Did the first dinosaurs wander across continents or stay put where they first evolved? The first dinosaurs evolved 230 million years ago when the continents were assembled into one landmass called Pangea.

The question of early dinosaur movements remained unclear until the discovery of some exciting new fossils.

Fossil bones of Tawa, named after the Hopi word for the Puebloan sun god, were recovered from a dig site in northern New Mexico known as Hayden Quarry. The quarry is located on Ghost Ranch, where late painter Georgia O'Keefe once lived.

Fossil bones of several individuals were recovered, but the type specimen is a nearly complete skeleton of a juvenile that stood about 28 inches (70 centimeters) tall at the hips and was approximately 6 feet (about 2 meters) long, from snout to tail. Its body was about the size of a large dog, but with a much longer tail.

Based on an analysis of the relationships among Tawa and other early dinosaurs, the researchers hypothesize that dinosaurs originated in a part of Pangea that is now South America, diverging into theropods (like Tyrannosaurus rex), sauropodomorphs (like Apatosaurus) and ornithischians (like Triceratops); and then dispersed more than 220 million years ago across parts of Pangea that later became separate continents.

"This new dinosaur Tawa hallae changes our understanding of the relationships of early dinosaurs, and provides fantastic insight into the evolution of the skeleton of the first carnivorous dinosaurs" said Randall Irmis of the Utah Museum of Natural History and University of Utah, a co-author of the study.

In addition to Irmis, authors of the study included lead author Sterling Nesbit of the University of Texas at Austin; Nathan Smith of the University of Chicago and the Field Museum of Natural History; Alan Turner of Stony Brook University; Alex Downs of the Ruth Hall Museum of Paleontology in Abiquiu, N.M.; and Mark Norell of the American Museum of Natural History.

"If you have continents splitting apart, you get isolation," said Nesbitt. "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."

"This is a fleshed-out reconstruction of the new Triassic carnivorous dinosaur Tawa hallae. (Credit: Jorge Gonzalez.)"

Source: University of Utah