Anatomical peculiarities of the giant pterosaur Thanatosdrakon amaru (Azhdarchidae, Pterodactyloidea) from Upper Cretaceous deposits of Mendoza, Argentina

ORTIZ DAVID, LEONARDO DANIEL; KELLNER, ALEXANDER W.A.; GONZÁLEZ RIGA, BERNARDO J.

Toronto

Congreso; SVP 2022 Annual Meeting - Society of Vertebrate Paleontology; 2022

Society of Vertebrate Paleontology

The largest South American pterosaur, Thanatosdrakon amaru, represents an excellent case study to analyze the importance of expanding phylogenetic matrices with appendicular characters. Several phylogenetic results recover Thanatosdrakon deeply nested in the Azhdarchidae clade, as itpresents numerous characters in the humeri that are decisive in achieving these results. However, Thanatosdrakon presents unique characters that evidence a greater diversity in the classic morphologies described for azhdarchids. The preserved axial sequence shows a remarkable development of neural arches and very reduced vertebral centers. This structure is maintained from the posterior cervical vertebra to the dorsosacral vertebrae. The proximal syncarpal has amorphology similar to those described for azhdarchids, however, it presents a developed posterodistal process. Finally, the characteristics of the wing phalanges are singular, lacking the ventral ridge observed in many azhdarchids. Preliminary histological analyses indicate that the smallest specimen (UNCUYO-LD 307) is a juvenile-subadult, and these characteristics could be due, in part, to the ontogenetic stage of the specimen. In azhdarchids, the characters related tothe skull and middle cervical vertebrae are crucial for phylogenetic resolutions. Taxa lacking these structures are shown to be unstable in topologies. Detailed characterizations on other elements, such as the humerus, have partly solved these problems. However, there is a need to expand thenumber of characters in appendicular elements that would allow improved resolutions in less inclusive clades.