Comparative cranial and postcranial osteology of blanus species (squamata: amphisbaenia) from Türkiye: insights from morphological evolution and phylogeny

Abstract

The genus Blanus (Amphisbaenia: Blanidae) comprises fossorial, limbless reptiles with cryptic external morphology, making species delimitation particularly challenging. This study presents a comprehensive comparative osteological and geometric morphometric investigation of three Blanus species distributed in Türkiye—B. alexandri, B. aporus, and B. strauchi. Using both dry and cleared-and-stained specimens, diagnostic variations in cranial and postcranial skeletal elements, especially elements within the nasal, maxilla, vomer, squamosal, dentary, and coronoid bones, as well as vertebral counts were identified. A geometric morphometric analysis of the dorsal and ventral cranial morphology revealed distinct shape differences, particularly separating B. alexandri from the other two species along principal component axes. A phylogenetic analysis based on 45 discrete osteological characters supported the monophyly of the eastern Blanus clade, with B. alexandri forming a distinct lineage from B. aporus and B. strauchi. These findings emphasize the significance of skeletal morphology for resolving phylogenetic relationships and highlight the role of osteological characters in refining species boundaries within cryptic reptilian taxa. The integrative approach employed here underscores the evolutionary distinctiveness of Anatolian Blanus and enhances our understanding of morphological evolution in amphisbaenians.