Telltale imprints of air sacs in Tawa
fossils suggest that the new dinosaur species' neck and braincase had those features—just like modern birds. Birds are thought to have descended from theropod dinosaurs--two-legged carnivores that included Tawa
(artist's conception above) and T. rex.
"It's the most primitive animal that we've seen [air sacs] in," said paleontologist Sterling Nesbitt of the University of Texas at Austin, co-author of the December 10, 2009, study.
In addition to its typically theropod traits, Tawa
shares characteristics with the most primitive carnivorous dinosaurs. "The key thing is that it links this group of really early dinosaurs very nicely to later theropods," said paleontologist Hans-Dieter Sues, of the U.S. National Museum of Natural History, who was not part of the new study.
The mix of traits suggest that Tawa
descended from early species found in what is now South America, such as Herrerasaurus.
This would support the much disputed claim that Herrerasaurus
is in fact a theropod—and suggests that all theropods came from South America.
Image courtesy Sterling Nesbitt