Tomarctus brevirostris Cope, 1873

Smith, Kent, Czaplewski, Nicholas & Cifelli, Richard L., 2016, Middle Miocene carnivorans from the Monarch Mill Formation, Nevada, Acta Palaeontologica Polonica 61 (1), pp. 231-252 : 235

Tomarctus brevirostris Cope, 1873

Fig. 3A .

Type material: AMNH 8302 , dentary with m1 .

Type locality: Court House Butte , Weld County, Colorado, USA .

Type horizon: Pawnee Creek Formation , probably early Barstovian (Miocene) .

Material.—OMNH 54975, left edentulous dentary fragment; UCMP 141836, left dentary fragment with partial m1 and m2; UCMP 141908, left dentary fragment with p2, p4, partial m1, and m2; UCMP 141920, right dentary fragment with partial m1; and UCMP 141916, left m2. All specimens are from UCMP V70147 (OMNH V972), Eastgate, Churchill County, Nevada, USA; Monarch Mill Formation, Barstovian (Miocene).

Measurements.—See Table 2.

Description.—Among specimens from Eastgate, UCMP 141908 (mandible; Fig. 3A ) is the most diagnostic of Tomarctus brevirostris . The premolars are robust and bear accessory cuspules; p2 and p4 both have anterior cingular cusps, posterior accessory cusps, and posterior cingular cusps. The m1 is broken anteriorly, missing the trigonid, but the talonid is broad. The m2 is complete with the metaconid equal in height to the protoconid. In addition to these characters, the length and width of the p2, p4, and m2 ( Table 2) are consistent with those of T. brevirostris .

Remarks.—No cranial elements, upper teeth, or postcranial elements are known from Eastgate or the surrounding region. The premolars with accessory cusps allow us to assign the Eastgate specimens to Aelurodontina, and putatively primitive characters of the molars indicate referral to Tomarctus not Aelurodon ( Wang et al. 1999) : the m1 talonid is broad; the m2 metaconid is equal in height to the protoconid, and the metaconid is larger than in Aelurodon . The premolars are not as robust as they are in Aelurodon . In addition to these characters, the length and width of the cheek teeth are smaller than those for any species of Aelurodon listed by Wang et al. (1999).

Two species of Tomarctus ( T. hippophaga [ Matthew and Cook, 1909] and T. brevirostris Cope, 1873 ) were recognized by Wang et al. (1999). The species are mainly distinguished by characters that are not preserved in the Eastgate specimens, though Tomarctus hippophaga is smaller than T. brevirostris . The size of the specimens from Eastgate indicates referral to the larger species, T. brevirostris . This is the first reported occurrence of T. brevirostris for the Barstovian of Nevada.

Stratigraphic and geographic range.— Early Barstovian of California, Colorado, Nebraska, Nevada, and New Mexico, USA; late Barstovian of Colorado and Texas, USA ( Wang et al. 1999) .

Figures

Fig. 3. Canidae of the Eastgate LF, basal-most unit of the Monarch Mill Formation, Barstovian (Miocene), Churchill County, Nevada, USA. A. Tomarctus brevirostris, Cope, 1873, UCMP 141908, left dentary with p2, p4, partial m1, and m2 in lingual (A1), labial (A2), and occlusal (A3, stereopair) views. B. Leptocyon sp., UCMP 141482, right m1 in occlusal (B1), lingual (B2), and labial (B3) views.