Microparamys minutus ( Wilson, 1937 )

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 : 13-14

Microparamys minutus ( Wilson, 1937)

Figure 5.1-5 , Table 2

Referred specimens. From UCM Locality 92189: dP4, UCM 66310; P4, UCM 95695; M1 or 2, UCM 95696. From SDSNH Locality 5841: p4, SDSNH 110374; m1 or 2, SDSNH 110375. From SDSNH Locality 5843: dp4, SDSNH 110373. From DMNH Locality 4672: m1 or 2, DMNH 74140.

Description. The dP4 is in very early wear. Its paracone and metacone are distinct, compressed slightly anteroposteriorly, and about equal in size. The protocone is similar in size to that of the paracone and metacone and positioned slightly labial of the hypocone. The hypocone is robust, slightly larger than the protocone, and separated from the protocone by a distinct valley that is continuous with the valley between the metaloph and posterior cingulum. The anterior cingulum extends labially in an anteriorly extended wide arc from about the middle of the anterior wall of the tooth to terminate at the anterior base of the paracone. The protoloph is complete, extending lingually from the paracone to join a small protoconule and then continuing as a very low loph to the lingual edge of the paracone. The metaloph is complete, extending anterolingually from the metacone to join the posterolabial corner of the protocone. The mesostyle is distinct with a short lophule extending lingually from it that has a small accessory cuspule present at about the middle of the lophule. The posterior cingulum is robust, extending labially from the posterolabial edge of the hypocone to terminate at the posterior base of the metacone. The enamel is crenulated.

The P4 occlusal morphology is nearly identical to that of the dP4, but differs in having the anterior cingulum not flared anteriorly, resulting in a much narrower valley between the anterior cingulum and protoloph, a small, but distinct metaconule, and the enamel is more crenulated.

Confident separation of M1 from M2 cannot be made for isolated teeth of Microparamys . On UCM 95696, the protocone is the largest primary cusp. The hypocone is prominent and slightly smaller than the protocone. The paracone and metacone are the smallest primary cusps, slightly compressed anteroposteriorly, and about equal in size. The anterior cingulum is long, extending from the anterior base of the protocone to terminate at the anterior base of the paracone. The protoloph is complete, extending labially from the protocone to join the lingual edge of the paracone. The metaloph is complete, extending from the posterolabial edge of the protocone to join the labial edge of the metacone. The posterior cingulum is robust, extending labially from the hypocone to terminate at the posterior base of the metacone. The enamel is crenulated.

One tooth (SDSNH 110373) is identified as a dp4 because it is elongate anteroposteriorly and very similar in size and occlusal morphologically to those tentatively referred by Dawson (1968) to Microparamys minutus . Its talonid is relatively narrow with the metaconid slightly larger than the protoconid. The entoconid is compressed anteroposteriorly, and the hypoconid is compressed obliquely. The anterior cingulid is short and separated from the metaconid and protoconid by a shallow valley. The metalophulid II is incomplete, extending lingually from the protoconid to terminate near the posterolabial base of the metaconid. The hypolophid is complete, extending lingually in a gentle arc from the hypoconid to join the entoconid. The ectolophid is incomplete, extending anteriorly from the hypoconid to connect with a transversely elongate mesoconid. A small metastylid is present between the posterior terminus of a distinct metastylid ridge and the anterior base of the entoconid. The posterior cingulid is short and low, extending from about the middle of the hypolophid to terminate at the posterior base of the entoconid.

The p4 is in moderate wear. Its trigonid is significantly narrower than the talonid. The metaconid is slightly larger than the protoconid and positioned close to the protoconid with a very short, but complete, metalophulid II extending between them. The metastylid crest extends posteriorly from the metaconid to a very small metastylid. The hypoconid is the largest primary cusp. The entoconid is robust, with its apex positioned slightly anterior of the hypoconid apex. The anterior cingulid is a short lophid extending from the anterior edge of the metaconid to terminate near the anterolingual base of the protoconid. The posterior cingulid is complete, extending lingually in a weak arc from the hypoconid to the entoconid. The ectolophid is low, connecting a small mesoconid anteriorly to the protoconid and posteriorly to the hypoconid. The enamel in the central basin is lightly crenulated.

Confident separation of the m1 from m2 cannot be made for isolated teeth of Microparamys . The m1 or 2s have a subrectangular occlusal outline. The primary cusps are robust with the protocone, metacone and entoconid conical in shape, whereas the hypocone is slightly compressed obliquely. The anterior cingulid is strong, extending labially from the anterior edge of the metaconid to terminate near the anterior base of the protoconid, where it is weakly separated from the protoconid by a shallow valley that disappears with wear. The metalophulid II is incomplete, extending lingually from the protoconid to terminate near the posterolabial base of the metaconid. The hypolophid is short, either extending labially to terminate in the central basin or extending posterolabially to terminate near and at about the middle of the posterior cingulid. The posterior cingulid is relatively tall and complete, extending in an arc from the hypocone to join the posterior edge of the entoconid. A distinct metastylid is present at the posterior terminus of the metastylid ridge. The ectolophid is complete, connecting a small mesoconid anteriorly to the protoconid and posteriorly to the hypoconid. The enamel in the central basin is crenulated.

Remarks. In size and occlusal morphology, the premolars and molars are indistinguishable from those of Microparamys minutus ( Wilson, 1937; Wood, 1962; Dawson, 1968) and are referred to the species.

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.