- 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.
-
- Editor's Note: The original news release can be found
at http://www.unc.edu/news/newsserv/research/feduccia081402.htm
-
- Note: This story has been adapted from a news release
issued by University Of North Carolina At Chapel Hill for journalists and
other members of the public. If you wish to quote from any part of this
story, please credit University Of North Carolina At Chapel Hill as the
original source. You may also wish to include the following link in any
citation:
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