A thermometer to measure dinosaur body temperature: scientists show direct evidence of warm-bloodedness in giant sauropods

It was speculated for a few decades now that dinosaurs were endotherm (warm-blooded) creatures with high metabolism rates, comparable to birds and mammals. But all the gathered evidences were so far indirect and quite speculative. These include the fact that dinosaurs also thrived in polar climates, or that the spacing in dinosaur tracks show that they were able to run pretty fast.

Now a team of scientists from Caltech led by John Eiler found a way to directly measure the body temperature of long extinct animals. The team measured the concentrations of the rare isotopes carbon 13 and oxygen 18 in the mineral bioapatite found in dinosaur teeth. These isotopes would bond (“clump”) together more often with lower temperature, so measuring the clumping of the two isotopes can precisely tell the temperature the teeth were at when the animal was alive.

The method was applied to well preserved teeth of big upper Jurassic sauropods (Brachiosaurus and Camarasaurus) and the results show that their body temperature ranged between 36 to 38 ºC, which are comparable to mammals but a bit lower than what would have been predicted if endothermy were solely due to the gigantic size of these dinosaurs. This is an indication that sauropods must have developed efficient physiological or behavioral ways to regulate their body temperature to prevent overheating.

The idea is now to use the isotopic thermometer to measure the body temperature of a larger set of extinct animals, including the smaller dinosaurs that can't rely on size for endothermy.

References:

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, advanced online publication.

Arcusaurus pereirabdalorum, a new sauropodomorph dinosaur from the Early Jurassic of South Africa

Sauropodomorphs form a group of bipedal and quadrupedal herbivorous dinosaurs that reached gigantic proportions in the Jurassic and Cretaceous periods with the likes of Diplodocus, Argentinosaurus and Brachiosaurus. The Upper Elliot Formation of Early Jurassic age in South Africa is home of at least three species of sauropodomorphs. The best known is Massospondylus carinatus, with several specimens uncovered. The two other species are Massospondylus kaarae and Aardonyx celestae, both named very recently, while the status of Gryponyx africanus is unclear, and of Ignavusaurus rachelis, dubious.

Yet, another species, Arcusaurus pereirabdalorum, the smallest of them all, has been added to the list. Scattered remains of at least two individuals, probably juveniles, have been unearthed.
The generic name, which means “Rainbow lizard”, honors the people of South Africa, the “rainbow nation”. Interestingly, Arcusaurus, albeit its Plateosaurus-like deep snout, in the analysis looks very basal and came as a sister taxon of the triassic sauropodomorphs such as Thecodontosaurus and Efraasia. If this were the case, Arcusaurus would be a relict of the primitive Triassic sauropodomorphs that somehow made it to the Jurassic.

Adam M. Yates, Matthew F. Bonnan, and Johann Neveling have described the species in the May 2011 issue of the Journal of Vertebrate Paleontology.

References:

Barrett, P. M. 2009. A new basal sauropodomorph dinosaur from the upper Elliot Formation (Lower Jurassic) of South Africa. Journal of Vertebrate Paleontology 29:1032–1045.

Yates, A. M., M. F. Bonnan, J. Neveling, A. Chinsamy, and M. G. Blackbeard. 2010. A new transitional sauropodomorph dinosaur from the Early Jurassic of South Africa and the evolution of sauropod feeding and quadrupedalism. Proceedings of the Royal Society B 277:787–794.

Yates, A.M.,  M. F. Bonnan, and J. Neveling. 2011. A New Basal Sauropodomorph Dinosaur from the Early Jurassic of South Africa. Journal of Vertebrate Paleontology, 31(3):610-625.

Haya griva, a new dinosaur from the Late Cretaceous of Mongolia

Haya griva was named after the Hindu deity Hayagriva, an avatar of Vishnu characterized by a horse head. This is in reference to the horse-like elongated skull of this little dinosaur, the remains of which were recovered from the Late Cretaceous Javkhlant Formation in Mongolia of probable Santonian age.

Haya griva is a basal ornithopod, one of the many small herbivorous bipedal bird-hipped dinosaurs that were a common occurrence in the Cretaceous period throughout the world. Some well-known basal ornithopods include Hypsilophodon from Europe and Leallynasaura of Australia (featured in the 5th episode, “Spirits of the Ice Forests” of the WWD franchise). However, basal ornithopods are relatively rare in Asia, represented only by the Early Cretaceous genera Jeholosaurus and Changchungsaurus from China. Haya griva is the first named of this kind from the Late Cretaceous Asia. It is unclear if this apparent low diversity is real or due to sampling bias.

Another interesting fact about Haya griva is that one of the specimen was found with a large gastrolith in its stomach (stone swallowed by herbivorous animals to help them with digestion), only the second recorded gastrolith found in ornithopods. Haya griva is known from remains of 8 individuals at different ontological stages, including several skulls and one well preserved partial articulated postcranial skeleton.

The new genus was described by Peter J. Makovicky, Brandon M. Kilbourne, Rudyard W. Sadleir, and Mark A. Norell in the May issue of the Journal of vertebrate Paleontology.

References:

Makovicky, P.J., B. M. Kilbourne, R. W. Sadleir, and M. A. Norell. 2011. Journal of Vertebrate Paleontology, 31(3):626-640.

Thalassiodracon hawkinsi

Apart from the name (which means “sea dragon”), there is a priori nothing particularly impressive about the plesiosaur Thalassiodracon. With a body length of less than 2 meters, it lies on the small side size wise in this highly successful group of mesozoic marine reptiles that roamed the seas for some 150 millions years between the Late Triassic and the end of the Cretaceous. What so special about Thalassiodracon is that it happens to be the plesiosaurs’ earliest representative known from complete remains, and thus possibly one of the most primitive. A thorough study of the remains of Thalassiodracon would therefore likely hint clues about the evolutionary history of the entire group. The monotypic genus Thalassiodracon (with a single species T. hawkinsi named after the discoverer of the first fossil of the animal, Thomas Hawkins) is known from several skeletons from the late Triassic- Early Jurassic boundary of Somerset, England.

Plesiosaurs were traditionally divided into two morphology-based clades: the long-necked small-headed Plesiosauroidea (the plesiosaurs sensu stricto) with forms such as Plesiosaurus and Elasmosaurus, and the short-necked large-headed Pliosauroidea (the pliosaurs), represented by such animals as Kronosaurus and Liopleurodon of WWD fame. Thalassiodracon has been previously classified either as a basal Plesiosauroidea (Druckenmiller and Russell (2008), Smith and Dyke (2008), Ketchum and Benson (2010)) or a basal Pliosauroidea (O’Keefe (2001)).

A reexamination of the skull of a specimen of Thalassiodracon using a modern 3D imaging technique known as X-ray microtomography, and conducted by Roger B. J. Benson, Karl T. Bates, Mark R. Johnson, and Philip J. Withers, has revealed previously overlooked details of the cranial anatomy that helped solving the exact systematic position of this animal. The study shows that Thalassiodracon, albeit its relatively small skull and long neck is a basal member of the Pliosaurid family (the most derived family within the Pliosauroidea), to which belong the huge cretaceous marine monsters, Liopleurodon and Kronosaurus. A consequence of this phylogenetic placement is that the other large-headed short-necked family, the Rhomaleosauridae (which was the subject of a previous post) would have developed their morphology quite independently from the Pliosauridae. Thalassiodracon also extends the Pliosaurid lineage to the Late Triassic (The title of earliest pliosaurid was previously held by Hauffiosaurus from the Early Jurassic). The study by Benson and co-workers has just been published in the May 2011 issue of the Journal of Vertebrate Paleontology.

References:

Benson, R.B. J. , K. T. Bates, M. R. Johnson, and P. J. Withers. 2011. Cranial Anatomy of Thalassiodracon hawkinsii (Reptilia, Plesiosauria) from the Early Jurassic of Somerset, United Kingdom. 31(3):562-574.

Druckenmiller, P. S., and A. P. Russell. 2008. A phylogeny of Plesiosauria (Sauropterygia) and its bearing on the systematic status of Leptocleidus Andrews, 1922. Zootaxa 1863:1–120.

Ketchum, H. F., and R. B. J. Benson. 2010. Global interrelationships of Plesiosauria (Reptilia, Sauropterygia) and the pivotal role of taxon sampling in determining the outcome of phylogenetic analyses. Biological Reviews 85:361–392.

O’Keefe, F. R. 2001. A cladistic analysis and taxonomic revision of the Plesiosauria (Reptilia: Sauropterygia). Acta Zoologica Fennica 213:1–63.

Smith, A. S., and G. J. Dyke. 2008. The skull of the giant predatory pliosaur Rhomaleosaurus cramptoni: implications for plesiosaur phylogenetics. Naturwissenschaften 95:975– 980.

Storrs, G. W., and M. A. Taylor. 1996. Cranial anatomy of a new plesiosaur genus from the lowermost Lias (Rhaetian/Hettangian) of Street, Somerset, England. Journal of Vertebrate Paleontology 16:403–420.