High-resolution X-ray computed tomography of an Early Cretaceous gekkonomorph (Squamata) from Öösh (Övörkhangai; Mongolia)

Abstract

We describe the braincase of AMNH FR 21444, a gecko-like squamate from the Early Cretaceous of Mongolia, based on high-resolution X-ray computed tomography scans (CT scans) and incorporate it in a phylogenetic analysis of 36 squamate taxa scored for 226 morphological characters. Our analysis corroborates the Eublepharidae-Gekkonoidea split as the basal gekkotan dichotomy, but retrieves Teratoscincus as the sister-taxon to pygopodines + diplodactylines. The combination of plesiomorphic and apomorphic character states within AMNH FR 21444 demonstrates a decoupled evolutionary history between the braincase and the rest of the skull and mandible within gekkonomorph squamates. Enclosure of the lateral head vein and mandibular branch of the trigeminal nerve are both plesiomorphic for gekkonomorphs. The mechanisms responsible for the transition from the plesiomorphic skull roof of basal gekkonomorphs to the modern gekkotan condition cannot be anticipated given the current data.