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Tirotherium, new tribotherian mammal from Late Cretaceous of Alberta, Canada



Ben Creisler
bcreisler@gmail.com

A new paper:

Marisol Montellano-Ballesteros & Richard C. Fox (2015)
A new tribotherian (Mammalia, Boreosphenida) from the late Santonian
to early Campanian upper Milk River Formation, Alberta.
Canadian Journal of Earth Sciences 52(1): 77-83
doi: 10.1139/cjes-2014-0144
http://www.nrcresearchpress.com/doi/abs/10.1139/cjes-2014-0144?src=recsys#.VL0vWkfF_To



A new tribotherian mammal, Tirotherium aptum gen. et sp. nov., is
described from the late Santonian to early Campanian upper Milk River
Formation of Verdigris Coulee, southern Alberta, Canada. The new
mammal is known only from isolated teeth, five upper and three lower
molars. The upper molars represent two or possibly three pre-ultimate
loci and are marked by reduction and loss of the stylar shelf
anteriorly, loss of the stylocone, a paracone that is larger than the
metacone, weakly developed conules, a low, small protocone, and
specialized postvallum single-rank shear. The lower molars probably
represent two pre-ultimate loci and are characterized by an anteriorly
positioned paraconid, trenchant paracristid, small, posterolingual
metaconid, a distal metacristid, broadly open trigonid angle, and a
short, basined talonid in which the hypoconulid is closer to the
entoconid than to the hypoconid. The molars of Tirotherium most
closely resemble those of Picopsis Fox, 1980, a tribotherian that also
occurs in the upper Milk River Formation, but the molars of
Tirotherium are significantly larger than those of Picopsis.
Nonetheless, Tirotherium aptum is best classified in the Picopsidae, a
boreosphenidan family of tiny mammalian faunivores of uncertain
relationships to other tribotherians, and displaying a unique mosaic
of primitive and derived characters.