Palaeictops bridgeri ( Simpson, 1959 )

Velazco, Paúl M. & Novacek, Michael J., 2016, Systematics of the genus Palaeictops Matthew, 1899 (Mammalia: Leptictidae), with the description of two new species from the Middle Eocene of Utah and Wyoming, American Museum Novitates 2016 (3867), pp. 1-42 : 12-16

Palaeictops bridgeri ( Simpson, 1959)

Figure 7 , table 1

Diacodon bridgeri Simpson, 1959: 1–4 , fig. 1.

Palaeictops bridgeri Van Valen, 1967: 232 . First use of current name combination.

HOLOTYPE: AMNH 56032 , consisting of a right ramus that retains p5–m3 (fig. 7).

TYPE LOCALITY: Locality 6 (Misery Quarry) of McGrew (1959) in the vicinity of Tabernacle Butte, Wyoming. Upper Bridger Formation, Middle Eocene (Bridgerian NALMA).

DIAGNOSIS: Like Palaeictops altimontis (see diagnosis below) and unlike other species of the genus in having a p5 with a low paraconid bordered posteriorly by a distinctly opened, lingual prefossid, a shortened talonid, and a deeply excavated talonid basin opened lingually and bordered posteriorly by steep faces of the entoconid and hypoconid (fig. 7). Both the types of P. bridgeri and P. altimontis have slightly worn, but low trigonids on m1–m3. Differs from P. altimontis in larger size (length of m1–m 3 in P. bridgeri equals 11.23 mm, length in P. altimontis equals 9.18 mm.), and in having a p5 metaconid positioned more posteriorly relative to the protoconid and a more anteroposteriorly “opened” trigonid due to a more salient paraconid on m2. M2 possibly referable to P. bridgeri is more transverse with a shallower ectoflexus than M2 of P. altimontis .

a The dentition of this specimen is worn down, approximate measurements are given for size comparison with the other species.

DISTRIBUTION: Bridger Formation, Bridger Basin, western Wyoming, Middle Eocene (Bridgerian NALMA).

REFERRED MATERIAL: AMNH 9873, left M2, Main locality, Tabernacle Butte, Sublette Co., Wyoming. Upper Bridger Formation.

REMARKS: Palaeictops bridgeri was clearly described and illustrated by Simpson (1959) who first noted the distinctive characters of its lower, last premolar. The new Palaeictops altimontis species from the Tepee Trail locality (see below) is most similar to P. bridgeri , but the two species differ in size and in details of the lower dentition. Moreover, the possibility that a leptictid M2 (AMNH 98731) from Tabernacle Butte is referable to P. bridgeri provides further evidence for the distinction of this species from P. altimontis .

Figures

FIG. 7. Right ramus of Palaeictops bridgeri AMNH 56032 (holotype), containing p5–m3, in (clockwise from upper left) lateral, occlusal, and medial views. Scale bar = 1 cm.