Belongs within: Euungulata.
The Phenacodontidae are a family of herbivorous cursorial mammals from the Palaeocene and Eocene of North America and Europe. Size estimates for phenacodontids range up to over fifty kilos for the larger Phenacodus species (Thewissen 1990), about the size of a small sheep. Thewissen (1990) suggested that Phenacodus may have been sexually dimorphic in the size of the paranasal sinuses and that this dimorphism may have been related to sound production.
Characters (from Thewissen 1990): Teeth bunodont to bunolophodont. P4 with talonid basin and subequal protoconid and metaconid. Paraconid of lower molars absent or small. P3 with small protocone, P4 with paracone, metacone, and protocone. M1-2 with hypocone and often with mesostyle. Dental formula 3.1.4.3 / 3.1.4.3. Humerus with weak deltopectoral crest and supracondylar foramen. Ulna strong with anterior process distally. Five digits in hand and foot. Femur with third trochanter. Fibula complete. Astragalus with convex head.
Phenacodontidae
|--LophocionHD04
|--Meniscotherium Cope 1874PMF88, C77
| |--M. chamense Cope 1874C77
| |--M. priscum Granger 1915T90
| |--M. robustum Thorpe 1934G52
| |--M. tapiacitis Cope 1882G52
| `--M. terraerubrae Cope 1881M94, G52 [=M. chamense terraerubraeG52; incl. Hyracops socialis Marsh 1892G52]
`--Phenacodus Cope 1873 [incl. Almogaver Crusafont & Villalta 1955, Eohyus Marsh 1894, Opisthotomus Cope 1875]T90
|--*P. primaevus Cope 1873 (n. d.) [incl. *Eohyus distans Marsh 1894]T90
|--P. astutus (Cope 1875) [=Opisthotomus astutus]T90
|--P. bisonensis Gazin 1956T90
|--P. condali (Crusafont & Villalta 1955) [=Almogaver condali]T90
|--‘Opisthotomus’ flagrans Cope 1875C77
|--P. grangeri Simpson 1935 [incl. Tetraclaenodon transitus Dorr 1958]T90
|--P. hemiconus Cope 1882 (n. d.) [=P. primaevus hemiconus]T90
|--P. intermedius Granger 1915T90
|--P. lemoinei Thewissen 1990T90
|--P. magnus Thewissen 1990T90
|--P. matthewi Simpson 1935 [incl. P. gidleyi Simpson 1935]T90
|--P. nuniensis Cope 1885 (n. d.)T90
|--P. omnivorus Cope 1874 (n. d.)T90
|--P. sulcatus Cope 1874C77
|--P. teilhardi Simpson 1929 [incl. P. europaeus Teilhard de Chardin 1927 non Ruetimeyer 1888]T90
|--P. trilobatus Cope 1882 [incl. P. primaevus robustus Granger 1915]T90
|--P. villaltae Crusafont Pairo 1956T90
|--P. vortmani (Cope 1880) (see below for synonymy)T90
`--P. zuniensisD07
Phenacodus vortmani (Cope 1880) [=Hyracotherium vortmani, P. wortmani; incl. P. almiensis Gazin 1942, P. apternus Cope 1882, P. copei Granger 1915]T90
*Type species of generic name indicated
References
[C77] Cope, E. D. 1877. Report upon the extinct Vertebrata obtained in New Mexico by parties of the expedition of 1874. Geographical Surveys West of the One Hundredth Meridian 4 (2): i–iv, 1–370.
[D07] Dixon, D. 2007. The Complete Illustrated Encyclopedia of Dinosaurs & Prehistoric Creatures. Hermes House: London.
[G52] Gazin, C. L. 1952. The Lower Eocene Knight Formation of western Wyoming and its mammalian faunas. Smithsonian Miscellaneous Collections 117 (18): 1–82, 11 pls.
[HD04] Hooker, J. J., & D. Dashzeveg. 2004. The origin of chalicotheres (Perissodactyla, Mammalia). Palaeontology 47 (6): 1363–1386.
[M94] MacPhee, R. D. E. 1994. Morphology, adaptations, and relationships of Plesiorycteropus, and a diagnosis of a new order of eutherian mammals. Bulletin of the American Museum of Natural History 220: 1–214.
[PMF88] Prothero, D. R., E. M. Manning & M. Fischer. 1988. The phylogeny of the ungulates. In: Benton, M. J. (ed.) The Phylogeny and Classification of the Tetrapods vol. 2. Mammals pp. 201–234. Clarendon Press: Oxford.
[T90] Thewissen, J. G. M. 1990. Evolution of Paleocene and Eocene Phenacodontidae (Mammalia, Condylarthra). Museum of Paleontology Papers on Paleontology 29: 1–107.