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Write 5 pages thesis on the topic evolution of the horse. Hyracotherium, the earliest relative of the modern horse lived 55mya, during the Lower Eocene epoch. Around 150 known fossil species descended from the Hyracotherium, most of which became extinct and resulted in an evolutionary dead-end. This paper shall focus upon major genera of the supposed line of ancestral descendants from Hyracotherium to the modern horse. No references are made to tangential genera.Hyracotherium: The genus Hyracotherium lived during the lower to middle Eocene. It was a small dog-sized mammal with four toes on its forefeet and three on the rear. It had low-crowned teeth with horse-like ridged molars. The face was short with centred, forward facing eye sockets and a short distance between the front and cheek teeth [diastema]. Its physical characteristics suggest that it inhabited forested areas and browsed upon foliage (Garner, 2005. Tufts University, 1998).Orohippus: Appears during the middle Eocene, circa 2mya after Hyracotherium and existed from 52-45mya. It is believed that Orohippus evolved from a species of Hyracotherium but different species from the two genera co-existed during this epoch. Orohippus characteristics were much the same as Hyracotherium bar the vestiges of the 1st and 2nd toes, which vanished (Tufts University, 1998. Hunt, 1995).Epihippus: Appears 47mya in the middle Eocene. Epihippus characteristics were alike the previous genera bar a continuing evolution of the teeth. The rear premolars had evolved to become like molars, suggesting that the Epihippus was eating more hard foliage (Hunt, 1995).Mesohippus: Mesohippus was a sheep-sized descendant of the Orohippus that became extinct sometime in the middle Oligocene and lived circa 37-32mya. It too was a browsing animal with low-crowned teeth but had evolved to have only three toes on its forefeet. Its cranial capacity had also noticeably increased (Hunt, 1995).