oreodonts
Oreodont are extinct Artiodactylids (even-toed mammals) most closely related to
camels and pigs, with no close relatives living today. All are herbivorous, browsing on a
diet of leaves and young shoots. Although tempting to think of them as feeding on
"grass", true grasses did not appear until the late Oligocene, evolving and expanding
widely during the Miocene as savannahs appeared during the cooling and drying of the
that epoch.
Creodont’s fed on different types of vegetation than many modern artiodactylids do and
therefore occupied an ecologically different niche than many living ungulates. True
grazers such as equids did not start to appear until the middle Miocene when grasses
became the dominant type of low forage. Found only in North America, oreodont would
eventually rival the large and diverse extant populations of modern bovid artiodactylous
in Africa (antelopes, wildebeest, and buffalo) or the equally diverse populations of deer
and goats of Asia.
Oreodont are separated into two Families; Agriochoeridae was the earlier of the two
families and consisted of a morphologically homogeneous group recorded from the latest
Bridgerian or early Uintan North American Land Mammal Ages (NALMA) of the Lower
to Middle Eocene to early Arikareean NALMA of the late Oligocene.
Although artiodactyls, all eight genera of agrichoerid oreodont
ABSTRACT-Remains of an oreodont identified as Merychyus sp. cf. M. calaminthus have
been recovered from non-marine strata of the Orocopia Mountains in Southern
California. This is the first direct chronostratigraphic evidence as to the age of these
deposits. Merychyus calaminthus occurs with faunas of late Arikareean age (early
Miocene) in the Tick Canyon Formation of the Soledad Basin, California, and is related
to oreodont that occur in late Arikareean faunas in the Great Plains and New Mexico.
Inasmuch as the Orocopia specimen appears to come from about the middle of the nonmarine section there, the age of most, but not necessarily all, of these beds is early
Miocene or younger. Formerly, The non marine strata of the Orocopia Mountains were
correlated with the
As reported by Crowell and Susuki (1959), Tertiary strata in the Orocopia
Mountains, east of the Salton Sea in Southern California (Text-fig. 1), consist of the
marine Maniobra Formation and unconformable superjacent non- marine strata. The
early and middle Eocene age of the Maniobra (Crowell and Susuki, 1959) was modified
to middle Eocene (Crowell, 1962) and the age of the no marine strata has
Been given as Miocene? and Oligocene (?) in The same two works. age Of these unnamed non-marine rocks was assigned, reason- ably, on the basis of superposition, there
being no direct chronostratigraphic evidence. Subsequently Crowell (1962) noted that in
gross stratigraphy the non marine rocks of the
We present new evidence as to the age of the non marine strata of the Orocopia mountain
area and suggest that at least part of these are time-correlative with the Tick Canyon
Formation in the Soledad
Oreodonts survived from the late Eocene through the early Miocene and are extremely
abundant in some formations. Regardless of their abundance, however, all but one
member of the Agriochoeridae failed to survive past the Chadronian NALMA. Only the
largest merydoidodontid oreodont, apparently better adapted to feeding on tougher
vegetation, survived until the early Miocene. Then increased aridity and cooling favored
the evolution of grasses, thus eliminating the last of this primitive browsing superfamily
that failed to adapt to climatic conditions that favored the evolution of true grazers like
the horse.
If oreodont skulls from these three states alone were more thoroughly studied, the
taxonomic diversity of Chadronian through Arikareean oreodonts would undoubtedly
increase, and our understanding of a major mammalian component of the Cenozoic
would be greater.