Eugeneodus

Eugeneodus had jaws lined with flattened, rectangular teeth termed pavement teeth, which had sharp edges and a series of ridges along their edge. Unlike in some of its relatives, these teeth didn't form sharp cutting blades. Along the midline of its Meckel's cartilages (lower jaws) was a row of teeth forming a tooth-whorl.^[1][6] The palatoquadrates (upper jaws) were not fused to the chondrocranium (braincase), but were relatively small and tightely braced against the skull.^[1][7] The body was fusiform, and the tail fin was lunate (crescent-shaped) and homocercal.^[1] No specimens of E. richardsoni preserve pelvic fins or claspers,^[1] and these are thought to have been absent in life.^[8] The internal skeleton of the tail fin consisted of neural and haemal arches, but unlike in other closely related fishes these were not fused together.^[1] Exteriorly, the body was covered by a coating of small placoid scales termed lepidomoria.^[9][10][11] These scales came in the form of both unfused, leaf-shaped scales and masses of fused scales all growing from the same base.^[9][11]

Eugeneodus is the type genus of the family Eugeneodontidae and the broader order Eugeneodontiformes,^[1][6][12] which are named after the genus.^[5] The superfamily which includes Eugeneodontidae has been referred to as either Caseodontoidea or Eugeneodontoidei.^[1][12][13]

Eugeneodus was regarded as the most skeletally primitive eugeneodont by Zangerl.^[1]