The morphology of the inner ear of squamate reptiles and its bearing on the origin of snakes

The inner ear morphology of 80 snake and lizard species, representative of a range of ecologies, is here analysed and compared to that of the fossil stem snakeDinilysia patagonica, using three-dimensional geometric morphometrics. Inner ear morphology is linked to phylogeny (we find here a strong phylogenetic signal in the data that can complicate ecological correlations), but also correlated with ecology, withDinilysiaresembling certain semi-fossorial forms (XenopeltisandCylindrophis), consistent with previous reports. We here also find striking resemblances betweenDinilysiaand some semi-aquatic snakes, such asMyron(Caenophidia, Homalopsidae). Therefore, the inner ear morphology ofDinilysiais consistent with semi-aquatic as well as semi-fossorial habits: the most similar forms are either semi-fossorial burrowers with a strong affinity to water (XenopeltisandCylindrophis) or amphibious, intertidal forms which shelter in burrows (Myron).Notably,Dinilysiadoes not cluster as closely with snakes with exclusively terrestrial or obligate burrowing habits (e.g. scolecophidians and uropeltids). Moreover, despite the above similarities,Dinilysiaalso occupies a totally unique morphospace, raising issues with linking it with any particular ecological category.