Cimolodon

Cimolodon is a genus of mammal from the Upper Cretaceous of North America. It was a member of the extinct order of Multituberculata within the suborder Cimolodonta and possibly the family Cimolodontidae.

The genus Cimolodon was named by Othniel Charles Marsh in 1889. It is also known as Allacodon (partly); Cimolomys (partly); Halodon (Marsh 1889); Nanomys ("small mouse") (Marsh 1889); nomyops (Marsh 1892); Ptilodus (partly). While some Cimolomys material has indeed been referred to Cimolodon, that doesn't necessarily mean that the whole genus or a particular species has. It could well be that one-time Cimolodon fossils have subsequently also been referred to Cimolomys as well.

"Cimolodon seems to be more closely related to the Paracimexomys group than are other ptilodontoideans," (Kielan-Jaworowska & Hurum, 2001, p. 404). Odd as it may sound, the placement of this genus within Cimolodontidae is tentative. Its tooth enamel is gigantoprismatic, while its possible relatives favor a microprismatic style (p. 418 ibid.).

Species

Cimolodon electus (Fox R.C. 1971) is known from the Upper Cretaceous of the Upper Milk River Formation in Alberta, Canada. The holotype is in the collection of the University of Alberta. Possible finds have been reported from New Mexico. Weight is estimated at 19g, about half the weight of a modern rat.

Cimolodon nitidus (Marsh O.C. 1889) is also known as Allacodon lentus (Marsh 1889); Allacodon rarus (Marsh 1892); Cimolomys bellus (Marsh 1889); Cimolomys digona (Marsh 1899); Cimolomys gracilis (Marsh 1889); Cimolomys minutes; Cimolomys nitidus; Halodon serratus (Marsh 1889); Nanomyops minitus (Marsh 1892); Nanomys minitus (Marsh 1889); and Ptilodus serratus (Gidley 1909). It is known from Upper Cretaceous strata of the Lance Formation of Wyoming, Utah, Montana and South Dakota (United States and Canada). It weighed about 230 g. Simpson referred this species to C. gracilis in 1929. Subsequently, it has been reallocated to C. nitidus by various authors, apparently beginning with Clemens in 1963.

Cimolodon pervus (Marsh O.C. 1892) is also known from the Upper Cretaceous Lance Formation of Wyoming. This species was first tentatively referred to as P. cf. carvus, (Krause, 1980). It had a weight of about 190 g.

Cimolodon similis (Fox R.C. 1971) is known from the Upper Cretaceous of Utah. This holotype is also in the University of Alberta. It had a body weight around 125 g, about five standard mice.

References

• Marsh (1892), "Discovery of Cretaceous Mammalia. Pt. III." Am. J. Sci. (3) xliii, p. 249-262.
• Fox (1971), "Early Campanian multituberculates (Mammalia: Allotheria) from the upper Milk River Formation, Alberta." Canadian Journal of Earth Sci 8: 916.
• Kielan-Jaworowska Z. & Hurum J.H. (2001), "Phylogeny and Systematics of multituberculate mammals." Paleontology 44, p. 389-429.
• Marsh (1889), "Discovery of Cretaceous Mammalia." Am. J. Sci. (3), 38, p. 177-180.
• Simpson (1929), "American Mesozoic Mammalia." Mem. Peabody Mus. Nat. Hist. iii (i), p. 1-235.
• Much of this information has been derived from Mesozoic Mammals: Ptilodontoidea, an Internet directory.