Few things are as disappointing as learning that no pterosaurs survived the K/Pg extinction. This has always been especially hard for me to emotionally accept due to their immense diversity. The typical explanation usually told is that they were wiped out with the non-avian dinosaurs after the chicxulub impact, and that they were barely alive by that time anyway because all the birds had filled up the flying niches. However recent evidence indicates that pterosaurs actually were doing very well up until 65 million years ago. Why they went extinct may have nothing to do with birds or a failure to diversify. Serial size reduction allowed for smaller pterosaurs to survive through other extinctions. Reaching sexual maturity before being fully grown allowed for smaller hatchlings maturing more quickly, allowing for more reduction in size by accelerating evolution somewhat. So if there were smaller pterosaurs at the end of the Cretaceous, AND pterosaurs have previously proven to be capable of relatively rapid phylogenetic size decreases, why did no pterosaurs survive?
The Cretaceous is more known for its giant, “small-plane sized” pterosaurs (Arambourgiania, Quetzalcoatlus, and one that’s been in the news more recently for “terrorizing” Transylvania: Hatzegopteryx). For background pterosaurs are split into two major suborders, with Rhamphorhynchoids being a paraphyletic group characterized by having teeth, long tails, and a cruropatagium that stretched between the feet (like how bats have it). Most were small and lacked bony head crests. They appeared in the Triassic and went extinct during the Cretaceous though there is no strong evidence to indicate they were outcompeted by pterodactyloids which is a common assumption.
Pterodactyloids, the other suborder, did not appear until the late Jurassic and were much more successful and diverse in the Cretaceous. While all pterosaurs are outstanding creatures, the pterosaurs this post is concerned with would all be pterodactlyoid members.
No fossils of pterosaurs have been found from after the K/Pg extinction (and I don’t believe there ever will be 😦 ). But while there are certainly no pterosaurs alive today, there is a lot of evidence indicating that pterosaurs were actually quite diverse even at the end of the Cretaceous, and that some were even very small. The discovery of small pterosaurs from the late Cretaceous does seem to indicate that the reason for their clade’s total extinction was not simply because they were just “too large.”
Small pterosaurs may have been more abundant in Cretaceous than previously thought
A small azhdarchoid (azhdarchoids being the most recent common ancestor of Quetzalcoatlus and Tapejara, and all its descendents) pterosaur was discovered from the Campanian Northumberland Formation of British Columbia. With an estimated 1.5m wingspan, the pterosaur specimen is described as being about the size of a large seagull. The specimen found might not actually be an azcharchoid, but it certainly was from a pterosaur. Researchers were able to analyze the bones to determine whether or not it was juvenile or adult and found that the specimen was either fully grown or very close to being fully grown. For more on that, read the paper here.
Pterosaurs preserve terribly. They’re bones are hollow, their skeletons are fragile, they didn’t routinely die in nice, preserving environments. During the Cretaceous, pterosaurs shifted from marine to more non-marine habitats. This may account for the lack of data on small, difficult to preserve pterosaur fossils in the late Cretaceous. Terrestrial habitats do not preserve fragile fossils. Even much larger, denser bones do not often preserve well in terrestrial environments. The fossils that have been found from pterosaurs of this period are usually in very bad shape and are only fragments of the entire skeleton. Often times, fossils have to be looked at by many bird and pterosaur specialists before it can even be determined that the bone WAS from a pterosaur. There is a lot of growing evidence suggesting that smaller pterosaurs in the late Cretaceous were not as rare as once believed.
Birds not the cause of pterosaur extinction
Pterosaurs were excellent fliers, almost definitely warm-blooded like birds (due to the energy expense of their lifestyle) and seemed able to adapt to a wide variety of niches. So it’s strange to imagine them going extinct due to their failure to diversify in the presence of birds. A study showed that pterosaurs actually diversified more after birds appeared. Pterosaurs had about a 160 million-year run on Earth and were relatively similar morphologically for the first 70 million years. They then began to experiment, trying out many modes of life. As birds became more successful, the pterosaurs actually responded by diversifying more. The emergence of birds (at least 50 million years after the first pterosaurs), encouraged the pterosaurs to try out new diets and feeding styles as seen by the rapid diversification of skull shapes in the fossil record. The general direction they went towards was much larger bodies. This was when the famous giant Quetzcoatlus types emerged.
- A small azhdarchoid pterosaur from the latest Cretaceous, the age of flying giants. Martin-Silverstone, Elizabeth, et al. Royal Society Open Science. 2016.
- Evolution of morphological disparity in pterosaurs. Katherine Prentice, Marcello Ruta, Michael Benton – Journal of Systematic Palaeontology – 2011