Our fine-feathered friends ... dinosaurs?
NEW HAVEN, CONN.
Did baby Tyrannosaurus rex tumble out of its eggshell as a downy fuzzball? Three years ago, that notion would have drawn snickers from many paleontologists. After all, most people held that feathers originated with birds.Skip to next paragraph
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Last June, that dogma crumbled when Chinese, Canadian, and American researchers unveiled the first unambiguous fossils of flightless feather-bearing dinosaurs, pulled from deposits in China's Liaoning Province.
Now, new studies of these fossils suggest that a more Barney-like image of T. rex Jr. may not be far from the truth. Detailed analyses of the initial Chinese fossils and of fresh specimens of the same species are prompting several paleontologists to move these feathered dinosaurs earlier on the avian ancestral tree.
As the gap widens between these creatures and the first known prehistoric bird, archaeopteryx, these researchers not only are more convinced than ever that birds are direct descendants of two-legged, meat-eating dinosaurs. They posit that a wide range of these prehistoric theropods sported feathers - either as juveniles or throughout their lives. That, in turn, is sending scientists on a search for fresh explanations for the evolution of feathers and flight.
"These Chinese feathered dinosaurs are opening new realms of research," says Thomas Holtz, a vertebrate paleontologist at the University of Maryland at College Park.
The new results - and speculation on their implications - formed the nucleus of a symposium held earlier this month at Yale University in New Haven, Conn. The meeting was held to honor John Ostrom, who is widely credited for research that revived the idea that birds are linked to theropod dinosaurs - a theory that emerged in the 1860s and quickly became mired in controversy.
Coat of hollow filaments
The fossil celebrities include caudipteryx and protoarchaepteryx, dating back 120 million years. First reported in the journal Nature eight months ago, each shows clear evidence of feathers. Another species of similar age, sinosauropteryx, appears to be covered with hollow filaments that many have interpreted to be forerunners to feathers.
As more specimens of these species have come to light, "we've got better information on their anatomy. They exhibit many characters that you wouldn't find in a bird," says Philip Currie, curator of dinosaurs and birds at the Royal Tyrrell Museum of Paleontology in Alberta, Canada.
Thus, although these fossils are younger than the 140 million-year-old archaeopteryx, their skeletal features are sufficiently different to suggest they come from more primitive branches of a group of theropods known as coelurasaurs.
In terms of their evolutionary history, Dr. Currie says, sinosauropteryx is one of the most primitive coelurasaurs, with caudipteryx about half way up that branch and proto-
archaeopteryx higher still. Yet even then, protoarchaeopteryx falls several steps below archaeopteryx.
Making such connections is no mean feat. Researchers spend countless hours poring over fossils, noting the tiniest differences in bones and joints, assigning each of these "characters" a code, then building a database. Computers spend weeks sorting through the information before they produce a family tree that establishes possible linkages.