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Altacreodus, Ambilestes, and Scollardius, newly named Cretaceous mammals from North America

Ben Creisler

A new online paper:

Richard C. Fox (2015)
A revision of the Late Cretaceous–Paleocene eutherian mammal
Cimolestes Marsh, 1889.
Canadian Journal of Earth Sciences (advance online publication)
doi: 10.1139/cjes-2015-0113

Cimolestes Marsh is a North American eutherian mammal primarily known
from latest Cretaceous deposits in Alberta, Wyoming, Saskatchewan, and
Montana. At present, five species of Cimolestes are considered valid,
all Lancian in age; they include one of the largest North American
Late Cretaceous therian mammals as well as one of the smallest, a size
range far exceeding that within other genera of tribosphenic therians
contemporary with Cimolestes, such as the leptictoid eutherian
Gypsonictops Simpson or genera of alphadontid or pediomyid marsupials.
Moreover, the species of Cimolestes display a disparity of dental
morphology in addition to size well in excess of interspecific
differences within these genera. Given these considerations,
Cimolestes is clearly a grade-taxon, uniting species sharing an
adaptively subzalambdodont dentition, but showing divergent
specializations within this pattern that are inconsistent with
monophyly of its presently included species. To correct these
imbalances, this paper limits Cimolestes to Cimolestes incisus Marsh
and Cimolestes stirtoni Clemens; Cimolestes magnus Clemens and
Russell, Cimolestes cerberoides Lillegraven, and Cimolestes
propalaeoryctes Lillegraven are reclassified in the new genera
Altacreodus, Ambilestes, and Scollardius, respectively. Altacreodus
magnus, having a massive shearing dentition, is reconfirmed as showing
a relationship to some Tertiary ‘creodonts’ not shared by other
species of Lancian cimolestids; Ambilestes cerberoides exhibits a
distinctive molar wear pattern that emphasized horizontal grinding,
not orthal shear; Scollardius propalaeoryctes, the smallest species in
this revision and having hyper-faunivorous molars, was not ancestral
to Paleogene Palaeoryctidae, as indicated in part by contradictions in
premolar number and morphology.