Xenocranium

Xenocranium ("strange skull") is a monotypic genus of extinct epoicotheriid mammal whose fossils were recovered from late Eocene of the American state of Wyoming. The single species is Xenocranium pileorivale.

Xenocranium
Temporal range: Late Eocene
Artist reconstruction of
Xenocranium pileorivale
compared to the size of a human hand.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: †Palaeanodonta
Family: †Epoicotheriidae
Genus: †Xenocranium
Colbert, 1942
Species:
†X. pileorivale
Binomial name
†Xenocranium pileorivale

Etymology

The name Xenocranium comes from the Ancient Greek words xenos and cranios, meaning "strange" and "skull" respectively, after its unique skull arrangement. The specific epithet is derived from pileus meaning "hat" and rivale meaning "brook", in reference to the nearby township of Hat Creek, Wyoming, U.S.A.[1]

Description

Xenocranium pileorivale possesses many traits indicative of a subterranean lifestyle, 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 formula is 0.1.41.1.5.[3]

Palaeoecology

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 Formation of Nebraska.[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]

Phylogenetic tree

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

 Pholidotamorpha 

Pholidota (sensu stricto)

 †Palaeanodonta 

†Escavadodontidae

 ? 

†Amelotabes

 ? 

†Melaniella

†Ernanodontidae

†Metacheiromys

†Palaeanodon

 †Metacheiromyinae

†Brachianodon

†Mylanodon

†Propalaeanodontinae

†Metacheiromyidae

 ? 

†Arcticanodon

 †Epoicotheriidae 

†Alocodontulum

†Auroratherium

†Pentapassalus

†Tubulodon

†Dipassalus

 †Epoicotheriinae 

†Tetrapassalus

 †Xenocranium 

†Xenocranium pileorivale

†Epoicotherium

†Molaetherium

 (Pholidota [sensu lato]) 

References
  1. E. H. Colbert (1942). Edentate from the Oligocene of Wyoming. Notulae Naturae. Academy of Natural Sciences, No. 109. ISBN 978-1-60483-109-2.
  2. Rose, Kenneth D.; Emry, Robert J. (1983). "Extraordinary fossorial adaptations in the oligocene palaeanodonts Epoicotherium and Xenocranium (Mammalia)". Journal of Morphology. 175 (1): 33–56. doi:10.1002/jmor.1051750105. ISSN 1097-4687. PMID 30053775. S2CID 51727274.
  3. Postilla. Peabody Museum of Natural History. 1894.
  4. Scott, William Berryman (1913). A History of Land Mammals in the Western Hemisphere. MacMillan.
  5. Kenneth D. Rose (2008). "Palaeanodonta and Pholidota". In Janis, Christine M; Gunnell, Gregg F; Uhen, Mark D (eds.). 9 - Palaeanodonta and Pholidota. pp. 135–146. doi:10.1017/CBO9780511541438.010. ISBN 9780511541438.
  6. Gaudin, Timothy (2009). "The Phylogeny of Living and Extinct Pangolins (Mammalia, Pholidota) and Associated Taxa: A Morphology Based Analysis" (PDF). Journal of Mammalian Evolution. Heidelberg, Germany: Springer Science+Business Media. 16 (4): 235–305. doi:10.1007/s10914-009-9119-9. S2CID 1773698.
  7. Kondrashov, Peter; Agadjanian, Alexandre K. (2012). "A nearly complete skeleton of Ernanodon (Mammalia, Palaeanodonta) from Mongolia: morphofunctional analysis". Journal of Vertebrate Paleontology. 32 (5): 983–1001. doi:10.1080/02724634.2012.694319. ISSN 0272-4634. S2CID 86059673.
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