Scientist's Finds Spur New Thinking on Dino Evolution

D.L. Parsell
National Geographic News
February 19, 2002

One after another, the new dinosaur discoveries that Paul Sereno and his colleagues have made over the past decade are remarkable. But thrilling as they are individually, the fossils also excite Sereno because they are helping to fill in the big picture of dinosaur evolution.

What are such discoveries telling him?

For one thing, that the breakup of the ancient supercontinent Pangaea was not rapid, as widely believed, but slow enough to drastically limit dinosaur evolution in the region.

The pace of the continental breakup, he argues, had distinct evolutionary impacts on dinosaur characteristics and lineages.

Fossils, when viewed together, hold clues to broad patterns of evolution. Since the start of his career in the 1980s, Sereno has been interested in reconstructing the dinosaur family tree—the "phylogeny" of dinosaurs. He hopes to map dinosaur descent by tracing the many evolutionary changes recorded in dinosaur skeletons.

Calling dinsosaurs "a greatly underserved group," Sereno predicted at a lecture this week in Boston that soon "we will see answers to major evolutionary questions that have long been unaddressed." The University of Chicago paleontologist, who is a National Geographic Society explorer-in-residence, was speaking at the annual meeting of the American Association for the Advancement of Science.

Among the questions Sereno is working to understand is the role of biogeography in dinosaur evolution—continental drift and possible migration over temporary land bridges. "This was a global group, entirely land-based," he said. "How did something as drastic as the breakup of the supercontinent affect evolution?"

Another line of inquiry: what accounts for the high levels of diversity that occurred among dinosaurs well before they globally dispersed and became the dominant animals on Earth until their extinction 65 million years ago.

"What exists is a very different course from [that of] mammals and other groups," Sereno said. "It's almost like a Cambrian radiation in terms of tremendous diversity."

Wide Spectrum of Dinosaur Life

Scientists' understanding of dinosaurs has advanced by leaps in recent years, Sereno noted, because of new discoveries that shed light on dinosaurs from when they first appeared, in the middle Triassic, to their final radiations at the end of the Cretaceous.

Sereno and his colleagues have contributed significantly to those findings, especially through their excavations in Africa, where harsh conditions had limited dinosaur hunting until recent years.

Soon after beginning field work in Argentnia in the late 1980s, Sereno and his teams discovered highy complete skeletons of two of the oldest dinosaurs ever found. The fossils of the two theropods, known as Herrerasaurus (named for a member of the expedition) and Eoraptor ("dawn raptor"), dated from 228 million years ago—the era when dinosaurs first arose.

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