The end of Pterosphenus

    Pterosphenus is a genus of large fossil snake from the Eocene of North and South America, North Africa and South Asia. Pterosphenus is considered a palaeophiine, along with the also very large snake Palaeophis; and both genera have several described species. While the type-species of the former, Pt. schucherti, was named by Lucas (1898), the type-species of the latter, Pa. toliapicus, was named by Owen (1841). In 2025, Datta & Bajpai conducted a phylogenetic analysis of Palaeophiinae, the majority rule consensus of which is shown below.

Fig. 1. 50% majority rule of the strict consensus of the phylogenetic analysis of Palaeophiinae from Datta & Bajpai (2025).

    Palaeophis species were recovered in a successive series towards the node containing all species of Pterosphenus, leading to a taxonomic problem. If Pterosphenus is really a distinct taxon from Palaeophis, thus many different taxa are being assigned to Palaeophis, overestimating it's actual diversity. Conversely, if Pterosphenus falls within the range of morphological variability of Palaeophis, thus the diversity of the latter is being underestimated - as Pterosphenus is currently recognized as a different taxon.

    Following the phylogenetic framework of Datta & Bajpai (2025), there are some ways to solve this:

    1) we do not solve and continue treating Palaeophis and Pterosphenus as currently defined, recognizing that the former represents a successive grade leading to Pterosphenus morphological array (and thus is not a real biological entity);

    2) we just lump Pterosphenus into Palaeophis - since the latter has priority -, thereby making Palaeophis effectively monophyletic;

    3) we maintain Palaeophis and Pterosphenus as valid taxa, but constrain the diversity of the former. As shown in the cladogram above, the type-species of Palaeophis nests with Pa. colossaeus. Their clade, in turn, is sister taxon to the clade containing all Pterosphenus species. Thus, Palaeophis could be constrained to Pa. toliapicus and Pa. colossaeus node, making it perfectly valid without having to invalidate Pterosphenus. However, this solution creates another “problem”: all the other species previously considered as Palaeophis (six) should receive a new generic epithet each.

    Thus, to conservate Palaeophis and to evitate the creation of new names that could cause more confusion and taxonomic troubles in the future, I suggest that the second option should be adopted: i. e., Pterosphenus should be regarded as a junior synonym of Palaeophis. This would increase the morphological and ecological diversity of Palaeophis, specially considering there's a phylogenetic trend in increase aquafility in paleophiines (Datta & Bajpai, 2025).

Reference 

Datta, D. & Bajpai, S. 2025. Fossil snakes from the Eocene of India: new material with comments on phylogenetic relations and biogeographic and paleoecological implications. Journal of Paleontology, 99(2): 403-429. DOI:10.1017/jpa.2025.10101.