The era of the dinosaurs was drawing to a close and would have ended with the natural extinction of the great lizards whether or not a giant asteroid had slammed into the Earth, a study released Monday showed.

The study, unveiled at the annual meeting of the Geological Society of America, cast doubts on the doomsday scenario of a huge object from outer space crashing into Earth 66 million years ago, kicking up a huge cloud of dust that blotted out the sun for weeks and killed off the cold-blooded reptiles while hardier mammals survived."No data supporting the impact theory of dinosaur extinction exists, " said David Archibald, a biology professor from San Diego State University who helped devise the "Blackjack Model" of prehistoric survival. The model shows that luck and "evolutionary skill" was responsible for the survival of species following the dinosaur-dominated Cretaceous Period.

Archibald and his colleagues - Peter Dodson of the University of Pennsylvania and Robert M. Sullivan of the San Diego Natural History Museum - have decided that the 16 to 20 dinosaur species left when the theoretical asteroid hit the planet at the end of the Cretaceous Period were already dying out because of a lack of genetic diversity and the loss of habitat caused by changes in the Earth's land formations.

"The impact theory predicted a mass extinction killing up to 75 percent of all species," Archibald said. "Instead of 75 percent extinction, upwards of 65 percent of the vertebrae species survived the end of the Age of Dinosaurs."

The study was based on more than 150,000 fossils of 111 species of dinosaurs, mammals, fishes and various reptiles.

The scientists said that 93 percent of the dinosaur species that had existed since the beginning of time had already died out by the time the asteroid collision would have occurred.

Rather than the overnight elimination of the dinosaur, fossil records from the period known to scientists as the K-T Boundary, reflect what the researchers believe was the natural end of the dinosaur line.

"What we are seeing is just the extinction of this 7 percent," Sullivan said. "Animals evolve and animals become extinct."

Many dinosaur lines evolved into modern birds while others simply ended at various times in history.

"Until people understand the strong bird-dinosaur relationship, we will continue to discuss their extinction," Sullivan said.