Mongolian Fossil Unlocks History of Birds
Friday, January 12, 2001

The ancient fossil of a bird discovered by Mongolian scientists has
unlocked some keys to the evolution of flight and the ancestry
of birds.

The analysis of the 80-million-year-old fossil, published this week in the
journal Nature, shows that "all of the birds living today have a most
recent common ancestor," said Yale
University paleontologist Julia Clarke in a press release.

"This fossil is just outside the group or 'clade' that includes the
descendants of that common ancestor," Clarke added. She says it's the
best-preserved specimen of a close relative to that
ancestor found in over 100 years.

Clarke said the fossil shows that, contrary to what scientists previously
believed, the ancestors of living birds were not restricted to near-shore
habitats through competition with another
lineage of birds.

Instead, this species of bird, Apsaravis ukhaana, lived in the continental
interior, away from the coastline. Ancestors of living birds were, at that
time, already occupying diverse habitats as
different as those of seagulls and pigeons today.

The new fossil also sheds some light on the evolution of flying. A feature
on one of the fossil's bones indicates the bird had a specific muscle
arrangement in common with living birds that
plays a key role in the transition from the upstroke to the down stroke
during flight.

This specimen is the oldest known example of the muscle group. "We have no
evidence of it evolutionarily before the new fossil," said Clarke.

Paleontologists found the nearly complete specimen of the small
pigeon-sized bird at Ukhaa Tolgod in the Gobi Desert of southern Mongolia.

The fossil was analyzed by Clarke, a doctoral candidate in vertebrate
paleontology at Yale University, and by Mark Norell, chair and curator of
the Division of Paleontology at the American
Museum of Natural History.

The find was the product of joint expeditions of the American Museum of
Natural History in New York and the Mongolian Academy of Sciences.
 

Oryginal:  http://www.foxnews.com/scitech/011201/bird.sml

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