Fossils Hint at Dinosaur's Demise

WASHINGTON--Filling in part of an 80 million-year historical gap, fossils found in Utah suggest long-necked dinosaurs may have eaten themselves into oblivion by helping to destroy North American forests. That allowed the rise of shorter, horned dinosaurs that fed on shrubs.

Researchers also uncovered fossils suggesting that a toothy dinosaur migrated from Asia and evolved in the Americas into Tyrannosaurus rex, the most fearsome meat eater in history, said Richard L. Cifelli, lead author of a study in the Proceedings of the National Academy of Sciences that will be published today.

Fossils unearthed in Emery County, Utah, are the first for terrestrial animals and plants from a historical gap that began 145 million years ago and continued until just a few millions years before the dinosaurs became extinct 65 million years ago, Cifelli said.

"This gap has been like a twilight zone in the age of dinosaurs," said Cifelli. Although it was clear that great changes occurred during that gap, little was known because there were few fossils. "This is the first lighted room in a darkened house," he said.

Louis C. Jacobs, a noted dinosaur expert at Southern Methodist University, said the Utah fossil discoveries are "hugely" important because they help give a picture of the world during an unknown period.

"There were very major changes then in the ecosystems of the Earth," he said. "What they have done is to document a portion of that change for the first time and put a date on it."

Cifelli said the Utah dig uncovered more than 6,000 fossils representing about 80 different types of animals. They were dated to about 100 million years ago. This is 45 million years into the "twilight zone" gap, he said.

What emerges is a surprising picture, he said.

"The early dinosaurs in North America were dominated by the longnecks, the sauropods," said Cifelli. They were so common 145 million years ago, he said, "it was like it had rained sauropods over the American West."

He said the huge appetite of the sauropods had a major effect on the continent and its forests of primitive plants.

"The sauropods were so big they could go through and clear-cut an area," he said. "After these mowing machines went by, the flowering plants would take over the land. They are fast growing and rapid colonizers."