Dakotamys

Dakotamys is an mammal genus that lived during the Upper Cretaceous. It shared the world with dinosaurs. This small creature was a member of the also extinct order of Multituberculata.
For those of a technical disposition, it's within the Suborder of Cimolodonta, and a member of the Paracimexomys group.

Genus: Dakotamys Eaton JG, 1995
'Dakota mouse'
Dakota refers to the Dakota Formation. It's a geological term, rather than a geographical one.
"Paracimexomys and Dakotamys... resemble the Eobaataridae in the structure of the upper and lower molars, with cusps showing a tendency to coalesce, and with ornamentation of grooves and ribs on the molars," (Kielan-Jaworowska & Hurum, 2001, p.403).

Species: Dakotamys malcomi Eaton JG, 1995
Place: Dakota Formation, Utah
Country: USA
Age: Cenomanian, Upper Cretaceous
Remarks: Weighed perhaps 25g. The type specimen lives at Oklahoma. Some material from Utah has subsequently been reassigned to a different genus, Cedaromys Eaton & Cifelli, 2001.
"Dakotamys" Tedrow & Korth, 1997 was a description of fossil rodents, which were subsequently renamed Dakotallomys. These two species, D. lillegraveni and D. pelycomyoides, really are from Dakota, (South), but are obviously not multituberculates.
Reference: Eaton (1995), Cenomanian and Turonian (Early Late Cretaceous) multituberculate mammals from southwestern Utah., Journal of Vert Paleo 15(4), p.761-784.

Page references: 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/cimolod.htm) MESOZOIC MAMMALS; 'basal' Cimolodonta, Cimolomyidae, Boffidae and Kogaionidae, an internet directory. As that's my webpage, there are no issues of copyright. Trevor Dykes)