Both Hemphillian and Blancan mammals are recorded from the Panaca Fm.; however, the Blancan mammals greatly outnumber the Hemphillian mammals, both in number of specimens and number of taxa. All of the small mammals reported above are from sites that are interpreted to be of Blancan NALMA.
The most common small mammals from the Panaca Fm. are cricetid and heteromyid rodents, plus some of the rabbits. The cricetid rodents are excluded from this report, as they greatly exceed the number of taxa known from these deposits. They are described in a separate report by Mou (this volume). Complete faunal list of the Panaca l.f. can be seen in
Lindsay et al., tables 1 and 2 (2002). The shrews, rabbits, geomyid, and heteromyid rodents of the Panaca l.f. are described in this report.
The Panaca shrews include Paranotiosorex panacaensis, new genus and species, plus an incisor and maxillary fragment of a shrew, ?Paranotiosorex sp. that do not fit into the morphology of P. panacaensis and might represent another species. Paranotiososrex, n. gen. is distinguished from the extant desert shrew Notiosorex crawfordi, which has a range confined to the deserts of the southwest United States and northern Mexico, based primarily on having an oval upper articulation and less offset lower articulation of the mandible. Other than Notiosorex, shrews (Sorex, Cryptotis, and Blarina) are widespread throughout North America during the late Cenozoic.
Rabbits underwent an explosive diversification during the Hemphillian and Blancan NALMAs, reflected in five species of the genus Hypolagus (H. edensis, H. tedfordi, H. cf. H. ringoldensis, H. gidleyi, and H. regalis), one species of Pewelagus (P. dawsonae), one species of Lepoides (L. lepoides), one species of Nekrolagus (N. progressus), and possibly a species of Pronotolagus (?Pronotolagus sp.) recorded from the Panaca l.f. This diversity of rabbits greatly exceeds the modern diversity of rabbits in North America, but is not unusual relative to many Blancan faunas (White 1991), although it exceeds that of the Blancan Taunton local fauna of Washington (White and Morgan 1995) and the Irvingtonian Vallecito local fauna of California (White 1984). The extinct genera Pewelagus and Lepoides are the most abundant rabbits in the Panaca l.f., with most of the other taxa recorded from only a handful of specimens. The record of H. tedfordi in the Panaca l.f. is a range extension; H. tedfordi is known primarily from Clarendonian and Hemphillian NALMAs.
The only gopher recorded from the Panaca l.f. is Pliogeomys parvus, also recorded from the Blancan Hagerman local fauna of Idaho.
Heteromyid rodents from the Panaca l.f. include a good sample of Perognathus mclaughlini, a small perognathine; one tooth of Oregonomys sp. (a P4); and three teeth of ?Cupidinimus sp. and very good samples of two dipodomyine species, Prodipodomys (P. minor and P. tiheni). The Panaca record of ?Cupidinimus sp. is a range extension: Cupidinimus is known primarily from Barstovian, and Clarendonian NALMAs.
Age of the Panaca l.f. is considered early Blancan. This is based in part on the faunal assemblage and in part on the correlation of the Panaca l.f. sequence with the interval of chrons C3n.2r through C3n.3r (Lindsay et al. 2002, figure 10) of the GPTS. The magnetic polarity sequence of the Panaca sections are placed relative to the GPTS with the Healdsburg Tephra, dated 4.69 Ma (using the 27.84 Ma monitor for the Fish Canyon sanidine interlaboratory standard), located above the fossil sites near the top of chron C3n.2n in the Rodent Hill section. Details of the magnetostratigraphy are explained in
Lindsay et al. (2002). The Panaca l.f. represents one of the earliest Blancan faunas, according to the correlation of the Hemphillian-Blancan boundary near the top of chron C3n.4n, as interpreted by
Lindsay et al. (2002). Stage of evolution of the small mammal assemblage, especially the arvicolid rodents, also supports a very early Blancan age (Mou 1997,
Small mammals of the Panaca l.f. are most similar to the Hemphillian Redington l.f. in Arizona (Jacobs 1977), the Hemphillian Edson l.f. in Kansas (Hibbard 1939), the Blancan Saw Rock Canyon l.f. in Kansas (Hibbard 1952,
Zakrzewski 1970), the Blancan Deer Park l.f. in Kansas (Martin et al. 2002), the Blancan Verde l.f. in Arizona (Czaplewski 1990), the 111 Ranch l.f. in Arizona (Tomida 1987), the Blancan Hagerman l.f. in Idaho (Zakrzewski 1969), and the Blancan Arroyo Seco l.f. in California (White 1984).