Sciuravidae, , Walsh, 1997

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 : 30-31

Sciuravidae , genus and species undetermined

Figure 8.5-7 , Table 4

Referred specimens. From SDSNH Locality 5841: partial p4, SDSNH 140176. From SDSNH Locality 5844: P4, SDSNH 110462; partial p4, SDSNH 110454.

Description. Two small, partial lower premolars and one complete upper premolar were recovered from the TBM. The P4 (SDSNH 110462) from SDSNH Locality 5844 is small with a transversely oval occlusal outline. The primary cusps are rounded and relatively robust with the protocone being the largest cusp, the paracone and metacone about equal in size, and the hypocone being the smallest primary cusp, but still very distinct. A relatively deep valley separates the protocone from the hypocone. The anterior cingulum is short, extending lingually from the anterior base of the paracone to near the anterolabial base of the protocone. The protoloph is low, but complete, extending from the protocone to the paracone, with a short spur originating from about the middle of the protoloph that extends anteriorly almost connecting with the anterior cingulum. The metaloph is low and incomplete, extending anterolingually from the metacone towards the protocone, but terminates before reaching the labial base of the protocone. The posterior cingulum is prominent, extending from the hypocone to the posterior base of the metacone.

The well worn partial p4 (SDSNH 110454) from SDSNH Locality 5844 is small. It is missing the protoconid and the anterior half of the metaconid, but even in its broken state, certain characters can still be discerned. Although the enamel wall is broken away from the anterolabial edge of the tooth, the overall occlusal outline appears to have been relatively short anteroposteriorly, with the trigonid much narrower than the talonid. Based on the posterior half of the metaconid, it is relatively large. The hypoconid is large. The entoconid is distinct, anteroposteriorly compressed and smaller than the hypoconid. The hypolophid extends posterolabially from the entoconid to terminate near the origin of the posterior cingulid from the hypoconid. The posterior cingulid is distinct, relatively thick, and extends lingually from the hypoconid to terminate at the posterior base of the entoconid.

The partial p4 from SDSNH Locality 5841 is in very early wear and is missing the anterolingual corner of the tooth, including the metaconid. Even in its broken state, certain characters can still be discerned. It is very small, with the anteroposterior length relatively short and, based on the labial inclination along the labial border, the trigonid was significantly narrower than the talonid. The protoconid is robust. The hypoconid is rounded and slightly smaller than the protoconid. The entoconid is distinct, anteroposteriorly compressed, and slightly smaller than the hypoconid. A very small, isolated mesoconid is present between the protoconid and hypoconid. A short cristid is present that extends posterolabially from the entoconid to terminate close to the posterior cingulid. The posterior cingulid is robust, extending lingually from the hypoconid to terminate near the posterior base of the entoconid.

Remarks. The P4 was listed in the SDSNH catalog as Pauromys sp. In size and occlusal morphology, the P4 from SDSNH Locality 5844 is indistinguishable from those of Pauromys sp. from Powder Wash ( Dawson, 1968). SDSNH Locality 5844 yielded two sciuravid species (sp. A and sp. C). If the P4 is conspecific with sciuravid sp. A, then this species would have a greatly reduced P4 indicating that it probably belongs in Pauromys . However, if the P4 is conspecific with the smaller sciuravid sp. C, then this species would not have a greatly reduced P4 and would probably not represent Pauromys . Thus, to which of these two species the P4 belongs cannot be determined and it adds little to the generic assignment of either sciuravid sp. A. or sp. B. A similar situation exists for the partial p4 from SDSNH Locality 5844.

The partial p4 from SDSNH Locality 5841 is extremely small, with its length within the observed ranges of those of Pauromys lillegraveni and Pauromys sp. from Powder Wash ( Dawson, 1968; Walsh, 1997), but longer than that of Pauromys perditus ( Dawson, 1968) . Unfortunately, there are no small to medium-small sciuravid teeth known from SDSNH Locality 5844.

In summary, three small premolars have been recovered from the TBM that are similar morphologically to those of Pauromys . However, their generic status cannot be determined due to the lack of adequate samples and intact dentitions and the fact that several different small to medium-small sized sciuravids occur in the TBM. Therefore, these premolars are assigned to Sciuravidae without generic or specific allocation.

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.