Descrição e análise morfológica dos ossos do crânio em Amphisbaena arda e Amphisbaena vermicularis (Squamata: Amphisbaenidae)

Abstract

Amphisbaenians (Amphisbaenia) are fossorial reptiles with a robust, ossified skull, ideal for making movements that help them excavate the ground at different levels of compaction while forming their underground galleries. Amphisbaenia are one of the least studied clades in the order Squamata. As a result, many anatomical descriptions are restricted to external morphology, limiting understanding of their evolution and adaptations. This is the case of the amphisbaenid species Amphisbaena vermicularis and Amphisbaena arda, which are similar externally, but whose cranial morphology is little known (A. vermicularis) or completely undescribed (A. arda). Amphisbaena vermicularis occurs along the diagonal of open areas in Brazil and Bolivia, while A. arda is known only from its holotype, collected in the paleodunes of the São Francisco River, Bahia, Brazil. Using three-dimensional computed tomography (CT) scans, this study aimed to investigate the cranial osteology of A. arda and A. vermicularis. In the first chapter, we described the skull bones of the two species and assess whether their cranial morphology differs. Our findings revealed some differences between the species, especially in the sagittal crest of the parietal bone, the ascending process and the transverse occipital crest of the occipital complex. We also found intraspecific variation in A. vermicularis, with specimens showing bones whose morphology differed from their conspecifics, but not from A. arda. This intraspecific variation in A. vermicularis cannot be attributed to soil characteristics, as the specimens studied are from the same locality. The size of the specimens and the characteristics of the soil may influence the differences observed between A. arda and A. vermicularis, since the only specimen of A. arda was the largest in the sample, and the type of soil varies between the collection sites of the two species. In the second chapter, we tested the existence of sexual dimorphism in the shape of the skull of Amphisbaena vermicularis. Our results revealed no evidence of sexual dimorphism in the skull, as both males and females of Amphisbaena vermicularis studied here showed overlap in shape, despite the tendency of males to have slightly larger and narrower skulls. However, differences in skull shape were observed between populations. We conclude that the cranial bone structure of A. vermicularis is highly preserved, with most of the changes occurring in the anterior and middle segments of the skull.