Paleontologists found the fossils of a pterosaur the size of a cat — and it’s not just cute as hell, it’s also an important cue for whether ancient birds outcompeted the smallest flying reptiles. This teensy pterosaur, in fact, is from the late Cretaceous, around 83 to 72 million years ago, a time when the largest pterosaurs were as big as giraffes and small pterosaurs were thought to be mostly extinct.
The small pterosaur, described in a study published today in the journal Royal Society Open Science, is one of the very few discovered in North America. It’s a reminder that there’s still so much we don’t know about how diverse pterosaur populations were at the end of the Cretaceous, right before dinosaurs and pterosaurs went extinct.
"It’s so much smaller than anything else we have from that time period," says lead study author Elizabeth Martin, a paleobiology PhD student at the University of Southampton, in the UK. "It’s got to be sort of the age of flying giants, and here we have something that’s kind of more similar to a modern large bird."
Pterosaurs were the earliest vertebrates known to conquer the skies, gliding and flapping their wings to travel through the air. They were close cousins of dinosaurs and they lived all over the planet. Over 150 millions years, they evolved from small flying reptiles to large and diverse species that had elaborate crests and specialized teeth to crush seashells. Toward the end of the Cretaceous, around 100 to 66 million years ago, most pterosaurs were enormous, with wingspans of 36 feet and weighing up to 550 pounds. Some were as big as F-16 fighter jets.
It’s a bit less clear what happened to small pterosaurs at that time. One hypothesis suggests that small pterosaurs were outcompeted by birds, says Mark Witton, a pterosaur expert and study co-author. The idea is that ancient birds took over the smaller ecological niches previously dominated by small pterosaurs, pushing the flying reptiles to evolve into bigger and bigger animals.
The Hornby pterosaur had a wingspan of almost five feet
Today’s study challenges that idea. The small pterosaur found on Hornby Island in Canada suggests that birds hadn’t yet pushed the smallest flying reptiles out of the air; small pterosaurs were still around in the late Cretaceous, living alongside the flying giants. The Hornby pterosaur had a wingspan of almost five feet, much smaller than the huge pterosaurs known to exist at the time. "It shows that [small] pterosaurs were not at least totally on their way out," says Brian Andres, a pterosaur expert and visiting assistant professor at the University of South Florida, who did not take part in the study.
Only a few fossil remains of the pterosaur were found, and researchers used them to estimate the size of the animal. The bones were discovered in 2008 — 10 pieces in total, including part of a left humerus, from the animal’s wing, and three vertebrae. By studying the bones, their sizes and internal structures, the researchers concluded that the Hornby pterosaur belonged to a group of short-winged reptiles with no teeth called azhdarchoid pterosaurs. They also concluded that the Hornby pterosaur was not the baby of a large species, but an actual small animal that was almost fully grown. It was as big as a cat. "That’s unexpected," Witton says. "That’s what we’re quite excited about with this animal."
Finding pterosaur fossils is incredibly rare
Finding pterosaur fossils is incredibly rare. Pterosaur bones were hollow and thin-walled, which made great skeletons for flying — but not so much for preservation through millennia. Finding small pterosaur fossils is even rarer, because smaller animals are harder to find. "There are not many specimens from this time period so I was really quite intrigued they found a new one," Andres says.
The specimen described in today’s paper, however, is far from complete — and that leaves room for error. Alexander Kellner, a paleontologist at the Museu Nacional in Brazil who didn’t work on the study, says it’s impossible to know what group the Hornby pterosaur belonged to, or what it looked like. "The specimen is very very fragmentary," Kellner says. "There’s no way with that specimen that you can make any distinction." Still, Kellner agrees that the few fossils point to a small pterosaur that was almost fully grown.
The only way to learn more about pterosaurs and the role ancient birds may have played in the extinction of the small ones is to find more fossils. "We’re really dealing with negative evidence and that’s not a useful thing for scientists," says Witton. "We need more information. We need more fossils."