Tyrannosaurus rex from the American Museum of Natural History.
Today is the fourth and final day of the SVP meeting.
After lots of mammal talks, I decided to watch some of the dinosaur talks today for a change of pace. Takanobu Tsuihiji of Ohio University and several colleagues presented on a skeleton of a juvenile Tarbosaurus bataar from Mongolia. Tarbosaurus is a close relative of the North American Tyrannosaurus (in fact some people consider them to be the same genus.) The new skeleton was from a very young animal, and demonstrates how tyrannosaur body proportions change as they grow (what’s known as “allometric growth”.) The new specimen may also have an effect on the interpretation of Nanotyrannus lancensis, a small tyrannosaur from North America. There has been a long-term debate over whether Nanotyrannus actually represents a different species, or is just a juvenile Tyrannosaurus. Comparison to the growth patterns in Tarbosaurus suggests that Nanotyrannus may actually be a separate species from Tyrannosaurus.
After the morning break I briefly went back to the mammal session to hear Justin Yeakel, Paul Koch, and Nathaniel Dominy (all from UC-Santa Cruz) speak on feeding patterns in modern African carnivores. Their technique is a good example of the subtle approaches paleontologists sometimes have to resort to in order to determine the lifestyles of extinct organisms.
Different types of plants will tend to vary in the amounts of different elemental isotopes they contain. For example, grasses tend to have slightly higher concentrations of Carbon-13 (C13) than trees do. If an herbivore is a grazer that eats grass, it will have slightly higher amounts of C13 in its bones than a browser that eats leaves. Likewise, a predator that eats grazing animals will have more C13 in its bones than a predator that eats browsers.
The UC-Santa Cruz study compared various isotope ratios in lions, hyaenas, and African wild dogs and found that there are measurable differences between them. Lions, for example, mostly eat grazers while hyaenas were much more diverse in their feeding, eating all kinds of different animals. When applied to Pleistocene animals, they found that the big cats Homotherium and Smilodon usually showed isotope ratios similar to modern lions, while the dire wolf (Canis dirus) showed a more hyaena-like pattern.
Just before lunch Matthew Lamanna from the Carnegie Museum and colleagues presented on new therizinosaur material from China. The therizinosaurs are a fascinating group of theropod dinosaurs that were long a mystery to paleontologists. They were originally only known from their large forelimbs and huge claws, and there used to be some question as to whether or not they were even dinosaurs. In recent years better material has been discovered in Asia and in North America that showed that they were in fact large dinosaurs. But they unexpectedly turned out to be related to the much smaller Oviraptor and its relatives, making the giant therizinosaurs close relatives of the birds. It even turns out that at least one therizinosaur had primitive feathers.