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Archaeopteryx was not very bird-like

Archaeopteryx lacked rapid bone growth, the hallmark of birds

American Museum of Natural History


IMAGE: This is the slab and counter slab of the Munich Archaeopteryx. view more

Credit: Mick Ellison/AMNH

New research published this week clips the wings of Archaeopteryx. First found in Germany in the 1860's and dating to 150 million years ago, Archaeopteryx has long been considered the iconic first bird. But microscopic imaging of bone structure published in PLoS One shows that this famously feathered fossil grew much slower than living birds and more like non-avian dinosaurs. The bones of more recently discovered bird fossils like Confuciusornis, a primitive but toothless bird from the Yixian Formation in China that appeared after Archaeopteryx, demonstrate rapid growth more similar to that of modern birds. This means rapid bone growth--long thought a prerequisite for flight--was not necessary for taking to the air.





Chinese fossils were equally important to sample so that Archaeopteryx could be placed in context. Because of co-author Zhonghe Zhou of the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences, samples were taken from Jeholornis prima, a long-tailed specimen considered an early bird, and the short-tailed Sapeornis chaochengensi that had three fingers and teeth. The group also sampled the closest relatives among dinosaurs to the birds including Velociraptor mongoliensis and miniaturized species such as Mahakala omnogova that is similar in size to Archaeopteryx.

All chips were analyzed under polarizing microscopy. The bone types for the early birds Archaeopteryx, Jeholornis, and Sapeornis are comparable to those of same-sized dinosaurs--animals that grew considerably slower than living birds. The blood vessels are very small, the bone is very dense, and the "osteocyte lacunae," or the location of bone cells, are flattened and parallel.

The opposite pattern holds for more advanced bird fossils such as the roughly 94 million-year-old Ichthyornis dispar from North America. The bone is well-vascularized, which means that it was well-supplied with blood vessels, and the bone structure is woven, with randomly oriented bone fibers, indicating fast growth with no annual growth lines. This is the bone histology of modern birds.


"When first I looked at the Archaeopteryx, it looked like lizard bone," says Erickson. "This told me right off the bat that Archaeopteryx was an animal that grew slowly. This was a surprise and not what was expected for a same-sized living bird." In fact, analysis of numerous fossils showed the team that dinosaurs grew more slowly, pound for pound, than living birds, and that bird-like metabolic characteristics were not present in the ancestor of Archaeopteryx and modern birds. The team outlines a growth curve that indicates that Archaeopteryx reached adult size in about 970 days, that none of the known Archaeopteryx specimens are adults (confirming previous speculation), and that adult Archaeopteryx were probably the size of a raven, much larger than previously thought.




In addition to Erickson, Norell, Rauhut and Zhou, authors include Alan Turner (Department of Anatomical Sciences, Stony Brook University) and Brian Inouye (Department of Biological Science, Florida State University). This research was generously funded by a DFG grant RA 1012/4 to Rauhut, NSF DBI 0446224 and EAR 04418649 grants to Erickson, an NSF ATOL 0228693 grant to Norell, the Major Basic Research Projects [2006CB806400] of MST of China to Zhou, and the American Museum of Natural History.
