Hyracodon, Amynodon and Metamynodon

Hyracotherium leporinum (Owen 1841; 78 cm long; Eocene, 55-45 mya; BMNH C21361) was derived from a sister to Tapirus and Heptodon is a sister. Both are basal to the horse/rhino clade represented by Equus and Ceratotherium.

Canines remained. A diastema separated it from the premolars. Manus has four hoofed toes. Pes has three hoofed toes.

Amynodon advenus (Marsh 1877; 1m in length; Oligocene-Eocene, 40-23 mya) was originally considered an aquatic rhino. Here it nests with Mesohippus. The long neck and other traits are more horse-like than rhino-like. Manual digit 5 was retained. The skull was deeper as in basal forms like Hyracotherium.

Metamynodon planifrons (Scott and Osborn 1867; Early Eocene; 4m long) This hippo-mimic nests with aquatic rhinos like Amnyodon in the LRT. Note the large self-sharpening canines and short cervicals. The calcaneum is long.

Holbrook LT and Lucas SG 1997. A new genus of rhinocerotoid from the Eocene of Utah and the status of North American "Forstercooperia". Journal of Vertebrate Paleontology 17 (2): 384–396.

Marsh OC 1877. Notice of some new vertebrate fossils. American Journal of Arts and Sciences 14:249-256

Owen R 1841. Description of the Fossil Remains of a Mammal (Hyracotherium leporinum) and of a Bird (Lithornis vulturinus) from the London Clay. Transactions of the Geological Society of London, Series 2, VI: 203-208.

Froehlich DJ 2002. Quo vadis eohippus? The systematics and taxonomy of the early Eocene equids (Perissodactyla). Zoological Journal of the Linnean Society. 134 (2): 141–256.

Scott WB and Osborn HF 1887. Preliminary account of the fossil mammals from the White River formation contained in the Museum of Comparative Zoology. Bulletin of the Museum of Comparative Zoölogy at Harvard College 13(5):151–171.

wiki/Hyracotherium
wiki/Amynodontidae
wiki/Metamynodon

Mammalia

Ornithorhynchus and kin

Marsupials - Metatheria

Eomaia and kin

Placentalia 2

Tupaia and kin

Placentalia 1

Primates – Chiroptera

Notharctus and kin

Carnivora

Nandinia and kin