The field crew that excavated Tawa hallae in 2006: Kevin Padian, Sterling Nesbitt, Alan Turner, Nate Smith, Randy Irmis, Amy Balanoff, and Gabe Bever. Photo: Nathan Smith, Field Museum of Natural History
Last week, two University of California Museum of Paleontology alums, Sterling Nesbitt and Randall Irmis, described a new species of dinosaur in the journal Science. The new species, Tawa hallae, sheds light on early dinosaur evolution — and the importance of the UCMP's collections.
Tawa's bones were first found by hikers in Ghost Ranch, New Mexico, in 2004. Around that time, Sterling and Randy were doing fieldwork at the nearby Petrified Forest National Park in northern Arizona, excavating fossils from rock layers from the Late Triassic — the same rock formation where the new fossils were found. That fall, park paleontologist Alex Downs approached Sterling and Randy at a scientific meeting and asked them if they'd be interested in excavating and describing what appeared to be a novel species. At that time, Randy was a graduate student at Berkeley, and Sterling had finished his undergrad at Berkeley and begun graduate school at Columbia. They decided to collaborate with Alex to describe the specimens and made plans to start fieldwork during the summer of 2006.
"Three weeks before our first major expedition," says Sterling, "the provost at the American Museum of Natural History called and asked if I'd like to be accompanied by an NSF-funded IMAX movie crew." They wanted to film the excavation of the fossils for a movie, Dinosaurs Alive!. Sterling was a little worried that the filming would interfere with his fieldwork, but he agreed. The film crew followed Sterling, Randy, and the rest of the team for a week and a half. Sterling needn't have worried about having enough time to do his research — there was plenty of down time. "IMAX film is expensive," he says, and the film crew spent a lot of time setting up each shot. During some of this down time, Sterling was excavating the area where the hikers had found the fossils. "That's when I hit the ankle bone of the articulated leg of what became the holotype."
Other early dinosaur fossils are not as complete or as well preserved as those of Tawa hallae. Sterling, Randy, and the team found two nearly complete skeletons, as well as bones from several other individuals. Some of the bones are so well preserved that you can see very fine details, like the places where the muscles once attached. The neck vertebrae and the bones of the braincase have small depressions with raised rims — suggesting that there were air sacs adjacent to these bones. The air sacs filled up the depressions. Modern birds have air sacs attached to their bones, which they use for respiration. As Sterling and Randy write in their paper (co-authored by Nate Smith, Alan Turner, Alex Downs, and Mark Norell), we can't know if Tawa's air sacs served a similar function. However, we do know that Tawa is the earliest dinosaur with a pneumatic skeleton.
Tawa is particularly important because it fills a gap between early carnivorous dinosaurs, found in South America (where dinosaurs are thought to have originated), and later carnivorous dinosaurs found throughout the world. Randy, Sterling, Nate, and Alan figured out where Tawa fit by comparing it to other specimens, many of which were in the UCMP's collection. "The UCMP collection was instrumental in helping us understand what was at Ghost Ranch," says Randy. Sterling also points out the importance of the museum's collections, both in this study and in his paleontological education. "I came to Berkeley for the paleo," he says. As an undergrad, "I was in the collections a couple times a week, learning anatomy, learning what the fossil record is really like."
"This project really had its genesis when we were all graduate students," says Randy. "This study speaks to what a fantastic program we have at Berkeley, that we can have such fantastic research coming out of a graduate student-led project."
Randy is now an Assistant Professor at the University of Utah, and Sterling is a post-doc at the University of Texas Austin. Both intend to continue working at Ghost Ranch — "I plan to go back for many years to come," says Randy. "It's an amazing site." And, they plan to continue working in the UCMP collections – they'll be back in January. Check the UCMP blog for an update!
Sterling and Randy are currently collaborating with UCMP graduate student Sarah Werning, Kevin Padian, Nate Smith, and Alan Turner, to examine the growth and bone histology of early dinosaurs (including Tawa) and their relatives from Ghost Ranch. Stay tuned for an upcoming blog about dinosaur bone histology in the New Year.
Sterling and Randy's work was funded by a National Geographic grant to UCMP Faculty Curator Kevin Padian and by grants from Integrative Biology, UCMP’s Welles Fund, and the UCMP Graduate Student Research Award. Learn how you can support graduate student research at the UCMP.
There has been some great news coverage about Tawa hallae. To learn more, check the National Science Foundation's Special Report: Tawa hallae – it includes an audio slide show, a press conference, and lots of photos. There is an interview with Sterling in this Science magazine podcast, and an interview with Randy in this blog from the Utah Museum of Natural History. Also check out this article from the San Francisco Chronicle.