Ontogeny of the skull of the blind snake Amerotyphlops brongersmianus (Typhlopidae, Scolecophidia) and its relevance to the evolution of the ophidian skeleton

Description

Blind snakes are the most basal group of extant snakes and one of the least known in terms of morphology, biogeography and ecology. They are small snakes of fossorial habits that exhibit tubular bodies, smooth scales and a remarkable reduction of eyes and head escalation. The morphology of their skulls is highly modified with respect to the rest of the snakes and is conditioned both by a particular system of feeding mechanism, as well as by the mechanical demands imposed by the fossorial habits. The aim of this project is to provide new information about the evolution of the snake skull through the analysis of the complete ontogenetic sequence of the skull of Amerotyphlops brongersmianus, which is a relatively large (SVL = 300 mm on average), oviparous, blind snake species belonging to the family Typhlopidae. The study was carried out entirely on the basis of 3D reconstructions based on micro-CT data, which allowed the accurate representation of anatomical structures with their natural shapes, orientations and spatial relations in minute size embryos. This study represents the first contribution on the embryonic development of the skeleton of a blind snake, and preliminary results were presented in the XXI Argentinian Congress of Herpetology 2021. The analysis of the ontogenetic sequence showed the delayed development of some traits simultaneously with clearly peramorphic traits. We also evaluated data on the size changes relative to skull growth of the main elements of the gnathic complex, and we observed considerable shape change of the skull during late ontogeny. In summary, the unique skull anatomy of blind snakes displays plesiomorphic and highly autapomorphic features, as an outcome of heterochronic processes and miniaturization, shaped by functional constraints related with the highly specialized feeding mechanism under the selective pressures of a fossorial lifestyle.

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