Pterosaurs were the first flying vertebrates appearing initially in Late Triassic. The group achieved high levels of morphologic and taxonomic diversity during the Mesozoic, with more than 200 species recognized so far. From the Late Triassic to the end of the Cretaceous, the evolution of pterosaurs resulted in a variety of eco-morphological adaptations, as evidenced by differences in skull shape, dentition, neck length, tail length and wing span. Because of the fragile nature of their skeletons the fossil record of pterosaurs is strongly biased towards marine and lacustrine depositional environments. Therefore, Triassic pterosaurs are extraordinarily rare and consists of fewer than 30 specimens, including single bones. With the single exception of Arcticodactylus cromptonellus from fluvial deposits in Greenland, the other specimens are known from marine strata in the Alps.
Pterosaurs have been divided into two major groups: “rhamphorhynchoids” and “pterodactyloids”. Rhamphorhynchoids are characterized by a long tail, and short neck and metacarpus. Pterodactyloids have a much larger body size range, an elongated neck and metacarpus, and a relatively short tail.
Caelestiventus hanseni, from the Upper Triassic of North America, is the oldest pterosaur ever discovered, and it predates all known desert pterosaurs by more than 65 million years. The generic name comes from the Latin language: caelestis, ‘heavenly or divine’, and ventus, ‘wind’. The species name, ‘hanseni’, honors Robin L. Hansen, a geologist, who facilitated work at the Saints & Sinners Quarry.
The holotype, BYU 20707, includes the left maxilla fused with the jugal, the right maxilla, the right nasal, the fused frontoparietals, the right and left mandibular rami, the right terminal wing phalanx and three fragments of indeterminate bones. The maxilla, jugal, frontoparietal, and mandibular rami of the specimen are pneumatic. The unfused skull and mandibular elements suggest that BYU 20707 was skeletally immature or had indeterminate growth. Based on the relationship between the length of the terminal wing phalanges and wing span in other non-pterodactyloid pterosaurs the new taxon would have a wing span greater than 1.5 m.
Caelestiventus hanseni is placed as sister taxon to Dimorphodon macronyx. Both share the following derived features: a ventral blade along the dentary that forms a rostral keel and becomes a flange distally; a diastema between the second large mandibular tooth and the following smaller teeth; the overall morphology of the maxilla; the shape of the external naris and antorbital fenestra; the external naris by far the largest skull opening; the orbit smaller than the antorbital fenestra; and teeth with bicuspid apices. But despite their morphological similarity, C. hanseni and D. macronyx lived in very different environments. Dimorphodon, discovered by Mary Anning, was an island dweller in a humid climate and was preserved in the marine Blue Lias of southern England.
The significance of C. hanseni lies in its exceptional state of preservation, and its close phylogenetic relationship with Dimorphodon macronyx, indicating that dimorphodontids originated by the Late Triassic and survived the end-Triassic extinction event.
Brooks B. Britt et al. Caelestiventus hanseni gen. et sp. nov. extends the desert-dwelling pterosaur record back 65 million years, Nature Ecology & Evolution (2018). DOI: 10.1038/s41559-018-0627-y