21st January 2011, 9:29am
New fossil sheds light on pterosaur sex life
“Mrs T”, a female Darwinopterus (wingspan 0.78 m) preserved together with her egg. Picture credit: L The discovery of an ancient fossil, nicknamed ‘Mrs T’, has allowed scientists for the first time to sex pterodactyls – flying reptiles that lived alongside dinosaurs between 220-65 million years ago.

The find was made by an international team of researchers from the Universities of Leicester, Lincoln and the Geological Institute, Beijing. Details of the unique new find are published today (21 January) in the journal Science.

Pterosaurs, flying reptiles, also known as pterodactyls, dominated the skies in the Mesozoic Era and featured prominently in Spielberg’s Jurassic Park III and are a classic feature of many dinosaur movies. The discovery of a flying reptile fossilised together with an egg in Jurassic rocks (about 160 million years old) in China provides insight into reproduction and is the first direct evidence for gender in these extinct fliers. This fossil shows that females were crestless, solving the long-standing problem of what some pterosaurs did with their spectacular head crests: showy displays by males.

The new discovery, christened “Mrs T” (a contraction of “Mrs Pterodactyl”) by the research team, was made in Jurassic rocks of Liaoning Province in northeast China and seems to represent a tragic accident. The well developed shell shows that Mrs T was just about ready to lay her egg when she was killed in an accident that broke her left forearm, possibly the result of a storm, or perhaps even a volcanic eruption, which were common in this part of China around 160 million years ago.

This individual of Darwinopterus (a type of pterosaur from China first described by the same team of scientists in 2009) has an egg and must be female. This type of discovery, in which gender can be determined with certainty, is extremely rare in the fossil record, and the first to be reported for pterosaurs.

Dr Charles Deeming, an embryologist in the Department of Biological Sciences at the University of Lincoln, was part of the research team that studied the fossil. He said: “This was a great find – we could compare this soft-shelled pterosaur egg with other pterosaur eggs in the fossil record and use its dimensions to predict its likely size and even how big the hatchling was going to be.”

Dr Deeming continued “The pterosaur’s eggshell is typical of relatively small eggs of modern lizards and snakes, not the relatively large hard-shelled eggs of birds, and so incubation would have been in an underground nest.”

This fossil tells us much more about the sex life of pterosaurs. Head crests are commonly seen on fossil pterosaurs and in the most spectacular cases these can reach five times the height of the skull. Scientists have long suspected that these crests were used for some kind of display or signalling and may have been confined to males, while females were crestless. Unfortunately, in the absence of any direct evidence for gender this idea remained speculative and crested and crestless forms were often separated into completely different species.

Dr David Unwin, a Pterosaur expert at the University of Leicester, also worked on the specimen and said: “Mrs T shows two features that distinguish her from male individuals of Darwinopterus. She has relatively large hips, to accommodate the passage of eggs, but no head crest. Males, on the other hand, have relatively small hips and a well developed head crest. Presumably they used this crest to intimidate rivals, or to attract mates such as Mrs T. As long as the skull or hips are preserved we can now confidently identify males and females of Darwinopterus and, even more importantly, we can use this technique to sex other pterosaurs because they often show differences in head crests and hips just as in Darwinopterus.”

Dr Unwin added: “Gender is one of the most fundamental of biological attributes, but extremely difficult to pinpoint with any certainty in the fossil record. Being able to sex pterosaurs is a major step forward. Finally, we have a good explanation for pterosaur head crests, a problem that has puzzled scientists for more than 100 years. Now, we can exploit our knowledge of pterosaur gender to research entirely new areas such as population structure and behaviour. We can also play matchmaker for pterosaurs bringing back together long separated males and females in the single species to which they both belong."
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