Ancient winged reptiles called pterosaurs were so successful that they ruled Earth's skies for tens of millions of years, according to a study published in the journal ZooKeys.
The fearsome fliers, part of a family of pterosaurs named Azhdarchidae, get their name from azdarha, the Persian word for "dragon." Unlike earlier pterosaurs, they had no teeth, and they dominated from late in the Cretaceous period (around 90 million years ago) until the extinction event that also killed off the dinosaurs some 66 million years ago.
"This shift in dominance from toothed to toothless pterodactyloids apparently reflects some fundamental changes in Cretaceous ecosystems, which we still poorly understand," study author Alexander Averianov of the Russian Academy of Sciences wrote in the paper.
Pterosaurs are not dinosaurs, and they're definitely not ancient birds, which are the living descendants of the dinosaurs. But understanding these large predators can give insight into the ancient ecosystem as well as the origins of flight, as pterosaurs are thought to be the first animals after insects to develop powered flight.
Pterosaur fossils are tough to find, the study authors point out, because their fragile bones haven't survived as well as dinosaur remains have.
"Pterosaur bones were thin and fragile, much like bird bones, and they often drifted apart, shattered, or became scrambled before they could be preserved," according to the American Museum of Natural History.
Thus, it's often pretty difficult to tell how the few fossils that do exist are related to one another, according to the paper.
"Azhdarchidae currently represents a real nightmare for pterosaur taxonomists: Most taxa are known from few fragmentary bones, which often do not overlap between named taxa, the few articulated skeletons are poorly preserved," Averianov wrote, and some of the best material "has remained undescribed for 40 years."
For the ZooKeys study, Averianov surveyed and analyzed the known research to help straighten out the fossil record. The findings also showed that although their bones are challenging to find, the pterosaurs were probably quite successful in a wide variety of habitats, but were more commonly found near large lakes and rivers and especially in near-shore marine environments.