Systemodon

Systemodon is a genus of early Eocene mammal of Wasatchian age (ca. 55-50 mya). It was one of many mammals originally considered the earliest horses, long classified in the genus Hyracotherium (commonly known as Eohippus). These were dog-sized animals that in life would have looked vaguely like a paca, mara, or chevrotain (though they were perissodactyls, not rodents or artiodactyls.) The type species, S. tapirinus, is represented by 24 individuals from a locale called the Castillo pocket in the Huerfano Formation of Colorado. This well-preserved deposit allows researchers to reconstruct aspects of the environment and lifestyle of the species.