( estrial crocodiles and mammals. Exc...)Newly discovered birdlike dinosaur is oldest raptor ever found in South America

"Except for its faunal composition, La Buitrera resembles the Gobi desert in its abundance of fossils and their exquisite state of preservation," Apestegua adds.

A cast of the unusual dinosaur is on public display on the upper floor of The Field Museum in the MacDonald's Preparation Lab. It will be part of Evolving Planet, a permanent exhibition that opens March 10, 2006.

Drifting continents

About 200 million years ago, all of the Earth's land was amassed in one supercontinent called Pangaea. During the Middle and Late Jurassic, Pangaea split into two landmasses. Laurasia, composed of North America, Asia and Europe, drifted to the north; Gondwana, composed of the southern hemisphere continents plus India, drifted to the south.

Until recently, dromaeosaurs (swift-running, bi-pedal, birdlike dinosaurs) have been found only in Cretaceous rocks of Asia and North America, northern continents that were part of Laurasia. (Laurasian dromaeosaurs include the famous Velociraptor from the Gobi Desert, the large Utahraptor from the American West, and the recently discovered Microraptor and Sinornithosaurus from China, both of which preserve amazing traces of bird-like plumage.) This distribution led scientists to believe that dromaeosaurs originated in Laurasia after it drifted apart from Gondwana.

In the last few years, however, a handful of specimens of possible dromaeosaurs or early birds have been discovered on southern continents. Nevertheless, their incomplete preservation led to some ambiguity and debate regarding their identities.

The new discovery provides definitive evidence that dromaeosaurs also lived in South America, which was part of Gondwana. As a result, dromaeosaurs must have originated when all of the continents were still assembled in a single landmass during the Jurassic as far back as 180 million years ago--much earlier than previously thought.

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Source:Field Museum