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Sasayamamylos, new Early Cretaceous eutherian mammal from Japan



From: Ben Creisler
bcreisler@gmail.com

A new online paper:

Nao Kusuhashi, Yukiyasu Tsutsumi, Haruo Saegusa, Kenji Horie, Tadahiro
Ikeda, Kazumi Yokoyama and Kazuyuki Shiraishi (2013)
A new Early Cretaceous eutherian mammal from the Sasayama Group, Hyogo, Japan.
Proceedings of the Royal Society B 280 (1759): 20130142 (advance
online publication)
doi: 10.1098/rspb.2013.0142
http://rspb.royalsocietypublishing.org/content/280/1759/20130142.abstract


We here describe a new Early Cretaceous (early Albian) eutherian
mammal, Sasayamamylos kawaii gen. et sp. nov., from the ‘Lower
Formation’ of the Sasayama Group, Hyogo Prefecture, Japan.
Sasayamamylos kawaii is characterized by a robust dentary, a distinct
angle on the ventral margin of the dentary at the posterior end of the
mandibular symphysis, a lower dental formula of 3–4 : 1 : 4 : 3, a
robust lower canine, a non-molariform lower ultimate premolar, and a
secondarily reduced entoconid on the molars. To date, S. kawaii is the
earliest known eutherian mammal possessing only four premolars, which
demonstrates that the reduction in the premolar count in eutherians
started in the late Early Cretaceous. The occurrence of S. kawaii
implies that the relatively rapid diversification of eutherians in the
mid-Cretaceous had already started by the early Albian.