Goodwin and Martin—Sciurid rodent diversity of the Meade Basin
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Figure 3. Measured dimensions, and orientation and dental terminology for (1) lower (FHSM VP-18159; left p4 of I. tridecemlineatus from Cudahy) and (2) upper teeth (UMMP 42319C; leftM1 orM2 of P. franklinii from Cudahy). Scale bars = 1mm Abbreviations: ac = anterior cingulum, buc = buccal, dis = distal, hpcd = hypoconid, L = length, lin = lingual, mes = mesial, mst = mesostyle, mtc = metacone, mtcd = metaconid, mtcl = metaconule, mtl = metaloph, mtld = metalophid, pc = posterior cingulum, prc = paracone, ptc = protocone, ptcd = protoconid, ptl = protoloph, ptld = protolophid, TlW = width across the talonid, TrW = width across the trigonid,W = width at paracone.
stratigraphic framework by allocating geographically isolated sites to the same “formations” based on faunal content rather than lithology. For example, the Kingsdown Formation, originally named for late Pleistocene sediments in Clark County, was extended by Hibbard and Taylor (1960) to the Big Springs Ranch in Meade County to include the Cragin Quarry vertebrate assemblage. Schultz (1969) continued this approach, applying the name Cragin Quarry to one of four superposed Late Pleistocene faunal levels that he recognized farther south in Meade County on the XI Ranch. Our current perspective is that it is very difficult to correlate the many isolated Late Pleistocene depositional environments, and we pursue a more cautious interpretation. Primarily through the careful field-mapping pro- gram directed by the late J. Honey, we have been able to determine the stratigraphic position of most of Hibbard’s fossil assemblages, but we have refrained from using many of Hibbard’s geologic names and marker units (e.g., the Angel gravel) or extending formational names beyond the sediments in which they were initially described (Martin et al., 2000). Late Pleistocene sediments on the Big Springs Ranch containing the Cragin Quarry assemblage cannot be securely correlated in time with sediments on the XI Ranch, with the latter apparently representing localized sinkhole and collapse features (Kapp, 1965). Because the name Cragin Quarry in both places has led to considerable confusion regarding faunal composition and could potentially create mistaken conclusions regarding faunal turnover, we here name the Kapp horizon for the Cragin Quarry level of Schultz (1969) on the XI Ranch, in honor of Ronald O. Kapp’s (1965) detailed fossil pollen analyses on both the Big Springs and XI ranches. Localities from which rodent assemblages were collected within the Meade Basin system are shown in Fig. 2. Because
rodent assemblages were collected from a limited vertical horizon (<1.0 m) at each locality noted in Figure 2, the name of the locality and the assemblage derived from it are here used synonymously. A few Neogene assemblages including sciurid remains listed in Table 1 do not appear in Figure 2, either because rodents were poorly represented or their stratigraphic positions were not precisely determined. None of the late Pleistocene assemblages (from Adams through Robert) in Table 1 is shown in Figure 2, but their temporal placement can be found in Martin and Peláez-Campomanes (2014). We follow the International Commission on Stratigraphy 2015 International Chronostratigraphic Chart and consider the base of the Pleistocene at 2.58 Ma. The early Pleistocene ranges from 2.58–0.78Ma (million years ago), Middle Pleistocene from 0.78–0.13 Ma, and Late Pleistocene from 0.13–0.01 Ma. Fossils referred to each of the following species are listed
in the appendix (provided as Supplemental Data 1), organized alphabetically by genus and species, stratigraphically by age (early and late Pliocene; early, Middle, and Late Pleistocene), alphabetically by locality within age category, by element (skulls, maxillae, upper cheek teeth, dentaries, lower cheek teeth), then alphanumerically by museum acronym and catalog number.
Repositories and institutional abbreviations.—One of us (HTG) inspected sciurid fossils (skulls, jaws, maxillae with teeth; most isolated teeth; N>1,000) from the Meade Basin in the vertebrate fossil collections of the University of Kansas (KUVP) and University of Michigan Museumof Paleontology (UMMP), as well as more recent collections made during the MBRP and curated by the Fort Hayes State Museum (FHSM).
Systematic paleontology
Family Sciuridae Fischer deWaldheim, 1817 Tribe Marmotini Pocock, 1923
Genus Ammospermophilus Merriam, 1892 Ammospermophilus sp. Figure 4.1
Remarks.—Ammospermophilus today incorporates four or five extant species of antelope squirrels (Hall, 1981; Alvarez- Castaneda, 2007) of the southwestern deserts, with the closest approach to the Meade Basin being populations of Texas antelope squirrels (Ammospermophilus interpres [Merriam, 1890]), ~600 kmto theWSWin central NewMexico (Hall, 1981). Early Pliocene fossils from XIT 1B and Wiens B are assigned to Ammospermophilus based on small size (all teeth; Table 2) and, for m1 or m2, narrow transverse width and well-developed metalophid (Fig. 4.1) that resemble some individuals of extant Ammospermophilus (Fig. 4.2), but differ sharply from Pliocene Ictidomys meadensis in tooth size and proportions (Fig. 4.3). Ammospermophilus has not previously been recognized in the
Figure 2. Stratigraphic relationships of Meade Basin fossil assemblages. MPTS, magnetic polarity time scale; Ma, millions of years ago; C, Chron; r, reversed; n, normal; Br, Brunhes; Ma, Matuyama; Ga, Gauss; Gi, Gilbert; Jar, Jaramillo; Old, Olduvai; Reun, Reunion; Mam, Mammoth; Coch, Cochiti; Nun, Nunivak; Sud, Sidufjall; Thv, Thvera; Crk, Creek; Tol, Toledo; Huck R, Huckleberry Ridge; Gr., gravel; CC, calcium carbonate layer; (N) and (R), Normal and Reversed polarity; Rap, Raptor; C., Canyon; RZ, rodent zones.
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