Variation in the Jaws and Teeth of the Amphisbaenian Zygaspis from Southern Africa

Abstract

Amphisbaenians are an understudied family of worm‐like reptiles consisting of over 150 extant species in 23 genera. Relatively little is known about the cranial anatomy of the group because most members of the clade are small and poorly represented in collections. With skulls of some species only a few millimeters long, traditional anatomical methods are difficult to use. Collection curators are also hesitant to allow destructive analysis of specimens, because few specimens are generally available. Most modern studies of cranial anatomy of amphisbaenians are based upon high‐resolution X‐ray CT scans. CT scanning is nondestructive and allows for detailed examination of even small elements. Most of those studies remain focused on a single specimen and therefore do not account for variation beyond potential asymmetry in a single specimen. We focus on a collection of specimens from a single genus, Zygaspis, and examine their upper and lower jaws and teeth to better estimate morphological variation within a tightly circumscribed clade of Amphisbaenans. The cranial anatomy of Z. quadrifrons is well described, although the description is based on a single specimen. That baseline description now allows for both inter‐ and intraspecific variation to be estimated by expanding the previous work to include other specimens of Z. quadrifrons and other species in the genus. Here, we examined Z. quadrifrons, Z. vandami, Z. niger, Z. ferox, Z. violacea, Z. dolichomenta, and Z. kafuensis, whose collective distribution spans most of southern Africa from the southern reaches of the Democratic Republic of the Congo and the Tanzania/Mozambique border to southern South Africa. One adult specimen from each species was CT scanned and analyzed with Amira software. We examined over 20 dental and mandibular characters, including tooth count, size, and orientation, the presence or absence of specific teeth and processes, and the morphology of the coronoid articulation with other elements of the mandible. We found significant variation in several features, including apparent variation in replacement teeth. Our preliminary results suggest that inter‐ and intraspecific variation does exist and should be accounted for in functional and phylogenetic studies. Further analysis of the genus, with an increased sample size and broadening to incorporate other cranial variables, would allow enhanced exploration of the morphological variation that occurs within Zygaspis.Support or Funding InformationSam Houston State University