Pauromys 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 : 25-30

Pauromys sp. , cf. P. perditus Troxell, 1923a

Figure 8.1 , Table 4

Referred specimen. From SDSNH Locality 5842: m1, SDSNH 110414.

Description. The trigonid of SDSNH 110414 is considerably narrower than the talonid, a character that is often observed in the p4 and m1 of rodents. It has a distinct, small anterior appression facet, which confirms its identity as an m1 and not a p4. SDSNH 110414 exhibits the following additional characters: 1) an elongate occlusal outline; 2) an anterior cingulid that extends from the anterior base of the protoconid to the anterior base of the metaconid; 3) a low, but complete, metalophulid that extends lingually from the posterolingual corner of the protoconid to the posterolabial corner of the metaconid; 4) a relatively large hypoconid and entoconid; 5) a short hypolophid that extends labially and slightly posteriorly from the entoconid to terminate near the origin of the posterior cingulid from the hypoconid; 6) a distinct, isolated, ovalshaped mesoconid; 7) a distinct posterior cingulid that extends lingually from the hypoconid to terminate near the posterolabial base of the entoconid; and 8) very small size.

Remarks. Pauromys perditus is known only from the holotype, a partial dentary with p3-m3. SDSNH 110414 is the only lower molar from the TBM that is equal in size and agrees well in occlusal morphology to the m 1 in the holotype of P.perditus ( Troxell, 1923a; Dawson, 1968). An unambiguous assignment of a single, isolated tooth to P. perditus would not be prudent without additional representative teeth, especially p4, to confirm its identity. Therefore, we only compare SDSNH 110414 to the species, as P. sp., cf. P. perditus .

Sciuravid sp. A

Figure 9.1-9 , Table 5

Referred specimens. From UCM Locality 92189: M1 or 2, UCM 68425, 68903, 70910, 71413, 95763, 95696; m1, UCM 95694, 95812, 71414; m2, UCM 68969, 71415, 77428, 95754, 95755, 95757, 95698, 95699; m3, UCM 71516, 95752, 95756. Tentatively referred specimens from SDSNH Locality 5844: m1, SDSNH 110398; m2, SDSNH 10458, 110459, 110460; m3, SDSNH 110440.

Description. Six upper molars from UCM Locality 92189, either M1 or M2s, are compatible in size and occlusal morphology. They have a strong anterior cingulum that extends lingually from the anterior base of the paracone to about three-quarters of width of the tooth where it is separated from the protocone by a shallow valley. The protocone and paracone are robust and slightly compressed transversely, with the paracone just slightly smaller than the protocone. The hypocone and metacone are distinct, about equal in size and smaller than the protocone and paracone. The protocone and hypocone are separated by a moderately deep valley that continues into the central basin. The protoloph is a complete, relatively tall crest extending from the protocone to the paracone. The protoconule is represented as a slight swelling on the protoloph. The metaloph extends anterolabially from the hypocone and then bifurcates with one crest turning posteriorly to join the metacone and one crest continuing into the central basin of the tooth, terminating short of the protoloph as an incomplete endoloph. A small metastylid is present in three teeth. A small cuspule (anterocone) is present on the lingual terminus of the anterior cingulum in five teeth. The posterior cingulum is robust, extending from the hypocone to the posterior base of the metacone.

UCM Locality 92189 yielded 14 lower molars that are compatible in size and occlusal morphology. Although similar in occlusal morphology, first lower molars were tentatively differentiated from second lower molars because they exhibit distinctly narrower trigonids relative to their talonids, which is typical of the m1s of most Sciuravidae . They have a distinct anterior cingulid that extends lingually from the anterior base of the metaconid to near the anterior base of the protoconid, where it is separated from the protoconid by a shallow valley. The primary cusps (protoconid, hypoconid, metaconid, and entoconid) are robust. The metalophulid II (posterior arm of the protoconid) is incomplete, wherein it extends posterolingually from the protocone to terminate near the posterolabial base of the metaconid. A distinct hypolophid is lacking (i.e., the entoconid has only a very slight labial extension towards the hypoconid). The mesoconid is moderately elongate transversely and isolated from the protoconid and hypoconid, and in five teeth there are two small, cuspulids present on the mesoconid. A small mesostylid is present on six teeth. The posterior cingulid is robust, extending posterolingually from the hypoconid to terminate near the posterior base of the entoconid, where it is separated from the entoconid by a shallow valley. The third lower molars are very similar in occlusal morphology to the m1-2, but can be easily distinguished by having a more elongate occlusal outline, a more complete posterior cingulid (posteroloph) that extends in a larger arc from the hypoconid to the entoconid, and they lack posterior appression facets.

SDSNH Locality 5844 yielded five lower molars that are indistinguishable in occlusal morphology from the above sample from UCM Locality 92189, but differ by being, on average, slightly smaller in size.

Remarks. The molars from UCM Locality 92189 represent the largest sample of sciuravid teeth from a single locality in the TBM that are compatible in size and occlusal morphology. The lower molars exhibit dental characters typical of those of Sciuravidae , including an incomplete metalophulid II that terminates near the posterolabial base of the metaconid, and an isolated mesoconid. In addition, the lower molars basically lack a hypolophid, a character seen in certain sciuravid taxa, such as Pauromys perditus , P. lillegraveni , Pauromys sp. from Power Wash, and ' Pauromys ' schaubi . UCM Locality 92189 yielded only one other sciuravid tooth, an upper molar (UCM 68672) that differs from the other sciuravid upper molars by being significantly smaller in size (see remarks below of sciuravid sp. C). Thus, it is reasonable to assume that the upper and lower molars from UCM Locality 92189 that agree in size and occlusal morphology are conspecific. Five sciuravid lower molars from higher in the section at SDSNH Locality 5844 cannot be distinguished morphologically from the sample of molars from UCM Locality 92189, but are on average slightly smaller in size (4-8% smaller). This size difference is not regarded as being significant enough to separate these molars specifically from the sample from UCM Locality 92189 and they are tentatively regarded as conspecific with that sample. Unfortunately, no sciuravid premolars have been recovered from UCM Locality 92189, which would help clarify the generic status of this sciuravid. However, two relatively small sciuravid premolars, a P4 and partial p4, were recovered from SDSNH Locality 5844 (see remarks below on Sciuravidae , genus and species undetermined). Whether these premolars are conspecific with the medium-small sciuravid teeth from UCM Locality 92189 and SDSNH Locality 5844 cannot be determined because a second smaller sciuravid species is also recorded from these two localities. Thus, without intact dentitions, the premolars could belong to either sciuravid species.

A few additional distinctions can be noted regarding sciuravid sp. A. It is similar in size to Pauromys exallos , slightly larger than Pauromys lillegraveni , significantly smaller than species of Sciuravus , Tillomys , and Taxymys , and significantly larger than Pauromys perditus , Pauromys sp. from Powder Wash, and ' Pauromys ' schaubi . It further differs from Sciuravus and Tillomys by lacking a distinct hypolophid and from ' P.' schaubi by having the m1-2 mesoconid isolated from the hypoconid. Thus, sciuravid sp. A probably represents a distinct species that was previously unknown from the Bridger Formation. However, we refrained from giving it a formal specific name because its generic assignment cannot be determined with confidence.

Sciuravid sp. B

Figure 8.2 , Table 4

Referred specimens. From SDSNH Locality 5787: M1 or 2, SDSNH 110412.

Description. SDSNH 110412 is very small with a square occlusal outline. The anterior cingulum is distinct, extending lingually from the anterolabial base of the paracone to the anterior base of the protocone, where it is separated from the protocone by a shallow valley. The primary cusps (protocone, paracone, metacone, and hypocone) are moderately robust, rounded, and nearly equal in size. The protoloph is incomplete, extending anterolabially from the protocone to terminate anterior to the anterolingual base of the paracone. The protocone and hypocone are separated by a deep valley that continues labially into the central basin. The endoloph is incomplete, extending anterolabially from the hypoconid into the central basin. The metaloph is a low crest connecting the hypocone to the metacone. A small mesostyle is present between the paracone and metacone. The posterior cingulum is moderately robust, but low, extending labially from the hypocone to the posterior base of the metacone.

Remarks. One small, isolated upper molar was recovered from SDSNH Locality 5787 that exhibits an occlusal morphology that is compatible with those of Sciuravidae , including an incomplete protoloph and incomplete endoloph, characters which also differentiate it from the upper molars of the eomyid Metanoiamys . In size, the ap of SDSNH 110412 is slightly larger than that of the m1-2 of Pauromys perditus and slightly smaller than that of the m1-2 of ' Pauromys ' schaubi . However, assignment to either of these two species cannot be made because they are known only from lower dentitions. SDSNH 110412 is significantly smaller than the upper molars referred above to sciuravid sp. A. Thus, all that can be said is that SDSNH 110412 appears to represent a small sciuravid species and is informally assigned to sciuravid sp. B.

sciuravid sp. C

Figure 8.3-4 , Table 4

Referred specimens. From UCM Locality 92189: M1 or 2, UCM 68672. From SDSNH Locality 5844:

M1 or 2, SDSNH 110443, 110447; m3, SDSNH 110439, 110441.

Description. The two upper molars from SDSNH Locality 5844 and one upper molar from UCM Locality 92189 are indistinguishable in size and occlusal morphology. They have a trigon that is wider than the talon. The anterior cingulum is robust, extending lingually from the anterolabial corner of the paracone for about three-quarters the width of the tooth, terminating just labial of the level of the protocone apex where it is separated from the protocone by a shallow valley. A small anterocone is present at the lingual terminus of the anterior cingulum. The primary cusps (protocone, paracone, hypocone, and metacone) are rounded and relatively robust. The protoloph is a complete low crest extending from the protocone to the paracone. The endoloph is a low crest that is nearly complete, extending anterolabially from the hypocone and terminating very close to the protoloph. The metaloph is a low, complete crest extending from the hypocone to the metacone. A small mesostyle is present on two of the molars. The posterior cingulum is moderately robust, extending from the hypocone to the posterior base of the metacone.

Two m3s from SDSNH Locality 5844 are compatible in size to the upper molars. They have a thick, low anterior cingulid that extends labially from the labial base of the metaconid to terminate near the anterolabial corner of the tooth, where it is separated from the protoconid by a shallow valley. The primary cusps (protoconid, metaconid, entoconid, and hypoconid) are rounded and relatively robust. The metalophulid II (posterior arm of the protoconid) is incomplete, extending lingually from the protoconid to terminate near the posterolabial base of the metaconid. The mesoconid is isolated from the protoconid and hypoconid. On one tooth, a short, low hypolophid extends labially, nearly joining the mesoconid, whereas a hypolophid is lacking on the other tooth. The posterior cingulid is thick, extending lingually in an arc from the hypoconid to terminate at the posterolingual corner of the tooth, where it is separated from the entoconid by a distinct valley.

Remarks. The upper molars and lower molars are compatible in size, suggesting that they may be conspecific and are referred to the informal taxon sciuravid sp. C. The upper molars differ from the M1 or 2 assigned above to sciuravid sp. B by being slightly smaller and by having a complete protoloph and nearly complete endoloph. The lower molars are typical of those of Sciuravidae by having an incomplete metalophulid II and an isolated mesoconid. In size and occlusal morphology, the molars of sciuravid sp. C are very similar to those of Pauromys sp. from Powder Wash ( Dawson, 1968), including upper molars (M1 or 2) that have the trigons noticeably wider than the talons, complete protolophs and nearly complete endolophs. In size, the molars are also compatible with those of ' Pauromys ' schaubi , but this species is known only from a single partial dentary with well worn m1-2, so comparison of its occlusal morphology to that of sciuravid sp. C cannot be made. In summary, sciuravid sp. C appears to represent a third species of Sciuravidae from the TBM, but its relationships to the previously recognized smaller Bridgerian sciuravids cannot be determined.

Figures

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.