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Argillomys, new Early Cretaceous mammal from Maryland

From: Ben Creisler

Another paper in the new issue of Canadian Journal of Earth Sciences,
this time with the new taxon Argillomys.

Richard L. Cifelli, Cynthia L. Gordon & Thomas R. Lipka (2013)
New multituberculate mammal from the Early Cretaceous of eastern North America.
Canadian Journal of Earth Sciences 50(3): 315-323
doi: 10.1139/e2012-051

Multituberculates, though among the most commonly encountered
mammalian fossils of the Mesozoic, are poorly known from the North
American Early Cretaceous, with only one taxon named to date. Herein
we describe Argillomys marylandensis, gen. et sp. nov., from the Early
Cretaceous of Maryland, based on an isolated M2. Argillomys represents
the second mammal known from the Arundel Clay facies of the Patuxent
Formation (Lower Cretaceous: Aptian). Though distinctive in its
combination of characters (e.g., enamel ornamentation consisting of
ribs and grooves only, cusp formula 2:4, presence of distinct cusp on
anterobuccal ridge, enlargement of second cusp on buccal row, central
position of ultimate cusp in lingual row, great relative length), the
broader affinities of Argillomys cannot be established because of
non-representation of the antemolar dentition. Based on lack of
apomorphies commonly seen among Cimolodonta (e.g., three or more cusps
present in buccal row, fusion of cusps in lingual row, cusps strongly
pyramidal and separated by narrow grooves), we provisionally regard
Argillomys as a multituberculate of “plagiaulacidan” grade.
Intriguingly, it is comparable in certain respects to some unnamed
Paulchoffatiidae, a family otherwise known from the Late Jurassic –
Early Cretaceous of the Iberian Peninsula.