Early Deer, Leptomeryx evansi, Fossil Jaw Section, Badlands, South Dakota, D336

Description

Type: This is a fossil jaw section of the early Deer,
Leptomeryx evansi
.
Locality: Private land in Pennington County, South Dakota
Age: Oligocene, 30 Million Years Ago
Note that ruler increments are 1/16 inch.
Hypertragulidae, Hornless runinants
Musk deer-like selenodonts, Leptomeryx
Hornless ruminants - Although not a biological level of classification, several groups of small hornless ruminants were present during the early Cenozoic of North America but none were related to each other beyond being artiodactyls. The Eocene saw three families of hornless ruminants enter North America from Eurasia in separate immigrations. The Hypertragulidae include a group of selenodonts (ruminants) most closely resembling the unrelated musk deer of Asia. Two families, Hypertragulidae and Leptomercycidae, have been found in Chadronian and later formations within the White River Badlands, including the genera Hypsiodus, Hypertragulus, and Leptomeryx. All are early ruminants and part of the selenodont radiation that began in the middle Eocene. Their upper molars typically had two pairs of crescents, the concave faces labially directed. When interlocked with matching crescents on the molars of the lower mandible, this dentition was extremely effective at cutting and shredding leafy vegetation. One of the most distinguishing factors of this group is the presence of two toes on the rear feet and four toes on the forefeet. The most notable form found in the White River Badlands was Protoceras celer, with it's strange bumpy horns and fang-like upper canines. These are most commonly found in the Protoceras beds of the upper Oligocene which are named after them.
The numbers of fossil remains of these genera varies markedly. The tiny Hypsiodus is rare from the late Eocene and Oligocene but elsewhere became locally abundant in the Miocene. The larger Leptomeryx became more abundant and diverse during the Oligocene, probably playing a major role as selective browsers and frugivores in forest understory and woodland settings. The rarity of complete skulls and skeletons remains of Leptomeryx probably reflects an overall body size that was nearly wholly consumed by predators. The much smaller Hypsiodus and Hypertragulus presumably may have taken refuge in borrows of large tortoises, a habit that in turn led to their more abundant fossil record, and complete skulls and skeletons of both genera have been recorded in White River formations. Today neither hypertragulids nor leptomercycids have close descendents.