Comparative skull osteology of Amphisbaena arda and Amphisbaena vermicularis (Squamata: Amphisbaenidae).

The skull anatomy of amphisbaenians directly influences their capacity to burrow and is crucial for the study of their systematics, which ultimately contributes to our comprehension of their evolution and ecology. In this study, we employed three-dimensional X-ray computed tomography to provide a detailed description and comprehensive comparison of the skull anatomy of two amphisbaenian species with similar external morphology, Amphisbaena arda and Amphisbaena vermicularis. Our findings revealed some differences between the species, especially in the sagittal crest of the parietal bone, the ascendant process, and the transverse occipital crest of the occipital complex. We also found intraspecific variation within A. vermicularis, with some specimens displaying morphology that differed from their conspecifics but not from A. arda. The observed intraspecific variation within A. vermicularis cannot be attributed to soil features because all specimens came from the same locality. Specimen size and soil type may play a role in the observed differences between A. arda and A. vermicularis, as the single A. arda specimen is the largest of our sample and soil type and texture differ between the collection sites of the two species.