New fossil suggests life during the late Cretaceous was not quite what we thought

When we imagine the world of the Cretaceous period, millions of years before the Chicxulub meteorite smashed into the Gulf of Mexico, usually we think of gigantic animals. Dinosaurs smashed through the forests, and giant flying reptiles called pterosaurs ruled the skies with their 10-meter wingspans. But a new discovery of a small pterosaur, with a wingspan of only about a meter, has overturned this popular idea.

This unnamed pterosaur, likely related to the much larger azhdarchid pterosaurs of the same period, is described in a paper published in Royal Society Open Science. Two fragments of its skeleton were discovered on Hornby Island, British Columbia, providing just enough material for scientists to verify that it was not simply an adolescent version of a larger animal. Based on the telltale shape of its vertebrae, the researchers are convinced it's not a bird, but they don't have enough remains to say for certain where this new species would fit into the evolutionary tree. Study lead Elizabeth Martin-Silverstone told Nature, "It’s quite different from other animals we’ve studied. There hasn’t really been evidence before of small pterosaurs at this time period." This finding is a surprise, because many paleontologists believed that pterosaurs evolved to be larger and larger as the Cretaceous wore on.

These small pterosaurs probably lived alongside the first birds. This revelation overturns one hypothesis about why the pterosaurs died out, which is that birds out-competed the small pterosaurs—leaving only the big pterosaurs, who went extinct in the aftermath of the same bolide impact that wiped out the large, non-winged dinosaurs. If birds and small pterosaurs co-existed for millions of years, it seems unlikely that the story was as simple as birds out-competing them.

Paleontologist Darren Naish, creator of the Tetrapod Zoology blog, has written extensively about the evolution of pterosaurs and told Ars via e-mail that this new study is "exciting stuff." He added that it fits with other recent data showing that the latest Cretaceous pterosaurs were more diverse and anatomically varied than previously thought. That gigantic head you see on the pterosaurs in paleontologist Mark Witton's pictures above, however, is common across these animals regardless of size. "The azhdarchoid skull is often way bigger than the body," Naish said.

What Martin-Silverstone and her colleagues can say for certain is that many more small pterosaurs existed than we can see in the fossil record. Because the pterosaur's bones were light and hollow, they were not preserved as well as the bones of their heftier cohorts. This discovery also underscores one of the profound difficulties that paleontologists face as they try to make sense of ecosystems that existed millions of years ago. Often, the fossil record does not reflect the true diversity of animal and plant species, and we may be missing crucial clues that could tell us why some life forms survived while others didn't.

Royal Society Open Science, 2016. DOI: 10.1098/rsos.160333

Listing image by Mark Witton