Geologist claims a few dinosaurs survived extinction event

Washington Post Staff Writer
Saturday, January 29, 2011; 10:07 PM

And now, another episode of "Dinosaur Survivor."

In this show, the question isn't which dinosaur to throw off the island. Instead, scientists ask whether any of the ancient reptiles survived the cataclysmic strike of a space rock in the Gulf of Mexico some 65 million years ago.

Representing the no team: Pretty much every dinosaur hunter in the world.

Representing the yes team: A retired federal geologist from New Mexico, James Fassett.

For 25 years, Fassett has been touting a fossilized femur he found as proof that a pocket of long-necked herbivores called sauropods survived for hundreds of thousands of years after all the other dinosaurs.

"I'm not totally a Lone Ranger," Fassett said of his theory. "But I guess I am still in the minority."

In the latest installment of this long-running series, Fassett and two colleagues report in the journal Geology that a new technique dates the femur to 700,000 years after the extinction event.

But few experts are buying it. One of Fassett's critics offered a sarcastic response. "Anything is possible," said Spencer Lucas, a paleontologist at the New Mexico Museum of Natural History and Science in Albuquerque. "There could also be a Bigfoot in my back yard."

With the new dating technique, Larry Heaman and Antonio Simonetti from the University of Alberta in Edmonton vaporized tiny bits of Fassett's fossil with a laser. They then measured the amount of uranium and lead in the resulting dust. Because uranium radioactively decays into lead over millions of years, the process acts as an atomic clock.

If proved, the laser technique could revolutionize fossil dating, said Paul Renne, director of the nonprofit Berkeley Geochronology Center in California. Currently, paleontologists date fossils indirectly, by determining the age of the rocks in which they're found or by hunting for specks of fossilized pollen nearby, which also offer strong age clues. In contrast, the laser blasting method attempts to date fossils directly.

However, Renne and several other fossil-dating experts said the technique is too new to be reliable. "Uranium-lead dating is tricky business," said Alan Koenig, a rock-dating expert with the U.S. Geological Survey in Denver.

A primary concern: It is impossible to know when, exactly, uranium leached into the bone. After the sauropod died in what is now northern New Mexico, the calcium in its bones was eventually replaced by harder, longer-lasting minerals, including uranium. That's the fossilization process. But paleontologists say there is no way to know how long this might take. "It could be 10 years; it could be a million," Renne said.

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