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Wednesday, July 25, 2007

Dinosaurs coexisted with their ancestorsStory Highlights

Dinosaurs shared the Earth for millions of years with the species that were their ancestors, a new study concludes
Dinosaurs arose in the Late Triassic, between 235 million and 200 million years ago, and came to dominate the planet in the Jurassic, 200 million to 120 million years ago.
Scientists had thought the dinosaurs rapidly replaced their ancestor species. Indeed, until 2003, when a creature called Silesaurus was discovered in Poland, no dinosaur precursors had been found from the Late Triassic.
Now, researchers report in the journal Science they have evidence from northern New Mexico that dinosaurs and their precursor species coexisted for tens of millions of years.
Matthew T. Carrano, curator of dinosauria at the Smithsonian's National Museum of Natural History, said there has been a long-standing debate over whether dinosaurs replaced earlier species gradually or suddenly.
"What they have is a snapshot of the transition, and it's clear there is a persistent environment with dinosaurs and these other older animals. So, at least in this place in the southwestern U.S., it was not abrupt," said Carrano, who was not part of the research team.
"Finding dinosaur precursors ... together with dinosaurs tells us something about the pace of changeover. If there was any competition between the precursors and dinosaurs, then it was a very prolonged competition," Randall Irmis, a graduate student at the University of California, Berkeley and co-author of the report, said in a statement.
The team reported finding 1,300 fossil specimens, including several complete bones, at Hayden Quarry at Ghost Ranch, an area made famous through the paintings of Georgia O'Keeffe.
There were no complete skeletons, and researchers are continuing to work at the site.
Their finds included bones from both early dinosaurs and dinosaur precursors as well as remains of crocodile ancestors, fish and amphibians, all dating between 220 million and 210 million years ago.
Included were leg bones of the carnivorous Chindesaurus bryansmalli, a close relative of the Coelophysis, a well-known Triassic dinosaur. They said both walked on two legs, reminiscent of the much later Velociraptor depicted in the film "Jurassic Park."
They also found remains of a Dromomeron romeri, a relative of the 235 million-year-old Argentinian middle Triassic precursor called Lagerpeton. Dromomeron was between three and five feet long, the authors concluded.
Another discovery was an unnamed, four-footed beaked grazer about three times the size of Dromomeron, they said.


Dinosaurs and their precursor species coexisted for tens of millions of years
Scientists had thought dinosaurs rapidly replaced their ancestor species
Dinosaurs arose between 235 million and 200 million years ago
They dominated the planet 200 million to 120 million years ago

The research was funded by>the National Geographic Society, the Theodore Roosevelt Memorial Fund and the Jurassic Foundation


From Wikipedia, the free encyclopedia

The Jurassic Period is a major unit of the geologic timescale that extends from about 199.6 ± 0.6 Ma (million years ago) to 145.4 ± 4.0 Ma, the end of the Triassic to the beginning of the Cretaceous. As with other geologic periods, the rock beds that define the start and end of the period are well identified but the exact dates are uncertain by 5 - 10 million years. The Jurassic constitutes the middle period of the Mesozoic era, also known as the "Age of Dinosaurs". The start of the period is marked by the major Triassic-Jurassic extinction event.
The Jurassic was named by
Alexandre Brogniart for the extensive marine limestone exposures of the Jura Mountains, in the region where Germany, France and Switzerland meet.
Mesozoic era

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