The bony anatomy of Chadian Synodontis (Osteichthyes, Teleostei, Siluriformes, Mochokidae): interspecific variations and specific characters

The genus Synodontis Cuvier, 1816 (Siluriformes, Mochokidae) numbers about 120 species and is exclusive to the freshwater of Africa except Maghreb and Cape Province. It is one of the most widespread catfish of African freshwater. The Synodontis fossil record covers the last 18 Myr and most of the Synodontis fossil bones are found in a disarticulated state. The identification of the fossils at a specific level is so far impossible, because we lack an osteological study of the species. Here, we present the study of the osteology of eleven Synodontis species living in Chad: S. batensoda Rüppell, 1832, S. clarias (Linnaeus, 1758), S. courteti Pellegrin, 1906, S. eupterus Boulenger, 1901, S. filamentosus Boulenger, 1901, S. membranaceus (Geoffroy Saint-Hilaire, 1809), S. nigrita Valenciennes, 1840, S. ocellifer Boulenger, 1900, S. schall (Bloch & Schneider, 1801), S. sorex Günther, 1864 and S. violaceus Pellegrin, 1919. Each species is characterized based on its bony anatomy. The morphological variability within and between the species is discussed. The entire skeleton is described, bone by bone. A total of 61 osteological characters, both qualitative and quantitative are established. We emphasize the bones that are well preserved in the fossil, i.e. the mesethmoid, the lateral ethmoid, the frontal, the supraoccipital, the cleithrum, the pectoral spine, the middle nucal plate and the dorsal spine. As a first result, the Chadian Synodontis species can be recognized on the basis of bony characters only. Second, we are also able to attribute isolated bones to nominative species or to a group of species. At last, we note that no osteological character legitimates the distinction of the genera Hemisynodontis Bleeker, 1862 and Brachysynodontis Bleeker, 1862.