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Fwd: New Fossil Found in Mongolia Provides Insight into the Origin of Living Birds and the Evolution of Flight
This press release from Yale University has more details on
Apsaravis. Dinogeorge had posted the Nature abstract. Press releases
are supposed to be publicized, so I consider this the best way to put
up a description without violating anybody's copyrights. -- Jeff Hecht
CONTACT: Jacqueline Weaver 203-432-8555 #186
New Fossil Found in Mongolia Provides Insight into the Origin of
Living Birds and the Evolution of Flight
New Haven, Conn. - The discovery in Mongolia of the fossil of a new
bird, Apsaravis ukhaana, that lived about 80 million years ago,
sheds new light on the evolution of birds.
The nearly complete specimen of the small pigeon-sized bird was
found at the locality Ukhaa Tolgod in the Gobi Desert of Southern
Mongolia as part of the ongoing joint expeditions of the American
Museum of Natural History in New York and the Mongolian Academy of
The find, announced this week in the journal Nature, was analyzed by
Julia Clarke, a doctoral candidate in vertebrate paleontology at
Yale University, and Mark Norell, chair and curator of the Division
of Paleontology at the American Museum of Natural History. The
discovery is particularly important because the new bird comes from
a part of the evolutionary tree close to the origin of all living
birds and that is not well represented in the fossil record.
"All of the birds living today have a most recent common ancestor
that they share," said Clarke, who is in Yale's Department of
Geology. "This fossil is just outside the group or 'clade' that
includes the decendants of that common ancestor. It is the best
preserved specimen of a fossil from close to the radiation of all
living birds discovered in over 100 years."
The finding is the most significant from this part of the avian tree
since the discovery of specimens of the closest relative to living
birds, Ichthyornis, first discovered more than 100 years ago in
Kansas. These specimens of Ichthyornis are part of the permanent
collection at Yale's Peabody Museum of Natural History.
Clarke said the fossil dispels the notion that the ornithurines, or
nearest relatives to today's existing birds, were restricted to near
shore environments while the interior was dominated by another
lineage of fossil birds known as the "opposite birds" or
Enantiornithes. The Enantiornithes are comparatively abundant in
terrestrial deposits in the fossil record of Mesozoic, but went
extinct at the end of the Cretaceous period, 65 million years ago.
"The new find suggests there was no reason to believe that there was
a restriction of the nearest relative of living birds to coastlines
by this lineage of 'opposite birds,'" Clarke said. "Here is a near
relative of living birds that is from a locality in a continental
interior that was buried adjacent to abundant sand dunes."
The Apsaravis specimen from these terrestrial deposits reveals that
the nearest relatives of the lineage including living birds were not
restricted to a near shore or marine habitat and wading bird
ecology, but that they were already occupying diverse environments
and ecologies as different as those of seagulls and pigeons today.
The finding also has important implications in the current thinking
about the evolution of birds after the origin of flight. The new
fossil has a feature on a bone of its hand that indicates a muscle
arrangement connecting the movement of the hand to movement of the
forearm. This muscle arrangement seen in living birds performs a key
role in transition from the upstroke to the down stroke.
"This automated part of the flight stroke was thought to be present
before the origin of flight in other non-flighted theropod
dinosaurs," Clarke said. "While other parts of the flight stroke
were present in these other theropods, this part of the flight
stroke is first clearly present only long after flight itself
Though earlier birds actively propelled themselves through the air,
their flight was different from flight as we know it today in living
birds. "This particular muscle arrangement is present in all
flighted living birds today," Clarke said, "but we have no evidence
of it evolutionarily before the new fossil."
Jeff Hecht Boston Correspondent New Scientist magazine
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