Mammal specimens from a new Pleistocene-age locality near Priest River, Idaho have been identified from at least nine different taxa including muskrat, beaver, porcupine, deer, horse, pronghorn antelope, canid, lynx and bear. A right mandible containing i1 and m1-m2 is of an Ondatra sp. of muskrat. The m1is significantly shorter, narrower and the L/W ratio smaller than that of extant and extinct O. zebethicus. Yet the m1 length and width are both larger than either O. idahoensis and O. annectens. The beaver is represented by an isolated incisor, two lower molars and one upper molar. All three molars share the S enamel occlusal pattern seen Castor, contrasting with the occlusal pattern of Dipoides. The one external striid and three internal striids on the lower molars that are unequal in length indicate Castor californicus rather than C. canadensis. A p4 and m1 of a species of Erethizon porcupine are significantly larger than the p4 and m1 of either E. bathygnathum or E. dorsatum. The deer specimens include a complete right M2 and a near complete m3. The M2 has four distinct main cusps, a prominent paracone, a paracone rib, a metastyle and a very small entostyle, suggesting that this is a species of Bretzia, albeit smaller than B. pseudalces. A P2, dP3 and dp3 of Plessipus idahoensis is also present. Finally, a m1 of Capromeryx, a buccal half of a right P3 assigned to Lynx sp., the buccal half of a left p3 assigned to Ursus sp. and a right m1 of a non-extant Canis sp. are also present.
The Priest River local fauna cannot be older than 2.58 Ma or the beginning of Blancan V (= early Pleistocene) because of FAD for Erethizon from South America at GABI1. The Priest River l. f. cannot be younger than 1.72 Ma (end of Blancan V) as Plesippus has its LAD in Froman Ferry l. f. at the end of Blancan V. Capromeryx tauntonensis was previously restricted to Blancan IV and the Taunton l. f. from central Washington and C. tauntonensis would be a time range extension into the Blancan V NALMA sub-age, which argues against the Priest River l. f. being younger than Blancan V.
This is the first mammalian fauna known from northern Idaho as previously known Cenozoic faunas from the Inland Northwest region are the early to late Blancan faunas, from the Glenn’s Ferry Fm. in southwest Idaho, some 570 miles south of the new site and the early to mid- Blancan faunas from the Ringold Fm. in south, central Washington, 225 miles southwest of the new site.
Blua, Marlena; Welch, Jonathon; and Magone, Neville, "A Late Blancan Local Fauna From Northern Idaho" (2020). 2020 Symposium Posters. 55.
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