DIOGO, R.*; OLIVEIRA, O.; PARMENTIER, E.; CHARDON, M.; VANDEWALLE, P.: THE ORIGIN AND TRANSFORMATION OF CATFISH (TELEOSTEI: SILURIFORMES) PALATINE-MAXILLARY SYSTEM: AN EXAMPLE OF ADAPTIVE MACROEVOLUTION
The adaptive value of siluriform barbels in muddy waters dwellers and nocturnal fish is evident and was moreover demonstrated experimentally. The maxillary ones are characterized by their connection to a mobile mechanism, the palatine-maxillary system (PMS), which is constituted by the maxillary, the palatine and more or less specialized ligaments and muscles responsible for their movements. Siluriform sister-groups (Gymnotiformes and Characiformes) do not have barbels at all and do not present any structure prefiguring barbels, particularly the maxillary barbels, which are the only ones present in the most primitive catfishes, the diplomystids. In fact, catfish PMS is based on two basic siluroid synapomorphies: 1) a skeletal uncoupling between the palatine bone and the the rest of the suspensorium; 2) a muscular uncoupling of the adductor arcus palatini, leading to the differentiation of the extensor tentaculi muscle, which is associated with the abduction of the maxillary barbel. So, unless improbably well preserved fossils would be described in the future, a gap will remain between the diplomystids and the gymnotiforms and characiforms. However, departing from the Diplomystidae, it seems possible to follow evolutionary lines leading to more specialized PMS types. Our study focus precisely on the evolution of the PMS among catfish. For each morphological transformation, the way it was realized is hypothetized and the probable adaptive advantage it brings is analysed.