Equus, Plagiolophus, Lambdotherium and Miohippus

Miohippus anceps (= Anchitherium, March 1874; 1m in length; Late Eocene-Oligocene) was twice as long as Mesohippus with eyes located a little further back on the skull. One species adjusted to forest life. The other was adapted to the prairies.

Plagiolophus huerzeleri (Pomel 1847; Remy 2004; Middle Eocene-Oligocene; est. 2m in length) nests in the LRT with Equus the modern horse. The canine is larger. The maxilla ventral rim is straight. Four molars and two premolars are present in the maxilla. The frontal is extending to close off the orbit.

Lambotherium popoagicum (Cope 1880; Eocene, 50mya). Here Lambdotherium nests with the equiid, Plagiolophus. A deep premaxilla and tall cranium are shared traits.

Equus ferus (Linneaus 1758; extant) includes several extant horses, mules, zebras and perhaps a giant rhino-like horse like Paraceratherium all derived from a sister to Miohippus in the large reptile tree. The preorbital region is longer, the frontal produces a postorbital bar that contacts the squamosal. The premolars are molarized. All four limbs end in a single toe, digit 3.

Cope ED 1880. The bad lands of the Wind River and their fauna. The American Naturalist 14(10):745-748.

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

Marsh OC 1874. Notice of new equine mammals from the Tertiary formation. American Journal of Science 7(39):247-258.

Pomel A 1847. Note critique sur le genre Palaeotherium. Bulletin de la Société géologique de France 2(4): 584-587.

Remy JA 2004. Le genre Plagiolophus (Palaeotheriidae, Perissodactyla, Mammalia): révision systématique, morphologie et histologie dentaires, anatomie crânienne, essai d'interprétation fonctionnelle. Palaeovertebrata. 33 (1–4): 17–281.

wiki/Equus
wiki/Miohippus
wiki/Plagiolophus_(animal)
wiki/Lambdotherium