Variation in the Cranial Osteology in the Genus Zygaspis

Amphisbaenians are a group of limbless, fossorial reptiles that are recognized today as a highly specialized group of lizards. In this project, the inter- and intraspecific variation of the cranial osteology of seven of the eight currently recognized species of the amphisbaenian genus Zygaspis was assessed and unique morphological features among them were identified. A total of 15 specimens from the seven species were micro-CT scanned (Z. quadrifrons (5), Z. vandami (2), Z. nigra (2), Z. violacea (2), Z. dolichomenta (1), Z. ferox (1) and Z. kafuensis (2)). The software program Avizo 9.7.0 was used to digitally isolate the individual cranial bones of each specimen. The cranial anatomy of Z. quadrifrons has been previously described, providing a baseline for comparison to other Z. quadrifrons specimens and the remaining species of the genus. Our results demonstrate that cranial variation does exist, even in specimens of the same species. Most of the bones were similar in general form, with minimal differences. Some had no recognized pattern and displayed their own variation of features (the parietal, septomaxilla, vomer, and tabulosphenoid). Asymmetry among the paired bones of the same specimen was observed in the ectopterygoid of Z. dolichomenta, the nasal & quadrate of Z. kafuensis, and the prefrontal of Z. violacea. Morphological features of certain cranial bones that help distinguish a species includes the shape of the nasal process of the premaxilla in Z. quadrifrons, the anterior ball shape of the extracolumella in Z. niger, and the pronounced notch on the pterygoid and lateral inflection of the choanal processes of the vomer in Z. kafuensis. These descriptions of the species of Zygaspis suggests that inter- and intraspecific variation should be accounted for in functional and phylogenetic studies. This study provides further comparable material for other qualitative amphisbaenian studies.