Entomolestes westgatei, Murphey & Kelly, 2017

Murphey, Paul C. & Kelly, Thomas S., 2017, Mammals from the earliest Uintan (middle Eocene) Turtle Bluff Member, Bridger Formation, southwestern Wyoming, USA, Part 2: Apatotheria, Lipotyphla, Carnivoramorpha, Condylartha, Dinocerata, Perissodactyla and Artiodactyla, Palaeontologia Electronica (Cambridge, England: 2003) 20 (2), pp. 1-51 : 11-14

Entomolestes westgatei new species

Figures 4 and 5 , Table 2

zoobank.org/ EEE540D5-BB9D-411D-B1CD-0CCF3E7729E7

Holotype. Partial dentary with Lp4-m1, UCM 95687 .

Hypodym. From UCM Locality 92189: Lp 4, UCM 68540 ; partial dentary with Lp 4-m1, UCM 95686 ; partial dentary with partial Lp 4 and m1, UCM 78746 ; partial dentary with partial Rm 1 and m2-3, UCM 67884 ; Rm 2, UCM 68423 ; Lm 2, UCM 68973 . Type locality. UCM 92189 , 2 m above the base of the Turtle Bluff Member, Bridger Formation , Wyoming .

Distribution and age. Known only from type locality. Earliest Uintan (Ui1a).

Diagnosis. Entomolestes westgatei differs from Entomolestes grangeri Matthew, 1909 , by having the following: 1) a smaller, more reduced p4; 2) p4 talonid lacking a central cristid from posterior wall of trigonid; and 3) a smaller, more reduced m3.

Etymology. Patronym for James Westgate of the Department of Earth and Space Sciences, Lamar University, in honor of his many contributions on Eocene mammals.

Description. Robinson (1968b) and Novacek et al. (1985) regarded the lower antemolars of Entomolestes grangeri to consist of 3 incisors, a canine and 4 premolars, whereas Krishtalka and West (1977) regarded its lower antemolars to consist of 3 incisors and 5 premolars (p1 or dp1 and p2-p5) with the canine lacking. It should be noted that in our descriptions below, we follow the more traditional antemolar assignments of Robinson (1968b) and Novacek et al. (1985).

Two of the partial dentaries preserve alveoli anterior to p4. UCM 95686 has three alveoli and one partial alveolus anterior to p4 ( Figure 5.1-2 ). The two alveoli directly anterior to p4 are positioned close together with the anterior alveolus slightly smaller than the posterior. These two alveoli appear to represent those of the roots of p3, indicating its anterior root was smaller than its posterior root. The third alveolus anterior to p4 is circular and separated from the first two alveoli by a space. The most anterior partial alveolus has a circular posterior border and is separated from the third alveolus by a space. The partial alveolus and third alveolus anterior to p4 may represent those of the p2 or possibly those of two separate, single rooted teeth (p1-2?). UCM 95687 has two alveoli anterior to p4 ( Figure 5.3-4 ). The one directly anterior to p4 is hourglass shaped with the anterior portion slightly narrower, indicating that it held a p3 with two roots or two closely appressed roots. The second alveolus anterior to p4 is circular in shape and appears to represent that of the posterior root of p2 or possibly that of a single rooted p2. Thus, the p3 appears to have been two rooted, as in Entomolestes grangeri Matthew, 1909 ( Robinson, 1968b; Krishtalka and West, 1977), however, whether the p2 was single or two rooted is uncertain. If the p2 was two rooted then it would have been relatively large because the two circular alveoli anterior of the p3 alveoli are large and separated by a short space. It appears more likely that the two circular alveoli anterior of p3 represent two separate, single rooted teeth.

The mental foramen of UCM 95686 is positioned below and between the roots of p3, whereas that of UCM 95687 is positioned slightly more anteriorly, below the anterior root of p3 ( Figure 5.2 and 5.4 ).

The p4 is reduced relative to the m1 with a mean p4 ap/m1 ap ratio of 0.59. The p4 paraconid is relatively strong and projects anterolingually forming a distinct notch between it and the protoconid in labial view. The protoconid is robust, but moderate in height, slightly lower than that of the m1 protoconid. The talonid is very short with a shallow basin. The anterior cingulid ascends steeply from the anterolabial base of the protoconid to the apex of the paraconid.

The molars decrease in size posteriorly. The talonid and trigonid are V-shaped with the talonid only moderately lower in height than the trigonid, especially on m3. The paraconid is anterolingually projecting, low, and blade-like. The conical metaconid is lower in height than the protoconid on m1-2 and about equal in height on m3. The entoconid is anteroposteriorly elongated and tall, but progressively flattens with wear. The entocristid is robust and relatively tall, extending from the entoconid to the metaconid. The small hypoconulid is positioned labially, close to the entoconid, giving these cusps a twinned appearance. The m1 cristid obliqua extends anterolingually from the hypoconid to terminate just labial of the notch between the protoconid and metaconid, whereas the m2-3 cristids obliqua extend towards the metaconids, terminating near the bases of the metaconids. The anterior cingulid is distinct, extending lingually from the anterolabial base of the protoconid to the anterolingual base of the paraconid.

Remarks. Entomolestes grangeri was first described by Matthew (1909) from the lower part of the Bridger Formation (Br2). Subsequently, other investigators have reported its occurrence in the TBM (e.g., Evanoff et al., 1994; Murphey, 2001; Gunnell et al., 2009). The Entomolestes specimens from the TBM exhibit occlusal morphologies that are very similar overall to those of E. grangeri , including the following ( Matthew, 1909; Robinson, 1968b; Delson, 1971; Krishtalka, 1976a; Krishtalka and West, 1977; Novacek et al., 1985; Gunnell et al., 2008b): 1) a premolariform p4 with a projecting paraconid forming a characteristic notch between it and the protoconid in labial view, a protoconid of moderate height, a short talonid, and a distinct anterior cingulid; and 2) lower molars that decrease in size posteriorly with low, blade-like paraconids, V-shaped trigonids and talonids, exodaenodont labial margins, tall, anteroposteriorly elongated entoconids, robust, relatively tall entocristids, and labially positioned hypoconulids that are smaller and lower in height than the entoconids. However, the TBM specimens exhibit differences from the holotype and topotypic sample of E. grangeri ( Robinson, 1968b; Krishtalka and West, 1977) from lower in the Bridger Formation. Most significant are the sizes of p4 relative to m1and m3 relative to m2. In E. grangeri , the mean p4 ap/m1 ap ratio for seven intact dentitions is 0.702 ( Robinson, 1968b; Krishtalka and West, 1977), whereas that of the two TBM intact dentitions is 0.588, a 16% difference. Also, the TBM p4s are absolutely smaller than those of E. grangeri with a mean p4 ap of 0.92 mm, whereas the mean p4 ap for seven specimens of E. grangeri ( Robinson, 1968b; Krishtalka and West, 1977) is 1.23 mm, a 26% difference. In E. grangeri , the mean m3 ap/m2 ap ratio is 0.85, whereas that of the only TBM intact dentition with m1-3 is 0.77, a 9% difference. Also, the TBM m3 is absolutely smaller than that of E. grangeri with an ap of 1.08 mm, whereas the mean of three m3s of E. grangeri ( Robinson, 1968b; Krishtalka and West, 1977) is 1.27 mm, a 15% difference. Although the TBM specimens appear to have a two rooted p3, like that of E. grangeri , the p2 may have had a single, relatively large, circular root, whereas that of E. grangeri is two rooted ( Krishtalka and West, 1977). In the holotype of E. grangeri and referred specimens, a central cristid is present in the p4 talonid that extends from the posterior wall of the trigonid to the posterior border of the talonid ( Krishtalka and West, 1977; Novacek et al., 1985), whereas on the TBM p4s this central talonid cristid is lacking. All of the above differences are significant enough to specifically separate the TBM specimens from E. grangeri , and, as such, they are assigned to the new species, E. westgatei .

Grandorder SORICOMORPHA Fischer von Waldheim, 1817

Family GEOLABIDIDAE McKenna, 1960b

Genus CENTETODON Marsh, 1872b

Centetodon bembicophagus Lillegraven, McKenna, and Krishtalka, 1981

Figure 6.1-4 , Table 2

Referred specimens. From SDSNH Locality 5841: LM3, SDSNH 110347; Lp4, SDSNH 110391. From DMNH Locality 4672: Lm1 or 2, DMNH 75256; Lm3, DMNH 75257. From UCM Locality 92189: LP4, UCM 68681; Lm1 or 2, UCM 68899; Rm1 or 2, 71128.

Description. The cheek teeth from the TBM have occlusal morphologies typical of Centetodon . All of the lower molars are missing a portion of the anterolabial cingulid. Lillegraven et al. (1981) previously provided comprehensive descriptions of the upper and lower cheek teeth of Centetodon bemicophagus . The new specimens from the TBM do not provide any new information regarding the species, so detailed descriptions are not necessary.

Remarks. Three species of Centetodon , C. bemicophagus , C. pulcher Marsh, 1872b , and C. bacchanalis ( McGrew, 1959) , have been recognized from the Bridger Formation in the Bridger Basin ( McKenna et al., 1962; West, 1973a; Lillegraven et al., 1981; Gunnell et al., 2008b). Lillegraven et al. (1981) noted that the holotype of C. bucchanalis from the Bridger Formation at Tabernacle Butte ( McGrew, 1959) consists of a partial dentary with heavily worn m2-3 and is probably a synonym of C. pulcher , but could also be regarded as an indeterminate species (nomen dubium) of the genus. All of the Bridgerian species exhibit similar occlusal morphologies and are differentiated primarily by size. Centetodon bemicophagus is the smallest of the Bridgerian species ( Lillegraven et al., 1981). The eight teeth from the TBM agree well in size and occlusal morphology to those of C. bemicophagus and are referred to the species.

Figures

FIGURE 4. Entomolestes westgatei new species from TBM. 1-2, partial dentary with Lp4-m1 (UCM 95687, holotype) in labial (1) and occlusal (2) views. 3-5, partial dentary with partial Rm1 and m2-3 (UCM 67884) in occlusal (3), labial (4), and lingual (5) views. Scale bar equals 1 mm.

FIGURE 5. Entomolestes westgatei new species from TBM. Specimens showing position of mental foramen (MF) and alveoli for antemolars anterior of p4. See text for proposed alveolar homologies. 1-2, partial dentary with Lp4-m1 (UCM 95686, m1 not shown) in occlusal (1) and labial (2) views. 3-4, partial dentary with Lp4-m1 (UCM 95687, holotype, m1 not shown) in occlusal (3) and labial (4) views. Scale bar equals 1 mm.

FIGURE 6. Geolabididae from TBM. 1-4, Centetodon bembicophagus: LP4 (UCM 68681) in occlusal view (1); partial Lm1 or 2 (UCM 68899) in occlusal view (2); Lm1 or 2 (DMNH 75256) in occlusal view (3); Lm3 (DMNH 75257) in occlusal view (4). 5-10, Centetodon pulcher: partial dentary with Lp4-m1 (UCM 95767) in occlusal (5) and labial (6) views; Rm1 or 2 (UCM 95768) in occlusal view (7); partial dentary with Lp1 and p4-m3 (UCM 68963) in occlusal (8), labial (9), and lingual (10) views. Scale bar equals 1 mm.