The first fossil record of an aquatic caecilian (Gymnophiona: Typhlonectidae)

Abstract

The lissamphibian clade Gymnophiona includes approximately 220 recognized modern species known by the English vernacular as caecilians and characterized by their elongated and annulated bodies, without girdles or limbs. Fossils of caecilians are particularly rare and mostly limited to isolated vertebrae. Until now, only four bona fide Gymnophionomorpha species have been named based on fossils. Only one of these (Apodops pricei) is a crown-group caecilian, but its affinities with modern caecilians are uncertain because the material is limited to one damaged vertebra and is currently lost. Here we describe a new genus and species of caecilian from the Oligocene Tremembé Formation, Brazil, based on a partially preserved fossil skeleton (including elements of the skull and postcranium) that is damaged but still partly articulated. We investigated the fossil caecilian’s anatomy using high-resolution microcomputed tomography, and then compared it to the osteology of modern species. We interpret the fossil as a member of Typhlonectidae, a family of caecilians well known for their aquatic and semi-aquatic lifestyles. This new record represents the first record for caecilians from the Oligocene and also the first fossil species confidently assigned to an extant caecilian family.