The pelvic girdle in extant gonorynchiformes (Teleostei: Otomorpha)

Otophysi is one of the most important fish taxa of the world, as they make up for roughly 28% of all fish species and about two-thirds of all freshwater species worldwide. To understand their success and evolutionary history their sister-group, the Gonorynchiformes, take a key-position, e.g., for reconstructing morphological conditions in the latest common ancestors. Gonorynchiformes comprising only 40 species and have been often studied for that reason. Their pelvic girdle, however, got only little attention so far. Therefore, we studied this structure in extant gonorynchiforms and described the ontogeny in Kneria stappersii. In gonorynchiforms: (1) their basipterygium is principally flat (without dorsal or ventral projections) and placed in horizontal position, (2) has a ‘simple’ shape, i.e., it has only a single anterior process with small cartilaginous tips and becomes wider in its posterior part with a medial portion connecting to the basipterygium of the other side; (3) three radials and a pelvic splint are present, and (4) a prominent posterior process is missing. Although, the morphological situation is a lot similar as seen in clupeiforms and alepocephaliforms. Therefore, these characters have likely been present in the stem of Otomorpha, Ostariophysi, and Otophysi, but within the latter taxon eventually, a higher diversity of pelvic girdle morphology arose during evolution.