The caudal skeleton of a 20 mm Triodon and homology of its components

Abstract

We provide a detailed description of the caudal skeleton of the smallest specimen of a three-tooth puffer on record, a 20 mm standard length Triodon macropterus. The compound centrum supports the parhypural and five hypurals. Hypural five, which has a cartilaginous core, was interpreted erroneously by Tyler (1970, 1980) as uroneural 2, a structure that is not preformed in cartilage in acanthomorphs. We also found a second epural in Triodon, which was not reported by Tyler (1970, 1980). Both hypural 5 and epural 2 are also present in the two larger specimens of Triodon we studied. We discuss previous descriptions of the caudal-fin skeleton of Triodon and conclude by re-emphasizing the unexpectedly large number of putatively plesiomorphic characters of Triodon compared to all other plectognaths.