The vertebrate fauna of the Upper Permian of Niger—VII. Cranial anatomy and relationships of Bunostegos akokanensis (Pareiasauria)

Abstract

ABSTRACT We describe newly recovered cranial material of Bunostegos akokanensis, a pareiasaurian reptile known from the Upper Permian Moradi Formation of northern Niger. Bunostegos is highly autapomorphic, with diagnostic cranial features including two or three hemispherical bosses located above and between the external nares; laterally projecting supraorbital ‘horn’ formed by an enlarged postfrontal; large foramen present on ventral surface of postfrontal; and hemispherical supratemporal boss located at posterolateral corner of skull roof. We addressed the phylogenetic position of Bunostegos by incorporating it into a cladistic analysis of 29 parareptilian taxa (including all 21 currently valid pareiasaurs) and 127 cranial and postcranial characters. The results of this analysis place Bunostegos as more derived than middle Permian forms such as Bradysaurus and as the sister taxon to the clade including Deltavjatia plus Velosauria. Certain characters, such as the pattern of cranial ornamentation and the size and placement of the tabulars, appear to be more similar to more derived pareiasaurs such as Elginia from Scotland and Arganaceras from Morocco, but the most parsimonious tree topology indicates that these features were evolved independently in the Nigerien form. The lack of both dicynodont herbivores and Glossopteris, combined with the presence of a giant herbivorous captorhinid, indicates a markedly different community structure in the Permian of Niger compared with those for contemporaneous southern Pangean basins (i.e., Karoo, Luangwa, Ruhuhu). The endemic tetrapod fauna of Niger supports the theory that central Pangea was biogeographically isolated from the rest of the supercontinent by desert-like conditions during Late Permian times. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP