Now scientists have found the fossil of a remarkably petite pterosaur, one that lived just 77 million years ago — long after small winged reptiles were thought to have been edged out of the evolutionary game by rapidly adapting birds.
The new fossil, described in the journal Royal Society Open Science, shows a pterosaur with a wingspan of less than five feet across. With its wings folded up against its tiny body, the creature would have been no larger than a modern domestic cat, standing just a foot tall (though that beak probably would have kept it from being very snuggly). According to analysis of the creature's bones — which, to be fair, are in pretty rough shape — the researchers feel confident that their specimen was an adult, not the baby of some heftier flier.
"This new pterosaur is exciting because it suggests that small pterosaurs were present all the way until the end of the Cretaceous, and weren't outcompeted by birds," lead study author Elizabeth Martin-Silverstone, a paleobiology graduate student at the University of Southampton, said in a statement.
Researchers have long noted that juvenile versions of the big pterosaurs of the Late Cretaceous are few and far between in the fossil record. Since these giant reptiles must have been babies once, the lack of fossil evidence suggests that smaller specimens might not have held up as well. That could explain why species like the one Martin-Silverstone identified have proved elusive.
"The hollow bones of pterosaurs are notoriously poorly preserved, and larger animals seem to be preferentially preserved in similarly aged Late Cretaceous ecosystems of North America," she added. "This suggests that a small pterosaur would very rarely be preserved, but not necessarily that they didn't exist."
If scientists can find more of these small specimens — perhaps even some lurking, misidentified and neglected, in museum archives — it could discredit a recently developed theory of pterosaur evolution. Because scientists had watched small pterosaurs give way to behemoths in the fossil record just as avian dinosaurs shrank down into birds as we know them, it was reasonable to assume that small birds had edged pterosaurs out of their small-flying-thing niche, forcing them to get bigger or go extinct.
But the same poor preservation that Martin-Silverstone and her colleagues use to account for the absence of tiny pterosaurs in the fossil record means that not everyone will accept their results. Their fossil, found in what is now British Columbia, is incomplete — a forelimb, a few vertebrae, and various tiny fragments of bone — and its 77 million years in the ground have not been very kind to it. The pieces are so sparse that the researchers declined to try to name the animal as a new species, because it would be difficult to prove just what other creatures it was most closely related to.
“The authors have done a good job given the limited data,” Richard Butler of the University of Birmingham told National Geographic. But Butler wasn't convinced that the bones didn't come from a juvenile pterosaur — or another kind of animal entirely. “A pterosaur identity is probable … but they cannot be completely certain that it is not a bird," he said.
The main argument for the creature's non-avian identity rests in its vertebrae: The researchers believe they see something called a notarium, a section of fused vertebrae that pterosaurs developed late in their lineage that helped them support powerful, muscled wings. Birds, which were developing flight but came from a completely separate evolutionary lineage, didn't have this structure.
This nameless little pterosaur has probably told scientists all it can from its scant, broken bones. But other specimens could help fill in the gaps of the story.
"What we have now — it's not enough to understand this weird phenomenon at the end of the Cretaceous, where there aren't any small pterosaurs," study co-author Mark Witton, a paleontologist at the University of Portsmouth, told Live Science. "There are so many things in museums that people aren't looking out for. What we want to do is put these things on the radar of researchers and curators, so we can start to build up a good-quality data set of these small specimens."