Diacodexis

Diacodexis is an extinct genus of small herbivore mammal belonging to the family Dichobunidae which lived in North America and Asia from 55.4 mya—46.2 mya. and existing for approximately 9.2 million years.

Description
It is the oldest known even-toed ungulate. In life, it would have resembled a modern duiker, measuring about 50 centimetres (1.6 ft) in body length, but with a much longer tail. Unlike most later species of artiodactyl, it still had five toes on each foot, although the third and fourth toes were already elongated. It may also have had small hooves on each toe. Its teeth suggest that it was a herbivorous browser.[1]

As suggested by its long legs, Diacodexis is believed to have been fast-running, capable of leaping relatively far.

Morphology
Fossil specimens of four individuals' body mass were examined by Legendre & Roth 1988.
 * Specimen 1: 3.22 kg (7.1 lb)
 * Specimen 2: 2.89 kg (6.4 lb)
 * Specimen 3: 2.62 kg (5.8 lb)
 * Specimen 4: 2.24 kg (4.9 lb)