Mesodma

Mesodma is a mammal genus from the Upper Cretaceous to 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, family Neoplagiaulacidae.

Genus: Mesodma Jepsen GL, 1940
Aka: Cimexomys (partly); Cimolomys (partly); Halodon Marsh, 1889? (partly); Parectypodus (partly); Ptilodon[?] (partly)
Remarks: This genus has been the subject of much revision.

Species: Mesodma ambigua Jepsen GL, 1940
Place: Mantua Lentil, Wyoming
Country: USA
Age: Maastrichtian-Puercan, Upper Cretaceous-Paleocene
Remarks: This has been cited as a possible descendant of M. thompsoni. It weighed about as much as a couple of well-fed mice, (55g).
Reference: Jepsen (1940), Paleocene faunas of the Polecat Bench formation, Park County, Wyoming. Pro. Amer. Philos. Soc, 83, p.217-341, 21 figs., 5pls.

Species: Mesodma formosa (Marsh OC, 1889) Clemens WA, 1964a (Source for Clemens: Dr John Alroy’s database)
Aka: Cimolomys formosus Osborn HF, 1891; Cimolomys gracilis (Marsh, 1889) Simpson, 1929; Halodon formosus Marsh, 1889; M. formosus; Ptilodon[?] formosus Gidley, 1909
Place: Hell Creek & Frenchman Formation
Country: USA & Canada
Age: Maastrichtian-Puercan, Upper Cretaceous-Paleocene
Remarks: Possibly also known from Utah. Weighed about 30g.
References: Marsh (1889), Discovery of Cretaceous Mammalia. Am. J. Sci. (3) xxxviii, p.177-180.
Osborn (1891); A review of the Cretaceous Mammalia. Proc. Acad. Nat. Sci., Phila.: 124 - 135.
Simpson (1929), American Mesozoic Mammalia. Mem. Peabody Mus. Nat. Hist. iii (i): p.1-235.
Clemens (1963), Fossil mammals of the type Lance formation Wyoming. Part I. Introduction and Multituberculata. Univ. Calif. Pub;. Geol. Sci. 48, p.1-105. (According to Peabody Museum database.)

Species: Mesodma garfieldensis Archibald JD, 1982
Place: Hells Hollow, Montana
Country: USA
Age: Puercan, Lower Paleocene
Remarks: Probable weight was around 40g.
Reference: Archibald (1982), A study of Mammalia and geology across the Cretaceous-Tertiary boundary in Garfield County, Montana. Univ. of Calif. Publ. Geol. Sci. 122xvi+, 286pp.

Species: Mesodma hensleighi Lillegraven JA, 1969
Place: Hell Creek Formation & Saskatchewan
Country: USA & Canada
Age: Campanian, Upper Cretaceous
Remarks: The holotype[?]’s in the collection of the University of Alberta. The animal weighed something like 15 g.
Reference:

Species: Mesodma primaeva (Lamb, 1902) Clemens, 1964a
Aka: Cimolomys primaevus Simpson, 1929; Parectypodus primaeva; Ptilodus primaevus Lamb, 1902
Place: Montana & Wyoming
Country: USA
Age: Campanian, Upper Cretaceous – Lower Paleocene
Remarks: I’ve also seen the name M. primaevus. I’m assuming this is a spelling variation, rather than a distinct species.
Reference:

Species: Mesodma pygmaea Sloan RE, 1987
Place: Gidley Quarry, Montana & Wyoming & Alberta
Country: USA & Canada
Age: Torrejonian-Tiffanian, Middle Paleocene
Remarks: Very pygmaea indeed, about 8g.
Reference:

Species: Mesodma senecta Fox, 1971a
Place:
Country:
Age: Campanian, Upper Cretaceous
Remarks: A further Alberta University holotype[?]. Bodyweight of about 50g.
Reference:

Species: Mesodma thompsoni Clemens WA, 1963?/4?
Aka: Cimolodon nitidus Marsh, 1889; Cimolomys gracilis (Marsh, 1889) Simpson, 1929; Cimolomys nitidus
Place: St Mary River Formation & Montana & Wyoming
Country: Canada & USA
Age: Maastrichtian-Puercan, Upper Cretaceous-Paleocene
Remarks: Weighed about 55g).
Reference:

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/ptilodon.htm) MESOZOIC MAMMALS; Ptilodontoidea, an internet directory. As that's my webpage, there are no issues of copyright. Trevor Dykes)