!

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)

Kronosaurus queenslandicus

2011-12-23T15:05:00.000-08:00

Fig. 1.- Reconstruction of Kronosaurus queenslandicus chasing a plesiosaur.

The most famous of the pliosaurs before WWD eclipsed it with an oversized Liopleurodon. This large (9-10 meters) marine reptile lived in the open oceans of Australia during the Aptian-Albian stage of the Early Cretaceous and was hunting large preys such as the long-necked plesiosaurs. It is known from at least three individuals, one being the iconic Harvard skeleton which was reconstructed with too many dorsal vertebrae making Kronosaurus a bit longer than it really was. A second species, named Kronosaurus boyacensis was found in Northern Colombia.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)

References:

Hampe O. 1992. Ein großwüchsiger Pliosauride (Reptilia: Plesiosauria) aus der Unterkreide (oberes Aptium) von Kolumbien. Courier Forschungsinstitut Senckenberg 145: 1-32.

Longman H. A. 1924. A new gigantic marine reptile from the Queensland Cretaceous, Kronosaurus queenslandicus new genus and species. Memoirs of the Queensland Museum 8: 26–28.

Aegyptocetus tarfa

2011-12-21T08:49:00.000-08:00

The fossil of this early primitive whale was found cut into multiple slabs from a marbleized limestone imported in Italy. Put back together, it reveals an unusual Protocetid whale with a peculiar skull angled more like the Remingtonocetids such as Remingtonocetus and Dalanistes than the other protocetids and the basilosaurids. Bite marks on the ribs indicated that this particular individual was attacked by a large shark. The fossil came from the Gebel Hof Formation (Middle Eocene) of Wadi Tarfa in the Eastern Desert of Egypt.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)

Reference:

G. Bianucci and P. D. Gingerich. 2011. Aegyptocetus tarfa, n. gen. et sp. (Mammalia, Cetacea), from the middle Eocene of Egypt: clinorhynchy, olfaction, and hearing in a protocetid whale. Journal of Vertebrate Paleontology 31(6):1173-1188

Spinops sternbergorum

2011-12-09T22:11:00.001-08:00

Fig 1.- Life reconstruction of Spinops sternbergorum.

This dinosaur was “rediscovered” within the precinct of the Natural History Museum in London, almost a century after it was excavated in the Dinosaur Park Formation in Alberta, Canada. It was only very recently realized that the long forgotten skull fragments belong to a new species.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)

Fig 2.- Detail.

Reference:

Farke, A.A., Ryan, M.J., Barrett, P.M., Tanke, D.H., Braman, D.R., Loewen, M.A., and Graham, M.R. 2011. A new centrosaurine from the Late Cretaceous of Alberta, Canada, and the evolution of parietal ornamentation in horned dinosaurs. Acta Palaeontologica Polonica 56 (4): 691–702.

Abstract: In 1916, a centrosaurine dinosaur bonebed was excavated within the Campanian−aged deposits of what is now Dinosaur Provincial Park, Alberta, Canada. Specimens from this now−lost quarry, including two parietals, a squamosal, a skull missing the frill, and an incomplete dentary, were purchased by The Natural History Museum, London. The material was recently reprepared and identified herein as a previously unknown taxon, Spinops sternbergorum gen. et sp. nov. Based upon the available locality data and paleopalynology, the quarry lies in either the upper part of the Oldman Formation or the lower part of the Dinosaur Park Formation. The facial region of the partial skull is similar to putative mature specimens of Centrosaurus spp. and Styracosaurus albertensis, with short, rounded postorbital horncores and a large, erect nasal horncore. Parietal ornamentation is consistent on both known parietals and is unique among ceratopsids. Bilateral, procurved parietal hooks occupy the P1 (medial−most) position on the dorsal surface of the parietal and are very similar to those seen in Centrosaurus apertus. Epiparietals in the P2 or possibly P3 position (lateral to P1) manifest as extremely elongate, caudally directed spikes, unlike the condition in C. apertus, S. albertensis, or any other “derived” centrosaurine. Cladistic analysis suggests that S. sternbergorum is closely related to Centrosaurus and Styracosaurus. Historically, based upon the condition in Styracosaurus and related centrosaurines, it was assumed that the medial−most elongated spikes on centrosaurine parietals correspond to the P3 epiparietal position. The exception illustrated in the new taxon suggests that homologies of epiparietals among basal centrosaurines (e.g., Albertaceratops and Diabloceratops) and derived centrosaurines (e.g., Styracosaurus and “pachyrhinosaurs”) should be reconsidered. The medially−placed, caudally−directed “P3” process of basal centrosaurines may, in fact, be homologous with P2.

Cuspicephalus scarfi

2011-12-04T17:06:00.001-08:00

Fig 1.- Reconstruction of Cuspicephalus scarfi.

In the series of British prehistoric animals, let me this time introduce you to a pterosaur. Cuspicephalus is known from a partial skull unearthed in the Kimmeridge Clay Formation (Late Jurassic) of Dorset. This critter is possibly related to the Chinese Darwinopterus.

A new monofenestratan pterosaur from the Kimmeridge Clay Formation (Upper Jurassic, Kimmeridgian) of Dorset, England, David M. Martill and Steve Etches, Acta Palaeontologica Polonica (2011) in press

Abstract: A new specimen of slender skulled monofenestratan pterosaur from the Late Jurassic Kimmeridge Clay Formation of Dorset, UK, is referred to the new genus and species Cuspicephalus scarfi. The dentition and posterior skull morphology suggest affinities with Darwinopterus, but a close relationship cannot be proved. There are also some similarities with the pterodactyloid Germanodactylus cristatus, but the presence of teeth on the distal rostrum excludes it from that genus. Pterosaur remains are rare in the Upper Jurassic of the UK and this specimen represents the first significant cranial remains of a pterosaur from the Kimmeridge Clay Formation, and possibly the first non-pterodactyloid monofenestratan outside China.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)

References:

David M. Martill and Steve Etches. 2011. A new monofenestratan pterosaur from the Kimmeridge Clay Formation (Upper Jurassic, Kimmeridgian) of Dorset, England. Acta Palaeontologica Polonica in press.

Thescelosaurus assiniboiensis

2011-12-04T16:37:00.001-08:00

Fig 1.- Reconstruction of Thescelosaurus.

Thescelosaurus is one of those dinosaurs, which did not gain much popularity despite the fact that it is today quite well known scientifically. Even the first specimen, excavated in 1891, remained in its shipping crates for years before being briefly described in 1913 receiving the appropriate name of ‘Thescelosaurus neglectus’ (meaning ‘neglected wondrous lizard’). Several skeletons, some quite complete, of this little ornithopod have been discovered since then in the United States and Canada. The genus received some media attention in year 2000, when one of the specimens from South Dakota named “Willo” was thought to contain a fossilized heart, a claim, which was later, rejected. To the currently recognized two species, T. neglectus and T. garbanii, a third, the smaller T. assiniboiensis, has just been described out of a specimen from Saskatchewan.

Brown; Caleb M.; Boyd, Clint A.; and Russell, Anthony P. 2011. A new basal ornithopod dinosaur (Frenchman Formation, Saskatchewan, Canada), and implications for late Maastrichtian ornithischian diversity in North America. Zoological Journal of the Linnean Society 163 (4): 1157–1198.

Abstract: A small, articulated basal ornithopod skeleton from the Frenchman Formation (late Maastrichtian) of Saskatchewan (RSM P 1225.1), previously referred to the taxon Thescelosaurus, differs from both recognized species of this taxon (Thescelosaurus neglectus and Thescelosaurus garbanii). The differences are taxonomically informative and we recognize this specimen as the holotype of a new species, Thescelosaurus assiniboiensis sp. nov., diagnosed by the presence of two autapomorphies, and displaying plesiomorphic traits more similar to those of Parksosaurus, than to those of the other Thescelosaurus species. The Frenchman Formation also harbours an intriguing faunal assemblage in which Thescelosaurus represents one of the most abundant dinosaur taxa, and preserves a relatively high proportion of small (putatively juvenile and subadult) specimens of many dinosaur taxa. Further work that increases the faunal sample from this formation, and that permits quantitative comparisons with contemporary formations, will determine whether or not these differences are well supported, and will determine their ultimate palaeobiological significance. Identification of a third species of Thescelosaurus from the late Maastrichtian of North America suggests that this taxon was more diverse than previously recognized, and shows an increase in diversity from the Campanian through the late Maastrichtian, contrasting the trends seen in most other ornithischian clades.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)

References:
Brown; Caleb M.; Boyd, Clint A.; and Russell, Anthony P. 2011. A new basal ornithopod dinosaur (Frenchman Formation, Saskatchewan, Canada), and implications for late Maastrichtian ornithischian diversity in North America. Zoological Journal of the Linnean Society 163 (4): 1157–1198.

Aristosuchus pusillus

2011-12-04T12:54:00.001-08:00

Fig 1.- Reconstruction of Aristosuchus.

Continuing the series of British dinosaurs with the compsognathid Aristosuchus… This one is known from fragmentary postcranial remains from the Isle of Wight, dating from the Early Cretaceous Barremian stage, and originally described in 1876 by Sir Richard Owen (as “Poikilopleuron pusillus”). This little dinosaur was probably very similar to the Late Jurassic Compsognathus from Germany and France and measured about 2 meters in length.

Fig 2.- Reconstruction of Aristosuchus. Detail.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)

References:

D. Naish. 2002. The historical taxonomy of the Lower Cretaceous theropods (Dinosauria) Calamospondylus and Aristosuchus from the Isle of Wight. Proceedings of the Geologists' Association 113:153-163.

R. Owen. 1876. Monograph on the fossil Reptilia of the Wealden and Purbeck formations. Supplement no. VII. Crocodilia (Poikilopleuron) and Dinosauria? (Chondrosteosaurus). [Wealden.]. The Palaeontographical Society, London 1876:1-7

H. G. Seeley. 1887. On Aristosuchus pusillus (Owen), being further notes on the fossils described by Sir R. Owen as Poikilopleuron pusillus, Owen. Quarterly Journal of the Geological Society of London 43:221-228

Jeholornis palmapenis

2011-11-30T00:03:00.001-08:00

Fig 1.- A reconstruction of Jeholornis palmapenis.

A new paper just came out (I am not quite sure if the pun in the abstract is intended):

New species of Jeholornis with complete caudal integument
Jingmai K. O'Connor, Chengkai Sun, Xing Xu, Xiaolin Wana & Zhonghe Zhou
Historical Biology, Available online: 29 Nov 2011

Abstract: The Early Cretaceous long bony-tailed bird Jeholornis prima displays characters both more basal than Archaeopteryx and more derived, exemplifying the mosaic distribution of advanced avian features that characterises early avian evolution and obfuscates attempts to understand early bird relationships. The current diversity of Jeholornithiformes is controversial, since multiple possibly synonymous genera were named simultaneously. Here, we provide the first definitive evidence of a second species belonging to this clade, and erect the new taxon J. palmapenis sp. nov. This new specimen reveals the tail integument of Jeholornithiformes, the morphology of which appears to have no aerodynamic benefit suggesting this clade evolved plumage patterns that were primarily for display.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)

Archie the Black

2011-11-27T09:11:00.001-08:00

Fig. 1.- Archaeopteryx might have been robed in black.

There is definitely a lot going on for Archaeopteryx, on the 150th anniversary year of its first description by science. After the discovery of the 11th specimen, followed by its demotion then reinstatement as a basal bird, another piece of information has recently surfaced about the celebrated Urvogel: its color.

In a presentation this month at the 71st annual meeting of the Society of Vertebrate Paleontology in Las Vegas, Nevada, Ryan Carney and co-workers provided a glimpse of what Archaeopteryx may have look like in real life.

Using scanning electron microscopy and energy dispersive x-ray analyses, the team examined the iconic single feather attributed to Archaeopteryx, and detected fossilized melanosomes in it. By comparing the shape of the ancient pigment with those from 115 feathers coming from 87 species of modern birds, the team was able to determine that the color of the feather was black with 95% probability.

Fig 2.- The single feather examined for the color study of Archaeopteryx. The fossil has been described by von Meyer in 1861. (Picture credit: H. Raab, though Wikipedia)

Of course, the results from a single feather do not indicate that Archie was all robed in black like a raven, but they indicate that a least part of its plumage was dark.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com).

References:

R. Carney, J. Vinther, M. Shawkey, L. d’Alba & J. Ackermann. 2011. Black Feather Color in Archaeopteryx. 2011 Society of Vertebrate Paleontology Annual Meeting Abstracts, p 84.

Archaeopteryx is back on the Avialian tree...

2011-11-05T13:27:00.000-07:00

Fig 1.- Archaeopteryx back on its perch?

In the midst of the discovery of the 11th specimen of Archaeopteryx, almost complete (missing the head) with extensive feather impressions, a new paper published in Biology Letters, challenged the recent view expressed a few months earlier that it was not an Avialan (bird in the restricted sense) after all. Australian scientists Michael S. Y. Lee and Trevor H. Worthy, using the same sets of 374 characters than those defined by Xing Xu and co-workers in their Nature paper, employed a different and more sophisticated mathematical method in their phylogenetic analysis and arrived to a somewhat different conclusion.

Xu et al. used the maximum parsimony approach to obtain their evolutionary tree of birds and bird-like dinosaurs, while Lee used the more sophisticated maximum-likelihood and the related Bayesian inference methods. Under maximum parsimony, the preferred phylogenetic tree is the one that requires the least number of evolutionary changes to explain the observed sets of characters (or traits). Whereas generally valid, this assumption can be problematic in cases such as when some of the traits are evolving much faster than others or when some taxa have very long branches. The maximum-likelihood method is a seemingly more powerful (and computationally intensive) parametric statistical technique that uses an explicit model for character evolution and therefore is not subject to the same pitfalls. Maximum likelihood will pick the most probable tree that explains the observed data.

Fig 2.- Simplified tree according to Lee & Worthy, 2011.

The most important result of the Australian team new analysis of bird ancestry is that it puts solidly (in the sense that the measured level of accuracy given by the analysis is higher than with the parsimony approach) Archaeopteryx back on the Avialian tree as a basal bird. One of the consequences is that the typical forelimb-powered flight of birds would have only evolved once, while deinonychosaurian dinosaurs such as Microraptor would have discovered four-winged flight. Interestingly and on the side note, the odd scansopterygids, appear in the maximum likelihood analysis as deeply nested within the Avialians.

Is this new phylogenetic analysis establishing with certainty the evolutionary position of Archaeopteryx as the ancestral bird? Probably not… Pitfalls of the maximum parsimony method are reduced when taken more characters into account. We note for instance than in D. Naish & et al.’s study (2011), almost 3 times more characters (1025) were taken into account in a parsimony approach and the conclusion is somewhat similar to Xu et al. in the sense that Archaeopteryx is out of the Avialian tree.

References:

Michael S. Y. Lee & Trevor H. Worthy. 2011. Likelihood reinstates Archaeopteryx as a primitve bird. Biology letters. Published online before print.

Darren Naish, Gareth Dyke, Andrea Cau, François Escuillié and Pascal Godefroit. 2011. A gigantic bird from the Upper Cretaceous of Central Asia. Biology Letters. Published online before print. Electronic supplementary info.

Xing Xu, Hailu You, Kai Du and Fenglu Han. 2011. An Archaeopteryx-like theropod from China and the origin of Avialae. Nature 475: 465–470.