Uintasorex parvulus Matthew, 1909

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 : 6-8

Uintasorex parvulus Matthew, 1909

Figure 3.1-4 , Table 1

Referred specimens. From SDSNH Locality 5841: partial M1 or 2, SDSNH 110359; dp4, SDSNH 110358. From DMNH Locality 4672: m2, DMNH 75287. From UCM Locality 92189: partial i1, UCM 95766.

Description. The partial M1 or 2 has a broken anterolabial corner and is missing part of the paracone. Its paracone and metacone are conical, with the paracone slightly larger than the metacone. The protocone is the largest primary cusp and is positioned anterior of the transverse midline of the tooth. The preprotocrista and postprotocrista extend labially from the protocone as low crests in gentle arcs to join a distinct protoconule and metaconule, respectively. Although their labial termini are broken away, a distinct preparaconule crista extends labially from the paraconule and a precingulum (anterior cingulum) extends labially from the anterolingual base of the protocone. The posterior cingulum extends from the posterolingual base of the protocone to terminate at the posterior base of the metacone.

One partial lower incisor (UCM 95766) from UCM Locality 92189 has the extreme anterior end of the tip missing and a small wedge along the dorsal edge anterior to the crown base broken off. It is very small, with a dorsoventral width of 1.05 mm and a labiolingual width of 0.62 mm near the base of the crown. UCM 95766 is typical of the lower incisors of Uintasorex ( Gazin, 1958; Szalay, 1969b), including a lanceolate shape with a sharp dorsal edge, a thin ridge or crest along the ventral lingual border that extends anteriorly from near the base of the crown to the tip, and a long, relatively straight root.

The dp4 is in very early wear. Its trigonid is open labially between the paraconid and metaconid, and significantly narrower than the talonid, but only moderately taller than the talonid. The protoconid is the largest trigonid cusp. The paracristid extends anterolingually in an arc from the protoconid apex to join a weak, shelf-like paraconid. The protocristid extends lingually from the protoconid apex to join a small metaconid. The cristid obliqua extends anterolingually from the hypoconid apex to join the posterior base of the protoconid. The hypoconid and entoconid are distinct cusps, widely separated, resulting in a wide talonid basin. A low postcingulid extends lingually from the hypoconid to terminate at a very small hypoconulid (only a slight expansion), which is separated from the entoconid by a very shallow notch. A small posterior cingulid extends lingually from the posterior base of the hypoconid to terminate near the middle of the postcingulid. The hypoflexid notch is shallow.

DMNH 75287 is identified as an m2 because it lacks a paraconid and the trigonid is closed labially ( Szalay, 1969b; Krishtalka, 1978). Its trigonid is moderately taller than the talonid. The protoconid and metaconid are distinct cusps connected anteriorly by a relatively tall paracristid and posteriorly by a low protocristid. The entoconid and hypoconid are robust. The postcingulid extends lingually from the hypoconid to a small hypoconulid that is positioned close to the entoconid, but is separated from it by a distinct notch. The cristid obliqua extends anterolingually from the apex of the hypoconid to terminate at the posterior base of the protoconid. The ectocingulid (labial cingulid) is prominent, extending from the anterolabial base of the hypoconid to the anterior base of the protoconid. The hypoflexid notch is shallow.

Remarks. Uintasorex is relatively rare in Eocene faunas. Two species of Uintasorex are currently recognized: U. parvulus from the Bridgerian of Wyoming and U. montezumicus Lillegraven, 1976 , from the Uintan of the San Diego area of southern California ( Matthew, 1909; Szalay, 1969b; Golz and Lillegraven, 1977; Nelson, 1977; Rudman, 1981; Walsh, 1991, 1996; Silcox and Gunnell, 2008). Additional samples of Uintasorex have also been described, but their specific statuses have been left in open nomenclature. These include U. sp. from the early Bridgerian Green River Formation, Wyoming ( Gazin, 1958; Szalay, 1969b), U. sp., cf. U. parvulus from Uintan Tepee Trail Formation at Badwater Creek, Wyoming ( Robinson, 1968b; Krishtalka, 1978), U. sp., cf. U. parvulus from late Wasatchian Red Desert region, Wyoming ( Gazin, 1962), U. sp., cf. U. montezumicus from the late Uintan Tapo Canyon Local Fauna of the Sespe Formation, California ( Kelly and Whistler, 1994), and cf. Uintasorex sp. from the middle Duchesnean Simi Valley Landfill Local Fauna of the Sespe Formation, California ( Kelly, 2010). In addition, two other uintasoricine genera are known from the Bridgerian of Wyoming, Alveojunctus minutus Bown, 1982 , from the Aycross Formation and Bartelsia pentadactyla Gunnell, 2012 , from the Wasatch Formation at South Pass.

The partial i1 and m2 can be confidently assigned to U. parvulus because they are indistinguishable in size and occlusal morphology to those described for the species (e.g., Matthew, 1909; Gazin, 1958; Szalay, 1969b; Rudman, 1981). The m2 differs from the lower molars of U. montezumicus by being slightly larger and by having a robust ectocingulid (labial cingulid). It can be easily distinguished from the lower molar of Alveojunctus by being significantly smaller and by having a relatively narrower talonid basin. It can also be easily distinguished from the lower molars of Bartelsia by being larger and by having the trigonid relatively narrower than the talonid, the trigonid height relatively taller than the talonid and a much more robust ectocingulid.

To the best of our knowledge, the dp4 of Uintasorex has not been previously described. SDSNH 110358 is molariform and very similar in size and occlusal morphology to the m1 of Uintasorex parvulus except for a narrower trigonid relative to the talonid width and a more anteriorly projecting trigonid that is more open labially, characters seen in other early primate dp4s (e.g., Godinot, 1983; Bloch et al., 2010; Rose et al., 2009). Thus, we tentatively assign it to U. parvulus .

The partial M1 or 2 (SDSNH 110359) is very similar in occlusal morphology to those of U. montezumicus ( Lillegraven, 1976) and U. sp. from the early Bridgerian Green River Formation ( Szalay, 1969b) and can be confidently assigned to the genus. SDSNH 110359 is larger relative to the referred m2 (DMNH 75287) than one might expect, so it could be argued that these teeth are not conspecific. Although the upper molars of U. parvulus have not been previously described, the M1-2s of U. montezumicus and U. sp. from the Green River Formation correlate well in their observed ranges in size to those of their m1-2s. The m2s of U. parvulus vary in size, with an ap observed range of 1.09-1.40 mm ( Szalay, 1969b; Rudman, 1981; Silcox and Gunnell, 2008; Gunnell, 2012). Although SDSNH 110359 is broken, its ap is 1.18 mm and, even accounting for the missing anterolabial corner of the tooth, its complete ap would have been considerably less than 1.40 mm, the largest reported m2 ap for U. parvulus . Therefore, the relative difference in size of SDSNH 110359 to that of the referred m2 is regarded as individual variation, and it is also assigned to U. parvulus .

Figures

FIGURE 3. Microsyopidae from TBM. 1-4, Uintasorex parvulus: 1, RM1 or 2, SDSNH 110359; 2-3, Rdp4, SDSNH 110358; 4, Lm2, DMNH 75287. 5-7, Microsyops annectans: 5, Rm1, UCM 68541; 6-7, partial dentary with Rm2, UCM 70315. 1-2, 4-6, occlusal views. 3 and 7, labial views. Scale bars equal 1 mm for 1-6 and scale bar for 7 equals 5 mm.

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.