New specimens and neotype designation of Thisbemys brevicrista (Rodentia, Ischyromyidae) from the middle Eocene clarify the distinction between T. corrugatus and T. plicatus. (5th May 2015)

• Record Type: Journal Article
• Authors: Anderson, Deborah K.
• Is Part Of: Journal of paleontology. Volume 89:Number 2(2015)
• Page Start: 318
• Page End: 330
• Publication Date: 2015-05-05
• Subjects: Fossils -- Classification -- Periodicals; Paleontology -- Periodicals; Paléontologie -- Périodiques; Fossils -- Classification; Paleontology; Paleontologie; Periodicals; Electronic journals; 560.5
• DOI: 10.1017/jpa.2014.27
• Languages: English
• ISSNs: 0022-3360

Abstract

<abstract abstract-type="normal"> <title>Abstract</title> <p>Newly discovered mandibles and lower dentition of the middle Eocene rodent <italic>Thisbemys brevicrista</italic> from the Green River Basin, Wyoming, are the basis for a species re-diagnosis. Previously, only the upper dentition and a partial maxilla of <italic>T. brevicrista</italic> were known from Br3. New specimens from Br2 now include the lower molars, additional upper molars, and maxillary fragments including a partial zygomatic arch that preserves the relationship of the arch to the first upper molar. In addition, the presence of <italic>T. brevicrista</italic> at Br2 documents the co-existence of <italic>T. brevicrista</italic> with <italic>T. perditus, T. nini, T. plicatus, </italic> and <italic>T. corrugatus</italic>. Formerly, the latter two species were differentiated primarily using stratigraphy. Now, morphology and size can also be used. <italic>Thisbemys brevicrista</italic> is intermediate in size between <italic>T. plicatus</italic> and <italic>T. corrugatus</italic>, and can readily be distinguished from these species based on unique features of the upper and lower molars, which include an additional loph on the two anterior upper molars and a complete metalophid on m1-3. The original type specimen of <italic>T. brevicrista</italic> appears to be lost, thus a neotype is designated as part of the re-diagnosis. Discovery and description of the lower dentition and mandibles of <italic>T. brevicrista</italic> clarifies the alpha taxonomy of this species, and increases its utility for studies of phylogenetic relationships and for documenting Eocene mammalian diversity patterns.</p> </abstract>