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Evolution Of Crocodile Jaws


In Crocodile Evolution, the Bite Came Before the Body

John Roach
for National Geographic News
August 25, 2004

Today the crush of a crocodile's mighty jaws signals lights-out for many a
fish or other water-loving animal. But according to a new study, the
croc's characteristic jaws evolved on dry landand long before its
swim-tuned body.

The finding stems from the discovery of a well-preserved fossil of an
ancestor of crocodilians in northwestern China. A crocodilian is any
member of an order of reptiles that includes crocodiles, alligators,
caimans, gavials, and related extinct forms.

The discovery will be reported in tomorrow's issue of the journal Nature.

The creature, named Junggarsuchus sloani, was a three-foot-long
[one-meter-long] sphenosuchianone of a class of small, slender,
land-dwelling crocodilians that lived from about 230 million to 150
million years ago.

Junggarsuchus's skull shares many characteristics with skulls of modern
crocodilians. But its body is much more similar to those of
sphenosuchians, according to James Clark, an associate professor of
biology at the George Washington University in Washington, D.C.

In fact, the forelimbs of Junggarsuchus are more adapted to walking on
land than those of its sphenosuchian contemporaries, according to the
study led by Clark. Co-authors include Xu Xing and Yuan Wang, from the
Chinese Academy of Sciences in Beijing, and Catherine Forster, from Stony
Brook University in New York State.

Based on their analysis of the new fossil, the team concludes in Nature
that the skull of modern crocodiles evolved while the legs and body were
evolving toward greater walking ability, rather than toward greater
swimming ability.