Paciculus montanus Black 1961
Creators: name: Calede, Jonathan J.
name: Constenius, Kurt N.
name: Famoso, Nicholas A.
name: Kehl, Winifred A.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Mammalia
Rodentia
Muridae
Paciculus
Paciculus montanus

description: Paciculus montanus Black, 1961
(Fig. 6; Appendix 2)
Paciculus montanus Black, 1961: 10, fig. 4.
MATERIAL EXAMINED. — From CM Locality 5084: CM 87801, partial right dentary with incisor and m1-m2.
STRATIGRAPHIC AND GEOGRAPHIC RANGE. — Fort Logan Formation, upper member of the Kishenehn Formation, and middle as well as upper units of the Cabbage Patch beds (Renova Formation), western Montana, United States of America (early Arikareean). From Peterson Creek Local Fauna, eastern Idaho, United States of America (early Arikareean).
DESCRIPTION
CM 87801 is a large specimen of Paciculus (Fig.6; Appendix 1). The m1 is as long as in P. montanus, P. walshi (Lindsay et al. 2016), P.nebraskensis (Alker 1969), and the sample of Paciculus from the Cabbage Patch beds identified as P. cf. P. montanus (Table 6; Fig. 7A). It is much longer than any other species of the genus. A similar pattern can be observed in the m2 (Table 6; Fig. 7B); the Kishenehn Formation specimen is longer than any other species of the genus with the exceptions of P. nebraskensis and P. montanus. The widths of the teeth also place CM 87801 among the very largest Paciculus specimens. The shape of m1 is nearly identical to P. montanus and the Cabbage Patch sample as well as one extreme of the shapes found in P. insolitus (Cope 1879; Fig. 8). The shape of the m2 overlaps the range observed in both P. nebraskensis and P. montanus (Fig. 8).
The m1 of the Kishenehn Formation specimen (Fig. 6) shares a number of features with P. montanus that also differentiate it from P. walshi, including: 1) the presence of a distinct anteroconid; 2) a protoconid arm that is short and does not reach the anterior cingulum; 3) a short protolophid II, which, like half of the specimens of P. montanus observed by Lindsay et al. (2016), does not join the metaconid; and 4) a robust posterior arm of the protoconid that does not bifurcate, as in most specimens of P. montanus analyzed by Lindsay et al. (2016). Additionally, as in P. montanus, the m2 of the Kishenehn Formation specimen bears a long protolophid II. Unlike in P.walshi or P. cedrus Korth, 2014, but like in P. montanus, the anterior lingual cingulum of the m1 of CM 87801 extends from the anteroconid to the metaconid. The teeth of P. nebraskensis differ from those of CM 87801 by a shorter mesolophid of m1, a shorter protolophid II on m2, and the presence of an anterior cingulum of m2 (Korth 1992).
CM 87801 further differs from smaller species of Paciculus by several discrete morphological characters. The m1 of P. gloveri MacDonald, 1970 has a smaller protolophid I as well as a narrower, buccolingually straighter mesostylid than the Kishenehn Formation specimen. Additionally, P. gloveri bears a posterior spur on the metaconid of m2, has an isolated mesostylid, and has a very short protolophid II (Williams & Storer 1998), all characters not observed in the Kishenehn Formation fossil. P. copiosus (Korth 2010) bears an anteroconid on m2 unlike CM 87801. Unlike the Kishenehn Formation specimen, the m1 of P. dakotensis Korth, 2010 lacks a protolophid II and the protolophid II of the m2 does not reach the lingual edge of the tooth (Korth 2010). Additionally, the m2 of P. dakotensis (Korth 2010) bears an anterior cingulum extending lingually anterior to the metaconid, which is absent from the Kishenehn Formation fossil. Paciculus mcgregori (MacDonald, 1970) and the Kishenehn Formation fossil can be distinguished by the incomplete protolophid II of the former and very different anterior portions of m1 (Martin 1980). The m2 of P. cedrus, unlike the fossil from the Kishenehn Formation bears a short protolophid II disconnected from an isolated mesostylid as well as a distinct anterior cingulum (Korth 2014). The anterior portion of m1 of CM 87801 also differs from that observed in the type specimen (SDSM 56510). The Kishenehn Formation specimen, unlike P. insolitus, but like P. walshi, has a short ectolophid on m1 (Lindsay et al. 2016). Paciculus insolitus and CM 87801 can be further distinguished by differences in the shape of the mesostylid, the pattern of branching of the mesolophid and entolophid from the posterior mure, the size of the metaconid, and the morphology of the protoconid. The posterior cingula of the m1 and m2 of P. woodi are more mesiodistally oriented than in the Kishenehn Formation specimen, in which they are much more bucco-lingually oriented. In P. woodi (MacDonald 1963), the anterior mure is interrupted and therefore does not contact the protoconid in the m1; this is also the case in P. cedrus and P. insolitus, but not in CM 87801. The anterior cingulum of P. woodi lacks the long labial extension seen in CM 87801.
REMARKS
The size and morphology of CM 87801 support it being assigned to Paciculus montanus (Table 6). The holotype of the species is an upper dentition (Black 1961), so it is not currently possible to directly compare the material from the Kishenehn Formation with the type area specimens, however, there is no identifiable difference between CM 87801 and the known lower dentition of P. montanus. The material from the Cabbage Patch beds (Calede 2020) cannot be assigned with confidence to the species based on the rarity of the material and its worn state. However, the size of the lower teeth as well as the morphology of the upper teeth recovered are consistent with P. montanus (Rasmussen 1977; this paper). Future discoveries of dental remains from the Cabbage Patch beds are expected to confirm the presence of the species in this area of Montana in addition to the type area, the Peterson Creek Local Fauna of Idaho and, now, the Kishenehn Formation.
description: Published as part of Calede, Jonathan J., Constenius, Kurt N., Famoso, Nicholas A. & Kehl, Winifred A., 2024, Discovery of Oligocene-aged mammals in Glacier National Park (Kishenehn Formation), Montana, pp. 367-386 in Geodiversitas 46 (9) on pages 377-380, DOI: 10.5252/geodiversitas2024v46a9, http://zenodo.org/record/12531008