Tapirus, Homogalax, Protapirus and Heptodon

Heptodon (Pachynolophus) posticus (Cope 1882; Eocene, 50 mya; 1m in length) nests close to the base of tapirs in the LRT. Heptadon had reduced canines and developed a diastema (lack of teeth) posterior to them. The posterior cranium was slightly elevated. The manus had four digits. The pes had three.

Protapirus obliquidens (Filhol 1877; Early Oligocene to Early Miocene) nests with Tapirus in the large reptile tree, but shares some traits with Heptodon that Tapirus does not. Skull size is similar to both.

Homogalax protapirinus (Wortman 1896, Hay 1899, AMNH 42891, Early Eocene, 50mya, 15cm skull length) nests in the LRT basal to Tapirus. Post-crania indicates a fast cursorial lifestyle. Four molars are present.

Tapirus terrestris (Linneaus 1758) is the living Brazilian tapir, derived from a sister to Heptodon (below). This odd-toed ungulate has a retracted naris and a short soft-tissue trunk. The cranium rised in a tall crest. The body is short and bulky.

Skull image from digimorph.org and used with permission.

Colbert MW and Schoch RM 1998. Tapiroidea and other moropomorphs. In CM Janis, KM Scott, and LL Jacobs (eds.), Evolution of Tertiary mammals of North America 569-582.

Cope ED 1882. Paleontological Bulletin 34:187.

Cope ED 1882a. Contributions to the history of the Vertebrata of the lower Eocene of Wyoming and New Mexico, made during 1881. Proceedings of the American Philosophical Society: 139-197.

Cope ED 1882e. Note on Eocene Mammalia. American Naturalist 16:522.

Hay OP 1899. On the Names of Certain North American Fossil Vertebrates. Science 9(225):593-594.

Holbrook LT 1999. The Phylogeny and classification of tapiromorph perissodactyls (Mammalia). Cladistics 15(3):331-350.

Holbrook LT Lucas SG and Emry RJ 2004. Skulls of the Eocene Perissodactyls (Mammalia) Homogalax and Isectolophus. Journal of Vertebrate Paleontology 24. (4) 951-956.

Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

Minchen C and Chuan-kuei L 1965. Homogalax and Heptodon of Shantung. Vertebrata Palasiatica 9(1):, 15-22.

Rose KD 1996. Skeleton of early Eocene Homogalax and the origin of Perissodactyla. Palaeovertebrata 25 (2-4).243-260.

Wortman D 1896. Bulletin of the American Museum of Natural History 8: 91.

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wiki/Heptodon
wiki/Protapirus
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