Hyracodon

thumb|Skeletal reconstruction of Hyracodon Hyracodon ('hyrax tooth') is an extinct genus of perissodactyl mammal from the White River Formation.

== Description == Hyracodon was a lightly built, pony-like mammal about 1.5 m (5 ft) in length, with a large skull in comparison to the rest of the body. Hyracodon was much smaller than modern rhinocerotoides and differed very little in appearance from the primitive horses with which it was contemporaneous (32–26 million years ago). It had a short, broad snout and its long, slender limbs had three digits. When put next to the comtemporary Mesohippus, Hyracodon had a proportionally long neck, with robust vertebrae. Compared to earlier hyracodontids from the Uinta Formation, like Triplopus, Hyracodon had a more gracile manus structure. The median toe was enlarged whilst the lateral toes were greatly reduced. The molars of Hyracodon were similar to those of the modern day Rhinoceros, with the last upper molar assuming a triangular shape. The canines and incisors, however were quite different. In form, the anterior teeth of Hyracodon were small and similar in shape, being pointed and curved.left|thumb|H. nebraskensis skull, found near Hermosa, South Dakota.Like the primitive horses, hyracodonts inhabited open forests and wooded steppes and turned from browsing foliage to grazing grass. They died out without leaving any descendants and they mark the end of the phylogenetic branch of hornless, running rhinocerotoids.