October 9, 2009

Was First Bird Actually A Dinosaur?

Experts say new research reveals that the Archaeopteryx, which has long been viewed as the archetypal first bird, was actually a lot less "bird-like" than scientists originally thought.

Archaeopteryx (from the Greek for "ancient wing"), lived 150 million years ago during the Late Jurassic period in what is now Germany.

New microscopic images of the ancient cells and blood vessels inside the bones of the winged, feathered, claw-handed creature show unexpectedly slow growth and maturation that took years, similar to that found in dinosaurs, from which birds evolved, according to paleobiologist Gregory M. Erickson of The Florida State University, who led the study.

His team also found that the rapid bone growth common to all living birds, but surprisingly absent from the Archaeopteryx, was not necessary for avian dinosaur flight.

Erickson said living birds mature very quickly, which is why we rarely see baby birds among flocks of invariably identical-size pigeons.

"Slow-growing animals such as Archaeopteryx would look foreign to contemporary bird-watchers," he noted.

The researchers said almost nothing had been known of Archaeopteryx biology, but there had been debate as to how well it flew, if at all.

"Some have suggested that early bird physiology may have been very different from living birds, but no one had tested fossils that were close to the base of bird ancestry," Erickson said.

He and his colleagues set out to determine how Archaeopteryx grew and compare its growth to living birds, closely related non-avian dinosaurs, and other early birds that came after it.

The researchers went to the Bavarian State Collection for Paleontology and Geology, which houses a small juvenile Archaeopteryx that is one of 10 specimens discovered to date. From that specimen, they extracted tiny bone chips and then examined them microscopically. They then discovered that the bones of the juvenile Archaeopteryx were not the highly vascularized, fast-growing type, as in other avian dinosaurs.

Instead, they found lizard-like, dense, nearly avascular bone.

"It led us to ask, 'Did Archaeopteryx grow in a unique way?'" Erickson said.

Erickson said they learned that the adult would have been raven-sized and taken about 970 days to mature, while some same-size birds today can do likewise in eight or nine weeks.

Therefore, the maximal growth rates for Archaeopteryx resemble dinosaur rates, which are three times slower than living birds and four times faster than living reptiles.

"From these findings, we see that the physiological and metabolic transition into true birds occurred millions of years after Archaeopteryx," he said. "But, perhaps equally important, we've shown that avians were able to fly even with dinosaur physiology."

Mark Norell, Chair of the Division of Paleontology at the Museum and a co-author of the paper, said Archaeopteryx had comparable metabolism to the closely related Velociraptor.

"The genesis of modern bird biology has been a huge mystery. We knew that they are a kind of dinosaur, but we now know that the transition into true birds"”physiologically and metabolically"”happened well after Archaeopteryx."

Erickson suggested they have now shown that avian flight was achieved with the physiology of a dinosaur.


Image 1: Archaeopteryx bone microstructure shows flattened and parallel bone cells, or osteocyte lacunae. Credit: Gregory Erickson

Image 2: This is the slab and counter slab of the Munich Archaeopteryx. Credit: Mick Ellison/AMNH

Image 3: This is a bone samples from the Munich Archaeopteryx. Credit: Greg Erickson


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