Eugeneodus is an extinct genus of Eugeneodontidae Chondrichthyes from the Carboniferous of North America. A single species, E. richardsoni, is known , and both its genus and species name honor paleontologist Eugene S. Richardson Jr. It is differentiated from its close relatives by the unfused nature of the Neural arch and Haemal arch in its caudal fin and the anatomy of its flattened, rectangular teeth (termed pavement teeth). It is the type genus of the order Eugeneodontida.
Discovery and naming
Specimens now assigned to
Eugeneodus were first discovered during the late 1950s in Carboniferous-age
Shale in the Midwestern United States.
These fossils were first tentatively assigned to the genus
Agassizodus.
In 1981, the genus was formally described by researcher Rainer Zangerl, along with a single species,
Eugeneodus richardsoni.
Both the genus and species name honor paleontologist Eugene S. Richardson.
Description
Eugeneodus had jaws lined with flattened, rectangular teeth termed pavement teeth, which had sharp edges and a series of ridges along their edge, but were not blade-like.
Along the midline of its Meckel's cartilages (lower jaws) was a row of teeth forming a tooth-whorl.
The
Palatoquadrate (upper jaws) were not fused to the
chondrocranium (braincase), but were relatively small braced tightly against it.
The body was
fusiform, and the tail fin was lunate (crescent-shaped) and
homocercal.
No specimens of
E. richardsoni preserve pelvic fins or claspers,
and these are thought to have been absent in life.
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.
Exteriorly, the body was covered by a coating of small
placoid scales termed lepidomoria.
These scales came in the form of both unfused, leaf-shaped scales and masses of fused scales all growing from the same base.
Classification
Eugeneodus is the type genus of the family
Eugeneodontidae and the broader order
Eugeneodontida,
which are named after the genus.
The superfamily which includes Eugeneodontidae has been referred to as either Caseodontoidea or Eugeneodontoidei.
Eugeneodus was regarded as the most skeletally primitive eugeneodont by Zangerl.
