''Xenocranium'' ("strange skull") is an extinct

monotypic genus In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...

of placental mammal from extinct

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

subfamily Epoicotheriinae within extinct paraphyletic family

Epoicotheriidae Epoicotheriidae ("strange beasts") is an extinct paraphyletic family of insectivorous placental mammals within extinct order Palaeanodonta, that lived in North America, Asia and Europe from the late Paleocene to early Oligocene. Epoicotheriids we ...

in extinct order

Palaeanodonta Palaeanodonta ("ancient toothless animals") is an extinct clade of stem-pangolins. They were insectivorous (Myrmecophagy, myrmecophagous), possibly fossorial, and lived from the middle Paleocene to early Oligocene in North America, Europe and Asi ...

, that lived in

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

during the late

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

Etymology

The name of genus ''Xenocranium'' comes and , respectively after its unique skull arrangement. The specific epithet is derived and , in reference to the nearby township of Hat Creek,

Wyoming Wyoming ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States, Western United States. It borders Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho t ...

, U.S.A.

Description

''Xenocranium pileorivale'' was a highly specialized animal that was convergent with the talpids, golden moles and

marsupial mole Marsupial moles, the Notoryctidae family, are two species of highly specialized marsupial mammals that are found in the Australian interior. They are small burrowing marsupials that anatomically converge on fossorial placental mammals, such as ...

. It possesses many traits indicative of the lifestyle of a subterranean burrower, including small eyes, an upturned snout, muscular arms with large attachment points for the

triceps The triceps, or triceps brachii (Latin for "three-headed muscle of the arm"), is a large muscle on the ventral, back of the upper limb of many vertebrates. It consists of three parts: the medial, lateral, and long head. All three heads cross the ...

teres major The teres major muscle is a muscle of the upper limb. It attaches to the scapula and the humerus and is one of the seven scapulohumeral muscles. It is a thick but somewhat flattened muscle. The teres major muscle (from Latin ''teres'', meanin ...

, and carpal and

digital Digital usually refers to something using discrete digits, often binary digits. Businesses *Digital bank, a form of financial institution *Digital Equipment Corporation (DEC) or Digital, a computer company *Digital Research (DR or DRI), a software ...

flexor muscles. The

dental formula Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiology ...

is .

Palaeoecology

The holotype of ''Xenocranium pileorivale'' was recovered from the Brule Formation, 160 feet below the top of the

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

outcrop in the area, which correlates with the

Chadronian The Chadronian is a North American Land Mammal Age typically set from around 37,000,000 to 33,700,000 years BP, a period of . The Chadronian is preceded by the Duchesnean and followed by the Orellan NALMA stages. Relative to global geological c ...

age to the

Orellan The Orellan is a North American Land Mammal Age typically set from around 33,700,000 to 32,000,000 years BP, a period of . The Orellan is preceded by the Chadronian and followed by the Whitneyan NALMA stages. Relative to global geological chronolo ...

age under the NALMA classification. Later on, this layer was found to be from

Priabonian The Priabonian is, in the ICS's geologic timescale, the latest age or the upper stage of the Eocene Epoch or Series. It spans the time between . The Priabonian is preceded by the Bartonian and is followed by the Rupelian, the lowest stage ...

age of late

. Further remains have been found in the

White River Formation The White River Formation is a geologic formation of the Paleogene Period, in the northern Great Plains and central Rocky Mountains, within the United States. It has been found in northeastern Colorado, Dawes County in western Nebraska, Badland ...

Nebraska Nebraska ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Ka ...

. The animals from these formations constitute the

White River Fauna The White River Fauna are fossil animals found in the White River Group of South Dakota, North Dakota, Wyoming, Colorado and Nebraska in the United States. In southwest South Dakota and northwest Nebraska, these fossils are characteristic of the ...

, which included predators like '' Archaeotherium'' and ''

Hyaenodon ''Hyaenodon'' ("hyena-tooth") is an Extinction (biology), extinct genus of Carnivore, carnivorous Placentalia, placental mammals from extinct tribe Hyaenodontini within extinct subfamily Hyaenodontinae (in extinct Family (biology), family Hyaenod ...

'', and a large diversity of

herbivorous A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat n ...

mammals, such as the archaic horse ''

Mesohippus ''Mesohippus'' (Greek language, Greek: / meaning "middle" and / meaning "horse") is an extinct genus of early horse. It lived 37 to 32 million years ago in the Early Oligocene. Like many fossil horses, ''Mesohippus'' was common in North America. ...

'', the cursorial rhinoceros '' Hyracodon'', and the very common "

oreodont Merycoidodontoidea, previously known as "oreodonts" or " ruminating hogs," are an extinct superfamily of prehistoric cud-chewing artiodactyls with short faces and fang-like canine teeth. As their name implies, some of the better known forms we ...

" '' Merycoidodon''.

Phylogenetic tree

The phylogenetic relationships of genus ''Xenocranium'' is shown in the following cladogram:

References

{{Taxonbar, from=Q21369124 Palaeanodonta Prehistoric mammal genera Eocene mammals of North America

Etymology

Description

Palaeoecology

Phylogenetic tree

See also

References