Taxymys lucaris Marsh, 1872

Kelly, Thomas S. & Murphey, Paul C., 2016, Mammals from the earliest Uintan (middle Eocene) Turtle Bluff Member, Bridger Formation, southwestern Wyoming, USA, Part 1: Primates and Rodentia, Palaeontologia Electronica 7 (8), pp. 1-55 : 24-25

Taxymys lucaris Marsh, 1872

Figure 7.2-4 , Table 4

Referred specimens. From DMNH Locality 4672: M3, SDSNH 75336. From UCM Locality 92189: M1 or 2, UCM 68307, 68924, 95759, 95762; partial M3, UCM 68921.

Description. The M1 or 2s have a robust, but relatively short anterior cingulum that extends lingually from the paracone to the level of the origination of the protoloph from the protocone, where it is separated from the protoloph by a shallow valley. The protoloph is a complete, relatively tall crest extending from a robust, conical protocone to an anteroposteriorly compressed paracone. On one molar there is a slight swelling along the protoloph that appears to be an incipient protoconule, whereas the other three molars lack a protoconule. The protocone is separated from the hypocone by a distinct, relatively deep valley that extends labially into the central portion of the tooth. A small mesostyle is present between the paracone and metacone. The metaloph is a complete crest extending anterolabially from the hypocone to about the center of the tooth and then turns posterolabially to connect with the metacone. The posterior cingulum is robust, slightly lower in height than the metaloph, and extends labially from the hypocone to terminate at the posterior base of the metacone.

The M3 is in very early wear, with a rounded, triangular occlusal outline. The anterior cingulum is robust, but relatively short, extending labially from near the origin of the protoloph from the protocone to terminate at the anterior base of the paracone. The protocone is large and separated from the hypocone by a distinct valley that extends labially into the central portion of the tooth. The protoloph is complete, relatively tall, and extends in an arc from the protocone to the paracone. The metaloph is complete, extending anterolabially from the hypocone and then bifurcates, with a low crest extending to the mesostyle and a taller crest that turns posterolabially to connect with the metacone. The posterior cingulum is short, extending from the hypocone to the posterolingual base of the metacone.

Remarks. Taxymys lucaris is known only from upper dentitions, and Troxell (1923b) proposed that specimens assigned to the genus may actually represent the upper dentition of Tillomys , which is known only from lower dentitions. Although this scenario may be reasonable because their respective dentitions are compatible in size and occlusal morphology, we follow most previous investigators (e.g., Wilson, 1938b; Walton and Porter, 2008) and retain these two genera as distinct pending the discovery of associated upper and lower dentitions that would unambiguously clarify their taxonomic relationship. In size and occlusal morphology, the six TBM upper molars are indistinguishable from those of Taxymys lucaris and are assigned to the species.

Figures

FIGURE 7. Larger Sciuravidae from TBM. 1, Sciuravus nitidus, RP4, UCM 68430. 2-4, Taxymys lucaris: 2, RM1 or 2, UCM 68307; 3, LM1 or 2, UCM 95762; 4, LM3, DMNH 75336. 5-7, Tillomys senex: 5, Lm1 or 2, DMNH 75328; 6, Rm1 or 2, DMNH 75279; 7, Rm1 or 2, SDSNH 110363. 8-9, Tillomys? parvidens: 8, Rm1 or 2, SDSNH 110379; 9, Lm3, DMNH 75288. All occlusal views. Scale bar equals 1 mm.