Young dinos lived and died together

March 16th, 2009 - 1:22 pm ICT by IANS  

National Geographic Washington, March 16 (IANS) A herd of young birdlike dinosaurs met their death on the muddy margins of a lake some 90 million years ago, according to a team of Chinese and American palaeontologists.
Composed entirely of juveniles of a single species of ornithomimid dinosaur (Sinornithomimus dongi), the herd suggests that immature individuals were left to fend for themselves when adults were preoccupied with nesting or brooding.

“There were no adults or hatchlings,” said Paul Sereno, professor at the University of Chicago and National Geographic Explorer-in-Residence. “These youngsters were roaming around on their own,” remarked Tan Lin from the Department of Land and Resources of Inner Mongolia.

Within a pair of the skeletons, prepared for display in Sereno’s lab and airlifted back to China in late February, stomach stones and the animal’s last meals are preserved.

Sereno and Zhao Xijin, professor in the Chinese Academy of Sciences, led the 2001 expedition that found the fossils in the Gobi Desert in western Inner Mongolia.

Team members included David Varricchio of Montana State University (MSU), Jeffrey Wilson of the University of Michigan and Gabrielle Lyon of Project Exploration.

“Finding a mired herd is exceedingly rare among living animals,” said Varricchio, an assistant professor of palaeontology at MSU. “The best examples are from hoofed mammals,” such as water buffalo in Australia or feral horses in the American West, he said.

Sereno and associates then opened an expansive quarry, following one skeleton after another deep into the base of the hill. In sum, more than 25 individuals were excavated from the site. They range in age from one to seven years, as determined by the annual growth rings in their bones.

The details provided key evidence of an ancient tragedy. Two of the skeletons fell one right over the other. Although most of their skeletons lay on a flat horizontal plane, their hind legs were stuck deeply in the mud below, said a Chicago release.

Only their hip bones were missing, which was likely the handiwork of a scavenger working over the meatiest part of the body bodies shortly after the animals died.

The findings were published in Acta Palaeontologica Polonica.

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