A SPECTACULAR fossil, the only one known to contain an embryonic pterosaur, suggests the flying reptiles laid soft eggs rather than hard ones.
Fossilised dinosaur eggs are common, although very few contain the bones needed to identify the parents. Fossilised lizard and bird eggs have also been found but none from a pterosaur, until now.
The new find comes from the Liaoning fossil beds in north-eastern China, which are famed for preserving impressions of bird and dinosaur fossils. It dates from the early Cretaceous period around 121 million years ago and was preserved in the sediment of an ancient lake.
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The embryo is nearly complete, with its wing bones folded tightly to fit into a volume about the size of a chicken egg. Its elongated fourth finger and other bones clearly identify it as a pterosaur, say Xiaolin Wang and Zhonghe Zhou of the Institute of Vertebrate Paleontology and Paleoanthropology, Beijing (Nature, vol 429, p 621). They estimate that it would have had a wingspan of around 27 centimetres.
鈥淚t鈥檚 extremely exciting, a really great discovery,鈥� says pterosaur specialist Dave Unwin of the Humboldt University in Berlin, Germany. A key question is whether pterosaur eggs were hard like bird and dinosaur eggs, or soft like those of some other reptiles. Unwin suspects the latter, because the fossil was squashed flat without shattering as a hard shell would. That would mean that pterosaurs could not have sat on their eggs to incubate them, as even a lightly built creature would squash the soft shells.