A spectacular fossil apparently of a pterosaur and its egg may help to unlock the mystery of how the winged reptiles reproduced. The fossil鈥檚 discoverers think it provides evidence that the beasts produced clutches of young and provided no parental care 鈥� essentially suggesting that hatchlings could fly.
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聽million years ago the group evolved to include the largest flying animals ever to live 鈥� .
Yet much remains unknown about their biology and behaviour. Birds and crocodiles are pterosaurs鈥� closest living relatives, but the three groups have diverged enormously. Fossils had already shown that pterosaurs laid eggs 鈥� but few have been found, and we have no direct evidence of how they raised their young. The new fossil provides some tantalising clues, however.
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The end of Mrs T
Found in China, it is the remains of a Darwinopterus pterosaur 鈥� a genus with a . The new specimen 鈥� dubbed 鈥淢rs T鈥� or 鈥淢rs Pterodactyl鈥� 鈥� fractured a wing about 160 million years ago and sank to the muddy bottom of a lake. There the corpse鈥檚 decay apparently caused it to expel a single egg, says of the University of Leicester, UK. Sediment then buried the pterosaur with the egg between its legs (see picture).
The egg鈥檚 width matches that of the pterosaur鈥檚 pelvis, says Unwin 鈥� evidence that the animal could have laid the egg, and that the 鈥渕other鈥� and egg didn鈥檛 simply coincide by chance on the lake bed. Further analysis revealed that the eggshell is not composed of calcium carbonate as birds鈥� eggs are, although calcified fossils in the surrounding sediment show that conditions were suitable for preserving such material. Unwin says this is strong evidence that the shell was flexible and parchment-like, like those of lizards and other scaled reptiles, confirming earlier theories.
He and co-author Junchang L眉 of the Chinese Academy of Geological Sciences in Beijing, China, also note that the pterosaur egg is relatively small. They estimate the pterosaur weighed 110 to 220聽grams and the egg 6聽grams. Modern birds of a similar weight typically lay eggs two to three times heavier.
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.
鈥淲hen pterosaurs hatched, they were tiny versions of adults,鈥� Unwin told New 杏吧原创, and 鈥減robably鈥� could fly and survive on their own. In contrast, modern birds hatch with undeveloped wings, and require parental care to survive.
Where鈥檚 the crest?
Mrs T may crack another mystery of pterosaur sex 鈥� how to tell the males from the females. Some pterosaurs had crests on their heads, but others didn鈥檛. The 30 Darwinopterus fossils so far identified by researchers in China show a sharp distinction between two types 鈥� one with large crests and one without.
A piece of Mrs聽T鈥檚 skull is missing, but enough remains to show that she had no crest, says Unwin. He takes that as evidence that the crests were sexual displays for males, and notes that the crested Darwinopterus fossils tend to have small pelvises, as expected for males.
of the University of California, Berkeley, remains to be convinced on either count, however. He points out that crest size might have changed as the pterosaurs grew, as the skull ornamentation on horned dinosaurs did: Mrs聽T might lack a crest because she was young, not because she was female.
鈥淚t is not unusual for animals to be able to reproduce before being fully grown,鈥� he says. 鈥淓verything does that, except small mammals and small birds.鈥�
Padian also doubts pterosaurs could have laid many eggs. Mrs聽T鈥檚 egg 鈥渨as taking up the entire body cavity not occupied by the lungs鈥�, he says, so the pterosaur probably laid only one egg a time 鈥� although whether this influenced the amount of parental care invested in the young remains unclear.
Journal reference: , DOI: 10.1126/science.1197323
When this article was first posted, we incorrectly said that researchers had identified 30 to 40 Darwinopterus fossils in China
