Mesozoic Matters: July 2010
Here’s a brief survey of “news” items concerning the Age of Dinosaurs:
Scavaging by tyrannosaurine Tarbosaurusus: David W.E. Hone and Mahito Watabe published a study in Acta Palaeontologica Polonica online (abstract with pdf download free access) showing selective scavaging by a tyrannosaurine on the humerus of a Saurolophus. They discuss the various biting strategies of the predator based on the tooth marks on the bone. The fact that only the humerus was marked shows that it was not feeding at a fresh kill (in which case the more meatier parts would likely have been eaten first).
Kayentavenator: Robert Gay has described a new tetanuran theropod from the Early Jurassic of Arizona in Notes on Early Mesozoic Theropods (open access). The specimen is claimed to be the earliest known tetanuran in North America. Gay also argues that given that the other members of the clade exist only at the opposite end of Pangea and given the then separation of North America from Gondwana, the appearance of this tenanuran argues for an earlier appearance of the clade than the late Sinemurian/late Pliensbachian, in other words that tenanurans would have originated in the Triassic. Much comment on the publication took place in June on the Dinosaur Mailing List, but almost all of it had to do with whether Kayentavenator was validly named under ICZN regulations rather than on the substance of the paper. This proves once again that most non-lawyers prefer lawyering to what they actually do. Gay’s paper also presents new evidence (volumetric and biomechanial) that Coelophysis did not engage in cannabalism.
Predatory digging: Edward L. Simpson and others describe in Geology (subscription required) a find in the Upper Cretaceous Wahweap Formation in southern Utah of trace scratch marks by a maniraptoran dinosaur, perhaps a dromeosaurid or troodontid, in close association with a trace mammalian dens suggesting the dinosaur ussed digging techniques to obtain prey. Livescience.com reports on the find here. The Kutztown University news release is here.
Neck posture: In the June 2, 2010 Biology Letters of the Royal Society, Andreas Christian argues that at least some sauropods held their necks much like giraffes — at a 45° angle. His calculations were based on the Euhelopus zdanskyi, an Early Cretaceous sauropod (between 130 million and 112 million years ago) found in the Shandong Province in China. It was estimated to weigh some 8,400 pounds (3,800 kilograms) and roughly 36 to 39 feet (11 to 12 meters) in length from nose tip to tail tip. He calculates that the energy necessary to create adequate blood pressure for the brain is less than would be required to move the mass of the animal in search of ground vegetation. He argues that the same calculations would lead to the same results in Brachiosaurs. Also included in the biomechanical analysis is the stress placed on neck vertebrae at various postures.
Egg-warming with vents: In Nature Communications, June 29, 2010, Gerald Grellet-Tinner and Lucas E. Fiorelli report on findings from the Sanagasta Valley in La Rioja province, northwestern Argentina that certain neo-sauropods, including Chubutisaurus insignis, repeatedly returned to lay eggs a the same nesting site. The site was near thermal vents presumably to keep the eggs warm during incubation. Nature News says: “The team found that the eggs were large and thick-shelled when freshly laid, an adaptation that may have evolved to allow them to safely incubate in the acidic environment near geyser fountains.”
“Torosaurus” and Triceratops are the same animal: In a paper published in the Journal of Vertebrate Paleontology (subscription required), John B. Scannella and John R. Horner conclude that the two genera of ceratopsians described in the 1890s as Triceratops and “Torosaurus” are actually the same animal at different stages of development. The paper is based on a 10-year study of the skulls of over 30 specimens from the Hell Creek Formation in Montana as well as specimens from other museums. The key conclusion in the abstract, which explains the difference in shape of the skulls is: “Major changes in cranial morphology—including the opening of parietal fenestrae and the elongation of the squamosals—occur rapidly, very late in Triceratops ontogeny and result in the characteristic ‘Torosaurus’ morphology.” Under the accepted rules of taxonomy, according to this conclusion, “Torosaurus” should now be known under the name of Triceratops, which name was used for the earlier described specimen. The Montana State University press release on this finding can be found here. According to a post by Thomas R. Holtz, Jr. on the Dinosaur Mailing List, the finding should not greatly disrupt currently accepted phylogenetic analysis of ceratopsians, since “[i]n most recent aanlyses, Torosaurus, Triceratops, and Nedoceratops, (aka Diceratus aka Diceratops) fell out as each others’ closest relatives in one configuaration or another. Under the new taxonomy, they would all be the same operational taxonomic unit.”
Mojoceratops: A new species of chasmosaurine ceratopsians was described in the July 2010 issue of Journal of Paleontology (subscription required), the Mojoceratops perifania. (Chasmosaurines are ceratopsians with large frills and well-developed brow horns as opposed to the centrosaurines which have less well-developed brow horns and frills (but the frills have elaborate spikes) and larger nasal horns.) Mojoceratops was discovered in Western Canada in a late Cretaceous (Late Campanian) formation. Eight partial skulls were found at Dinosaur Provincial Park in Alberta. Nicholas Longrich of Yale came up the name at a drinking party. The “mojo” refers to the long heart shaped frill of the animal. The Yale press release, with photos of a skull, can be found here. The New York Times weighs in here, the Boston Globe here. And so we now know that paleontology stories involving alcohol and hype receive major media publicity.
Medusaceratops: Another new chasmosaurine ceratopsians was described in a book New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium, published by Indiana University Press. The book was edited by the describer Michael J. Ryan, a scientist at The Cleveland Museum of Natural History. The new species Medusaceratops lokii means “Loki’s horned-faced Medusa,” referring to the thickened, fossilized, snake-like hooks on the side of the frill. It was named after Loki, the Norse god of mischief, because the new dinosaur initially caused scientists some confusion, because the spiked frill initially suggested it was a centrosaurine (specifically the Albertaceratops, described in 2007). The animal, discovered in late Cretaceous (Campian) rocks in Montana. It is the oldest known chasmasaurine. The press release of the Cleveland Museum of Natural History, with a link to digital pictures, is found here.
Ojoceratops: In the same book from Indiana, Robert M. Sullivan and Spencer G. Lucas describe Ojoceratops fowleri, another chasmosaurine. Fragments of the animal had previously been considered “Torosaurs” but in 2005 in Bisti/De-na-zin Wilderness of northwest New Mexico Denver Fowler found a bone in front of the frill to show that it was an earlier ceratopsian more closely related to Triceratops. (Of course according to Scannella and Horner “Torosaurus” and Triceratops are the same animal.) Lucas is quoted as saying: “It could be an ancestor of Triceratops. It might also be a southern species of Triceratops.”
Island hopping by European ceratopsians: Attila Ősi, Richard J. Butler and David B. Weishampel describe the new Ajkaceratops kozmai, a relatively primitive neoceratopsian from the late Cretaceous (Santonian age) Hungary. The species most closely resembles ‘bagaceratopsids’ such as Bagaceratops and Magnirostris, previously known only from Late Cretaceous east Asia. Since Europe was then an archipelago in the Tethys Ocean, the species had to arrive where it was found by a series of “island hops.” The new species is described in the May 27, 2010 issue of Nature (subscription required). A release by the Research Information Center of the European Commission with a photo of the predentaries (the only material found were the premaxillae and rostral bones with fragments of the maxillae) is found here.
Sinoceratops: In the June 2010 issue of Chinese Science Bulletin (free access) Xu Xing and others describe the first ceratopsid outside of North America, a basal centrosaurine which they name Sinoceratops zhuchengensis. It bears similarities to both centrosaurines and chasmosaurine and was considerably larger than most other centrosaurines. It was found in the late Cretaceous Wangshi Group of Zhucheng, Shandong Province, China.
Albert Prieto-Márquez has two papers in the Zoological Journal of the Linnean Society. The first “Global phylogeny of Hadrosauridae (Dinosauria:Ornithopoda) using parsimony and Bayesian methods” (subscription required) redefines Hadrosauridae as the clade stemming from the most recent common ancestor of Hadrosaurus foulkii and Parasaurolophus walkeri. In “Global historical biogeography of hadrosaurid dinosaurs” (subscription required) he show that Hadrosauridae originated in North America and soon after dispersed to Asia no later than the Late Santonian. The split between saurolophines and lambeosaurines occurred in response to vicariance no later than the Late Santonian: the former clade originated in North America, whereas the latter did so in Asia. Saurolophine biogeographical history included a minimum of five dispersal events followed by vicariance.
Jeyawati rugoculus: A new species of basal hadrasauroid from the late Cretaceous western New Mexico is described in Douglas G. Wolfe and James I. Kirkland, “A new basal hadrosauroid (Dinosauria: Ornithopoda) from the Turonian of New Mexico,” Journal of Vertebrate Paleontology, 30(3): 799–812 (May 2010). A cladistic analysis indicates that Jeyawati was more basal thanShuangmiaosaurus, Telmatosaurus, and Bactrosaurus, but more derived than Eolambia, Probactrosaurus, and Protohadros. The University of Pennsylvania press release is found here.
5. Marine Reptiles
Thermal Regulation: In the June 11, 2010 issue of Science (subscription required) Aurélien Bernard and others report on a study of comparing the oxygen isotope compositions of the tooth phosphate of Mosasaurs, Ichtyosaurs and Pliosaurstheir to those of coexisting fish. They found that that the marine reptiles were able to maintain a constant and high body temperature, ranging from 35° ± 2°C to 39° ± 2°C, in oceanic environments ranging from tropical to cold temperate. The high body temperature is supposed to be owing to high metabolic rate required for fast swimming.
In a June 9, 2010 Biology Letters of the Royal Academy (free access) Tyler R. Lyson and others position turtles outside the Diapsids (the “Eureptiles”) in a sister clade to both squamate-tuatara clade and archosaur clade. The clade they fall in is called “Parareptiles” (Anapsids).
Xipantes: Joseph Hatcher, assistant curator at the Canadian Fossil Discovery Centre, announced the discovery last summer of the large Cretaceous predatory fish Xipantes outside of Morden, Manitoba. It appears to have been attacking the fin of a mosasaur.