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Parrot Fossil from the Cretaceous Pushes Back Origin of Modern Land Birds

by Robert Sanders, Public Affairs
posted November 18, 1998

The fossilized jaw of a parrot dating from the last days of the dinosaurs is the earliest known fossil of a modern land bird, says Thomas Stidham, a graduate student in the Department of Integrative Biology. The find provides the strongest evidence to date that modern birds evolved long before most scientists thought.

An analysis of the find, excavated from Cretaceous deposits in eastern Wyoming, appeared in the Nov. 5 issue of the British journal Nature.

"This find suggests that by the end of the Cretaceous period, around 65 to 70 million years ago, modern birds were an important group, at least in North America," said author Stidham.

"These data also indicate that modern bird groups, including parrots, may have been relatively unaffected by the mass extinction at the end of the Cretaceous period," he wrote in a scientific correspondence in Nature.

According to Stidham's advisor, paleontologist William Clemens, professor of integrative biology, "Tom has made an interesting discovery: that while modern birds survived the Cretaceous, more primitive birds with teeth became extinct. This heightens the mystery surrounding an explanation for the extinctions at the end of the Cretaceous. It's not clear why some animals survived and others didn't."

Primitive toothed birds, relatives of archaeopteryx, were the dominant bird group during most of the Cretaceous period, flapping amongst dinosaurs like Tyrannosaurus rex and triceratops. Toward the end of that period, however, modern toothless birds began to crowd them out, and the toothed birds went extinct around the end of the Cretaceous.

Until now the only modern bird fossils uncovered from the Cretaceous have been water birds: loons, duck-like waterfowl, shorebirds and tube-nosed seabirds like the albatross. The oldest of these dates from about 80 million years ago. This led many paleontologists to conclude that modern terrestrial birds arose after the major extinction at the end of the Cretaceous.

One reason for a lack of landbird fossils, however, may be that most paleontologists hunt for fossils in the deposits of past watery environments, such as ancient shorelines and river deltas, where few terrestrial birds would be expected, Stidham said.

As interest in ancient birds has risen over the past 10 years, more and older bird fossils have been identified, often from old museum collections. A separate line of evidence -- molecular studies of modern birds and the rate at which their DNA has changed with time -- also has placed the origin of modern birds, including parrots, in the Cretaceous. The new find confirms this hypothesis from molecular divergence data.

The fossilized lower jawbone Stidham analyzed was found by Clemens around 1960 in the Lance Formation of Niobrara County in eastern Wyoming. Excavated from an old river deposit, it sat in the Museum of Paleontology's collection until now, labeled as an unknown avian fossil.

Stidham, who is writing his doctoral thesis on the origins of modern birds, has rifled through these collections in search of interesting bird fossils, and to date has identified nearly a dozen new species. Until now all have been water birds.

He readily recognized this particular fossil as a parrot, which has a distinctive lower jaw normally covered by a horny, fingernail-like substance that forms the beak. Stidham X-rayed the jaw and found nerve and blood vessel tracks identical to those of modern parrots.

This specimen, only half an inch long, was probably from a bird about the size of a macaw, and most closely resembles the lories of Australia and some of the South American macaws. It thus is the oldest known parrot and the oldest reported modern land bird.


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