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The Eocene ischyromyid rodent Thisbemys from the Washakie Formation, Wyoming (early Eocene, late Bridgerian) with comments on the systematics of the genus

Published online by Cambridge University Press:  18 June 2020

William W. Korth Open the ORCID record for William W. Korth [Opens in a new window]
William W. Korth*
Affiliation:
Rochester Institute of Vertebrate Paleontology, 265 Carling Road, Rochester, NY14610 and Rochester Museum and Science Center, 657 East Avenue, Rochester, NY14607
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Abstract

A large sample (>100 specimens) of the fossil rodent Thisbemys Wood, 1959, from the early Eocene (late Bridgerian; Br3) Washakie Formation of Wyoming is described. Two species are recognized: a new species, T. intermedius n. sp., and Thisbemys cf. T. uintensis (Osborn, 1895). The large sample size of the former has allowed for a detailed study of variation in size and morphology within the species based on tooth-wear. As a result, some systematic changes in the species included in this genus are suggested: (1) T. brevicrista Ostrander, 1986, is limited to the holotype, and all specimens previously referred to T. brevicrista are likely referable to T. plicatus Wood, 1962; (2) statistical analysis supports the separation of T. plicatus from T. corrugatus Wood, 1959, based on its smaller size and less-crenulated cheek teeth, which corroborates their existence at different horizons (T. plicatus earlier Bridgerian [Br2], T. corrugatus late Bridgerian [Br3]); (3) Paramys delicatior Leidy, 1871, is suggested as the senior synonym of T. plicatus Wood, 1962; (4) T. perditus Wood, 1962, is limited to the early Eocene (Washatchian: Wa1-6); and (5) all specimens previously referred to T. nini Wood, 1962, except the holotype, are referred to T. perditus (fide Korth, 1984; contra Anderson, 2015).

UUID: http://zoobank.org/59c101e2-cd55-4dce-aeea-3da48c4fbd53

Type
Articles
Information
Journal of Paleontology , Volume 94 , Issue 6 , November 2020 , pp. 1180 - 1190
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Copyright
Copyright © 2020, The Paleontological Society

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