Achaenodon robustus enters the LRT between hippos and anthracobunids

First described by Cope 1873,
Achaenodon (Fig. 1) is traditionally considered an Eocene artiodactyl. That is incorrect.

Cambaytherium thewissi 
(Rose et al. 2014; Eocene, 55 mya; 45-75 lbs; Fig. 3) was originally considered a basal perissodactyl, but nests here between Hippopotamus (prior to the addition of Achaenodon) and Janjucetus. The canines and incisors are missing, perhaps absent. The posterior mandible had a long retroarticular process as in Anthracobune. Cambaytherium was found on the marine coastline of island India, close to where pakicetid walking whales and archaeocete swimming whales were convergently evolving from terrestrial tenrec ancestors, as we looked at a few days ago here.

References
Cope ED 1873. Fourth notice of extinct Vertebrata from the Bridger and the Green River Tertiaries. Paleontological Bulletin 17:1–4.
Rose, KD et al. (8 other authors) 2014. Early Eocene fossils suggest that the mammalian order Perissodactyla originated in India. Nature Communications 5 (5570).  doi:10.1038/ncomms6570.
Rose KD et al, 2020. Anatomy, Relationships, and Paleobiology of Cambaytherium (Mammalia, Perissodactylamorpha, Anthracobunia) from the lower Eocene of western India, Journal of Vertebrate Paleontology (2020). DOI: 10.1080/02724634.2020.1761370

wiki/Cambaytherium
wiki/Achaenodon

https://www.researchgate.net/publication/328388746_The_triple_origin_of_whales