Fossil range: Early Eocene
| †Sifrhippus sandrae|
Sifrhippus ("zero horse") is an extinct genus of horse. Sifrhippus is the oldest horse known from North America, and its fossils come from the earliest Eocene of the Bighorn Basin, Wyoming. Sifrhippus was a very small horse the size of a house cat.
- ↑ 1.0 1.1 Gingerich, P.D. (1989). "New earliest Wasatchian mammalian fauna from the Eocene of northwestern Wyoming: composition and diversity in a rarely sampled high-floodplain assemblage". University of Michigan Papers on Paleontology 28: 1–97. http://hdl.handle.net/2027.42/48628.
- ↑ Froehlich, D.J. (2002). "Quo vadis eohippus? The systematics and taxonomy of the early Eocene equids (Perissodactyla)". Zoological Journal of the Linnean Society 134 (2): 141–256. doi:10.1046/j.1096-3642.2002.00005.x.