Fossil of mom with egg reveals Pterosaur's female form

20th January 2011, Comments 0 comments

Her life came to a crashing end, but the fossil left by a flying reptile nicknamed Mrs T has shed light on what female pterosaurs looked like when they soared above Earth some 220-65 million years ago.

The 160 million-year-old fossil, showing an almost complete skeleton of a heavy-hipped Darwinopterus and her egg, was found in the Jurassic sedimentary rocks of China's northeastern Liaoning Province.

Pterosaurs were warm-blooded, winged creatures that flew alongside the dinosaurs and resembled a mix between a stork and a bat.

A team of British and Chinese researchers said in the journal Science the hawk-sized Mrs T (short for pterosaur) displays wider hips than males, and likely lacked the same distinct head crest that could be seen in the opposite sex.

"This type of discovery, in which gender can be determined with certainty, is extremely rare in the fossil record, and the first to be reported for pterosaurs," said David Unwin, a paleobiologist in the Department of Museum Studies at the University of Leicester.

"She has relatively large hips, to accommodate the passage of eggs, but no head crest," he said.

"Males, on the other hand, have relatively small hips and a well developed head crest. Presumably they used this crest to intimidate rivals, or to attract mates such as Mrs T."

Many of her other traits match those of 10 similar creatures found in the same rock formation -- an elongated neck and tail, an protruding beak-like mouth lined with slender teeth, and an extended fifth toe.

A team of scientists from the Universities of Leicester, Lincoln and the Geological Institute, Beijing studied the fossil, which was first identified in 2009, and gleaned clues of a violent end to the young creature's life.

Judging by the visible bone break near her wing, some kind of sudden accident like a volcanic eruption or a storm must have fractured the mother-to-be's forearm, making it impossible for her to fly, they said.

She plunged into a body of water and drowned. As her body grew waterlogged, it sank to the bottom. The egg, which looked like it was days from being laid, was pushed out of her decaying body.

"The association of the egg with the skeleton, at least in pterosaurs, is unique. We have no other similar sort of specimen," said Christopher Bennett, an expert at Fort Hays State University in Kansas who reviewed the research.

Bennett said she might have had some sort of head markings, though it was likely not the same flashy display grown by males to attract sex partners.

"I am not entirely convinced that this individual didn't have any crest. It is possible that it was a young adult and a bony crest had not yet grown," he said.

Nevertheless, the fossil is a "nice specimen" and shows that "females had a pelvis that was deeper and had a larger opening," Bennett said.

The find will also help researchers better identify previously found fossils as either male or female.

Unwin said Mrs T's egg was small and likely had a soft shell, much like the eggs of reptiles, and would have probably been buried before hatching.

"A small egg would require less investment in terms of materials and energy -- a distinct evolutionary advantage for active energetic fliers such as pterosaurs," said Unwin.

© 2011 AFP

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