Web address:
http://www.sciencedaily.com/releases/2011/05/
110518151822.htm
China Fossil Shows Bird, Crocodile Family Trees Split Earlier Than Thought
ScienceDaily (May 19, 2011) A fossil unearthed in China in the 1970s of a
creature that died about 247 million years ago, originally thought to be a
distant relative of both birds and crocodiles, turns out to have come from the
crocodile family tree after it had already split from the bird family tree,
according to research led by a University of Washington paleontologist.
The only known specimen of Xilousuchus sapingensis has been reexamined and is
now classified as an archosaur. Archosaurs, characterized by skulls with long,
narrow snouts and teeth set in sockets, include dinosaurs as well as crocodiles
and birds.
The new examination dates the X. sapingensis specimen to the early Triassic
period, 247 million to 252 million years ago, said Sterling Nesbitt, a UW
postdoctoral researcher in biology. That means the creature lived just a short
geological time after the largest mass extinction in Earth's history, 252
million years ago at the end of the Permian period, when as much as 95 percent
of marine life and 70 percent of land creatures perished. The evidence, he
said, places X. sapingensis on the crocodile side of the archosaur family tree.
"We're marching closer and closer to the Permian-Triassic boundary with the
origin of archosaurs," Nesbitt said. "And today the archosaurs are still the
dominant land vertebrate, when you look at the diversity of birds."
The work could sharpen debate among paleontologists about whether archosaurs
existed before the Permian period and survived the extinction event, or if only
archosaur precursors were on the scene before the end of the Permian.
"Archosaurs might have survived the extinction or they might have been a
product of the recovery from the extinction," Nesbitt said.
The research is published May 17 online in Earth and Environmental Science
Transactions of the Royal Society of Edinburgh, a journal of Cambridge
University in the United Kingdom.
Co-authors are Jun Liu of the American Museum of Natural History in New York
and Chun Li of the Institute of Vertebrate Paleontology and Paleoanthropology
in Beijing, China. Nesbitt did most of his work on the project while a
postdoctoral researcher at the University of Texas at Austin.
The X. sapingensis specimen -- a skull and 10 vertebrae -- was found in the
Heshanggou Formation in northern China, an area with deposits that date from
the early and mid-Triassic period, from 252 million to 230 million years ago,
and further back, before the mass extinction.
The fossil was originally classified as an archosauriform, a "cousin" of
archosaurs, rather than a true archosaur, but that was before the discovery of
more complete early archosaur specimens from other parts of the Triassic
period. The researchers examined bones from the specimen in detail, comparing
them to those from the closest relatives of archosaurs, and discovered that X.
sapingensis differed from virtually every archosauriform.
Among their findings was that bones at the tip of the jaw that bear the teeth
likely were not downturned as much as originally thought when the specimen was
first described in the 1980s. They also found that neural spines of the neck
formed the forward part of a sail similar to that found on another ancient
archosaur called Arizonasaurus, a very close relative of Xilousuchus found in
Arizona.
The family trees of birds and crocodiles meet somewhere in the early Triassic
and archosauriforms are the closest cousin to those archosaurs, Nesbitt said.
But the new research places X. sapingensis firmly within the archosaur family
tree, providing evidence that the early members of the crocodile and bird
family trees evolved earlier than previously thought.
"This animal is closer to a crocodile, but it's not a crocodile. If you saw it
today you wouldn't think it was a crocodile, especially not with a sail on its
back," he said.
The research was funded by the National Science Foundation, the Society of
Vertebrate Paleontology, the American Museum of Natural History and the Chinese
Academy of Sciences.
Email or share this story:
| More
Story Source:
The above story is reprinted (with editorial adaptations by ScienceDaily
staff) from materials provided by University of Washington. The original
article was written by Vince Stricherz.
Need to cite this story in your essay, paper, or report? Use one of the
following formats:
APA
MLA
University of Washington (2011, May 19). China fossil shows bird, crocodile
family trees split earlier than thought. ScienceDaily. Retrieved May 20, 2011,
from http://www.sciencedaily.com /releases/2011/05/110518151822.htm
Note: If no author is given, the source is cited instead.
Disclaimer: Views expressed in this article do not necessarily reflect those of
ScienceDaily or its staff.
------------------------------------
Post message: [email protected]
Subscribe : [email protected]
Unsubscribe : [email protected]
List owner : [email protected]
Homepage : http://proletar.8m.com/Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/proletar/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/proletar/join
(Yahoo! ID required)
<*> To change settings via email:
[email protected]
[email protected]
<*> To unsubscribe from this group, send an email to:
[email protected]
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
