Meniscoessus

Meniscoessus is a mammal genus from the Upper Cretaceous of North America, which was towards the end of ‘the age of the dinosaurs’. 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 Cimolomyidae.

Genus: Meniscoessus Cope ED, 1882
Aka: Cimolomys (partly); Dipriodon Marsh, 1889; Halodon Marsh, 1889; Oracodon Marsh, 1889; Moeniscoessus; Selenacodon Marsh, 1889 (partly); Tripriodon Marsh, 1889
Remarks: The history of this generic name is complicated and confusing. It’s attributed to Cope, 1882. Later, this was joined by "Meniscoessus" Marsh, 1889. The second usage apparently related to teeth described as belonging to small, carnivorous dinosaurs. These were further christened Dipriodon, Tripriodon and lord knows what else, including Triprotodon. Close similarities were then noticed with an already established dinosaur genus, Paronychodon Cope, 1876, also based on teeth from the Laramie Formation. Over time, an impressive school of names was synonymized under P. However, this is now considered a nomina dubia[?], and a non-dinosaurian dubious name to boot.
In 1929, Simpson published American Mesozoic Mammalia, (Mem. of the Peabody Museum, 3 pt. 1; i-xv). The name Tripriodon, (‘three saw tooth’), was resurrected. These ‘theropod’ teeth were actually mammalian. The mammal T. since seems to have also gone the way of the dubious dino.
At least, that’s my best shot at interpreting what I’ve read. I’ve listed Dipriodon and Tripriodon as synonyms of Meniscoessus, but I'm not convinced that's actually correct. I also fail to see how di might equal tri, don’t pretend to know where Oracodon fits in and have a headache.
Be that all as it may, Meniscoessus Cope is a valid multituberculate, and is known from some quite good remains, as well as a great many teeth. There do seem to be a lot of species though.
Reference: Cope (1882), Mammalia in the Laramie Formation. American Naturalist, 16, p.830-831.

Species: Meniscoessus collomensis Lillegraven JA, 1987
Place: Williams Fork Formation, Colorado
Country: USA
Age: Upper Cretaceous
Remarks: Known from only one site. Weight estimate, 1,4kg.
Reference: Lillegraven (1987), Stratigraphy and evolutionary implications of a new species of Meniscoessus (Multituberculata, Mammalia) from the Upper Cretaceous Williams Fork Formation, Moffat County, Colorado. Dakoterra 3, p.46-56.

Species: Meniscoessus conquistus Cope ED, 1882
Place: Colorado & St Mary River Formation
Country: USA & Canada
Age: Maastrichtian, Upper Cretaceous
Remarks:
Reference: Cope (1882), Mammalia in the Laramie formation. Amer. Naturalist xvi, p.830-831.

Species: Meniscoessus ferox Fox RC, 1971
Place: Upper Milk River Formation, Alberta
Country: Canada
Age: Campanian, Upper Cretaceous
Remarks: The holotype[?], collected in 1968, is in the University of Alberta collection.
Reference: Fox (1971), Early Campanian multituberculates (Mammalia: Allotheria) from the upper Milk River Formation, Alberta. Canadian J of Earth Sci., 8, p.916-938.

Species: Meniscoessus intermedius Fox RC, 1976
Place: Oldman Formation, Alberta & New Mexico, Utah & Wyoming
Country: Canada & USA
Age: Campanian - Maastrichtian, Upper Cretaceous
Remarks: Weighed about as much as a large rat, 500g.
Reference: Fox (1976), Cretaceous mammals (Meniscoessus intermedius, new species, and Alphadon[?] sp.) from the lowermost Oldman Formation, Alberta. Canadian J. of Earth Sciences, 13(9), p.1216-1222, 4 figs.

Species: Meniscoessus major (Russell, 1936)? Or possibly Russell, 1937, though it could even be both!
Aka: Cimolomys major Russell, 1936
Place: Alberta & Montana
Country: Canada & USA
Age: Campanian, Upper Cretaceous
Remarks: Weighed around a kilo. The holotype[?]’s in Alberta.
Reference:

Species: Meniscoessus robustus (Marsh OC, 1889)
Aka: Cimolomys sculptusy; Dipriodon lacunatus; D. lunatus Marsh, 1889; D. robustus Marsh, 1889; Halodon sculptus Marsh, 1889; </i>M. borealis</i> Simpson, 1927; M. coelatus; M. fragilis; M. greeni Wilson RW, 1987; M. lunatus; M. sculptus; Moeniscoessus robustus; Oracodon anceps Marsh, 1889; O. conulus Marsh, 1892; Selenacodon fragilis Marsh, 1889; Tripriodon coelatus Marsh, 1889 Place: Wyoming, Montana & South Dakota & St Mary’s River Formation.
Country: USA & Canada
Age: Maastrichtian, Upper Cretaceous – Paleocene?
Remarks: Marsh authored a swamp of names. Weight guestimate, 3,3kg. The first usage of M. robustus seems to go back to Osborn, 1891.
References: Marsh (1889), Discovery of Cretaceous Mammalia. Am. J. Sci. (3) xxxviii: 81-92.
Osborn (1891), A review of the Cretaceous Mammalia. Proc. Acad. Nat. Sci., Phila., p.124-135.
Simpson (1929), American Mesozoic Mammalia. Mem. Peabody Mus. Nat. Hist. iii (i), p.1-235.
Wilson (1987), Late Cretaceous (Fox Hills) multituberculates from the Red Owl local fauna of western South Dakota. Dakoterra 3, p.118-122.

Species: Meniscoessus seminoensis Eberle JJ & Lillegraven JA 1998a
Place: Ferris Formation, Wyoming
Country: USA
Age: Campanian - Maastrichtian, Upper Cretaceous
Remarks: 3,5cm of lower jaw, found near the Seminoe mountains. A close resemblance to M. robustus. Somewhere between ‘rat-sized’ and 3,5 kilos, depending upon which source. An alternative name for this location is Leave No Toad Unturned.
Reference:

Further remarks: Several other names have been in circulation. Meniscoessus bustus, Meniscoessus caperatus Marsh, 1889, Meniscoessus coelatus. The first is probably a variant of M. robustus, whilst the latter two seem to have been connected with dinosaur teeth.

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