Fwd: New Fossil Found in Mongolia Provides Insight into the Origin of Living Birds and the Evolution of Flight

[Jeff Hecht <jhecht@world.std.com>]

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 
> Sciences.
>
> 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 
> evolved."
>
> 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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