Microcosmodon

Microcosmodon is a mammal genus from the Paleocene of North America. It was a member of the extinct order of Multituberculata.
For those of a technical inclination, it's within the Suborder of Cimolodonta, and the family Microcosmodontidae.

Genus: Microcosmodon Jepsen GL, 1930

Species: Microcosmodon arcuatus Johnston PA & Fox RC, 1984
Place: Rav W-1, Saskatchewan
Country: Canada
Age: Puercan, Paleocene
Remarks: The holotype[?] is in the University of Alberta collection. When alive, the creature weighed about the same as a well fed mouse, (30g).
Reference: Johnston & Fox (1984), Paleocene and Late Cretaceous mammals from Saskatchewan, Canada. Palaeontogr. Abt. A: Paläozool., Stratigr. 186, p.163-222.

Species: Microcosmodon conus Jepsen GL, 1930
Place: Polecat Bench Formation, Wyoming & Saskatchewan
Country: USA & Canada
Age: Tiffanian, Paleocene
Remarks: A diminutive 15g species.
Reference: Jepsen (1930), New vertebrate fossils from the Lower Eocene of the Bighorn Basin, Wyoming. Proceedomgs of the American Philosophical Society, 83, p.217-341.

Species: Microcosmodon harleyi Weil A, 1998
Place: Tullock Formation, Montana
Country: USA
Age: Puercan, Paleocene
Remarks: "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). A 20 grammer.
Reference: Weil (1998), A new species of Microcosmodon (Mammalia: Multituberculata) from the Paleocene Tullock Formation of Montana, and an argument for the Micrcosmodontinae. PaleoBios 18.

Species: Microcosmodon rosei Krause DW, 1980
Place: Willwood Formation, Wyoming
Country: USA
Age: Clarforkian, Paleocene
Remarks: A fairly standard mouse-sized 25g+.
Reference: Krause (1980), J. of Paleont., 54(6).

Species: Microcosmodon woodi Holtzman RC & Wolberg DL, 1977
Aka: eucosmodontid woodi Weil, 1998
Place: Montana & North Dakota & Alberta
Country: USA & Canada
Age: Middle Paleocene
Remarks: Weil A (1998) found that this material "does not belong to this genus or subfamily."
Reference: Holtzman & Wolberg (1977), The Microsmodontinae and Microcosmodon woodi, new Multituberculata taxa (Mammalia) from the Late Paleocene of North America. Sci. Publ. of the Sci. Mus. of Minnesota, 4(1), p.1-13.

Page reference: Kielan-Jaworowska Z & Hurum JH (2001), Phylogeny and Systematics of multituberculate mammals. Paleontology 44, p.389-429.

(This information has been derived from [1] (http://home.arcor.de/ktdykes/taenio.htm) MESOZOIC MAMMALS; Eucosmodontidae, Microcosmodontidae and Taeniolabidoidea, an internet directory. As that's my webpage, there are no issues of copyright. Trevor Dykes)