ENTELODONTS FROM THE BIG BADLANDS OF SOUTH DAKOTA

Nearly half of all entelodonts have been described from the White River formations. The first, Archaeotherium mortoni, was described by Joseph Leidy in 1850 and is one of the first fossils described in North America from west of the Mississippi.

Entelodonts are widely recognized as suiform artiodactys with distinct pendulous flanges developed from the jugal bone and at least one, but normally two, pairs of knob-like tubercles on the dependent margin of the mandibular ramus. Both of these derived features served a primary function of supporting a modified musculature that facilitated large gape. In the cases of extreme derivation, which is seen in ontogenetically older larger specimens, the flanges and tubercles had a secondary display function.

Entelodonts display strong size dimorphism as well as ontogenetic variation. The jugal flanges and mandibular tubercles continued to modify, and in some cases enlarge, throughout the life of the animal. Thus, it is nearly impossible to find two identical skulls. The wide range of morphological variation has made it difficult to diagnose species within the family. The result has been that 56 species of entelodont have been described in the past 150 years, nearly half of these from the White River formations. Continuing study indicates that there are currently 10 recognizable species of entelodont representing two genera (Archaeotherium and Megachoerus) found in the White River formations of South Dakota. A third genus (Pelonax) is provisionally considered to be synonymous with Megachoerus.