Puercolestes undetermined

Clemens, William A., 2019, Puercolestes and Betonnia (Cimolestidae, Mammalia) from the early Paleocene (Puercan 3 Interval Zone) of northeastern Montana, U. S. A., PaleoBios 36, pp. 1-17 : 3-5

PUERCOLESTES SP. cf. PU. SIMPSONI

FIGS. 2, 3

Referred Specimens— Kerr Butte 1 locality: UCMP V75196. P4, M1–2: UCMP 218933. Garbani Channel Complex localities: P4: UCMP V73080, UCMP 186460. M1: UCMP V72127, UCMP 258056; UCMP V73080,

UCMP nos. 187987, 187989, 258016; UCMP V99438, UCMP 218934. M2: UCMP V72128, UCMP 218935; UCMP V73080, UCMP nos. 258022, 258023; UCMP V73082, UCMP 258044. M3: UCMP V72129, UCMP 258052; UCMP V73080, UCMP nos. 258021, 258025.

Basis for association— The following descriptions of P4, M1, and M2 are founded on the associated, but worn, teeth preserved in UCMP 218933. Where possible, morphological details are added from isolated teeth found in GCC localities. Isolated M3s from GCC localities resembling those of other cimolestids and of appropriate size ( Table 1) are tentatively referred.

Description

P4 —The parastylar lobe is mesially salient, situated directly mesial to the paracone, and supports a small parastyle ( Fig. 2). The metacone is small, closely approximated to the paracone, and linked to the metastylar lobe by a short postmetacrista. An ectocingulum is not present. The protocone is not as high or as large as the paracone. The area delimited by the pre- and postprotocrista is not basined. Distinct conules, as well as pre- and postcingula are not present. Like the molars, the crown of P4 is supported by three roots.

M1 —The parastylar lobe is positioned mesiobuccal to the paracone ( Fig. 2). On most M1s, a small cusp in the position of a stylocone is linked mesially by a low crest to a slightly larger parastyle and lingually to the base of the paracone by a low preparacrista. Distal to the stylocone the ectocingulum is relatively broad with minor crenulations along its buccal margin. In occlusal view, the mesial half of the ectocingulum is slightly expanded; the distal half is broader. In comparison to M2, the ectoflexus of M1 is shallow. The paracone is slightly higher and greater in volume than the metacone. Their bases are merged to approximately one half the height of the paracone. The trigon basin is narrow mesiodistally with the paraconule slightly closer to the protocone than the metaconule. The preparaconule crista continues across the mesial side of the paracone to reach the parastylar lobe. By contrast, the postmetaconule crista does not extend as far buccally ending above the apex of the metacone. Neither pre- nor postcingula are present.

M2 —The parastylar lobe mesial to the preparacrista is similar to that of M1 but slightly more expanded buccolingually ( Fig. 2). A small stylocone is present on some teeth. The subequal parastylar and metastylar lobes are separated by a deep ectoflexus, which is distinctly deeper than on M1. In comparison to M1, the paracone and slightly smaller metacone are more closely approximat- ed. A distinct preparaconular crista links the paraconule and parastylar lobe. Changes in slope mark the positions of the postparaconular and premetaconular cristae. The postmetaconular crista flares distally to form a distinct shelf ending above the postmetacrista. The trigon basin is narrow mesiodistally and longer buccolingually. On one tooth (UCMP 258044) the mesial and distal bases of the protocone are slightly inflated but, resembling other M2s, neither distinct pre- nor postcingula are present.

M3 —On M3s from the GCC localities that are tentatively referred to Puercolestes sp. cf. Pu. simpsoni , the parastylar lobe is large and carries a small parastyle ( Fig. 3). An indistinct crest links this cusp with the paracone. The ectocingulum is narrow with a slight ectoflexus. The paracone is closely approximated to the smaller metacone. The trigon area is narrow and elongated buccolingually. Its mesial margin is distinctly higher than the distal. As a result, the occlusal surface of the trigon is more a distodorsally sloping surface than an enclosed basin. The paraconule is much larger and closer to the protocone than the metaconule. Neither pre- nor postcingula are present.

Remarks

Puercolestes simpsoni was typified on fossils from Pu2 Interval Zone strata of the Nacimiento Formation exposed in the San Juan Basin, New Mexico ( Reynolds 1936). The holotype is a fragment of a skull preserving parts of its somewhat damaged postcanine dentition. Williamson et al. (2011, table 1) brought together in the hypodigm of this species nine upper premolars and molars that provided at least one standard dimension of length or width of the crown. Their hypodigm also included ten lower premolars and molars that provided at least one of these dimensions. The sample from Montana representing Pu. sp. cf. Pu. simpsoni consists of the associated P4, M1, and M2 (UCMP 218933) from the Kerr Ranch locality and 14 isolated upper premolars and molars providing at least one standard dimension of length or width of the crown from localities in the GCC. Other than their somewhat larger size, the teeth preserved in UCMP 218933 ( Table 1) do not significantly differ from their counterparts found in the GCC. Given the small size of the available samples, the small differences in their dental dimensions are provisionally interpreted as intraspecific variations.

In their revised diagnosis of Pu. simpsoni, Williamson et al. (2011) noted that its dentition is similar in size to that of Cimolestes incisus Marsh (1889) . This holds true for the teeth referred here to Pu. sp. cf. Pu. simpsoni . They also state, “Similar to species of Cimolestes and differs from Batodon and Procerberus in P4 parastylar lobe relatively smaller so that metastylar lobe larger than parastylar lobe (derived character)” ( Williamson et al. 2011, p. 164). This relationship in relative proportions of the crowns also characterizes the P4s of Pu. sp. cf. Pu. simpsoni from Montana. There is variation in other morphological characters of P4. A small but distinct metacone is present on the P4 of the holotype of Pu. simpsoni and the two P4s referred to Pu. sp. cf. Pu. simpsoni . However, Williamson et al. (2011) referred two P4s lacking a metacone from the Nacimiento Formation to Pu. simpsoni . They also note a difference from the holotype in the smaller size of their protocones. The protocones of the two P4s referred here to Pu. sp. cf. Pu. simpsoni are relatively large resembling the holotype of Pu. simpsoni .

In comparison to Cimolestes incisus Marsh, 1889 , the most obvious distinguishing character cited in the revised diagnosis of Pu. simpsoni is the high paraconid on p4 of one of the referred specimens (NMMNH P-34831). Williamson et al. (2011) also tentatively included in Pu. simpsoni a p4 (AMNH 59910) whose paraconid is relatively small, similar to premolars of Ci. incisus ( Fig. 4). AMNH 59910 was informally included in “Genus B” by Van Valen (1966, Plate 7, figs. 6, 7; also illustrated by Williamson et al. 2011, figs. 6C–E). Provisional inclu- sion of AMNH 59910 in the hypodigm of Pu. simpsoni invalidates one if not the most striking morphological difference between Pu. simpsoni and Ci. incisus cited by Williamson et al. 2011.

If comparisons are limited to the very small samples of P4s and upper molars from Montana and New Mexico, a case might be made to identify the material from Montana as representing a northern population of Pu. simpsoni . As discussed below, on the basis of the available samples from Montana, the p4s and lower molars probably referable to Pu. sp. cf. Pu. simpsoni and Betonnia sp. cf. Be. tsosia cannot be distinguished from one another. Until upper and lower dentitions of these two species are found in association and/or criteria are found to distinguish them and reconstruct a major part of the cheek tooth dentition, the P4s and upper molars from Montana are provisionally identified as Pu. sp. cf. Pu. simpsoni .