The specialized inner ear labyrinth of worm-lizards (Amphisbaenia: Squamata)

High-resolution computed tomography (HRCT) has become a widely used tool for studying the inner ear morphology of vertebrates. Amphisbaenians are one of the most specialized groups of fossorial reptiles but are poorly understood relative to other squamate reptile. In this paper we survey the anatomy of the inner and middle ear of these fossorial reptiles using HRCT models and we describe qualitatively and quantitatively (using 3D morphometrics) the anatomy of the inner ear. Amphisbaenians are diverse in skull anatomy, especially in the configuration of the snout, which correlates with digging modes. We demonstrate that the ear also exhibits a diversity of configurations, which are independent of phylogenetic relationships. Results from morphological analyses also allow us to describe 11 new potentially informative phylogenetic characters including some that help to diagnose amphisbaenians, such as: 1) the globular vestibule, ii) semicircular canals arranged in a circular trajectory, and iii) an extensive area of interaction between the columella footplate and the lagenar recess. Among extant amphisbaenians, Rhineura floridana has the most unusual inner ear configuration, including a horizontal semicircular canal that is in the same orientation as the inclined snout. The new morphological information helps us to better understand the morphology of headfirst-burrowing fossorial reptiles and contributes new data for resolution of phylogenetic relationships among amphisbaenians.

Can all snakes swim? A review of the evidence and testing species across phylogeny and morphological diversity

Alternative hypotheses suggest that the reptiles at the origin of snakes were primarily either burrowing, terrestrial or marine. It is possible that the ability to swim varies between the major snake lineages and lifestyles; for example, the highly fossorial blind snakes (Scolecophidia), a lineage that emerged early in snake evolution over 100 My ago, may not be able to swim. However, it is sometimes stated that all snakes can swim suggesting that swimming ability may not be discriminatory. To find out whether this is true, we used a systematic search (PRISMA), including personal communications and information on websites. Of the 3951 species considered, no information was found for 89 % of all snakes. Of the 454 species for which information was found, 382 species were aquatic, only 62 were terrestrial, 6 were arboreal, and only 4 were burrowing. Moreover, almost all belonged to the speciose Colubroides (e.g. 58 % Colubridae, 20 % Elapidae). No reliable information was available for important early diverging lineages (e.g. Scolocophidia, Aniliidae). Faced with this lack of information, we filled in important phylogenetic gaps by testing the swimming capacity of 103 diverse snake species and 13 species of diverse limbed and limbless ectothermic tetrapod vertebrates (Amphisbaenia, Lacertilia, Gymnophiona). All tests were positive. The results show that, 1) all snakes for which information is available (525 species) appear to be able to swim, 2) this is a trait shared by many land vertebrates that undulate laterally. As swimming ability is non-discriminatory, we need to collect detailed measurements on the performance, kinematics and energetic efficiency of swimming snakes. It is also necessary to finely describe the ecology and morphology of the species studied to better understand form∼function relationships and the occupation of ecological niches in snakes.

Largest known madtsoiid snake from warm Eocene period of India suggests intercontinental Gondwana dispersal

Here we report the discovery of fossils representing partial vertebral column of a giant madtsoiid snake from an early Middle Eocene (Lutetian, ~ 47 Ma) lignite-bearing succession in Kutch, western India. The estimated body length of ~ 11-15 m makes this new taxon (Vasuki indicus gen et sp. nov.) the largest known madtsoiid snake, which thrived during a warm geological interval with average temperatures estimated at ~ 28 °C. Phylogenetically, Vasuki forms a distinct clade with the Indian Late Cretaceous taxon Madtsoia pisdurensis and the North African Late Eocene Gigantophis garstini. Biogeographic considerations, seen in conjunction with its inter-relationship with other Indian and North African madtsoiids, suggest that Vasuki represents a relic lineage that originated in India. Subsequent India-Asia collision at ~ 50 Ma led to intercontinental dispersal of this lineage from the subcontinent into North Africa through southern Eurasia.

A conserved tooth resorption mechanism in modern and fossil snakes

Whether snakes evolved their elongated, limbless bodies or their specialized skulls and teeth first is a central question in squamate evolution. Identifying features shared between extant and fossil snakes is therefore key to unraveling the early evolution of this iconic reptile group. One promising candidate is their unusual mode of tooth replacement, whereby teeth are replaced without signs of external tooth resorption. We reveal through histological analysis that the lack of resorption pits in snakes is due to the unusual action of odontoclasts, which resorb dentine from within the pulp of the tooth. Internal tooth resorption is widespread in extant snakes, differs from replacement in other reptiles, and is even detectable via non-destructive μCT scanning, providing a method for identifying fossil snakes. We then detected internal tooth resorption in the fossil snake Yurlunggur, and one of the oldest snake fossils, Portugalophis, suggesting that it is one of the earliest innovations in Pan-Serpentes, likely preceding limb loss.