Find Gives Thumbs Down To Dinosaur-To-Bird Theory
A theory that birds evolved from dinosaurs may lose out by a thumb.
New research shows that birds lack the embryonic thumb that dinosaurs had, suggesting it is “almost impossible” for the species to be closely related.
Researchers at the University of North Carolina, Chapel Hill, made the discovery with a microscopic examination of stages of development in the embryos of birds. They show no vestige of a thumb that is present in primitive form in dinosaur fossils.
“We consider this to be unequivocal evidence that birds” did not evolve directly from dinosaurs, said Alan Feduccia, chairman of biology at North Carolina and co-author of a study published today in the journal Science. He said the finding is only one piece of a growing body of evidence that disputes the long-held dinosaurs-to-birds theory.
The North Carolina findings are dismissed by scientists at the American Museum of Natural History in New York, where the theory is enshrined as a part of a $30 million renovation that includes two dinosaur halls.
“There is a discrepancy between what the embryology tells us and what the fossils tell us,” said Mark Norell, a museum scientist. But he noted: “No one feature, such as the thumb, can sway things one way or the other.”
The museum, he said, still firmly believes that birds are “living dinosaurs.”
Other researchers, however, are less certain.
“The North Carolina work is very, very credible evidence,” said John A. Ruben of Oregon State University in Corvallis. “The idea that birds evolved from dinosaurs is definitely in trouble.”
Researchers who accept the bird-dinosaur connection, said Ruben, “will have to chew this one over very carefully. Actually, I don’t think there is enough evidence right now to say for sure where birds came from.”
Finding the mismatched digits of birds and dinosaurs, said dinosaur expert Storrs L. Olson of Washington’s Smithsonian Institution, “is the end of it, as far as I am concerned.
“There is no way that birds and dinosaurs could be directly related.”
The North Carolina study is based on the belief that animals sharing a common ancestry exhibit common features during embryonic formation. If birds are related to dinosaurs, there should be evidence in bird embryos of a thumb remnant.