The Origin and Transformation of the Palatine-Maxillary System of Catfish (Teleostei: Siluriformes): an Example of Macroevolution

Barbels are a general characteristic of Siluriformes, responsible for their popular name "catfish". Among the three types of catfish barbels - mandibular, maxillar and nasal - the maxillary ones are characterized by their connection to a mobile mechanism, the palatine-maxillary system (PMS). 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. So, in the absence of well preserved fossils, a gap remains between the diplomystids and the other ostariophysans. However, starting from the Diplomystidae, it seems possible to hypothesise evolutionary lines leading to more specialised PMS types. The present paper focuses on the evolution of the PMS among catfish. For each morphological transformation, the way it was realised is hypothesized and the probable adaptive advantage it brings is analysed.