Careful dating of new dinosaur fossils and volcanic ash around them by researchers from UC Davis and UC Berkeley casts doubt on the idea that dinosaurs appeared and opportunistically replaced other animals. Instead -- at least in one South American valley -- they seem to have existed side by side and gone through similar periods of extinction.
Geologists from Argentina and the United States announced earlier this month the discovery of a new dinosaur that roamed what is now South America 230 million years ago, at the beginning of the age of the dinosaurs. The newly discovered Eodramaeus, or "dawn runner," was a predatory dinosaur that walked (or ran) on two legs and weighed 10 to 15 pounds. The new fossil was described in a paper by Ricardo Martinez of the Universidad Nacional de San Juan, Argentina, and colleagues in the journal Science Jan. 14.
The fossils come from a valley in the foothills of the Andes in northwestern Argentina. More than 200 million years ago, it was a rift valley on the western edge of the supercontinent Pangaea, surrounded by volcanoes. It's one of the few places in the world where a piece of tectonically active continental margin has been preserved, said Isabel Montañez, a UC Davis geology professor and a co-author of the Science paper.
Montañez, with Brian Currie from Miami University, Ohio, and Paul Renne at UC Berkeley's Geochronology Center, have conducted earlier studies of the ancient soils from the valley, dating layers of ash and researching how the climate changed. Those climate studies have been published previously.
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