Notharctus robustior Leidy, 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 : 8-10

Notharctus robustior Leidy, 1872

Figure 4.1-3 , Table 1

Referred specimens. From UCM Locality 92189: partial M1 or 2, UCM 78457; partial M3, UCM 69054; partial dentary with p3 and partial p4, UCM 72600. From DMNH Locality 4672: M1, DMNH 75300.

Description. The M1 (DMNH 75300) is complete, but the other two upper molars are broken. UCM 78457 is missing the anterolabial portion, including most of the paracone and the parastyle, and UCM 69054 is missing the parastyle. The tooth position of UCM 78457 cannot be determined unequivocally from an isolated partial tooth, but it represents either M1 or 2. The M3 differs from the M1 or 2 by its smaller size, more lingually positioned metacone and by lacking a distinct, robust hypocone (= pseudohypocone, postprotocingula or protocone fold, see Gazin, 1958; Covert, 1990; Gunnell et al., 2008) that is separated from the protocone by a distinct notch. The upper molars exhibit the following additional characters: 1) large size; 2) a large, conical protocone; 3) a somewhat crescentic paracone and metacone, each with sharp, acute apices when unworn; 4) a V-shaped centrocrista with a prominent mesostyle; and 5) strong labial, lingual, anterior, and posterior cingula.

The p4 of UCM 72600 is well worn and broken with a small portion of the posterior wall missing, whereas the p3 is complete. The p3 exhibits a simple morphology with a moderately tall protoconid, a very small entoconid, weak lingual and anterolabial cingulids and is lacking a paraconid. Although worn, the following characters of the p4 can still be distinguished: 1) premolariform with a distinct, small paraconid and distinct metaconid; 2) an incipient entoconid; 3) an incipient hypoconid at the posterior termination of the cristid obliqua; and 4) weak labial and lingual cingulids.

Remarks. The TBM Notharctus specimens are indistinguishable in size and occlusal morphology to those of Notharctus robustior (e.g., Granger and Gregory, 1917; Robinson, 1957; Beard, 1988; Covert, 1990; Gunnell et al., 2008) and are referred to the species.

Figures

FIGURE 4. Primates from TBM. 1-3, Notharctus robustior: 1, RM1, DMNH 75300; partial RM1 or 2, UCM 78457; 3, partial RM3, UCM 69054. 4-5, Trogolemur myodes: 4, Rm2, UCM 78097; 5, Rm3, UCM 67883. 6, Washakius insignis, LM1 or 2, UCM 68541. 7-9, Omomys carteri: 7, LM3, 110357; 8, Lm1, SDSNH 110355; 9, Rm3, DMNH 75326. All occlusal views. Scale bar equals 1 mm.