Bones discovered in a New Mexico quarry indicate that the first dinosaurs appeared in what is now South America, with some migrating northward into the US as the continent began to split apart.
The 213-million-year-old fossils of previously unknown carnivorous dinosaur Tawa hallae include several of the best preserved dinosaur skeletons from the Triassic Period.
Tawa was about six feet long - the size of a large dog, but with a much longer tail.
"If you have continents splitting apart, you get isolation," said lead author Sterling Nesbit of the University of Texas at Austin. "So when barriers develop, you would expect that multiple carnivorous dinosaurs in a region should represent a closely related endemic radiation. But that is what we don’t see in early dinosaur evolution."
Instead, the research team found three distinct carnivorous dinosaurs – including Tawa – in the fossil-rich beds at Ghost Ranch. "When we analyzed the evolutionary relationships of these dinosaurs, we discovered that they were only distantly related, and that each species had close relatives in South America," said Randall Irmis of the University of Utah.
"This implies that each carnivorous dinosaur species descended from a separate lineage before arriving in [the part of Pangea that is now] North America, instead of all evolving from a local ancestor."
“The discovery of multiple dinosaur species in one place that emigrated from elsewhere got us wondering whether other Late Triassic reptiles show similar patterns” said Irmis. “It turns out a variety of other reptile groups made multiple trips from the northern and southern continents [then parts of Pangea] and back again during the Late Triassic, including other dinosaurs.”
Details appear in Science.