CHAPEL HILL -- To make an omelet, you need to break some eggs. Not nearly so well known is that breaking eggs also can lead to new information about the evolution of birds and dinosaurs, a topic of hot debate among leading biologists. Drs. Alan Feduccia and Julie Nowicki of the University of North Carolina at Chapel Hill have done just that. They opened a series of live ostrich eggs at various stages of development and found what they believe is proof that birds could not have descended from dinosaurs. They also discovered the first concrete evidence of a thumb in birds.
"Whatever the ancestor of birds was, it must have had five fingers, not the three-fingered hand of theropod dinosaurs," Feduccia said. "Scientists agree that dinosaurs developed 'hands' with digits one, two and three -- which are the same as the thumb, index and middle fingers of humans -- because digits four and five remain as vestiges or tiny bumps on early dinosaur skeletons. Apparently many dinosaurs developed very specialized, almost unique 'hands' for grasping and raking. "Our studies of ostrich embryos, however, showed conclusively that in birds, only digits two, three and four, which correspond to the human index, middle and ring fingers, develop, and we have pictures to prove it," said Feduccia, professor and former chair of biology at UNC. "This creates a new problem for those who insist that dinosaurs were ancestors of modern birds. How can a bird hand, for example, with digits two, three and four evolve from a dinosaur hand that has only digits one, two and three? That would be almost impossible."
A report on their investigations will appear online in the August issue of Naturwissenschaften, the top German biology journal, and soon afterwards in the print edition.
The new work involved microscopic examination of early skeletal development in ostrich embryos, he said. Nowicki, who received her doctorate in biology at UNC last year, and he found the critical period for major features of the skeletons of primitive birds like ostriches to appear occurred between days 8 and 15 of those birds' 42-day growth inside eggs.
The beginnings of arm bones and "fingers" begin to appear around day 8, Feduccia said. Those that would grow into the animals' thumbs, however, appear around day 14 and later disappear by about day 17.
"Because most such studies in birds have relied on embryos in the second half of development, usually at or near hatching, these studies have therefore used embryos that exhibit the form of fully developed chicks and have generated misleading results," he said. "Questions about development of bird hands were first addressed in 1821 by the famous German physician and anatomist Johann Friedrich Meckel for whom the cartilage of the lower jaw was named. But no one has produced convincing evidence for a thumb before. For us, this is very exciting."
The UNC evolutionary biologist has been a strong critic of the belief that dinosaurs gave rise to birds as some paleontologists have claimed since the 1970s. He also has been a major figure in the debate for 30 years.
"There are insurmountable problems with that theory," he said. "Beyond what we have just reported, there is the time problem in that superficially bird-like dinosaurs occurred some 25 million to 80 million years after the earliest known bird, which is 150 million years old."
Most of the bird-like dinosaurs were "looking at the meteor some 65 million years ago," he said, a reference to the giant meteor believed to have struck the Earth then and killed off all dinosaurs within a short time.
If one views a chicken skeleton and a dinosaur skeleton through binoculars they appear similar, but close and detailed examination reveals many differences, Feduccia said. Theropod dinosaurs, for example, had curved, serrated teeth, but the earliest birds had straight, unserrated peg-like teeth. They also had a different method of tooth implantation and replacement.
Findings from careful examinations of alligator and turtle embryos were consistent with those of birds, the scientist added.
Far more likely is that birds and dinosaurs had a much older common ancestor, he said. Many superficial similarities between birds and dinosaurs arose because both groups developed body designs for walking upright on two hind legs and began to resemble each other over millions of years. "It is now clear that the origin of birds is a much more complicated question than has been previously thought," Feduccia said.
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