New, Rare Fossil Forces Scientists to Rethink Early Dinosaur Evolution

Friday, December 11 3:38 pm

Illustration by Jorge Gonzalez

A new bipedal carnivore is clearing up questions about the early evolution of theropods, the group of dinosaurs that includes its recent relatives T. rex and birds. Tawa hallae, uncovered in New Mexican sediments from the Upper Triassic, has features that link it more closely with South American theropods than with local dinosaurs.  This means that while the supercontinent Pangaea was breaking apart, some early dinosaur groups from what is now South America moved north in at least several waves to become part of the local fauna.

“We would expect that all of the theropod dinosaurs found in the quarry were related to each other. But they are not,” says Sterling Nesbitt, who excavated at Ghost Ranch while a graduate student at the Museum and is now at the University of Texas at Austin. Part of this excavation was featured in the IMAX film Dinosaurs Alive.

“Finding dinosaurs this old and this complete in an area that has been prospected for over a hundred years is surprising,” says Museum Curator Mark Norell, a co-author of the paper published in Science. “T. hallae allows us to link the South American and North American theropod faunas for the first time.” Museum Research Associate Alan Turner, also at Stony Brook University, agrees. “We propose that early dinosaurs from South American got into North America at least three separate times.”

Read more stories about T. hallae from, among others, The New York Times, Scientific American, USA Today, The Independent, and the Associated Press.