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.

Shastasaurus liangae

Fig 1.- Shastasaurus sikanniensis is the largest known ichthyosaur with an estimated length of some 20 meters.

A new paper published in PLoS by P. Martin Sander and co-workers, just made the  ichthyosaurs an even more interesting and intriguing prehistoric critters. Ichthyosaurs are a group of extinct marine reptiles with streamline fish-like bodies that roamed the oceans from the Early Triassic to the Early Cretaceous periods.

A well-preserved specimen of the species previously described as Guanlingsaurus liangae from the Late Triassic of China shed light to a peculiar group of medium to large size ichthyosaurs called Shastasauridae. 

 
Compared to the standard body shape of ichthyosaurs (think Ophthalmosaurus of WWD fame), the new specimen is characterized by a diminutive head, with an entirely toothless and greatly reduced snout. The description of this new specimen led to a general revision of the genus Shastasaurus, based on S. pacificus from the Late Triassic of California, to include not only G. liangae (re-baptized S. liangae) but also the largest known ichthyosaur, S. sikanniensis (formerly Shonisaurus sikanniensis) from the Late Triassic of British Columbia.

Fig 2.- The medium size Shastasaurus liangae may have hunted bioluminescent squids in the deep sea using the technique of suction feeding, similarly to some modern Odontocete cetaceans.
 

The peculiar skull anatomy of S. liangae lead the authors of the study to hypothesize that the three species of Shastasaurus were specialized suction feeder that preyed on squids and fish. The relative rarity of Shastasaurus fossils as well as their association with fully pelagic invertebrates, indicates a pelagic lifestyle. An interesting idea suggested by the authors is that their relatively large eyes would have been perfect to hunt bioluminescent cephalopods in the deep sea.

References:

Nicholls EM, Manabe M (2004) Giant ichthyosaurs of the Triassic-A new species of Shonisaurus from the Pardonet Formation (Norian, Late Triassic) of British Columbia. Journal of Vertebrate Paleontology 24: 838–849.

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.

Yin G, Zhou X, Cao Z, Yu Y, Luo Y (2000) A preliminary study on the early Late Triassic reptiles from Guanling, Guizhou, China (in Chinese). Geology- Geochemistry 28: 1–23.

Cryptolacerta hassiaca

Fig 1.- Iberian worm lizards (Blanus cinereus)  by Richard Avery, from Wikipedia.

The worm lizards form a peculiar group of burrowing and legless reptiles that have a superficial resemblance to earthworms. These odd critters were traditionally placed in their own suborder, the Amphisbaenians, alongside the other two groups of Squamates, the snakes (Serpentes) and the lizards (Lacertilia). Molecular data (Townsend et al., 2004; Vidal et al., 2005) however have shown that they are in fact closely related to a particular family of old-world lizards, the Lacertidae (with representatives such as the European Green Lizard, Lacerta viridis and the common Wall Lizard, Podarcis muralis).

The fossil record of amphisbaenians is slim and their evolutionary history clouded with mystery. Previously, a paper published in Nature (Wu et al., 1993) described the taxon Sineoamphisbaena hexatabularis from the Upper Cretaceous of Inner Mongolia, as a stem amphisbaenian, but this conclusion turned out to be quite erroneous (Kearny, 2003).

Fig 2.- My reconstruction of Cryptolacerta hassiaca.

Now, a new Nature paper, written by Johannes Müller and co-workers present Cryptolacerta hassiaca from the Eocene Messel pit in Germany as a new ancestral amphisbaenian (Müller et al., 2011). Cryptolacerta is known from a single specimen consisting of a nearly complete articulated skeleton (missing only the end of the tail). It was small, very lizard-like in appearance but with relatively tiny limbs and a thickened skull. The structure of the skull of Cryptolacerta moreover supports the Lacertidae-Amphisbaenian molecular connection and indicates that skull reinforcement evolved before snake-like body in this particular group of headfirst burrowing reptiles.


References:

Kearny, M. 2003. The phylogenetic position of Sineoamphisbaena hexatabularis reexamined. J. Vert. Paleont. 23, 394-403.

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.

Townsend, T.M., Larson, A., Louis, E. & Macey, J.R. 2004. Molecular phylogenetics of Squamata: the position of snakes, amphisbaenians, and dibamids, and the root of the squamate tree. Syst. Biol. 53, 735-757.

Vidal, N. & Hedges, S.B. 2005. The phylogeny of squamate reptiles (lizards, and amphisbaenians) inferred from nine protein-coding genes. C. R. Biol. 328, 1000-1008.

Wu, X.-C. et al. 1993. Oldest known amphisbaenian from the Upper cretaceous of Chinese Inner Mongolia. Nature, 57-59.

Rhomaleosaurus cramptoni

A friend of mine has asked me for a reconstruction of Rhomaleosaurus cramptoni to illustrate a book he is writing on prehistoric animals from England. R. cramptoni is one of these marine reptiles belonging to a group called plesiosaurs. It lived during the Early Jurassic in the shallow sea that was covering most of Western Europe at that time.


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.

Rhomaleosaurus and related taxa (the rhomaleosaurid family) were kind of oddballs among the plesiosaurs, as they combine features of the two morphotypes, i.e. they have relatively long necks and relatively large heads. A comprehensive phylogenetic analysis by Adam S.Smith and Gareth J. Dyke (2008) placed them firmly within the pliosaurs as sister group to the Leptocleidoidea and the Pliosauridae (pliosaur sensu stricto).


Rhomaelosaurus cramptoni, originally described in 1863 as a species of Plesiosaurus, was medium-size, measuring something like 7 meters in length. It is known from a complete skeleton of an adult specimen, which was unearthed in 1848 near Whitby, Yorkshire. Besides R. cramptoni, two other species are still tentatively recognized within the genus, R. zetlandicus and R. thorntoni, both from the Early Jurassic of England. The species R. propinquus is considered a junior synonym of R. cramptoni. “R. victor”  (Early Jurassic of Germany) was transferred in 2010  to  the new genus Meyerasaurus and “R. megacephalus” (Lower Jurassic, England) was found to be more closely related to Eurycleidus and Macroplata than to the other species of Rhomaleosaurus and will most likely be redescribed as a new genus in the near future.  Rhomaelosaurids were a remarkably shorted lived family, being present only in the Early and perhaps in the Middle Jurassic.

Proportions for my reconstruction is based on the skeletal published by A. S. Smith (2008).



References:

Carte A, Bailey WH. 1863. “Description of a new species of Plesiosaurus, from the Lias, near Whitby, Yorkshire”. J R Dublin Soc 4:160–170.

O’Keefe FR. 2001. “A cladistic analysis and taxonomic revision of the Plesiosauria (Reptilia: Sauropterygia)”. Acta Zool Fenn 213: 1–63.

Smith AS, Dyke GJ. 2008. “The skull of the giant predatory pliosaur Rhomaleosaurus cramptoni: implications for plesiosaur phylogenetics” Naturwissenschaften. 95, pp 975-980.

Smith AS, Vincent P. 2010. "A new genus of pliosaur (Reptilia: Sauropterygia) from the Lower Jurassic of Holzmaden, Germany". Palaeontology 53 (5): 1049–1063.

Taylor MA. 1992. Functional anatomy of the head of the large aquatic predator Rhomaleosaurus zetlandicus (Plesiosauria: Reptilia) from the Toarcian (Lower Jurassic) of Yorkshire, England. Philos Trans R Soc Lond Ser B 335:247–280.