Wickia sp.

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 : 31-32

Wickia sp. , cf. W. brevirhinus Mihlbachler, 2008

Figure 12.4-10

Referred specimens. From DMNH Locality 4673: RI3, DMNH 75312; upper left canine, DMNH 75306; RP2, DMNH 75311; LM1, DMNH 75305; RM 3, DMNH 75304; partial Lp4?, DMNH 75314; Lm1, DMNH 75307.

Description. The brontothere teeth were recovered from DMNH Locality 4673 (= SDSNH 5844), which is the highest fossil yielding level within the TBM. Considering the similar degree of wear on the teeth, these specimens may represent a single individual. The upper incisor is large and caniform with a distinct lingual cingulum. The upper canine is moderately robust with a weak lingual cingulum that extends along the lingual base to the posterior base of the crown, and is also comparatively short in length, indicating that it may represent a female.

The P2 has an oblique, ovoid occlusal outline. The paracone is the tallest and largest primary cusp. The metacone is distinct and positioned relatively close to the paracone. The protocone is a low cusp positioned posteriorly, below the level of the metacone apex. The preparacrista is a weak ridge that descends rapidly from the paracone apex to join a small parastyle. The anterior, lingual, and posterior cingula are continuous, extending from the parastyle to the lingual base of the protocone and continuing to the posterolabial corner of the tooth.

In the upper molars the paracone and metacone are well developed, tilted lingually, and V-shaped, which together gives the ectoloph a wide W-shaped occlusal outline (selenodont). The parastyle and metastyle are robust, and the protocone is large and conical (bunodont). The anterior cingulum is prominent with a distinct cuspule present on its anterolingual portion (= anterolingual cingular cusp of Mihlbachler [2008]). A paraconule and metaconule are lacking. The M1 differs from the M3 by being smaller and relatively more transverse posteriorly due the presence of a large, conical hypocone, which is lacking on M3, and by having slightly weaker lingual and posterior cingula.

The m1 is almost complete, missing only a small portion of the posterior wall of the tooth. The occlusal outline is rectangular. The trigonid and talonid are well developed and, with wear, form a Wshaped lophid pattern in labial view (= M-shaped in lingual view). The protoconid and hypoconid are robust. The paraconid is weak, slightly obliquely compressed and connected to the protoconid by a strong paralophid. The metaconid is distinct, tall, and connected to the protoconid by a strong metalophid. A thick cristid obliqua extends anterolingually from the hypoconid to posterior wall of the metaconid. The hypolophid is well developed and extends posterolingually from the protoconid to the entoconid. The anterior, lingual, and posterior cingulids are connected, forming a continuous cingulid. A second partial cheek tooth, which probably represents p4, is only represented by the talonid, which is indistinguishable from the m1 talonid except for its slightly smaller size.

Remarks. The taxonomy of the Brontotheriidae was convoluted until Mihlbachler (2008) provided a comprehensive revision of the family. The only moderately large brontothere from the Twin Buttes Member (Br3) of the Bridger Formation is Telmatherium validus Marsh, 1872a , which co-occurs with the smaller Mesatirhinus junius ( Leidy, 1872b) . Telmatherium validus is also known from the lower Adobe Town Member of the Washakie Formation (Washakie A of Granger [1909]). The teeth of Telmatherium validus are very similar in size and occlusal morphology to those of Metatelmatherium ultimum ( Osborn, 1908) from the late Uintan of Utah and Wyoming and Wickia brevirhinus from the early Uintan of Wyoming ( Mihlbachler, 2008). These three taxa differ in certain cranial characters, but share a number of dental characters, including the following ( Mihlbachler, 2008): 1) large caniform upper incisors; 2) a simple P1; 3) a distinct P2 metacone; 3) upper premolars with a weak preprotocrista and lacking hypocones; 4) upper molars with weak labial ribs, thinned enamel on the lingual side of the ectoloph, a V-shaped paracone and metacone, and lacking a central fossa and cingular parastylar shelf; 5) large submolariform lower incisors; 6) an elongated p2 trigonid; 7) p2-3 lacking a metaconid; 8) p4 with a metaconid; 9) lower molars with shallow basins; and 10) a slender m3. Upper molar paraconules and metaconules are lacking in M. ultimum and W. brevirhinus , and are usually also lacking in T. validus . Wickia brevirhinus differs from T. validus by having upper molars with anterolingual cingular cusps present and a more poorly developed p2 talonid. Metatelmatherium ultimum also has upper molar anterolingual cingular cusps present, but differs from W. brevirhinus by having a better developed p2 talonid.

Mihlbachler (2008) noted that early Uintan W. brevirhinus appears to be morphologically intermediate between late Bridgerian T. validus and early Uintan M. ultimum . The TBM brontothere teeth exhibit the shared dental characters seen in T. validus , W. brevirhinus , and M. ultimum , and its M1 and M3 have a very distinct cusp on the anterolingual cingulum, which is lacking in T. validus . For this reason, we regard the TBM brontothere to represent a form that is more closely related to W. brevirhinus and M. ultimum than to T. validus . Since M. ultimum is not known to occur in the early Uintan, it would seem reasonable to tentatively assign the TBM brontothere to early Uintan Wickia , as Wickia sp. , cf. W. brevirhinus . Although we recognize that this referral is speculative until additional more complete specimens of the TBM brontothere are available, including cranial material, the presence of distinct anterolingual cingular cusps on the upper molars of the TBM brontothere eliminates its referral to T. validus . Assuming that the generic assignment is correct, then Wickia sp. , cf. W. brevirhinus would represent another taxon first appearance for the TBM, occurring high in the section at DMNH Locality 4673.

Figures

FIGURE 12. Dinocerata and Perissodactyla from TBM. 1-3, Uintatherium anceps: Lp2, (DMNH 75310) in occlusal view (1); RP3 or 4 (DMNH 75308) in occlusal view (2); Lm2 (DMNH 75309) in occlusal view (3). 4-10, Wickia sp., cf. W. brevirhinus: LC (DMNH 75306) in labial view (4); RI3 (DMNH 75312) in lingual view (5); RP2 (DMNH 75311) in occlusal view (6); LM1 (DMNH 75305) in occlusal view (7); RM3 (DMNH 75304) in occlusal view (8); partial Lp4? (DMNH 75314) in occlusal view (9); Lm1 (DMNH 75307) in occlusal view (10). Scale bar equals 10 mm.