13 Fossil taxa described in 1858

Aelurodon is an extinct canine genus of the subfamily Borophaginae which lived from the Barstovian land mammal age of the middle Miocene to the late Miocene epoch. Aelurodon existed for approximately 10.7 million years .

The dire wolf is an extinct species of the genus Canis. It is one of the most famous prehistoric carnivores in North America, along with its extinct competitor, the sabre-toothed cat Smilodon fatalis. The dire wolf lived in the Americas and China during the Late Pleistocene and Early Holocene epochs. The species was named in 1858, four years after the first specimen had been found. Two subspecies are recognized: Canis dirus guildayi and Canis dirus dirus. The dire wolf probably evolved from Armbruster's wolf in North America. The largest collection of its fossils has been obtained from the Rancho La Brea Tar Pits in Los Angeles.

Epicyon is a large, extinct, canid genus of the subfamily Borophaginae, native to North America. Epicyon existed for about 15 million years from the Hemingfordian age of the Early Miocene to the Hemphillian of the Late Miocene.

Hadrosaurus is a genus of hadrosaurid ornithopod dinosaurs that lived in North America during the Late Cretaceous Period in what is now the Woodbury Formation about 80 million to 78 million years ago. The holotype specimen was found in fluvial marine sedimentation, meaning that the corpse of the animal was transported by a river and washed out to sea.

Hypohippus is an extinct genus of three-toed horse, which lived 17–11 million years ago. It was the size of a pony, and fossils of it have been found in Nebraska, Colorado, and Montana.

Parahippus is an extinct equid, a relative of modern horses, asses and zebra. It was very similar to Miohippus, but slightly larger, at around 1 metre tall, at the withers.

Pliolophus is an extinct equid that lived in the Early Eocene of Britain.

Procamelus is an extinct genus of camel endemic to North America. It lived from the Middle to Late Miocene 16.0—5.3 mya, existing for approximately 11 million years . The name is derived from the Greek πρό, meaning "before" or denoting priority of order, and κάμελος ("camel"), thus meaning "fore-camel", "early camel" or "predecessor camel".

Promerycochoerus is an extinct genus of hippopotamus-like oreodont artiodactyl that lived in Central North America during the Early Miocene.

Protohippus is an extinct three-toed genus of horse. It was roughly the size of a modern donkey. Fossil evidence suggests that it lived during the Late Miocene, from about 13.6 Ma to 5.3 Ma.

Psephoderma is a genus of placodonts very similar to the related genera Placochelys and Cyamodus. Psephoderma had a flattened skull and a narrow, straight rostrum, much narrower than that of its relatives. Inside this skull, embedded in the jaws, were rounded teeth specialized for crushing the shellfish it ate. Unlike henodontid placodonts, Psephoderma's carapace was divided into two pieces, one on the shoulders and back, and another on the ventral end. Psephoderma grew to 180 centimetres (5.9 ft) long, larger than many of its relatives, and lived in the Late Triassic, about 210 million years ago. It was one of the last placodonts to live. Fossils of Psephoderma have been found in the Rhaetian deposits in the Alps and in England, hence the specific names.

Simocyon is a genus of extinct carnivoran mammal in the family Ailuridae. Simocyon, which was about the size of a mountain lion, lived in the late Miocene and early Pliocene epochs, and has been found in Europe, Asia, and rarely, North America and Africa.