''Merriamoceros'' is an extinct genus of

pronghorn The pronghorn (, ) (''Antilocapra americana'') is a species of artiodactyl (even-toed, hoofed) mammal indigenous to interior western and central North America. Though not an antelope, it is known colloquially in North America as the American a ...

. It is known from a single species, which is also the type species, ''M. coronatus''.

Discovery and naming

The type specimen (UCMP 20052) that defines this species is named ''Merriamoceros coronatus'' taking after its discoverer, J.M. Merriam. It is known from a partial skull (a single fragmentary horn or antler). Remains of ''Merriamoceros'' were found in rock formations dating to the

Early Miocene The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene epoch (geology), Epoch made up of two faunal stage, stages: the Aquitanian age, Aquitanian and Burdigalian stages. The sub-epoch lasted from 23.03 ± 0.05 annum, Ma to ...

period, 15.9 to 13.6

million years ago The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds. Usage Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago) ...

. Its type locality is Barstow, which is in a Barstovian terrestrial horizon in the Barstow Formation of

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

. ''Merriamoceros'' was originally named as a subspecies of ''

Ramoceros ''Ramoceros'' is an extinct genus of the artiodactyl family Antilocapridae endemic to Middle Miocene (Clarendonian) North America.Blount, Kitty and Crowley, Maggie. ''Encyclopedia of Dinosaurs & Prehistoric Life'', p. 271 (Penguin, 2008). Tax ...

'', but later J. T. Gregory elevated it to a generic level, stating that its palmate style horns were distinct characteristics and required a separate classification. The developmental series discussed by C. Frick further supports the hypothesis of homology between the horns of ''

'' and ''Merriamoceros'', with young ''Merriamoceros'' presenting three horns, reminiscent of those of '' Paramoceros''. The horn ontogeny of these two separate genera marks an evolutionarily distinct lineage.

Description

''Merriamoceros'' was a prehistoric relative of modern pronghorn (''

Antilocapra americana The pronghorn (, ) (''Antilocapra americana'') is a species of artiodactyl (even-toed, hoofed) mammal indigenous to interior western and central North America. Though not an antelope, it is known colloquially in North America as the American a ...

''), which is a species of

artiodactyl The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing poster ...

mammal indigenous to interior western and central North America. Its remains were found in California, and were characterized by a small body size and palmate horns. It is the oldest known member of the

Antilocapridae The Antilocapridae are a family of artiodactyls endemic to North America. Their closest extant relatives are the giraffids with which they comprise the superfamily Giraffoidea. Only one species, the pronghorn (''Antilocapra americana''), is ...

family, also known as the

s. It was closely related to ''

'' and ''

Merycodus ''Merycodus'' is an extinct genus of the artiodactyl family Antilocapridae. Fossils of this genus have been found in the Santa Fe Group of New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , s ...

''. It was, like its relatives, a quadruped herbivore and grazed on the grassy plains of its time. It is not known if ''Merriamoceros'' had any predators and much is still unknown about its paleobiology, but it is assumed that it was similar to the present day pronghorn and its extinct relatives. ''Merriamoceros'' was covered in a short fur and was likely a good runner. ''Merriamoceros'' had some of the most intricate cranial appendages in the family, where the tines were on top and along the outside edges of the horns. Like related species, these were likely initially covered in skin, which gradually rubbed off to expose the bone.

References

Miocene mammals of North America Miocene even-toed ungulates Prehistoric pronghorns Prehistoric even-toed ungulate genera {{paleo-eventoedungulate-stub