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Cover of the current issue of Science magazine
The story as it is being rewritten is that the first dinosaurs on Earth were relatively pint-sized animals and spent 15 million to 20 million years low in the minor leagues of in life's pecking order before they became the world's dominant animal life form. That idea runs counter to the prevailing theory that after dinosaurs first evolved, their numbers and their relative size exploded, quickly making them the dominant animal life form on Earth.
The newly discovered fossil that is shaking up old theories of a rapid rise of dinosaur dominance is not a dinosaur but a very close cousin, given the name by its discoverers as Dromomeron romeri (dro-MO-mer-on RO-mer-eye). It belonged to an archaic group of animals called "basal dinosauromorphs," or pre-dinosaurs.
Dinosauromorphs previously had been thought to have gone extinct as the first dinosaurs began to appear on Earth roughly 228 million years ago.
In fact, the discovery last year Dromomeron in the Ghost Ranch hills — first made famous in paintings by 20th Century American master Georgia O'Keeffe — shows that the 18-inch-high creatures lived and died alongside early dinosaurs not much bigger than it was.
"We can no longer say pre-dinosaurs went extinct, making room for the dinosaurs," said Nathan Smith, 27, one of Dromomeron's discoverers and a University of Chicago Ph.D. candidate and Field Museum research associate.
The discovery captured the cover story of Friday's edition of the research journal Science, an honor underscoring the importance of the find, marking the first time in history that dinosauromorph fossils have been found alongside true dinosaur fossils, proving they lived in the same time and place. Smith was one of four graduate students who are largely responsible for the discovery, having planned amongst themselves, recruiting just one full Ph.D. paleontologist and two others to assist them.
"This discovery is a very significant piece of work," said an admiring Nick Fraser, curator of vertebrate paleontology at the Virginia Museum of Natural History. Fraser, an authority on pre-dinosaur life, was not part of the discovery team.
"I think it answers some questions paleontologists have been seeking for a long time," Fraser said. "It tells us that the appearance of dinosaur life in the late Triassic period (208 million to 220 million years ago) was not, as we previously believed, a sudden, abrupt event."
The six-week Ghost Ranch dig largely is the work of four graduate students still working on their Ph.D.s: Smith, Randall Irmis of the University of California at Berkeley and Sterling Nesbitt and Alan Turner of Columbia University. To help them, they brought in the other three co-authors of the Science article, Ghost Ranch museum curator, Alex Downs, Daniel Woody from the University of Colorado, and Nesbitt's Berkeley doctoral advisor, the lone PhD, Kevin Padian.
"We're all good friends who have worked on projects together before," said Nesbitt. He and Irmis ran into a Ghost Ranch museum curator, Alex Downs, at a national paleontological convention, and when Downs showed them some strange fossil bones he had recently excavated.
"It is very hard to get a paper into Science, let alone the cover story," said Sterling Nesbitt of Columbia University, a graduate student on the dig. "We just happened to stumble on something very interesting in New Mexico."
Finding a basal dinosauromorph (pre-dinosaur) like Dromomeron living at the same time as true dinosaurs triggered a re-assessment of many late Triassic fossils sitting for years in various museum collections. Those searches are beginning to show previously misidentified and previously unexamined dinosauromorph fossils collected from many other late Cretaceous fossil beds around the world.
That data, combined with data from the Ghost Ranch quarry finds, underscores how long it took for dinosaurs to take over the world.
"Future theories on dinosaur origins will have to address the fact that early dinosaurs had co-existed with early cousins for a long period of time," said Smith.
"These things aren't necessarily direct ancestors to dinosaurs. They are side branches of an ancestor. But finding them gives us a clearer idea of how the earliest dinosaurs evolved."
Dromomeron, said Smith, were relatively fragile creatures about 18 inches high at the shoulder. The fossils recovered so far are incomplete and without an intact skull, so the discoverers don't yet know if they were meat eaters or herbivores. They also lack the forelimbs and tail, but it is "likely" that Dromomeron was a theropod, bi-pedal, a runner like meat-eating dinosaurs.
"I would say . . . is like what the early hominid Lucy (Australopithicus afarensis) is to modern humans — Homo sapiens," said Irmis, the difference being that Lucy was extinct perhaps three million years before modern humans appeared.
The Dromomeron fossils were recovered from a Ghost Ranch site called the Hayden Quarry. Among the true dinosaurs found with the Dromomeron fossils were Chindesaurus bryansmalli and a Coelophysoid, the latter one of the earliest known dinosaurs, dating back 228 million years.
Like Dromomeron, the early dinosaurs with which they shared territory were relatively pint-sized, said Smith, and likely had to run for their lives from large, powerful crocodilian predators that ruled the roost in those days, giant predators that reached 30 feet in length.
"At that time, even the largest dinosaurs aren't more than four or five feet high," Smith said.
Dromomeron and most of the other non-dinosaur species of that time did eventually go extinct rather suddenly at the end of the Triassic period and the beginning of the Jurassic, when dinosaurs truly took over the world, growing into the immense beasts so popular in modern imagination.
The Ghost Ranch has been of interest to paleontologists since American Museum paleontologist Edwin H. Colbert found a "graveyard" of Coelophysis bones in a ranch quarry in 1947.
He brought so much fossil-bearing rock back to the New York museum that some it had never been looked until Nesbitt began looking through it in 2005. Amongst the rocks he found an ancient crocodilian species new to science, which he named Effigia okeeffeae, in honor of Georgia O'Keefe, who loved to paint landscapes of the red cliffs in which the fossils were found.
(c) 2007, Chicago Tribune.
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