Pterosaurs, which include the pterodactyls and pteranodons, were the first vertebrates to achieve proper, flapping flight. In the popular imagination they are regarded as ‘flying dinosaurs’, whereas the anatomy of the two groups is significantly different. The first of them appeared in the Upper Triassic around 235 Ma ago, at roughly the same time as the earliest known dinosaurs. The anatomical differences make it difficult to decide on a common ancestry for the two. But detailed analysis of pterosaur anatomy suggests that they share enough features with dinosaurs, crocodiles and birds for all four groups to have descended from ancestral archosaurs that were living in the early Triassic, and they survived the mass extinction at the end of that Period. Birds, on the other hand, first appear in the fossil record during the Upper Jurassic 70 Ma later than pterosaurs. They are now widely regarded as descendants of early theropod dinosaurs, which are known commonly to have had fur and feathers.
Pterosaurs leapt into the public imagination in the final chapter of Sir Arthur Conan Doyle’s Lost World with a clatter of ‘dry, leathery wings’ as Professor George Challenger’s captive pterodactyl from northern Brazil’s isolated Roraima tepui plateau made its successful bid for escape from a Zoological Institute meeting in Queens Hall. Yet, far from being leathery, pterosaurs turned out, in the late 1990’s, to have carried filamentous pycnofibres akin to mammalian hair. Widespread reports in the world press during the week before Christmas in 2018 hailed a further development that may have rescued pterosaurs from Conan Doyle’s 1912 description before it sprang from its perch:
It was malicious, horrible, with two small red eyes as bright as points of burning coal. Its long, savage mouth, which it held half-open, was full of a double row of sharp-like teeth. Its shoulders were humped, and round them was draped what appeared to be a faded grey shawl. It was the devil of our childhood in person.
Two specimens from the Middle to Upper Jurassic Yanliiao lagerstätte in China show far more (Yang, Z. and 8 others 2018. Pterosaur integumentary structures with complex feather-like branching. Nature Ecology & Evolution, v. 3, p. 24-30; DOI: 10.1038/s41559-018-0728-7). Their pycnofibres show branching tufts, similar to those found in some theropods dinosaurs, including tyrannosaurs. They also resemble mammalian underfur fibres, whose air-trapping properties provide efficient thermal insulation. Both body and wings of these pterosaurs are furry, which the authors suggest may also have helped reduce drag during flight, while those around the mouth may have had a sensory function similar to those carried by some living birds. Moreover, some of the filaments contain black and red pigments.
Pterosaurs may have independently developed fur and feathers; a case of parallel evolution in response to similar evolutionary pressures facing dinosaurs, birds and mammals. Alternatively, they may have had a deep evolutionary origin in the common ancestors of all these animal groups as far back as the Upper Carboniferous and Lower Permian.
Related articles: Nature Editorial 2018. Fur and fossils. Nature, v. 564, p. 301-302; DOI: 10.1038/d41586-018-07800-4; King, A. 2018. Pterosaurs sported feathers, claim scientists (The Scientist); Conniff, R. 2018. Pterosaurs just keep getting weirder (Scientific American); New discovery pushes origin of feathers back by 70 million years (Science Daily)