Microparamys sp.

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 : 14-15

Microparamys sp.

Figure 5.6-9 , Table 2

Referred specimens. From SDSNH Locality 5841: p4, SDSNH 110360; m1, SDSNH 110361; m2, SDSNH 110362. From SDSNH Locality 5843: dP4, SDSNH 110395.

Description. The dP4 is in early wear. Its primary cusps are robust and conical with the protocone the largest, the paracone the second largest and the metacone and hypocone smaller and about equal in size. The hypocone is separated from the protocone by a shallow notch on the occlusal surface. The anterior cingulum is robust, extending lingually in a wide arc from the anterior base of the paracone to terminate along the anterior wall of the tooth, just labial of the level of the protoconule, resulting in a wide valley between it and the protoloph. The protoloph is nearly complete, with the lingual base of the paracone joining the labial base of a distinct protoconule and a short, low lophid extending from the protoconule to terminate on the anterolabial wall of the protocone. The metaloph is complete, extending lingually from the metacone to the posterolabial edge of the protocone and two cuspules are present at about the middle of the protoloph, the more lingual one being relatively large (= metaconule) and the more labial one being quite small (secondary metaconule or accessory cuspule). A relatively large, transversely elongate mesostyle is present between the paracone and metacone. The posterior cingulum is distinct, extending labially from the hypocone to the posterior edge of the metacone. The enamel in the central basin is lightly crenulated.

The p4 and two lower molars appear to represent a single individual because they were recovered from the same small batch of concentrate, exhibit nearly identical preservation in color and staining, are in the same stage of wear (unworn) and compatible in size. The larger lower molar is identified as m2, whereas the smaller molar, which has the trigonid slightly narrower relative to the talonid and a slightly more elongate anteroposterior occlusal outline, is identified as m1.

The p4 trigonid is significantly narrower than the talonid. The metaconid is robust and significantly larger than the protoconid. The hypoconid and entoconid are robust, with the entoconid subequal in size to the hypoconid. The anterior cingulid is short, extending lingually from the anterolingual base of the metaconid to terminate at the anterior base of the protoconid. The hypolophid is distinct and short, extending posteriorly from the entoconid to join the posterior cingulum near its labial terminus. The ectolophid is complete, connecting a distinct, oval mesoconid anteriorly to the protoconid and posteriorly to the hypoconid. The posterior cingulid is thick and relatively tall, extending labially in a gentle arc from the hypoconid to terminate near the lingual base of the entoconid, where it is separated from the entoconid by a shallow notch. The enamel in the central basin is lightly crenulated.

The m1 and m2 are very similar in occlusal morphology and have subrectangular occlusal outlines. The metaconid, protoconid, and entoconid are robust, with the metaconid slightly expanded anteroposteriorly. The hypoconid is large and slightly compressed obliquely. The anterior cingulum is prominent, extending lingually from the anterolingual corner of the metaconid to a distinct, lingual cuspule (= anteroconid) that is separated from the anterior base of the protoconid by a relatively deep valley. The metalophulid II is complete and low, extending labially from the protoconid to join the metaconid, resulting in a relatively deep trigonid basin that is isolated from the central basin. The hypolophid is incomplete, with two very low crests, one extending lingually from the entoconid and one labially from the hypoconid, that terminate in the central basin without connecting. The ectolophid is complete, connecting a distinct, oval mesoconid anteriorly to the protoconid and posteriorly to the hypoconid. The posterior cingulum is robust and relatively tall, extending in a gentle arc from the posterolabial edge of the hypoconid to terminate near the posterolingual base of the entoconid, where it is separated from the entoconid by a shallow notch. The enamel in the central basin is moderately crenulated.

Remarks. The presumably associated p4-m2 are similar in occlusal morphology to those of Microparamys minutus described above, but exhibit some notable differences. They are larger. In fact, their dimensions exceed the observed ranges of other samples of M. minutus from the Bridger Formation ( Wood, 1962; West, 1973; Dawson, 1968) and those of M. sp., cf. M. minutus described by Lillegraven (1977) from southern California. They have a weak metastylid ridge and lack a metastylid on m1-2, whereas M. minutus is characterized by having a strong m1-2 metastylid ridge with a metastylid commonly positioned at its posterior terminus ( Wood, 1962). The m1-2 further differ from those of M. minutus by the following: 1) a more cuspate labial terminus of the anterior cingulid (= anteroconid), resulting in a better separated and deeper valley between the anterior cingulid and metalophulid II; 2) a slightly more robust mesoconid; and 3) a slightly more distinct and complete metalophulid II. Similarly, the dP4 also exhibits some differences from the dP4 referred above to M. minutus by being larger and by having a relatively larger protocone and more distinct protoconule and metaconule. Emry and Korth (1989) described Microparamys sambucus from the early Bridgerian Elderberry Local Fauna of Nevada. The lower cheek teeth of the TBM Microparamys are very similar in occlusal morphology to those of M. sambucus , including a low, complete metalophulid II, a distinct labial cuspule on the anterior cingulid, and a reduced metastylid ridge. Their dimensions are also within the observed ranges for those of M. sambucus . All of the differences cited above could just represent individual variation, wherein these teeth represent extremes for M. minutus . However, we regard these differences as potentially significant and separate these teeth from those referred to M. minutus as an undetermined species of Microparamys .

Figures

FIGURE 5. Microparamys from TBM. 1-5, Microparamys minutus: 1, LdP4, UCM 66310; 2, LP4, UCM 95695; 3, LM1 or 2, UCM 95697; 4, Rp4, SDSNH 110374; 5, Lm1 or 2, DMNH 74140. 6-9, Microparamys sp.: 6, LdP4, SDSNH 110395; 7, Lp4, SDSNH 110360; 8, Lm1, SDSNH 110361; 9, Lm2, SDSNH 110362. All occlusal views. Scale bar equals 1 mm.

FIGURE 6. Thisbemys and Rodentia, family undetermined from TBM. 1, Thisbemys corrugatus, Rm1, UCM 70671. 2-3, Rodentia, family undetermined, Rm1 or 2, UCM 95700. 1-2, occlusal views. 3, oblique labial view. Scale bar equals 1 mm.

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.

FIGURE 8. Smaller Sciuravidae from TBM. 1, Pauromys sp., cf. P. perditus, Lm1, SDSNH 110414. 2, sciuravid sp. B, RM1 or 2, SDSNH 110412. 3-4, Sciuravid sp. C: 3, RM1 or 2, SDSNH 110443; 4, Lm3, SDSNH 110441. 5-7, Sciuravid premolars: 5, LP4, SDSNH 110462; 6, partial Rp4, SDSNH 110454; 7, partial Rp4, SDSNH 140176. All occlusal views. Scale bar equals 1 mm.

FIGURE 9. Sciuravid sp. A from TBM: 1, RM1 or 2, UCM 709102; 2, RM1 or 2, UCM 68903; 3, LM1 or 2, UCM 71413; 4, LM1 or 2, UCM 95763; 5, Rm1, UCM 95694; 6, Lm1 or 2, UCM 95757; 7, Rm1 or 2, SDSNH 110459; 8, Rm1 or 2, UCM 95699; 9, Lm3, UCM 95756. All occlusal views. Scale bar equals 1 mm.