Microcosmodon is a mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

 genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 from the Paleocene

Paleocene

The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...

 of North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

. It was a member of the extinct order Multituberculata

Multituberculata

The Multituberculata were a group of rodent-like mammals that existed for approximately one hundred and twenty million years—the longest fossil history of any mammal lineage—but were eventually outcompeted by rodents, becoming extinct during the early Oligocene. At least 200 species are...

, and lies within the suborder Cimolodonta

Cimolodonta

The Cimolodonta are a taxon of extinct mammals that lived from the Cretaceous to the Eocene. They were some of the more derived members of the extinct order Multituberculata. They probably lived something of a rodent-like existence until their ecological niche was assumed by true rodents...

 and family Microcosmodontidae

Microcosmodontidae

Microcosmodontidae is a poorly preserved family of fossil mammals within the extinct order Multituberculata. Representatives are known from the Upper Cretaceous though the Lower Paleocene of North America. The family is part of the suborder Cimolodonta...

. The genus Microcosmodon was named by G.L. Jepsen in 1930.

Species

The species Microcosmodon arcuatus was named by P.A. Johnston and R.C. Fox in 1984. Fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 remains have been found in the Puercan (Paleocene)-age strata

Stratum

In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...

 Rav W-1 of Saskatchewan

Saskatchewan

Saskatchewan is a prairie province in Canada, which has an area of . Saskatchewan is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, and on the south by the U.S. states of Montana and North Dakota....

, Canada

Canada

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

. The holotype

Holotype

A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...

 is in the University of Alberta

University of Alberta

The University of Alberta is a public research university located in Edmonton, Alberta, Canada. Founded in 1908 by Alexander Cameron Rutherford, the first premier of Alberta and Henry Marshall Tory, its first president, it is widely recognized as one of the best universities in Canada...

 collection. When alive, the creature weighed about the same as a well-fed mouse (about 30 g).

The type species

Type species

In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...

 Microcosmodon conus was named by G.L. Jepsen in 1930. Remains have been found in the Tiffanian (Paleocene)-age strata of the Polecat Bench Formation of Wyoming

Wyoming

Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...

 (USA) and Saskatchewan, Canada. This species would have weighed around 15 g.

The species Microcosmodon harleyi was named by A. Weil in 1998. Remains have been found in the Puercan (Paleocene)-age strata of the Tullock Formation in Montana

Montana

Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...

 (USA). "The presence of the new species suggests that microcosmodontine species richness in the Western Interior was as high at the beginning of the Paleocene as at its end," (Weil, 1998). The species would have weighed about 20 g.

The species Microcosmodon rosei was named by D.W. Krause in 1980. Remains have been found in the Clarforkian (Paleocene)-age strata of the Willwood Formation of Wyoming. This species weighed a fairly standard mouse-sized 25 g+.

The species Microcosmodon woodi was named by R.C. Holtzman and D.L. Wolberg in 1977. It is also known as Eucosmodontid woodi (Weil 1998). Remains have been found in the Middle Paleocene-age strata of Montana and North Dakota

North Dakota

North Dakota is a state located in the Midwestern region of the United States of America, along the Canadian border. The state is bordered by Canada to the north, Minnesota to the east, South Dakota to the south and Montana to the west. North Dakota is the 19th-largest state by area in the U.S....

 (USA) and Alberta

Alberta

Alberta is a province of Canada. It had an estimated population of 3.7 million in 2010 making it the most populous of Canada's three prairie provinces...

, Canada. However, Weil A. (1998) found that this material "does not belong to this genus or subfamily."