A comparative study of locomotion in the caeciliansDermophis mexicanusandTyphlonectes natans(Amphibia: Gymnophiona)

Abstract

We compared locomotion of two species of caecilian using x-ray videography of the animals traversing smooth-sided channels and a pegboard. Two channel widths were used, a body width channel and a body width +20% channel. The terrestrial caecilian,Dermophis mexicanus, used internal concertina locomotion in both channels and lateral undulation on the pegboard. The aquatic caecilian,Typhlonectes natans, was not able to move at all in the body width channel. In the wider channelTyphlonectesproceeded at the same speed asDermophiswhile using normal, rather than internal, concertina locomotion. On the pegboard,Typhlonectesused lateral undulation and achieved 2.5 times the speed managed byDermophis. A phylogenetic analysis of this, and other, evidence shows that (1) internal concertina evolved in the ancestor to extant caecilians and (2) internal concertina locomotion was secondarily lost in the aquatic caecilians.