robert karl stonjek

Triassic reptiles had live young
Report in Nature of sauropterygians is first evidence of viviparity in the
group
By Graciela Flores

The largest and most diverse group of Triassic aquatic reptiles gave birth
to live young, researchers report in this week's Nature. The finding in
sauropterygians is the first evidence of viviparity in this group of
animals, which lived throughout the Mesozoic era, from 250 to 65 million
years ago.

Paleontologists have been divided on the issue of whether sauropterygians
were oviparous or viviparous. Many contended that the reptiles laid their
eggs on the shores-as modern marine turtles do-while others argued that they
gave birth to live young in the water, study coauthor Xiao-chun Wu, of the
Canadian Museum of Nature, told The Scientist. "Until now, nobody had any
evidence [to support either position]," Wu said.

The evidence came in the form of two small, nearly complete, gravid
specimens of the sauropterygians Keichousaurus hui from the province of
Guizhou in southwestern China. Most of the embryos found within the nearly
12-inch long females were "head backwards," a position thought to be
abnormal, which the authors suspect could have caused the death of the two
mothers and their young.

"These two specimens speak very nicely, very neatly, and very cleanly [of
the fact] that the ability to give birth to live young arose very early on
in the evolution of these groups of reptiles," said Michael Caldwell of the
University of Alberta. "These results indicate that viviparity is a
primitive feature for this group."

Full Text at TheScientist
http://www.biomedcentral.com/news/20041118/01

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Robert Karl Stonjek