A review of the fossil record of caecilians (Lissamphibia: Gymnophionomorpha) with comments on its use to calibrate molecular timetrees

Abstract

Abstract Gymnophiona, popularly known as caecilians, the most poorly known major taxon of extant amphibians, are elongate and limbless tetrapods, with compact ossified skulls and reduced eyes, mainly adapted to fossorial life as adults. Caecilians are poorly represented in the fossil record, but despite the scarcity of fossil specimens described (only four named taxa, in addition to indeterminate fragmentary material), their fossils play a key role in our knowledge of the origin and evolution of Lissamphibia, as well as contribute directly to a better understanding of the phylogeny, taxonomy and biogeography of extant gymnophionan taxa. These records are scattered throughout geological time (from the Jurassic to the sub-Recent) and space (North and South America and Africa). Here, we revisit the caecilian fossil record, providing a brief description of all known extinct taxa described so far, along with general remarks about their impact on systematics, time range, and geographical distribution of the clade, as well as prospects for future research. Possible calibration constraints based on the caecilian fossil record are provided.