This fossil of an ancient winged reptile, bought from a farmer in China’s Liaoning province, tells a dramatic tale. About 160 million years ago, a female pterosaur fractured its wing and sank to the bottom of a muddy lake. Somehow, in the process of either dying or decomposing, she expelled a single egg, which has been preserved through the ages.
That’s the story that researchers told in a study published in the journal Science, anyway. And if the remarkably preserved fossil of the reptile Darwinopterus is female, they say, it sheds light on the sex differences and mating rituals of the extinct species. The preserved egg also seems to reveal new details of pterosaur reproduction.
Pterosaurs were the first vertebrates to take to the air, first appearing in the fossil record some 220 million years ago in the late Triassic period. Before their demise 65 million years ago the group evolved to include the largest flying animals ever to live – some had a wingspan of 10 metres. [New Scientist]
Assuming that this pterosaur was female, as the egg would indicate, researchers David Unwin and Junchang Lü then compared her to other specimens found before.
Her long, narrow beak lacks any adornment, while other individuals found nearby sport tall crests atop their heads. In fact, some 40 percent of the 133 known pterosaur species have such crests, the tallest reaching five times higher than the height of the head. [Washington Post]
The lack of a bony crest indicates on this fossil, known affectionately as “Mrs. T” or “Mrs. Pterosaur,” indicates that only males grew these natural ornaments–and probably used them in ostentatious mating displays, the scientists say.
Then they turned their attention to the round object below the pterosaur fossil’s pelvis. Its width, about 20 millimeters, matched the size pterosaur’s pelvis, increasing the odds that it was indeed the creature’s egg. But it doesn’t bear much resemblance to today’s bird eggs. The researchers’ analysis revealed that it wasn’t composed of hard calcium carbonate as birds’ eggs are; instead the crumpled eggshell appeared soft like today’s reptile eggs.
Unwin suggests that pterosaurs, like modern reptiles, may have buried many small eggs in ground where moisture could seep through their parchment-like eggs during incubation, nearly doubling their mass before hatching. [New Scientist]
But not everyone is convinced that the researchers have their story straight; paleontologist Kevin Padian, who wasn’t involved in the study, has a few critiques. For one thing, he says, the fossil’s lack of a bony head crest may not indicate its femininity–it may instead signal that the creature wasn’t fully mature.
He’s also not convinced that the round structure found with the pterosaur is an egg. Padian says it’s far too large to be an egg as it would take up much of the pterosaur’s body cavity. Plus, he says, reptiles lay dozens of eggs at a time. [ScienceNOW]
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Images: 1) Junchang Lu, 2) Mark Witton / University of Portsmouth