J. Alan Feduccia (UNC web page)
Unanswered question department: Did the earliest birds have Tarheels?
Posted on 08/15/2002 7:16:36 AM PDT by forsnax5
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.
(Excerpt) Read more at unc.edu ...
J. Alan Feduccia (UNC web page)
Unanswered question department: Did the earliest birds have Tarheels?
That's Archaeopteryx, the theropod dinosaur Deinonychus, and a modern bird (Hoatzin) that as a juvenile has a "throwback" clawed forelimb similar to fossil early birds but grows out of it to become a flying adult.
Fig. 1: Archaeopteryx Fig. 2: Deinonychus Fig. 3: Hoatzin chick Fig. 4: Hoatzin adult
From the article:
"Whatever the ancestor of birds was, it must have had five fingers, not the three-fingered hand of theropod dinosaurs," Feduccia said.The standard reptilian forelimb has five fingers, of course. Theropods evolved to lose two. Most scientists think birds simply inherited this same manus. In fact, this similarity was one of the lines of evidence that suggested a dinosaur ancestry for birds in the first place.
"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.I can't tell where the problem is. Maybe the observation of which fingers are lost on the dinosaur is wrong.
"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."Or maybe Feduccia is seeing what he wants, not what is there. I can't tell where the problem is, but it's unlikely that the figure above is just a misleading coincidence.
Who knows. Not being a subscriber, I can't see the full the article.
If birds evolved from thecodonts, so did the dinosaurs, and all other archosaurs ("ruling reptiles") including Crocodilians, which are the last surviving archosaurs, and all this happened long after archosaurs and leipedosaurs ("non-ruling reptiles") split. Therefore, whichever theory about birds is true, crocodiles are still more closely related to birds than they are to other living reptiles.
By DAVID WILLIAMSON
UNC News Services
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.
- 30 - Note: Feduccia can be reached at (252)-438-6545 (late mornings or late afternoons) Aug. 15th and 16th.
Next week: (919)962-3050; home: 919-942-3377 or feduccia@bio.unc.edu for a photograph of the embryo.
Not really. Unless, of course, he's an atheist.
Oops, I meant the full article in the online edition of Naturwissenschaften.
Your fossil diagrams are (probably) adult creatures. The premise of the article seems to be that it's not possible to determine which of the basic five "fingers" have developed in adult birds by looking at adult skeletons.
The hoatzin adult is an interesting example of rather dramatic changes in the life cycle of the bird. Reviewing the two skeletons as fossils a few million years from now, it would be difficult to see the actual relationship.
If what the article claims is true, it would appear that the later examples of feathered dinos were a second, never completed path to feathered flight.
The later feathered dinos are often interpreted by the "sibling relationship" (birds and dinos from a common ancestor) crowd as bird descendants going back into flightlessness. The error bars in the dates are large enough that the only clear "flyer" is Archaeopteryx at about 150 million years ago.
Archaeopteryx without the feathers looks like a fairly ordinary dromaeosaur, anyway. Much of the argument is about where you draw the line between what's a dinosaur and what's a bird.
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