Unexpected diversity of median caudal cartilages in teleosts

International audienceCaudal fin skeletons of teleost fishes have been well-studied in the context of phylogenetic relationships. However, the small cartilages at the distal end of the diastema, the ‘median caudal cartilages’, have gained only little attention so far. For the first time we here report their taxa-dependent variable three-dimensional structure. We investigated 143 species of 62 teleost families for this study. The shape and arrangement of these cartilages is uniform in some systematic groups, e.g. Alepocephalidae, Platytroctidae or Myctophiformes; in other taxa there is high intrataxon variability, e.g. Stomiiformes or Aulopiformes. Shape, number and presence/absence may even vary in certain species, e.g. Osmerus eperlanus, Thymallus thymallus or Gymnocorymbus ternetzi. The function of median caudal cartilages remains unclear. It has been suggested that they might be related to fin-ray support, although an obvious relation to fin rays is lacking in several taxa. Their presence and size is not dependent on the size of the diastema. Median caudal cartilages seem to have evolved at the base of clupeocephalans and occur in many taxa up to about aulopiforms, as well as single beryciforms. It seems that they are often reduced at different systematic levels and may have re-evolved in some taxa