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Trending Science: Spectacular egg fossil find helps to unlock the secrets of the ancient Pterosaurs

The discovery in the north-west of China of hundreds of fossilised eggs is allowing palaeontologists to better understand the flying pterosaur cousins of the dinosaurs, including new evidence that they were born flightless and needed to be cared for by their parents.

Fundamental Research

On Thursday 30 November, 2017, Chinese scientists announced that they had found 215 eggs of the fish-eating Hamipterus tianshanensis, a species of pterosaur that lived 120 million years ago and had a wingspan of more than 3.5 metres. Most excitingly, 16 of the unearthed eggs contain partial embryonic remains. The research has been published in the journal ‘Science’. Discovered at a site in the Xinjiang Uygur Autonomous Region, the find not only included the eggs but fossils of hundreds of male and female adult Hamipterus. Relatively few pterosaur fossils are preserved because of the animals’ fragile, thin-walled bones. Even rarer are fossils of young hatchlings, eggs and embryos, making it difficult to understand how different species grew. ‘We want to call this region ‘Pterosaur Eden,’’ commented palaeontologist Shunxing Jiang of the Chinese Academy of Sciences’ Institute of Vertebrae Palaeontology and Paleoanthropology. It would be a good name too, as even more eggs – possibly up to 300 – could be present on the site, with some buried under the exposed fossils. The first pterosaur embryo was found in China in 2004, but the egg and embryo were flattened and it was not clear exactly what type of pterosaur it was. The first three-dimensionally preserved pterosaur egg came from Argentina from an animal called Pterodaustro, previously known from several specimens and eggs that are mostly crushed. Until now, no pterosaur eggs had been found with embryos well-preserved in three dimensions. The embryonic bones discovered in Pterosaur Eden indicated that the hind legs of a baby Hamipterus developed more rapidly than crucial wing elements, as commented on by Alexander Kellner, a palaeontologist at the Museu Nacional in Rio de Janeiro, Brazil. ‘Some birds can fly on the same day they break out of the egg, while some others will need a long period of parental care. Our conclusion is that a baby Hamipterus could walk but not fly,’ said Jiang. If this hypothesis is indeed correct, then this would mean that the young hatchlings would have needed an extended period of parental care. Other evidence that strongly points in this direction is the fact that it appears the pterosaurs lived in a bustling colony near a large freshwater lake. Kellner cited evidence that females gathered together to lay eggs in nesting colonies and would return over the subsequent years to the same nesting site, a trend that has also been applied to other pterosaur species. By CT scanning the eggs, the researchers found an assortment of preserved bones, mainly from the wings and legs. Unlike other pterosaur embryos from China or Argentina, very little material from the skull appeared in the embryos, with only a single lower jaw preserved. The areas for the attachment of important flight muscles were either small or nonexistent in the unhatched animals, while the legs appeared to be more complete, giving credence to the idea that the juveniles were flightless.