3-D fossil eggs reveal how pterosaurs lived
Nest eggs The spectacular discovery of three dimensional 120-million year old pterosaur eggs provides a unique insight into the ancient flying reptiles' lifestyle.
Until now, only four pterosaur eggs had ever been found, and all were flattened during the process of fossilisation.
But Chinese scientists have unearthed five three-dimensional pterosaur eggs at a site in northwestern China that also includes no fewer than 40 adult individuals of a newly identified species that lived in a bustling colony near a large freshwater lake.
Their findings are reported in the journal Current Biology .
"This is definitely the most important pterosaur site ever found," says paleontologist Zhonghe Zhou, director of the Chinese Academy of Sciences' Institute of Vertebrate Paleontology and Paleoanthropology.
The pterosaur, Hamipterus tianshanensis, had a crest atop its elongated skull, pointy teeth for catching fish and a wingspan of more than 3.5 metres.
The five oblong eggs were "pliable" with a thin, hard outer layer marked by "cracking and crazing" covering a thick membrane inner layer, making them resemble the soft eggs of some modern snakes and lizards, says palaeontologist Xiaolin Wang, another of the researchers involved in the discovery.
"They are the best-preserved pterosaur eggs ever found," says Wang.
Snapshot of pterosaur life
The site is remarkable for what it reveals about how pterosaurs lived
At least 40 male and female individuals have been identified, and there may be hundreds in all.
This indicates pterosaurs lived in large colonies, says Wang, in this case nesting near the lake and burying eggs in moist sand to prevent them from becoming desiccated.
"One of the significant (aspects) of this discovery — hundreds of individuals and eggs together from one site — is that it confirms that pterosaurs were gregarious, and the population size is surprisingly large," says Zhou.
The fossils illustrated important sex differences in pterosaurs. For example, males possessed distinctly larger head crests.
"In Hamipterus, size, shape and robustness are decided by the gender," says Wang, adding that this contradicts a previous notion that "sexual dimorphism in pterosaurs was only reflected in the absence or presence of the crests."
The site, discovered in Xinjiang province in 2005, was preserved probably after the Cretaceous-period animals perished together in a large storm, says Zhou.
Pterosaurs were Earth's first flying vertebrates, with birds and bats appearing much later. They thrived from about 220 million years ago to 65 million years ago, when they were doomed by the asteroid that also killed the non-avian dinosaurs.
Knowledge about pterosaurs has been spotty, with their fragile skeletons not lending themselves well to fossilisation. Little has been known about their behaviour.
"I have been truly amazed by the abundance of bones and the number of eggs as well the great potential of more discoveries from the site," says Zhou.
The genus name, Hamipterus, means "Hami wing", honouring nearby Hami City. The species name, tianshanensis, refers to the nearby Tian Shan mountains.