CONICET | Buscador de Institutos y Recursos Humanos

Macrostomy is the anatomical feature present in macrostomatansnakes that permits the ingestion of entire prey with high cross-sectionalarea. It depends on several anatomical traits in the skeleton and soft tissues,of which the elongation of gnathic complex and backward rotation of thequadrate represent crucial skeletal requirements. Here, the relevance ofpostnatal development of these skull structures and their relationship withmacrohabitat and diet are explored. Contrary to the condition present inlizards and basal snakes that occupy underground macrohabitats, elements of thegnathic complex of most macrostomatan snakes that exploit surface macrohabitatsdisplay conspicuous elongation during postnatal growth, relative to the rest ofthe skull, as well as further backward rotation of the quadrate bone.Remarkably, several clades of small cryptozoic macrostomatans reverse thesepostnatal transformations and return to a diet based on prey with lowcross-sectional area such as annelids, insects or elongated vertebrates, thusresembling the condition present in underground basal snakes. Dietaryontogenetic shift observed in most macrostomatan snakes is directly linked withthis ontogenetic trajectory, indicating that this shift is acquiredprogressively as the gnathic complex elongates and the quadrate rotatesbackward during postnatal ontogeny. The numerous independent events ofreversion in the gnathic complex and prey type choice observed in underground macrostomatansand the presence of skeletal requirements for macrostomy in extinctnon-macrostomatan species reinforce the possibility that basal snakes representunderground survivors of clades that had the skeletal requirements for macrostomy.Taken together, the data presented here suggest that macrostomy has been shapedduring multiple episodes of occupation of underground and surface macrohabitatsthroughout the evolution of snakes.