Saturday, December 31, 2011

2011 in Paleontology

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)

Friday, December 23, 2011

Kronosaurus queenslandicus

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.

Wednesday, December 21, 2011

Aegyptocetus tarfa

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

Friday, December 9, 2011

Spinops sternbergorum

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.

Sunday, December 4, 2011

Cuspicephalus scarfi

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

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


 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

Wednesday, November 30, 2011

Jeholornis palmapenis

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)

Sunday, November 27, 2011

Archie the Black

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.

Saturday, November 5, 2011

Archaeopteryx is back on the Avialian tree...


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.

Saturday, October 29, 2011

Teeth hold clues to dinosaur migrations


Fig 1.- A migrating herd of Camarasaurus
The teeth shape and wear pattern could already tell a lot about the diet of long gone creatures. New scientific methods applied to fossil teeth allow deciphering even more subtle behavioral habits. Last year, oxygen isotope analysis performed on Spinosaurus teeth has already shown that the popular back-sailed theropod dinosaur had a semiaquatic lifestyle. More recently, a detailed distribution analysis of 13C and 18O isotopes in the teeth of several sauropod dinosaurs was used to measure their body temperature. Now, in a new paper by Henry C. Fricke, Justin Hencecroth and Marie E. Hoerner published in the journal Nature, variations in the 18O isotope content measured in the teeth of the common Morrison formation sauropod Camarasaurus, lead strong support to the migratory behavior of those dinosaurs. The ratio of isotopes varies with the water the dinosaur drank and is recorded in the teeth enamel. Water from low elevation wetlands have higher ratio of 18O than those coming from surface water and precipitations at higher altitude. Comparisons of the teeth isotope ratio with those of ancient soils and their variations show that Camarasaurus was seasonally migrating for food, traveling as much as several hundreds of kilometers. During the wet months, they were staying in the lowland basin, but during the dry seasons when drought was quite possible, they moved uplands in search of vegetation. Pretty neat…

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


References:

Amiot, R., Buffetaut, E., Lecuyer, C., Wang, X., Boudad, L., Ding, Z., Fourel, F., Hutt, S., Martineau, F., Medeiros, M., Mo, J., Simon, L., Suteethorn, V., Sweetman, S., Tong, H., Zhang, F., & Zhou, Z. (2010). Oxygen isotope evidence for semi-aquatic habits among spinosaurid theropods Geology, 38 (2), 139-142

Robert A. Eagle, Thomas Tütken, Taylor S. Martin, Aradhna K. Tripati, Henry C. Fricke, Melissa Connely, Richard L. Cifelli, and John M. Eiler, 2011, “Dinosaur Body Temperatures Determined from Isotopic (13C-18O) Ordering in Fossil Biominerals” Science. 333(6041):443-5.

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

Wednesday, October 26, 2011

A New Rebbachisaurid Sauropod from the Isle of Wight.



Fig 1.- Reconstruction of Rebbachisaurus. 

Rebbachisaurids are a rather obscure and poorly understood group of sauropod dinosaurs so far known only from the Early Cretaceous period of Africa, South America and Europe. A new find described in an article by Philip D. Mannion, Paul Upchurch and Stephen Hutt in this month issue of Cretaceous Research confirms the presence of this group on the Isle of Wight during the Early Cretaceous. The paper reports of a an anterior caudal vertebra from the Wessex Formation of Barremian age, discovered at Brightstone Bay on the Southwest coast of this little Island of the English Channel. No species name has been assigned to the fossil.

The type genus of the Rebbachisaurids, Rebbachisaurus was a sauropod, big plant-eating dinosaur similar to the famed Diplodocus, and member of the Diplodocoidea superfamily. It lived during the Early Cretaceous in what is now North Africa. It was first described in 1954 by R. Lavocat from fragmentary remains, consisting of a tail vertebra, a humerus (upper arm bone), a scapula (shoulder blade) and a sacrum, and collected from the Tegana Formation of Morocco. The species name is Rebbachisaurus garasbae. In 1960, A.F. de Lapparent described a second species, R. tamesnensis from various fragments of the Farak Formation of Niger, but this one is a bit dubious and can well belong to a completely different sauropod. More complete material from the Rio Limay Formation of Argentina including a partial skull has been referred to a third species, R. tessonei (Calvo & Salgado, 1995), and was used as proof of a land connection between Africa and South America in the Early Cretaceous, but the species has since been transferred to its own genus, Limaysaurus. So as today, the only species referable with certainty to the genus Rebbachisaurus is the Moroccan one described by Lavocat.

Fig 2.- Nigersaurus taqueti.

However, several closely related taxa have been described since then, mostly from South America, and a family, the Rebbachisauridae, has been erected by P. Sereno and co-workers in 1999 to regroup them. Although only known from Cretaceous strata, they appear to be basal members of the Diplodocoidea and therefore more primitive than the earlier Diplodocus and Apatosaurus from the late Jurassic period, indicating "a ghost lineage" from the Middle to Late Jurassic. Besides Rebbachisaurus and Limaysaurus, the Rebbachisaurids include the odd sauropod Nigersaurus taqueti, known from several well-preserved skeletons from the “Middle” (Aptian-Albian) Cretaceous of Niger, and described in the media as the “dinosaur with a vacuum cleaner mouth”. From the ten or so Rebbachisaurid taxa named so far, only Limaysaurus and Nigersaurus are known from relatively complete materials. All the others are very fragmentary so it is difficult to get a complete picture of this enigmatic family. One characteristic and common trait of this clade is the paddle-shaped scapular blade.

Besides Africa and South America, Rebbachisaurids were also living in Europe. The species Histriasaurus boscarottii, has been erected based on a few vertebrae from the Early Cretaceous (Hauterivian-Barremian) of Croatia (Dalla Vecchia, 1998), the most ancient member of the family so far and some materials from the Castrillo de la Reina Formation (Barremian-Aptian) of Spain have been reported by Pereda Superbiola et al. in 2003 and recently described in details under the name Demandasaurus darwini by Fernández-Baldor et al., in 2011. Finally, rebbachisaurids are also known from the Isle of Wight of England. A characteristic scapula (shoulder blade) collected by Nick Case in 1989 from the Wessex Formation on the southwest coast of the Isle of Wight has been described by Philip Mannion in 2009. In a recent cladistic analysis by Carballido et al., (2010), this British scapula comes, oddly, as a sister taxon of the South American Limaysausus tessonei. It is possible that the newly described caudal vertebra does belong to the same animal, even if the phylogenetic analysis placed it in a close kinship with the Spanish Demandasaurus and the African Nigersaurus, rather than with Limaysaurus. However, conclusions based on single incomplete bones are probably not to be entirely trusted until new discoveries are added to the analysis.

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

References:

J. O. Calvo and L. Salgado. 1995. Rebbachisaurus tessonei sp. nov. a new Sauropoda from the Albian-Cenomanian of Argentina; new evidence on the origin of the Diplodocidae. GAIA 11:13-33.

J. L. Carballido, A. C. Garrido, J. L. Canudo and L. Salgado. 2010. Redescription of Rayososaurus agrioensis Bonaparte (Sauropoda, Diplodocoidea), a rebbachisaurid from the early Late Cretaceous of Neuquén. Geobios 43:493-503.

F. M. Dalla Vecchia. 1998. Remains of Sauropoda (Reptilia, Saurischia) in the Lower Cretaceous (Upper Hauterivian/Lower Barremian) limestones of SW Istria (Croatia). Geologica Croatica 51(2):105-134.

F. Torcida Fernández-Baldor, J. I. Canudo, P. Huerta, D. Montero, X. Pereda Suberbiola and L. Salgado. 2011. Demandasaurus darwini, a new rebbachisaurid sauropod from the Early Cretaceous of the Iberian Peninsula. Acta Palaeontologica Polonica 56(3):535-552

A. F. d. Lapparent. 1960. Les Dinosauriens du "Continental intercalaire" du Saharal central [The dinosaurs of the "Continental Intercalaire" of the central Sahara]. Mémoires de la Société géologique de France, nouvelle série 39(88A):1-57

R. Lavocat. 1954. Sur les dinosauriens du Continental Intercalaire des Kem-Kem de la Daoura [On the dinosaurs from the Continental Intercalaire of the Kem Kem of the Doura]. Comptes Rendus 19th Intenational Geological Congress, 1952 1:65-68.

P. D. Mannion. 2009. A rebbachisaurid sauropod from the Lower Cretaceous of the Isle of Wight, England. Cretaceous Research 30:521-526.

P. D. Mannion, P. Upchurch, and S. Hutt. 2011. New rebbachisaurid (Dinosauria: Sauropoda) material from the Wessex Formation (Barremian, Early Cretaceous), Isle of Wight, United Kingdom. Cretaceous Research 32:774-780

X. Pereda Suberbiola, F. Torcida, L. A. Izquierdo, P. Huerta, D. Montero and G. Pérez. 2003. First rebbachisaurid dinosaur (Sauropoda, Diplodocoidea) from the early Cretaceous of Spain: palaeobiogeographical implications. Bulletin de la Societé Géologique de France 2003(5):471-479

L. Salgado, A. Garrido, S. E. Cocca and J. R. Cocca. 2004. Lower Cretaceous rebbachisaurid sauropods from Cerro Aguada del León (Lohan Cura Formation), Neuquén province, northwestern Patagonia, Argentina. Journal of Vertebrate Paleontology 24(4):903-912.

P. C. Sereno, A. L. Beck, D. B. Dutheil, H. C. E. Larsson, G. H. Lyon, B. Moussa, R. W. Sadleir, C. A. Sidor, D. J. Varricchio, G. P. Wilson, and J. A. Wilson. 1999. Cretaceous sauropods from the Sahara and the uneven rate of skeletal evolution among dinosaurs. Science 286:1342-1347.

Saturday, October 22, 2011

Scelidosaurus harrisoni, a basal thyreophoran from southern England




Fig 1.- A reconstruction of Scelidosaurus harrisonii.

The Black Ven cliff between Charmouth and Lyme Regis, in Dorset, southern England is world famous for its Early Jurassic fossils of marine animals such as ammonites and ichthyosaurs. It is also known for a single species of dinosaur that has only been found there, Scelidosaurus harrisoni. How this fully terrestrial animal ended up preserved in marine deposits is somewhat a mystery (carcasses were presumably washed to sea after death and quickly buried by layers of sand) but it allows getting a rare glimpse of the fauna that lived during the Early Jurassic period on the islands of Europe (Most of Western Europe was under a shallow sea at that time).

Scelidosaurus was known from quite some time having been described in 1861 by Sir Richard Owen based on a skull and various non-associated postcranial bits discovered near the village of Charmouth. The original material contains a right knee joint, a femur fragment and a phalanx (finger bone) that proved later to belong to one or several type of megalosaurs (theropod dinosaurs) (Newman, 1968). Some other elements described by Owen as belonging to a juvenile Scelidosaurus proved later to be from a hypsilophodont.  In the meantime, the postcranial skeleton associated to the original skull was uncovered and described by Owen in 1862. He named the species Scelidosaurus harrisonii, in honor of its discoverer, James Harrison.

Fig 2.- Original skull of Scelidosaurus in Owen's 1861 description of the genus. This skull is presently the lectotype as the holotype (a femur fragment) turned out to belong to a megalosaur.

These were the only fossils of the animal known for over a century and the exact affinities of the new dinosaur remained uncertain until fairly recently. The characteristic dermal scutes that make a kind of armor covering the body pointed to a close relationship with others armored ornithischians such as the stegosaurs, the ankylosaurs or the fabrosaurs. It was in turn considered a primitive stegosaur (von Zittel, 1902, Romer, 1956), an ankylosaur (Romer, 1968), a basal ornithopod (Thurlborn, 1977) and then generally considered a primitive ornithischian of some sort. A second skull previously described as a juvenile Scelidosaurus (Rixon, 1968) might actually belong to a hypsilophodont. Scutes from the Kayenta formation in Arizona were attributed to Scelidosaurus, which would indicate a large geographical range for the genus (Padian, 1989), but this identification has been questioned.

The uncertainty has dwindled in the last decade or so thanks in part to the fact that the original specimen described by Owen has been acid prepared so that it can be studied more thoroughly (Norman, 1996).  Also, new specimens of Scelidosaurus began to turn up in the 1990s. Dave Martill described two of them in 1991 and 2000. The first is a rather complete articulated skeleton including skull fragments.  It was found in 1985 near Charmouth in the Black Ven marls of Upper Sinemurian age. The second consists of a set of 8 articulated tail vertebrae and was acquired in 1998 from a private collection at the death of his owner, Prof. John Challinor. It unfortunately misses information about its provenance. A palynological analysis however indicates an Early Jurassic age from the same period as the Owen specimen (Late Hettangian- Sinemurian). Interestingly, both specimens show kerogenized traces of soft tissues indicating that the scutes (osteoderms) were covered by a horny sheath.  A third specimen was collected in the same area between Charmouth and Lyme Regis in 2000 by a local fossil collector, David Sole. It has been described as the most complete skeleton of a dinosaur ever found in the UK.

Carpenter (2001) places Scelidosaurus as a basal ankylosaur. However, most of the recent phylogenetical analysis including the latest comprehensive one on the Ankylosauria (Thompson et al., 2011) points toward an ancestral position of Scelidosaurus relatively to both the stegosaurs and ankylosaurs, as a basal member of the thyreophorans. Other genera probably related to it include the gracile Scutellosaurus lawleri from the Kayenta formation in Arizona (Sinemurian-Plienbaschian), and the rather enigmatic Emausaurus ernsti from the Toarcian of Germany. Tatisaurus oeheleri from the Lufeng formation of Yunnan might be another relative, although the remains are so fragmentary that it is difficult to be sure. The same can be said of Bienosaurus lufengensis from the same formation known from fragments of a skull, and Lusitanosaurus liasicus from the Early Jurassic of Portugal, also known from a few skull fragments and teeth.

 
 Fig 3.- Cast of a nearly complete skeleton of Scelidosaurus harrisonii found in 2000 and on display at the Charmouth Heritage Coast Center (photo by User:Ballista via wikipedia, CC3.0 licensed).

Scelidosaurus was a 4-meter long herbivorous dinosaur that probably walked on all fours although it was possibly able to stand on its hind legs from time to time. The body was covered with bony scutes called osteoderms as a protection against predators. Contrary to earlier depictions of the animal as a bulky quadruped, Scelidosaurus was probably more gracile in appearance with a relatively long neck compared to stegosaurs and ankylosaurs.

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

References:

K. Carpenter. 2001. Phylogenetic analysis of the Ankylosauria. In K. Carpenter (ed.), The Armored Dinosaurs. Indiana University Press, Bloomington 455-483a

D.M. Martill, 1991. Organically preserved dinosaur skin: taphonomic and biological implications. Modern Geology, 16, 61±68.

B. H. Newman. 1968. The Jurassic dinosaur Scelidosaurus harrisoni, Owen. Palaeontology 11(1):40-43

R. Owen. 1861. A monograph of a fossil dinosaur (Scelidosaurus harrisonii, Owen) of the Lower Lias, part I. Monographs on the British fossil Reptilia from the Oolitic Formations 1:1-14

R. Owen. 1862. A monograph of a fossil dinosaur (Scelidosaurus harrisonii, Owen) of the Lower Lias, part II. Monographs on the British fossil Reptilia from the Oolitic Formations 2:1-26.

K. Padian, 1989. Presence of the dinosaur Scelidosaurus indicates Jurassic age for the Kayenta Formation (Glen Canyon Group, northern Arizona). Geology. May 1989, v. 17; no. 5; p. 438-441

A.E. Rixon, 1968. The development of the remains of a small Scelidosaurus from a Lias
nodule. Mus. J. 67:315-321.

A. S. Romer. 1956. Osteology of the Reptiles, University of Chicago Press 1-772

A.S. Romer. 1968. Notes and Comments on Vertebrate Paleontology. Chicago Univ. Press, Chicago, 304 p.

R. S. Thompson, J.C. Parish, S. C. R. Maidment & P. M. Barrett, 2011.  Phylogeny of the ankylosaurian dinosaurs (Ornithischia: Thyreophora), Journal of Systematic Palaeontology, in press.

R. A. Thulborn. 1977. Relationships of the Lower Jurassic dinosaur Scelidosaurus harrisonii. Journal of Paleontology 51(4):725-739.

K. A. von Zittel, 1902. Text-book of Palaeontology, V. II. (Transl. C. R. Eastman). Macmillan, London and New York, 283 p.

Saturday, October 15, 2011

Two extraordinary paleontology finds this week: one good, one bad...




Fig 1.- Speed painting of the giant prehistoric kraken.

In the Triassic period, giant squids were roaming the oceans to pray on large ichthyosaurs the size of a school bus.  Mark McMenamin, a professor of Geology at Mount Holyoke College, MA, presented this claim at the last Geological Society of America conference in Minneapolis (October 10, 2011). The proof lays in the curious arrangement of vertebral disks observed in the remains of the ichthyosaur Shonisaurus. According to McMenamin, this can only be the work of some giant artsy prehistoric cephalopods portraying themselves on the sand with the bones of their hapless victims! This is probably the most ludicrous paleontological claim made since the treeosaur. Amazingly, some major news outlets took the bait (see for instance here).

 Fig 2.- Reconstruction of the Kelheim theropod.

The second extraordinary announcement of the week is the discovery of a 98% complete articulated skeleton of a young theropod dinosaur in Germany, the most complete ever found in Europe. The discovery has been unveiled by Oliver Rauhut, conservator of the Bavarian Paleontological and Geological collections in Munich. The press release unfortunately gave very little details about it. The fossil has been uncovered near Kelheim in Bavaria, and is, I would guess in view of the geology of the region, of Late Jurassic age (and not 135 MYA i.e. Early Cretaceous as said in the news). Judging from the photo of the skeleton that came with the release, it looks to be a compsognathid with a very long tail. General proportions of the skull and limbs are strikingly similar to Juravenator. But what do I know about this amazing yet unnamed theropod? Let’s wait for the full description of the fossil that will hopefully be published in the upcoming months.

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

Monday, September 19, 2011

Talos sampsoni, a new troodontid from Utah

After the Chinese Linhevenator, yet, another troodontid, Talos sampsoni, has just been described in the current issue of PLoS ONE. This one is from the distinct and quite specific fauna of the Kaiparowits formation of Utah, which included the unique ceratopsians Kosmoceratops, Utahceratops and Nasutuceratops, the tyrannosaurid Teratophoneus, the hadrosaur Gryposaurus and the Oviraptosaur Hagryphus. Talos is essentially known from remains of the hindlimbs plus a few other bits such as some  vertebrae, and a left ulna. It was probably similar in shape to the other derived troodonts with short forelimbs, long legs and had a sickle claw on each foot.
 

References:
Lindsay E. Zanno, David J. Varricchio, Patrick M. O'Connor, Alan L. Titus and Michael J. Knell. 2011. A new troodontid theropod, Talos sampsoni gen. et sp. nov., from the Upper Cretaceous Western Interior Basin of North America. PLoS ONE 9 (6): e24487.


Sunday, September 18, 2011

Pachyrhinosaurus perotorum, new boreal dinosaur from Alaska


Fig 1.- Pachyrhinosaurus perotorum.
 
Anthony R. Fiorillo, and Ronald S. Tykoski, from the Museum of Nature and Science, Dallas, TX, have just described a new species of Ceratopsian (Horned dinosaur), Pachyrhinosaurus perotorum from the Prince Creek formation of the North Slope in the northernmost region of Alaska. The species is based on two fragments of parietals (which in Ceratopsians are the bones that formed the frill) and a partial skull.



What makes P. perotorum special is that it was a boreal dinosaur. During the Late Cretaceous, Alaska was situated at latitudes similar or higher than its current geographical position, meaning that its northern inhabitants experienced, as of today, a yearly 6 month long winter night with freezing temperature. Polar dinosaurs are also known from the southern hemisphere with representatives of the early Cretaceous period such as the hypsilophodont Leallynasaura amicagraphica from Australia featured in WWD. The Late Cretaceous Prince Creek formation of Alaska, however, appears to be the richest trove of polar dinosaur bones from either hemisphere. The Kikak-Tegoseak Quarry where the P. perotorum remains were unearthed, also include bones of the raptors Dromaeosaurus albertensis and Troodon formosus as well as remains attributed to the tyrannosaur Gorgosaurus libratus, some hadrosaurs and the Pachycephalosaur Alaskacephale gangloffi.

Fig 2.- Pachyrhinosaurus canadensis.


P. perotorum is the third named species of the genus Pachyrhinosaurus which contains Ceratopsians with massive flattened bosses in place of the usual horns on the nose and above the eyes. The larger 6 meter long P. canadensis was described in 1950. It is known from the St Mary River (Upper Campanian-Lower Maastrichtian) and Horseshoe Canyon Formations (Lower Maastrichtian) of Alberta, Canada. The smaller 5 meter long P. lakustai, described in 2008 from the Wapiti Formation (Late Campanian) of Alberta, differs from P. canadensis by well-separated nasal and supraorbital bosses and by the presence of a comb of horns on the parietal bone just behind the eyes.
 
Fig 3.- Pachyrhinosaurus lakustai.

P. perotorum is the youngest (Lower Maastrichtian) of the three species, and about the same size as P. lakustai. It is characterized by the unique anterior parietal pair of horns just at the top edge of the parietal cavities (the large holes in the frill), and a narrow dome in a back portion of the nasal boss. The bizarre blunt rounded rostrum might just be an individual oddity (the partial skull is apparently from an aged individual). A recently discovered specimen numbered TMP 2002.76.1 (Housed at the Royal Tyrrel Museum), from the Dinosaur Park Formation, Alberta, which shows similarities with both Pachyrhinosaurus and Achelousaurus, might represent a fourth species.


Pachyrhinosaurus belongs to the Pachyrhinosauri tribe of the Centrosaurine Ceratopsian that also contains the basal genera with enlarged nasal horns Einiosaurus and Rubeosaurus, as well as the derived forms with nasal and supraorbital bosses, Achelousaurus.


Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)
 
References:
 
P. J. Currie, W. Langston, and D. H. Tanke. 2008. A new species of Pachyrhinosaurus (Dinosauria, Ceratopsidae) from the Upper Cretaceous of Alberta, Canada. In P. J. Currie, W. Langston Jr., D. H. Tanke (eds.), in A New Horned Dinosaur from an Upper Cretaceous Bone Bed in Alberta. NRC Research Press, Ottawa 1-108.

A.R. Fiorillo, and R.S.T. Tykoski, R.S.T.  2011. A new species of the centrosaurine ceratopsid Pachyrhinosaurus from the North Slope (Prince Creek Formation: Maastrichtian) of Alaska. Acta Palaeontologica Polonica. In press.


Monday, September 12, 2011

Linhevenator tani, a new troodontid from China

Fig 1.- Reconstruction of Linhevenator tani.

Troodontids are a family of very bird-like small theropods with long legs and enlarged braincases.  Phylogenetically, they are placed alongside the dromaeosaurs (Velociraptor, Deinonychus and friends) among the Deinonychosaurians, a sister group to the birds. Fossils of troodonts were found in Asia, Europe and North America in sediments dating from the Upper Jurassic to the Upper Cretaceous periods. Some of the better known troodonts include the Early Cretaceous Mei long (the shortest name given to a dinosaur, and meaning “sleeping dragon” because its exceptionally preserved articulated skeleton has been found in a sleeping position) and the Late Cretaceous Troodon formosus from North America, which was originally described on the basis of a single characteristic serrated tooth, but which is now known from multiple fragmentary specimens (previously referred as "Stenonychosaurus").

Fig 2.- The holotype (LH V0021) of Linhevenator tani (Xu et al., 2011). Licensed under CC 2.5. Scale bar is 2 cm.

Xing Xu and colleagues are reporting in the September 2011 issue of the open access journal PLoS ONE, a new troodontid from the Late Cretaceous Wulansuhai Formation of Bayan Mandahu, Inner Mongolia. The Wulansuhai Formation is equivalent to the famous Mongolian dinosaur bearing Djadokhta Formation of Campanian age. This new species, Linhevenator tani is known from a partly articulated skeleton that includes the skull, several vertebrae, pelvic girdle and limb elements. Although badly weathered, the remains are of particular interest are they are to date the most complete ones from a Late Cretaceous Troodontid and therefore likely to shed new lights on the more derived members of this family. Linhevenator was a rather large species (around 2-3 meters in length) characterized by rather short arms (the humeri measured only 40% of the length of the femur) and with a sickle clawed second digit on each foot similar to those of the dromaeosaurs, although these may be in fact common traits to all derived troodontids such as Troodon and Saurornithoides.

References:
Xing Xu, Qingwei Tan, Corwin Sullivan, Fenglu Han and Dong Xiao. 2011. A Short-Armed Troodontid Dinosaur from the Upper Cretaceous of Inner Mongolia and its Implications for Troodontid Evolution. PLoS ONE 6 (9): e22916


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


Monday, September 5, 2011

Stegosaurs of the British Isles


Fig 1.- Lexovisaurus durobrivensis (= Loricatosaurus priscus)

Compared to the Stegosaurs of North America, restricted to the sole Morrison Formation and represented only by 1 or 2 genera and a handful of species, all from the Kimmeridgian-Tithonian age of the Late Jurassic, the plated dinosaurs from England appear comparatively more diversified with up to 6 genera spanning from the Middle Jurassic to the Early Cretaceous. Unfortunately, the fossils there are for the most part quite scrappy, consisting of teeth, bits of plates and other bones, making their identification difficult or even dubious.  Susannah Maidment and colleagues in their 2008 general revision of the Stegosauria, have recognized only 2 valid species to the United Kingdom, Dacentrurus armatus and the newly erected Loricatosaurus priscus, but this is certainly an underestimation. Let’s make a quick overview of stegosaurian materials found in England.

Middle Jurassic Stegosaurs

The most ancient British stegosaurs date from the Bathonian stage (165-168 MYA) of the Middle Jurassic and consist of a few isolated bones, including a massive right femur of a juvenile individual from the Cornbrah formation of Oxfordshire (Upper Batthonian), two incomplete vertebrae from the Sharp’s Hill Formation of Oxfordshire and two large dermal plates from the Chipping Norton Formation of Gloucestershire. These bones were all referred to “Lexovisaurus” vetustus (= “Omosaurus” vetustus). All that can be said is that they are the oldest recorded Stegosaurids in the world (the family to which all the most derived stegosaurs such as Stegosaurus and Kentrosaurus belong) and that a least one large species was present in Europe at that time.

Next, from the Middle Callovian (161-165 MYA) Oxford Clay Formation came Lexovisaurus durobrivensis, known from two partial skeletons. Maidment et al, 2008 have invalidated the name Lexovisaurus, on the basis that no unique character could be found in the holotype specimen. In its stead, a new genus, Loricatosaurus, was erected for the second partial skeleton that includes vertebrae, various pelvic and limb elements, and a piece of dermal armor, and folded into the species Loricatosaurus priscus. A large dermal plate named ‘Omosaurus leedsi’ from the same locality may be from the same animal. A third partial skeleton from a contemporary formation in Normandy, France is also referred to Loricatosaurus priscus. However there is no real indication that Lexovisaurus durobrivensis and Loricatosaurus priscus represent different taxa and the two might well be the same. Loricatosaurus probably measured about 5-6 meters in length. It is characterized by relatively short limbs and narrow plates and spines on the back. Shoulder spines may or may not have been present (A previously reported shoulder spine in the skeleton turns out to be a tail spine instead).

Upper Jurassic Stegosaurs
Fig 2.- Dacentrurus armatus.

From the Coralline Oolite Formation, Yorkshire, of Middle Oxfordian age (156-161 MYA), came a poorly preserved femur of a juvenile individual that has been named ‘Omosaurus phillipsi’ (= ‘Dacentrurus phillipsi’). There is no real indication that it was a stegosaur at all and the name is considered a nomen dubium (dubious name).

From the Kimmeridge Clay Formation of Wiltshire, of Lower Kimmeridgian age (151-156 MYA), came Dacentrurus armatus, a partial skeleton preserved in a large slab on exhibit at the Natural History Museum of London. Some fragmentary materials from France, Spain and Portugal were also referred to Dacentrurus. It was a large stegosaur with an estimated length of some 8 meters. Its aspect is not well known, but it probably resembled the African Kentrosaurus. From the Kimmeridge Clay also came a few dermal spines named “Omosaurus hastiger” that might belong to the same animal than Dacentrurus

Fig 3.- Dacentrurus armatus holotype on display at the Natural History Museum in London (Credit: Emőke Dénes, via Wikipedia)

Early Cretaceous Stegosaurs

From the Lower Cretaceous Wealden Beds, Sussex of Valanginian age (136-140 MYA), came a partial right mandible, Regnosaurus northamptoni, that was variously attributed to the Ornithopod Iguanodon (Mantell, 1841), the ankylosaur Hylaeosaurus (Owen, 1858), a scelidosaur (Lydekker, 1888), and even a sauropod (Ostrom, 1970) until it was discarded as a nomen dubium (Coombs, 1971). However, more recently, Barrett & Upchurch, 1995, resuscitated Regnosaurus as a stegosaur and found it to be a relict of the old stegosaurian lineage that included the Chinese Huayangosaurus. The dubious Craterosaurus pottonensis, known from a single incomplete and poorly preserved dorsal vertebra, has been described as a stegosaur, but that is probably more wishful thinking. Interestingly Craterosaurus from Bedfordshire is probably also of Valanginian age.

Fig 4.- Regnosaurus northamtoni was a close relative of Huayangosaurus taibaii.


This concludes our tour of the stegosaurian remains of England.

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. Barret & P. Upchurch. 1995. Regnosaurus northamptoni, a stegosaurian dinosaur from the Lower Cretaceous of Southern England. Geological Magazine 132: 213–222.

P. M. Galton and H.P. Powell, H. P. 1983. Stegosaurian dinosaurs from the Bathonian (Middle Jurassic) of England, the earliest record of the Family Stegosauridae. Geobios 16: 219-229.

P. M. Galton. 1985. British plated dinosaurs (Ornithischia, Stegosauridae). Journal of Vertebrate Paleontology 5(3):211-254.

S. C. R. Maidment, D. B. Norman, P. M. Barrett and P. Upchurch. 2008. Systematics and phylogeny of Stegosauria (Dinosauria: Ornithischia). Journal of Systematic Palaeontology 6(4):367-407.

Saturday, September 3, 2011

Smok wawelski, giant Late Triassic Archosaur from Poland

The Wawel Dragon (in Polish ‘Smok Wawelski’) is a famous beast of the Polish folklore that was bringing havoc in the countryside near Krakow until a poor young cobbler’s apprentice saved the day by wittingly killing the monster and marrying the princess to live happily ever after.

This is the name chosen by the authors (G. Niedźwiedzki, T., Sulej, T., and J. Dzik) of a new article published in Acta Palaeontologica Polonica for an enigmatic archosaur that once roamed Poland during the very Late Triassic period, some 200-205 MYA. The animal is known from a braincase, skull fragments, pelvic elements, limb fragments and a few other bits found in the Lipie Śląskie claypit, near the village of Lisowice. The exact affinities of the animal are unresolved at this time as Smok displays a mixture of characteristics that pertain to both theropod dinosaurs and to more ancient archosaur lineages such as the ornithosuchids and rauisuchians (think Postosuchus of WWD fame). Some tridactyl fossilized footprints found in the vicinity might belong to the beast and show that it was bipedal. One thing is certain though: Smok was a large predator, with an estimated length of some 5-6 meters, and to date is the largest late Triassic predator ever found in Central Europe. 

The authors of the study state that the paper that has just been accepted for publication is only an initial report and that a full phylogenetical placement of Smok is still a WIP, the subject on the on-going PhD thesis by the first author. So we will likely hear more on Smok wawelski in the near future. Whatever Smok was, it shows the existence of large bipedal carnivores in the Late Triassic that anticipates the future theropod dinosaurs of the Jurassic and Cretaceous periods.

Reconstruction here is based on the published skeletal. Osteoderms are hypothetical.


References:
G. Niedźwiedzki, T. Sulej, and J. Dzik. 2011. A large predatory archosaur from the Late Triassic of Poland., in press.

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

Saturday, August 27, 2011

Nasutuceratops titusi, a new ceratopsian from Utah


The Kaiparowits Formation of Late Cretaceous Campanian age, in the Grand Staircase-Escalante National Monument, Southern Utah, has in recent years released a number of spectacular finds, including the ceratopsians Utahceratops and Kosmoceratops and the tyrannosaurid Teratophoneus.

This year sensation from Utah might well be another ceratopsian, Nasutuceratops titusi, known from an almost complete skull and an associated left forelimb, as well as skull fragments from two other individuals. Some skin impressions were also found with the forelimb. Nasutuceratops is still a nomen nudum (“naked name”), meaning it has not been officially and formally described in a published scientific journal yet. It has been named by Eric Karl Lund (advisor: Scott Sampson) in his Master of Science Geology thesis submitted to the faculty of the University of Utah in 2010. In a comprehensive phylogenetical analysis, this short snouted long horned centrosaurine ceratopsian was found to be closely related to the contemporary Avaceratops lammersi from Montana.


To my knowledge, the talented paleoartist Andrey Atuchin is the first one to have made a reconstruction of this intriguing animal. Mine is far from being as good as his but here it is nevertheless.

Update: it has been officially described in 2013 as Nasutoceratops titusi by Sampson et al (with an "o" instead of a "u").

Ref: Sampson, S. D., Lund, E. K., Loewen, M. A., Farke, A. A, Clayton, K. E. 2013. A remarkable short-snouted horned dinosaur from the Late Cretaceous (late Campanian) of southern Laramidia. Proceedings of the Royal Society B: Biological Sciences 280 (1766) 20131186.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission.