Based on Tawa
's links to earlier dinosaurs, the new study suggests that the first dinosaurs evolved in what is now South America. There, they quickly differentiated into
ornithischians (represented above by Triceratops
), sauropodomorphs (Apatasaurus, also seen above)
and theropods before migrating out in successive waves more than 220 million years ago.
s fossils were found alongside those of two other known theropod species that inhabited New Mexico at roughly the same time. The three species, though, were only very distantly related.
Instead, "each of the lineages has its closest relatives coming from South America," said Nesbitt, co-author of the December 2009 study—key evidence that theropods diversified in South America and then migrated out.
The natural history museum's Sues added, "When you think about it, it's not all that surprising. You had a gigantic supercontinent, Pangaea, and there weren't really any major obstacles to [dinosaurs] disseminating themselves around the world."
Image courtesy Zina Deretsky, National Science Foundation