Taxonomic revision of the giant marine snake genus Pterosphenus Lucas, 1898, based on new fossil material from the middle Eocene (Bartonian) Harudi Formation of Kachchh (Kutch) Basin, India

Fossil snakes of the family Palaeophiidae are primarily known from rare, isolated vertebrae, leading to a poor understanding of the intra- and inter-columnar variation within a palaeophiid species. This leads to ambiguity in the taxonomic identity of these snakes, as in the case of the Eocene-age marine snakes of the genus Pterosphenus, in which the majority of species have been described by characters of problematic taxonomic value. Here, we propose a taxonomic revision of the genus based on an articulated to semi-articulated section of the vertebral column at the anterior to mid trunk-transition of Pterosphenus schucherti discovered from the middle Eocene (Bartonian) Harudi Formation, Kachchh (Kutch) Basin. The characters that separate Pterosphenus schucherti from 'Pterosphenus schweinfurthi' and 'Pterosphenus biswasi,' viz., the height of the pterapophysis and the anterior concavity of the zygosphene, have been found to be non-diagnostic, and the latter two species have been synonymized with the type species. Additionally, we utilized 2D and 3D landmark-based geometric morphometry to determine the morphometric affinity of palaeophiids amongst the alethinophidian snakes. The body size of the snake was estimated based on extant snakes with a morphometric affinity to Palaeophiidae. The cosmopolitan distribution of Pterosphenus schucherti is modelled based on the sea surface temperature (SST) constraints of the modern cosmopolitan snake Hydrophis platurus, and the known fossil localities of the species. The present findings provide crucial insights into the global paleoecological landscape of the Eocene, and the interactions of Pterosphenus schucherti with other palaeophiid snakes as well as the other Eocene fauna.