Study: Dinosaurs, ancestors coexisted

[Manetho]

Study: Dinosaurs, ancestors coexisted
By RANDOLPH E. SCHMID, AP Science Writer
Thu Jul 19, 10:15 PM ET
 



This handout photo provided by the journal Science shows excavating to remove the rock that overlies the fossils ? this rock is called the 'overburden, ' above the Hayden Quarry in New Mexico, (AP Photo/Science)


WASHINGTON - 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.

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

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On the Net:

Science: http://www.sciencemag.org

[Manetho]

Ascent of dinosaurs more gradual than once thought
By Will Dunham
Thu Jul 19, 5:36 PM ET

 

A woman looks at models and fossils of a Gigantoraptor during a news conference in Beijing June 13, 2007. The ascent of the dinosaurs to the throne of the animal kingdom may have been more gradual than previously believed, scientists said on Thursday. (Claro Cortes IV/Reuters)


WASHINGTON (Reuters) - The ascent of the dinosaurs to the throne of the animal kingdom may have been more gradual than previously believed, scientists said on Thursday.

 
New fossil discoveries dating from about 215 million years ago showed some of the earliest dinosaurs lived for millions of years side by side with related animals long seen as their ancestors and precursors, scientists said on Thursday.

Many scientists had thought these reptiles -- very much like dinosaurs, but more primitive -- died out around the time of the appearance of the first true dinosaurs, which were dog-sized beasts not giants, roughly 230 million years ago.

"When dinosaurs first evolved, they were not very common and they were pretty small," said Randall Irmis of the University of California-Berkeley, who worked on the study.

"So they're not the dominant predators or creatures on land at all during most of the Triassic. And it's only really until the Jurassic when they really explode in diversity and reach these huge sizes that we're so familiar with," Irmis added.

Scientists previously hypothesized that the first dinosaurs quickly out-competed their more primitive cousins, known as "basal dinosauromorphs," condemning them to extinction. But the new findings indicate that any such competition was prolonged.

The newly found fossils from New Mexico dating from the Triassic period showed that the first dinosaurs co-existed with these animals -- "dinosaur wannabes," as one scientist called them -- for perhaps 15 to 20 million years.

"For the first time, we're finding the earliest dinosaurs and their closest relatives together," paleontologist Kevin Padian of the University of California-Berkeley, one of the researchers, said in a telephone interview.

"That tells us that the transition to the beginning of the age of dinosaurs was not a very-rapid affair and that, therefore, it wasn't instant competitive superiority."

Irmis said these dinosaur precursors are not thought to have been direct evolutionary ancestors of the dinosaurs but rather having shared a close common ancestor.

NEWLY DISCOVERED BEASTS

The scientists discovered new dinosaur precursors including one 3 to 5 feet long called Dromomeron and another unnamed one about three times larger that walked on four legs and ate plants with a beaked snout.

Relatively small bipedal carnivorous dinosaurs also were found, including Chindesaurus, which measured about 6 feet (2 meters) long, as well as remains of an apparent close relative of the well-known Triassic dinosaur carnivore Coelophysis.

The fossils were found at the Hayden Quarry at Ghost Ranch, a site that over the decades has yielded many exquisite fossils. For example, hundreds of Coelophysis fossils were found in the 1940s at Ghost Ranch, making it among the best documented of all dinosaurs.

These early Triassic dinosaurs were not the bullies and behemoths that later appeared in the Jurassic period, which started around 200 million years ago.

In fact, they were mere pipsqueaks next to some of their nasty neighbors. The scientists found remains of crocodile-like phytosaurs up to 25 feet long, and a relative of the equally long and vicious four-legged predator Postosuchus.

The New Mexico site at the time these animals lived was a lush environment with a vast river system, flood plains and forests with towering large conifer trees.