Protoreodon walshi
Small pig-like herbivore
Family: Agriochoeridae

Time
Eocene Epoch

In Our Region
Numerous skulls, jaws, and even partial skeletons of this species have been collected from fossil localities in San Diego County. These fossils occur in strata of late Uintan age (about 42-43 million years old) as exposed in Spring Valley, La Mesa, San Carlos, Scripps Ranch, Carlsbad, and Oceanside, in rock units known as the Mission Valley Formation and Santiago Formation.

Description
Protoreodon walshi is an extinct species of artiodactyl, distantly related to modern cows, deer, pigs, and camels. It is one of the oldest members of the Artiodactyla (even-toed ungulates) to possess crescent-shaped molar teeth, which are characteristic of most living members of the order. The Agriochoeridae and closely related Merycoidodontidae are exclusively North American artiodactyls that were very diverse during Eocene and Oligocene time, but finally became extinct at the end of the Miocene, about 5 million years ago.

An Inside Look This species of Protoreodon was known from several fragmentary fossils from San Diego for many years, but remained unnamed, even though it was widely understood by paleontologists to be a new species. After numerous complete skulls and jaws were collected in Oceanside during the widening of State Route 78 in 1991, Dr. Jessica Theodor formally named the new species after Steve Walsh, one of the Museum's paleontologists.

Protoreodon walshi, one of the oldest and most primitive known agriochoerid, was as large as a medium-sized dog. It had a strong lower jaw and distinct, tusk-like upper canine teeth. The canines were probably used in social displays between individual protoreodons and secondarily may have functioned in defense. The limbs of Protoreodon were short relative to those of most living artiodactyls. The feet were especially short, suggesting that Protoreodon was not a swift runner.

Ecology
This animal probably made its living by browsing upon the Eocene shrubbery. The discovery of abundant fossil remains of this species suggests that P. walshi probably was gregarious and may have lived in herds. It was likely preyed upon by some of the large carnivores in the local Eocene fauna, such as Tapocyon.

Text: Steven Walsh
Illustration: Jim Melli

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