''Xyronomys'' is an extinct genus of small

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s from the

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

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 ...

, with two described species. The genus lies within the extinct order

Multituberculata Multituberculata (commonly known as multituberculates, named for the multiple tubercles of their teeth) is an extinct Order (biology), order of rodent-like mammals with a fossil record spanning over 130 million years. They first appeared in the M ...

within the suborder

Cimolodonta Cimolodonta is a clade of Multituberculata, multituberculate mammals that lived from the Cretaceous to the Eocene. They probably lived something of a rodent-like existence until their ecological niche was assumed by true rodents. The more basal ...

and family

Neoplagiaulacidae Neoplagiaulacidae is a family of mammal within the extinct order Multituberculata. Fossil remains are known from the Upper Cretaceous through to the latest Eocene/early Oligocene. Representatives have been found in North America, Europe and Asia. ...

. The species ''Xyronomys swainae'' (J. K. Rigby, 1980) was found in Torrejonian (Paleocene)-age

strata In geology and related fields, a stratum (: strata) is a layer of Rock (geology), rock or sediment characterized by certain Lithology, lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by v ...

of Swain Quarry in

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 ...

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

. Represented by a couple of teeth, this genus was originally assigned to

Eucosmodontidae Eucosmodontidae is a poorly preserved family of fossil mammals within the extinct order Multituberculata. Representatives are known from strata dating from the Upper Cretaceous through the Lower Eocene of North America, as well as the Paleocene t ...

. Kielan-Jaworowska and Hurum (2001, p. 406) refer it to

on the basis of its possession of microprismatic enamel, i.e. the tooth enamel is built up from small prisms. A second species ''Xyronomys robinsoni'' was found in Puercan (Lower Paleocene)-age strata of

Colorado Colorado is a U.S. state, state in the Western United States. It is one of the Mountain states, sharing the Four Corners region with Arizona, New Mexico, and Utah. It is also bordered by Wyoming to the north, Nebraska to the northeast, Kansas ...

, US and was named by Middleton and Dewar in 2004. Material assigned to this genus has also been reported from Rav W-1 in

Saskatchewan Saskatchewan is a Provinces and territories of Canada, province in Western Canada. It is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and to the south by the ...

, Canada.

References

* Kielan-Jaworowska, Z. and Hurum, J.H. (2001), "Phylogeny and Systematics of multituberculate mammals", ''Paleontology'' 44:389-429. * Rigby, J.K. (1980), "Swain Quarry of the Fort Union Formation, Middle Paleocene (Torrejonian), Carbon County, Wyoming: geologic setting and mammalian fauna", ''Evolutionary Monographs'' 3, vi +179pp. * Much of this information has been derived fro
Mesozoic Mammals: Ptilodontoidea
an Internet directory. {{Taxonbar, from=Q8045587 Ptilodontoidea Paleocene mammals Paleocene genus extinctions Extinct mammals of North America Fossil taxa described in 1980 Prehistoric mammal genera