Parental pterosaurs: UCC research finds flying reptiles were good caregivers

Were the pterosaurs, flying reptiles from the days of the dinosaurs, capable of practising parental care? New research by scientists from UCC shows that larger pterosaurs were indeed caring parents – but only the larger species.

This solves a long-standing conundrum. To be able to fly soon after hatching from the egg, a bird or pterosaur must have well-developed wings. Studies of smaller pterosaurs from the Jurassic period showed that their babies already had large wings when they hatched and they could have wobbled into flight within a few days of birth.

But did this occur for the later pterosaurs which were much larger in size? In the Cretaceous period, pterosaurs usually had wingspans of 5 metres, and some even reached 10–15 metres.

“This was a difficult project,” says the study leader, Dr Zixiao Yang from UCC. “Luckily, we were able to use some classic specimens from the Jurassic of Europe and the Cretaceous of North America, together with new finds from China. By measuring the skulls, backbones, wings, and hind legs, we were able to test for differences in the relative growth of different parts of the body.”

The research focused on testing the allometry, or how the creatures’ characteristics changed with size. “We are all familiar with allometry in human babies, puppies and kittens – their heads, eyes and knees are huge, and the rest of the body grows faster to get to adult proportions. It’s the same with dinosaurs and pterosaurs. The babies have cute faces, with short noses, big eyes, and big heads,” Dr Yang said.

“The small, bird-sized, Jurassic pterosaurs were born with large wings and strong arms and legs, evidence that the babies could fly from birth. As they grew from baby to adult, their arms and legs showed negative allometry, meaning they started large and were then growing more slowly than the rest of the body.”

“But it was different for the Cretaceous giants. They also started as small babies, but the key limb bones show positive allometry through growth, suggesting a very different developmental model.”

“This means that the pterosaur giants had sacrificed low-input childcare for the need to grow huge eventually as adults. As it took much longer to become mature, the parents needed to protect their young from accidents. Investing in childcare by having non-flying babies was offset in evolutionary terms by allowing pterosaurs to evolve truly huge sizes.”

“We see the same thing in birds and mammals today. Some birds fly very young, and of course some mammals like cattle and antelopes are on their feet the day they are born. But this kind of behaviour is risky for the babies because they are often clumsy and are easy targets for predators; it’s costly also for the mother because the babies must have highly developed wings or legs at the point of birth,” he said. “So, we see the same thing in extinct pterosaurs. They were restricted in maximum body size until the end of the Jurassic, at which point their parental care behaviour changed, and then they could achieve huge sizes,” he added.