An oreodont with a diastema
Agriochoerus antiquus (Leidy 1850; Late Eocene to Oligocene; 38–16mya) was similar to Merycoidodon, but had a diastema with the loss of the anterior premolars and the addition of one molar. The dentary canines were larger. Oreodonts nest at the base of the hippo-mysticete clade in the large reptile tree (LRT, 1381 taxa) and between the Phenacodus clade and the Homalodotherium + artiodactyl clades.
Not an anthracothere. Not even an artiodactyl.
Merycopotamus dissimilis (Falconer & Cautley 1847; Middle Miocene to Late Pliocene; Fig. 2) was considered an Asian anthracothere (pig-like artiodactyl), but here nests between Ocepeia and Hippopotamus (Fig. 2) apart from the artiodactyls, closer to oreodonts and mesonychids. Note the migration of the orbit posteriorly, the re-appearance of the postfrontal and prefrontal, the massive dentary with massive retroarticular process and the larger dentary canine, as in hippos.
enlarge the dentary to a size that competes with the skull. Hippos do that. Few mammals enlarge the retro process of the dentary to such a large size. Hippos do that. The retro process anchors the jaw-closing masseter muscle complex.
I looked at none of these taxa firsthand.
Rather, the data came from photos and these taxa were added to the LRT. For doing this and continuing to do this for the last seven years I have incurred the disdain of paleontologists and would-be paleontologists world-wide. Judge for yourself whether or not the LRT has provided scientific value or pseudoscientific propaganda, as others assert without testing.
Falconer H and Cautley PT 1847. Fauna antiqua sivalensis, Atlas. Smith, Elder and Co., London, 136 pp.
Leidy J 1850. [Abstract of remarks made before a meeting of the Academy of Natural Sciences of Philadelphia, December 17th, 1850]. Proceedings of the Academy of Natural Sciences of Philadelphia 5(1):121-122.
Thorpe MR 1921. Two new forms of Agriochoerus. American Journal of Science (8): 111–126.