Comparative morphology of the finlet spines of the extant Polypteridae (Osteichthyes; Cladistia). Systematic interest
Identification of extant polypterid fishes has commonly been done by describing the morphology of the entire animal. Unfortunately, in the fossil record, these fishes appear frequently only as isolated finlet spines and/or scales, occasionally vertebrae. The present study aims to describe i) the finlet organization, ii) the finlet spine morphology of living Polypteridae, in order to establish diagnosis and to study the finlet spine variability at the species level. The spines are composed of bone and dentine, covered with ganoine on the anterior face. Among the extant Polypteridae, we observed specific variation in several morphological characters of finlet spines, especially the median groove and the basal, lateral, median, and posterior processes of the spine articular head. We show here that differences observed for finlet spines are significant enough to discriminate Polypteridae at the species level and, to a lesser extant, the three Polypterus bichir subspecies. These differences could be applied successfully to the fossil record but with some caution when the fossil material is scarce or/and more or less damaged.