2012 in Paleontology

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

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

            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…

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

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

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

 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