An overview of the postcranial osteology of caecilians (Gymnophiona, Lissamphibia)

Caecilians comprise a relatively small (~220 species) group (Gymnophiona) of snake-like or worm-like, mostly tropical amphibians. Most adult caecilians are fossorial, although some species may live in aquatic or semi-aquatic environments, either as larvae or adults. Caecilians exhibit numerous morphological features traditionally interpreted as adaptations to their specialized ecologies, such as a compact and well-ossified skull and an elongated body lacking both girdles and limbs. Caecilian vertebrae differ substantially from those of other amphibians in having amphicoelous centra, well-developed basapophyseal processes, pronounced posterosagittal processes and hypapophyseal keels, and low and flat neural arches. However, caecilian postcranial osteology has received little attention, and the vast majority of the species remain unstudied. Consequently, the variation in the vertebral morphology among caecilians is still unknown or poorly documented. Inconsistencies in the anatomical terminology used by different authors are potentially confusing and may hamper understanding of homologies. Here we present an overview of caecilian postcranial osteology, define the main structural features, including many not previously described, and propose a standardized nomenclature.