Rare fossil could explain the mystery of the missing pterosaurs

The Mesozoic Era is often called the Age of Dinosaurs ... which is more than a little unfair because it was also the Age of Pterosaurs. These flying reptiles ruled the skies for just as long as dinosaurs ruled the land. And now, a newly discovered tiny pterosaur from Canada is helping to unravel a mystery about these ancient winged beasts.

During their 165 million-year reign, pterosaurs evolved a range of sizes, from the smallest species with wingspans under half a metre to true giants that flew on wings ten metres from tip to tip. But something strange happens in the fossil record towards the end of the Age of Pterosaurs. During a time period called the Late Cretaceous, all of the little pterosaurs seem to disappear.

So what happened to all the little species? Some palaeontologists have wondered if competition with birds drove the smaller pterosaurs to an early extinction, but this new discovery suggests this wasn't the case.

An artist's reconstruction of the newly discovered mini-pterosaur. Image: Mark Witton

The new pterosaur was discovered in 2009 on Hornby Island in British Columbia. Not much is left of the animal – just an arm bone, several vertebrae, and some other bits and pieces – but it's enough for researchers to know that this pterosaur was petite, with an estimated wingspan of only about 1.5 metres. Based on the bone structure, palaeontologists can also tell this animal wasn't a baby – it was a small but almost fully grown pterosaur.

"The specimen is far from the prettiest or most complete pterosaur fossil you’ll ever see," says pterosaur expert Dr Mark Witton of the University of Portsmouth, "but it's still an exciting and significant find."

The fossil hails from the Late Cretaceous, 77 million years ago, meaning this little flier soared over what is now Canada when dinosaurs like the horned Albertaceratops and the fearsome Daspletosaurus roamed the land. It is also the first pterosaur of its size discovered from this time period. It appears the small pterosaurs didn't disappear after all ... but then why are they so hard to find?

The new pterosaur was about as tall as your pet cat. Image: Mark Witton

The most likely answer is something that palaeontologists have known for a long time: pterosaurs are bad at becoming fossils. "It's rare to find pterosaur fossils at all because their skeletons were lightweight and easily damaged once they died," says Witton. "And the small ones are the rarest of all." The authors point out that babies of large pterosaurs are also conspicuously missing from the Late Cretaceous fossil record, even though they obviously existed.

Small pterosaurs didn't go extinct early, they just don't fossilise well (this is called "preservation bias"). "This new pterosaur is exciting because it suggests that small pterosaurs were present all the way until the end of the Cretaceous,” says lead author Elizabeth Martin-Silverstone, a PhD student at the University of Southampton.

And some of these "missing" pterosaurs, she adds, might already have been discovered. "Researchers should check [museum] collections more carefully for misidentified or ignored pterosaur material."

When it comes to fossils, it isn’t always the biggest or most complete skeletons that end up being important. This small jumble of fragile bones is enough to hint at an entire range of previously unknown pterosaur diversity. And now that we know they’re out there, in fossil sites waiting to be dug up or in museum drawers waiting to be rediscovered, the hunt for tiny pterosaurs is on!