The bones of more recent bird fossils like Confuciusornis from the Yixian Formation in China which are more recent than Archaeopteryx demonstrate rapid growth more similar to that of modern birds, which means rapid bone growth, considered a prerequisite for flight, was not necessary for taking to the air.
"Dinosaurs had a very different metabolism from today's birds. It would take years for individuals to mature, and we found evidence for this same pattern in Archaeopteryx and its closest relatives," says Gregory Erickson of the Department of Biological Science at Florida State University, who is also a Research Associate at the American Museum of Natural History and first author of this paper. "Living birds mature very quickly and grow really, really fast. This is why we see flocks of pigeons that all look the same and rarely see baby birds. Animals like Archaeopteryx would be very foreign to a bird watcher."
Archaeopteryx bone microstructure shows flattened and parallel bone cells, or osteocyte lacunae. Credit: Gregory Erickson
The first Archaeopteryx skeleton was found in Germany just after Darwin's Origin of Species was published and its appearance was timely because the fossil combined bird-like (feathers and a wishbone) and reptilian (teeth, three fingers on hands, and a long bony tail) traits, it helped convince many about the veracity of evolutionary theory. In fact, the first suggestion that birds are related to dinosaurs was made by early proponent of evolution and Darwinian bulldog Thomas Henry Huxley in the 1860's.
"Archaeopteryx is the poster child for evolution," says Erickson. Ten skeletons and an isolated feather have been found.
Slab and counter slab of the Munich Archaeopteryx. Credit: Mick Ellison/AMNH
"For a long time, Archaeopteryx was considered the archetypical bird primarily because it had feathers, although it retained typical dinosaur features like a long tail and teeth. But the discovery of classical bird features like feathers and wishbones have recently been found in many non-avian dinosaurs blurring the line of what constitutes a bird," says Mark Norell, Chair of the Division of Paleontology at the Museum and a co-author of the paper.
Norell, Erickson, and colleagues looked at growth rate in Archaeopteryx and in birds and dinosaurs up and down the family tree by removing tiny, 250-micron chips from the long bones (specifically thigh bones and one of the shinbones). This process required an enormous amount of cooperation.
The Munich Archaeopteryx was sampled with the help of co-author Oliver Rauhut of the Bavarian State Collection for Palaeontology and Geology in Munich, who said "The Munich specimen is one of the more recently discovered specimens. Nevertheless, 'cutting up' this fossil to take samples of the bones was almost considered blasphemous until recently. But because the samples were very small and were removed with great skill by our preparator, the knowledge gained was more than worth the sacrifice."
Citation: Erickson GM, Rauhut OWM, Zhou Z, Turner AH, Inouye BD, et al. (2009) Was Dinosaurian Physiology Inherited by Birds? Reconciling Slow Growth in Archaeopteryx. PLoS ONE 4(10): e7390. doi:10.1371/journal.pone.0007390