New Fossil Find in New Mexico Named After Artist Georgia O'Keeffe
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Sketch courtesy of Sterling Nesbitt. |
Two leading paleontologists from the American Museum of Natural History and who are affiliated with Columbia University have discovered the fossil of a toothless crocodile relative that looks like a six-foot-long, two-legged dinosaur, but is actually a distant cousin of today's alligators and crocodiles.
The new finding is described in the journal Proceedings of the Royal Society B by Sterling J. Nesbitt, a graduate student enrolled at Columbia University who studies at the American Museum of Natural History and also is affiliated with the Columbia's Lamont-Doherty Earth Observatory, and Mark A. Norell, Curator in the Museum's Division of Paleontology, who is also an adjunct professor of earth and environmental sciences at Columbia.
They have have named the fossil Effigia okeeffeae〈奧氏靈鱷，暫譯〉.
Effigia means "ghost," referring to the decades that the fossil remained hidden from science. The species name, okeeffeae, honors the artist Georgia O'Keeffe, who lived near the site in northern New Mexico where the fossil was found.
Scientists say Effigia is a striking example of "convergence,"〈趨同演化〉 when two lineages evolve the same body plan.
"It is astounding to see so many advanced dinosaur features in an animal so closely related to modern crocodiles, Norell said. Obviously, this group of crocodiles and dinosaurs must have had similar habitats and probably fed in the same way, accounting for the similarities of the limbs and skull."
Other examples of convergence include marsupial mammals related to kangaroos and opossums that evolved into creatures resembling lions and wolves.
The features of Effigia okeeffeae also were unexpected. "It has large eyes, a beak, it walked on two feet and had small hands," Nesbitt said.
本文出自：COLUMBIA NEWS
Ancient crocodile ancestor stood on two legs
New York Times
Posted: Jan. 29, 2006
New York - Scientists at the American Museum of Natural History have discovered a fossil in New Mexico that they believe came from a 6-foot-long, two-legged dinosaur along the lines of a tyrannosaur or a velociraptor. But it is actually an ancient relative of today's alligators and crocodiles.
 Alligators and Crocodiles |
This artist's rendering of Effigia okeeffeae shows what scientists believe to be an ancient relative of today's alligators and crocodiles. They think a fossil found in New Mexico came from a reptile that actually looks more like a 6-foot-long, two-legged dinosaur along the lines of a tyrannosaur or a velociraptor. |
The discovery is a striking example of how different animals can evolve the same kind of body over and over again.
For almost 60 years, the 210-million-year-old fossil has been hiding in plain sight. It was lodged in a slab of rock dug up in 1947 in New Mexico by a team led by Edward Colbert, a paleontologist at the natural history museum.
The site is known for hundreds of fossils that kept Colbert busy for decades, and he left several slabs sitting unopened at the museum.
"We always collect more than we can study," said Mark Norell, the museum's current chairman of paleontology.
Last year, a graduate student, Sterling Nesbitt, began to open the slabs. The bones he found did not belong to a dinosaur; they showed distinctive features found only in crocodilians. That alone made the discovery exciting, because it represented one of the oldest crocodile-like fossils ever discovered. But it eventually became clear that the fossil was unlike any crocodile-like species ever found.
The reptile stood on its hind legs, keeping its tail erect. Its arms were tiny, its neck long, its eyes huge. It was toothless, and its jaws were covered in hard tissue, like a bird's beak. Although the fossil was more closely related to alligators and crocodiles, it resembled a group of dinosaurs that evolved 80 million years later.
Nesbitt and Norell named the fossil Effigia okeeffeae. It is an example of what biologists call convergence, when two lineages evolve the same body plan. Other examples of convergence include marsupial mammals related to kangaroos and opossums that evolved into creatures resembling lions and wolves.
Nesbitt and Norell have re-examined isolated bones claimed to be from dinosaurs of the same age and have concluded that they were actually relatives of crocodiles.
This diversity began to disappear about 200 million years ago.
The extinction of Effigia and other crocodile relatives may have allowed dinosaurs to take over their ecological roles.
本文出自：JS Online
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