Mesoreodon is an extinct genus of terrestrial herbivore of the family Merycoidodontidae, subfamily Merycoidodontinae (the oreodonts), endemic to North America during the Whitneyan stage of the Oligocene-Miocene epochs (33—20.6 mya) existing for approximately 12.4 million years.

[1] The following fossil species are known:[2] It was a large animal and ate the numerous low-growing plants and early grasses that sprung up on the plains of North America.

Fossils of Mesoreodon have been found in the Miocene deserts of California, the prairies of Nebraska, Wyoming, and South Dakota, southeastern Idaho, John Day Fossil Beds in Oregon, and Florida.

Mesoreodon had ossified vocal cords; the only other animal to have these in modern times is the howler monkey.

[3] Mesoreodon may have been a "screaming oreodont" using loud noises to intimidate its enemies and rivals.