Fossil find helps pinpoint origin of mammals
June 20th, 2007
Guillermo Rougier in the Gobi Desert
The discovery of a 65-million-year-old fossil in Mongolia offers new evidence that mammals began to thrive only after the dinosaurs died off.
The find contradicts recent studies suggesting that mammals originated as long as 129 million years ago and lived alongside dinosaurs, said Guillermo Rougier, a University of Louisville paleontologist who found the fossil.
Scientists have long struggled to pinpoint the origin of placental mammals because the characteristics that clearly identify a these species, including body hair and the ability to nurse their young, are rarely preserved in the fossil record. Recent DNA analyses have suggested they began as long as 129 million ago when dinosaurs still roamed the earth, but Rougier’s find contradicts that theory.
Rougier was working in the Gobi Desert with a team led by Michael Novacek of the American Museum of Natural History when he unearthed the fossil in 1997. After studying the remains for nearly a decade, researchers concluded they were from an extinct, shrew-like creature that was the ancestor of a placental mammal.
“Our study strongly suggests that no member of any of the living groups of placental mammals goes much beyond 64 million years ago when the dinosaurs disappeared,” Rougier said. “They may have exploited an ecological niche opened up by the disappearance of many dinosaur species.”
The team’s finding also is significant because it shows mammals originated in the northern continents of the globe rather than in the southern continents, he said.
A study about the discovery is scheduled to appear in the June 21 issue of the journal Nature.
John Wible, a former U of L paleontologist now at Pittsburgh’s Carnegie Museum of Natural History, was lead author on the paper. The Carnegie Museum, National Science Foundation and American Museum of Natural History funded the study.
