An unprecedented subcentral mid-trunk vertebral morphology for snakes: "Quasi-haemapophyses" in the African elapoid Atractaspis corpulenta kivuensis (Serpentes, Atractaspididae).

Snake vertebrae possess distinctive morphological features that differentiate them from those of other reptiles. While some of these structures are unique to particular snake groups, enabling direct taxonomic identifications, others are restricted to specific regions of the vertebral column. Among the latter are haemapophyses, paired structures emerging from the ventral surface of the centrum that characterize the caudal vertebrae of most, though not all, snakes. Practically confined to the caudal region, haemapophyses are absent from mid-trunk vertebrae, where other structures appear. Here, we report an extraordinary case of haemapophyses-like structures ("quasi-haemapophyses") occurring in mid-trunk vertebrae of the African elapoid snake Atractaspis corpulenta kivuensis. This bizarre taxon possesses, uniquely among all known snakes (extinct or extant), distinct "quasi-haemapophyses" throughout its mid-trunk and posterior trunk vertebrae, which diminish only in the posteriormost trunk region. Haemapophyses subsequently reappear, albeit in modified form, in the cloacal and caudal regions. In addition to a detailed analysis of vertebral morphology and intracolumnar variation, we compile and review all published figures of Atractaspis vertebrae, as well as providing documentation for additional species-rendering this the most comprehensive vertebral study conducted for the genus to date.