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Xenocranium

Xenocranium Temporal range: 35.8–33.9 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓ Late Eocene
Artist reconstruction of Xenocranium pileorivale compared to the size of a human hand.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	†Palaeanodonta
Family:	†Epoicotheriidae
Subfamily:	†Epoicotheriinae
Genus:	†Xenocranium Colbert, 1942[1]
Type species
†Xenocranium pileorivale Colbert, 1942

Xenocranium ("strange skull") is an extinct monotypic genus of placental mammal from extinct paraphyletic subfamily Epoicotheriinae within extinct paraphyletic family Epoicotheriidae in extinct order Palaeanodonta, that lived in North America during the late Eocene.

The name of genus Xenocranium comes from Ancient Greek ξένος (xénos) 'strange' and from Ancient Greek κρανίον (krāníon) 'skull', respectively after its unique skull arrangement.

The specific epithet is derived from Latin pileus 'hat' and from Latin rivalis 'brook', in reference to the nearby township of Hat Creek, Wyoming, U.S.A.^[1]

Xenocranium pileorivale was highly specialized animal that was convergent with the talpids, golden moles and marsupial mole. 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, teres major, and carpal and digital flexor muscles.^[2] The dental formulais0.1.41.1.5.^[3]

The holotype of Xenocranium pileorivale was recovered from the Brule Formation, 160 feet below the top of the Oligocene outcrop in the area,^[1] which correlates with the Chadronian age to the Orellan age under the NALMA classification. Later on, this layer was found to be from Priabonian age of late Eocene. Further remains have been found in the White River FormationofNebraska.^[3] The animals from these formations constitute the White River Fauna, which included predators like Archaeotherium and Hyaenodon, and a large diversity of herbivorous mammals, such as the archaic horse Mesohippus, the cursorial rhinoceros Hyracodon, and the very common "oreodont" Merycoidodon.^[4]

The phylogenetic relationships of genus Xenocranium is shown in the following cladogram:^[5][6][7]

• Mammal classification
• Epoicotheriinae