Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary

Abstract

Pterosaurs were the first vertebrates to evolve powered flight and the largest animals to ever take wing. The pterosaurs persisted for over 150 million years before disappearing at the end of the Cretaceous, but the patterns of and processes driving their extinction remain unclear. Only a single family, Azhdarchidae, is definitively known from the late Maastrichtian, suggesting a gradual decline in diversity in the Late Cretaceous, with the Cretaceous–Paleogene (K-Pg) extinction eliminating a few late-surviving species. However, this apparent pattern may simply reflect poor sampling of fossils. Here, we describe a diverse pterosaur assemblage from the late Maastrichtian of Morocco that includes not only Azhdarchidae but the youngest known Pteranodontidae and Nyctosauridae. With 3 families and at least 7 species present, the assemblage represents the most diverse known Late Cretaceous pterosaur assemblage and dramatically increases the diversity of Maastrichtian pterosaurs. At least 3 families—Pteranodontidae, Nyctosauridae, and Azhdarchidae—persisted into the late Maastrichtian. Late Maastrichtian pterosaurs show increased niche occupation relative to earlier, Santonian-Campanian faunas and successfully outcompeted birds at large sizes. These patterns suggest an abrupt mass extinction of pterosaurs at the K-Pg boundary.

Cryodrakon boreas, gen. et sp. nov., a Late Cretaceous Canadian azhdarchid pterosaur

“…However, we agree with Cohen et al (2018) that there are differences in morphology between the two and that this unnamed azhdarchid is not likely to be the same taxon as represented by the Cryodrakon material. Longrich et al (2018) show a single small and elongate azhdarchid mid cervical. This shows a dorsal accessory pneumatopore and apparently ventrally positioned lateral ones (though the specimen is badly crushed) similar to Cryodrakon.…”

“…Alanqa-Some cervical material has been referred to this taxon (Averianov, 2014) although the holotype specimen is represented only by cranial material (Ibrahim et al, 2010) and this may not be an azhdarchid (Longrich et al, 2018). The specimen is a highly incomplete posterior end of a cervical vertebra and few details can be ascertained tough unlike Cryodrakon, it has only short postexapophyses.…”

Neck biomechanics indicate that giant Transylvanian azhdarchid pterosaurs were short-necked arch predators

“…Azhdarchids dominate pterosaur faunas in the Maastrichtian, with only two localities recording non-azhdarchid pterosaurs from this time (Price, 1953; Longrich, Martill & Andres, 2016). Assumptions that azhdarchids were morphologically uniform have led to proposals that Maastrichtian pterosaurs were ecologically constrained at the end of the Cretaceous, and that their extinction represents the unspectacular end of a long, gradual pterosaurian decline (Unwin, 2005; Witton, 2013).…”

A Late Cretaceous Lonchodectid?

“…Both bulbous and uncinated morphologies are present in taxa covering a wide range of flight styles and ecological roles (Witton 2008, Witton 2010, Witton 2013, Longrich 2018 among others), while rectangular and obdurate morphologies are much more narrowly located, the former in an unambiguously monophyletic clade of scavenging soarers (Witton 2013) while the latter are in an ostensibly monophyletic clade with an unclear ecological niche (see Phylogenetic Analysis and Lonchodectid Ecology below). Therefore, it seems that anterior ulnar joint morphologies correlate much more strongly with phylogenetic signals than biomechanical ones.…”