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Some dinosaurs may have survived the great extinction

A geologist points to evidence from New Mexico that a large population of leaf-eating, egg-laying ceratopsians and sauropods lived on for another 500,000 years. Other experts are skeptical.

May 02, 2009|John Johnson Jr.

The idea that some dinosaurs survived the great extinction 65 million years ago has long tickled the imaginations of authors and filmmakers, who love putting half-dressed women in danger from the claws and jaws of giant creatures often described as "some kinda eating machine."

Now comes evidence from a dinosaur-hunter in New Mexico that a population of dinosaurs did indeed survive the cataclysm at the end of the Cretaceous era. That's when many scientists think a giant asteroid plunged into the ocean off modern-day Mexico, disrupting the climate so much that the dinosaurs died off en masse.

Jim Fassett, an emeritus geologist with the U.S. Geological Survey who has been digging in the San Juan Basin near the Colorado-New Mexico border, says it appears a sizable population of ceratopsians and sauropods, a class of giant, dim-witted leaf-eaters such as the brachiosaurus, hung on for another 500,000 years in the basin.

"There might even have been some T. rexes, based on some teeth we found," Fassett said in a phone interview Thursday. His research is being published in the journal Palaeontologia Electronica.

Fassett said he found a number of bones that were clearly dated to the Paleocene epoch, the period that followed the Cretaceous in which mammals began to scurry their way to the top of the food chain.

It's not uncommon for bones from one period to be found in geological strata from another. That usually happens when water exhumes and redistributes the bones.

But Fassett said he doesn't believe that happened in the San Juan Basin. As proof, he points to his discovery of 34 bones from a single hadrosaur: If they had been washed away from their original location, they would almost certainly have been separated, not found together.The San Juan Basin is a well-known repository for dinosaur bones. Paleontologists have been investigating the region at least since the beginning of the 20th century. But if Fassett is correct, the mystery is why this would be the place dinosaurs made their last stand.

As opposed to Arthur Conan Doyle's "Lost World" and the movie "King Kong," both of which located their dinosaur havens on far-flung islands, the San Juan Basin is not particularly remote. It's also disturbingly close, geographically speaking, to the Yucatan peninsula, the site of the asteroid collision.

Fassett offered two possible explanations. Since the species of dinosaurs he found at San Juan were egg-layers, perhaps the worst of the cataclysm had passed by the time the eggs of the next generation hatched. It's also possible, Fassett said, that when the asteroid hit, these survivors were living somewhere else, such as Alaska, where many Cretaceous-era dinosaur bones have been found.

Driven south by the frigid weather unleashed by the asteroid collision, they could have made the San Juan Basin their last home.

David Polly, the journal's executive editor, said Fassett's conclusions are controversial. Many paleontologists are likely to remain skeptical, he wrote in a news release accompanying the paper.

But he pointed out that it is well known that a few Cretaceous species with dinosaur bloodlines, such as crocodiles and birds, survived not only into the Paleocene but right through to modern times.

So the possibility that pockets of other types of dinosaurs also persisted for a while is not so hard to believe.

"One thing is certain," Polly said. "If dinosaurs did survive, they were not as widespread as they were before the end of the Cretaceous and did not persist for long."

So even if the San Juan dinosaurs survived a million years into the Paleocene, that leaves them more than 60 million years short of being able to chase Fay Wray through the forest.

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john.johnson@latimes.com

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