Palaeictops robustus, Velazco & Novacek, 2016

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 : 30

Palaeictops robustus , new species

Figures 16–18 , table 1

HOLOTYPE: CM 11954 , consisting of a damaged skull that retains P1–P2, P4–M3 on the left side; the right side retains one incisor possibly corresponding to I2, as well as P4–M1 (fig. 16A–B). Left ramus with i1–3, c, p1, p2, and edentulous right ramus (figs. 17, 18).

TYPE HORIZON AND LOCALITY: Leland Bench Wash, 4 mi. west of Ouray , Utah; Wagonhound Member, Uinta B horizon, Middle Eocene (Uintan NALMA) .

ETYMOLOGY: From Latin robustus , “hard” or “strong.” Refers to the notably large size of the skull.

DIAGNOSIS: Teeth (badly worn) less transverse than in Prodiacodon or Myrmecoboides . Single sagittal crest unlike Leptictis but like Palaeictops altimontis and P. bicuspis (figs. 2A, 13A, 16A; Novacek, 1986: fig. 2). Significantly larger than all other North American leptictid species (see table 1; cf. Novacek, 1977: table 2).

DESCRIPTION AND COMPARISONS: The skull of Palaeictops robustus , despite its poor condition, reveals several features of taxonomic interest. It possesses traits that are shared with Palaeictops altimontis but differ in Leptictis . There is only a single sagittal crest (fig. 16A). The postglenoid process (though damaged) is weak and confined to the lateral glenoid region. The postglenoid foramen is posterior (rather than posteromedial) to the postglenoid process (fig. 16A). The promontorium is broad and rounded, with a very weak median petrosal crest. There is a broadly expanded dorsal lip of the cochlear fossula.

The right side of the skull shows the base of a large canine. Anterior to this tooth, there is a damaged alveolus and, more anteriorly, the base of an incisor. Beyond the incisor, the premaxilla protrudes to form the floor to the external nares. There is no clear evidence of additional incisor alveoli, so it is likely that the tooth in question is I2, and as in other leptictids, there were only two upper incisors. The dorsal rim of the coronoid process of the mandible is rounded, rather than the hooklike dorsal coronoid process of Leptictis and Prodiacodon tauricinerei (figs. 17, 18).

REMARKS: The teeth in this specimen are so badly worn that reference to Leptictidae is open to question. However, the last upper premolar is of dimensions that suggest its molariform construction (fig. 16A–B). Otherwise, Palaeictops robustus might just as well be a pantolestid. This species marks the youngest occurrence of Palaeictops .

Figures

FIG. 16. The skull of Palaeictops robustus CM 11954 (holotype), containing P1–P2, P4–M3 on the left side; the right side retains one incisor possibly corresponding to I2, as well as P4–M1. A, dorsal (top) and ventral (bottom) views and B, right lateral (top) and left lateral (bottom) views. Scale bar = 2 cm.

FIG. 17. Left ramus of Palaeictops robustus CM 11954 (holotype), containing i1–3, c, p1, and p2, in medial (top) and lateral (bottom) views. Scale bar = 2 cm.

FIG. 18. Right ramus of Palaeictops robustus CM 11954 (holotype) in lateral (top) and medial (bottom) views. Scale bar = 2 cm.