Comparative cranial osteology of Blanus (Squamata: Amphisbaenia)

Worm lizards, or amphisbaenians, of the genus Blanus are found in various countries around the Mediterranean Sea. In addition to four extinct species, seven extant taxa are currently recognized. Here, we present the first comparative analysis of the cranial osteology of Blanus including all extant species. The results of this analysis show a homogeneous morphology among skull bones, with few morphological features that can be used to discriminate among different Blanus species. No clear osteological diagnostic features can be identified for any single species. The most taxonomically significant bones are the premaxilla and the quadrate. In particular, the premaxillae can be used to discriminate perfectly between the two molecular-based clades into which extant blanids are currently separated. Despite the relatively similar skull morphology, detailed comparative osteological studies such as this one are useful to evaluate the phylogenetic affinities of extant and extinct taxa. The extinct Blanus mendezi, for example, recalls the western Blanus species in the morphology of the premaxilla and some of the eastern ones in the morphology of the quadrate. The inclusion of these features in future phylogenetic analyses will be of utmost importance to clarify the affinities of this and other Blanus species, both extinct and extant.