for National Geographic News
An isolated group of dinosaurs somehow survived the catastrophic event that wiped out most of their kind some 65.5 million years ago, a new study suggests.
Dinosaurs of this "lost world," in a remote region of the U.S. West, may have outlived their doomed relatives by as much as half a million years, according to James Fassett, an emeritus scientist with the U.S. Geological Survey in Santa Fe, New Mexico.
There, the bones of hadrosaurs, tyrannosaurs, anklyosaurs, and several other species were found together in a sandstone formation that dates to the Paleocene epoch—the time period after the so-called Cretaceous-Tertiary (K-T) extinction event, which is thought to have killed off the dinosaurs.
As with his past research, Fassett's latest find is likely to continue sparking controversy among paleontologists.
"Every few years someone claims to have [found] Paleocene 'surviving' dinosaurs," said Hans-Dieter Sues, associate director for research and collections at the Smithsonian Institution's National Museum of Natural History.
But so far, such fossils have eventually turned out to be older remains.
In his new study, appearing in the April 2009 issue of the journal Palaeontologia Electronica, Fassett argues that a single hadrosaur fossil helps prove that the San Juan dinos really are from the Paleocene.
After previous "survivor" finds, it was determined that the dinosaurs in question, initially entombed in sand or mud, had their bones exposed again later by natural forces such as river erosion.
The bones were then redeposited in younger rock layers, making them appear to belong to an earlier era.
But paleontologists found a concentration of 34 bones from a single hadrosaur in the San Juan Basin sandstone.
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