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Late Pleistocene vertebrates from a rockshelter in Cimarron County, Oklahoma.

Numerous archeological sites occur in the Panhandle of Oklahoma, but only one of them has been reported to include fossils of vertebrates from the Pleistocene epoch. During the 1920s and 1930s, numerous rockshelters and shallow caves in the black Mesa area at the northwestern corner of Cimarron County, Oklahoma (36[degrees]56'N, 102[degrees]59'W), were partly excavated or looted in searches for archeological materials. in this area, nearly 50 rockshelters bearing signs of habitation by prehistoric humans have been recorded; most were excavated poorly and vandalized between 1929 and the outbreak of world War II (Bement and Carmichael, 2003). In one of these sites, known to archeologists as 34Ci-70, fossils of vertebrates from the Pleistocene were found beneath stratigraphic levels bearing archeological materials attributed to the Basketmaker culture (Schoff and Stovall, 1943). In a review of the geology of Cimarron County, Schoff and Stovall (1943:119) mentioned the occurrence of "elephants" (mammoths) and "Equus complicatus and Camelops (early Pleistocene age) in the indian shelter caves underlying the debris of an Indian culture...." The shelter they referred to (actually only one shelter is involved) is now cataloged as Oklahoma Museum of Natural History Vertebrate Paleontology (OMNH VP) locality V1039. The site is a small rockshelter in the base of the Cheyenne Sandstone Member of the Purgatoire Formation near the edge of the Quaternary floodplain terrace of Tesesquite Creek (Fig. 1; W. D. Heran et al., http://pubs.usgs.gov/of/2003/ofr-03-247/). In 1940, J. W. Stovall was curator of vertebrate paleontology at the OMNH and became interested in these fossils through a collector named R. C. Tate. Stovall either made or acquired from Tate a small collection from OMNH locality V1039 (Lintz and Zabawa, 1984) in the deposit underlying the archeological deposit. He also made preliminary sketches of the rockshelter and its strata. A sheet of paper with a plan and profile of the shelter are preserved in the archives of the OMNH VP collection (Fig. 2). The plan is drawn and labeled with fountain pen (Fig. 2a); the handwriting does not appear to be that of Stovall; possibly it was Tate. The entrance to the rockshelter as shown in the sketch is smaller than at present. Possibly, the profile-sketch was drawn somewhat inaccurately from memory or shows the area excavated rather than a level contour of the shelter based upon a local datum, or perhaps, the entrance was modified for ease of access during or after excavation. The accompanying sketch (Fig. 2b) on the reverse of the paper probably was used as a thought exercise in planning for the small cave inset in Schoff and Stovall (1943:figure 9); this stratigraphic column diagrams the entire span of rock formations in the Cimarron Valley and Black Mesa area. Handwritten labels on the profile-diagram from left to right read: "Basket Maker Culture," "Pleistocene bones," and "Supposed Stream bed at time of deposition of fossils." Stovall and Schoff (1943:122) noted: "Fossil remains in the stream-laid portion of the cave deposits consist of fragmentary bones, all more or less permineralized. Many of them are not identifiable, but among them are identifiable fragments of Equus complicatus,and Camelops, and a fragment of the pelvis of an elephant. These are of early Pleistocene age; and, therefore, indicate that the water-laid cave deposits are not older than early Pleistocene." In the same publication, Schoff and Stovall (1943:129-130) listed nine localities of occurrence of the remains of mammoths in Cimarron County, which Stovall had identified as Elephas (=Mammuthus) columbi and Archidiskodon (=Mammuthus) imperator. However, they provided no specimen numbers and the specimens are not in the OMNH VP collection, so the identification of specimens, especially those called M. imperator, cannot be checked. One of the localities for mammoths in Cimarron County also yielded a tooth that Stovall tentatively identified as Equus niobrarensis (Schoff and Stovall, 1943).

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Stovall died in 1953; his field notes are lost, and he was never able to study or publish the Pleistocene vertebrates from the rockshelter OMNH V1039. In addition, R. C. Tate of Kenton, Oklahoma, recovered remains of several other vertebrates from this same rockshelter, as indicated by Schoff and Stovall (1943:121) and also indicated on a small piece of cardboard associated with the fossils. The piece of cardboard is undated and reads "Indian Sheter [sic] Cimarron Co. Okla. Coll R. C. Tate On Tesequet Creek. south of highway."

Rockshelter V1039 occurs in the Mesa de Maya-Black Mesa subregion of the Southwestern Tablelands ecoregion of the United States (Woods et al., 2005). The locality is south of the eastern tip of Black Mesa. Black Mesa is the easternmost tip of the much larger Mesa de Maya that extends ca. 65 km westward into New Mexico and southeastern Colorado. A series of basalt flows of late Neogene (Pliocene) age caps Mesa de Maya and Black Mesa. Topographically, the area consists of many small flat-topped mesas and rocky slopes dissected by tributaries of the Cimarron River. Elevations vary from ca. 1,500 m atop Black Mesa to 1,200 m in the valley floor, with many mesas rising ca. 120 m above the valley floor. Rockshelter V1039 is at an elevation of ca. 1,345 m and is just a few meters above the floor of Tesesquite Canyon. The floor of Tesesquite Canyon varies between ca. 1,310 and 1,340 m elevation, and the top of the adjoining mesa above the rockshelter is ca. 1,400 m. Vegetation of the Mesa de Maya region is a blend of the plants of foothills of the Rocky Mountains and the high-plains shortgrass prairie of the Great Plains (Rogers, 1953). Today, cattle graze the immediate vicinity of the rockshelter. Dominant plants are short grasses (especially Bouteloua), junipers (Juniperus monosperma and J. scopulorum), honey mesquites (Prosopis glandulosa), cane chollas (Cylindropuntia imbricata), and yuccas (Yucca glauca; Fig. 1).

Although many questions will remain unanswered about excavation of this site >70 years ago, it seems appropriate to document the Pleistocene paleofauna and associated available archival materials for the locality. Accordingly, this paper records the assemblage of vertebrates from the Pleistocene in the OMNH collection from locality V1039.

We identified fossils by direct comparison with bones of recent and fossil vertebrates in collections of the OMNH. Several bones from the Pleistocene deposit in the rockshelter were fractured by a swelling from within, whereas other bones are much better preserved and nearly intact. The fractured pieces appear slightly exploded, i.e., the fragments retain their original relative positions but are separated slightly by widened cracks because of internal expansion. The expansion gives the impression that some of the bones are from a somewhat larger animal than recent comparative examples of the same species. This postdepositional enlargement was taken into consideration when comparisons were made with recent specimens. in addition, many bones show a few to numerous fine subparallel scratch marks, scraping of the surfaces, and tool marks indicative of careless or inexpert preparation in the laboratory.

We submitted a piece from a partial cheek tooth of Mammuthus cf. M. columbi containing enamel, dentine, and cementum to Rafter Radiocarbon Laboratory in New zealand for dating by radiocarbon using accelerator mass spectrometry. Enamel was separated from other components of the tooth, and all surfaces of the sample (NZA 38012) were scraped with a scalpel. The sample was washed in sodium hypochlorate and acetic acid, etched in hydrochloric acid, ground with a mortar and pestle, and treated with phosphoric acid evolution. The conventional radiocarbon age of the tooth fragment is 23,980 [+ or -] 130 years before present, confirming the late Pleistocene age for the bone deposit indicated by several of the extinct vertebrates. The age of the mammoth is about representative of the fauna as a whole, but of course, it cannot be assumed that all of the other species are contemporaneous; each taxon or specimen would have to be dated separately to determine its age.

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SYSTEMATIC PALEONTOLOGY

Class Aves

Order Anseriformes

Family Anatidae

Branta canadensis (Canada goose)

Material--OMNH 74683, proximal end of right carpometacarpus.

Discussion--Measurements (in mm) are: depth of proximal end from tip of process of metacarpal I to caudal part of carpal trochlea, 22.2; transverse width of carpal trochlea measured at the proximal edge of the articular facet, 11.4. The partial carpometacarpus (Figs. 3a and 3b) belongs to a large member of the Anserini (swans and geese). It is smaller than the carpometacarpus of the swans Cygnus buccinator and C. columbianus. Moreover, the specimen pertains to a goose rather than a swan because the process of metacarpal I (terminology follows Howard, 1929) is high, the proximal edge of the process of metacarpal i is nearly perpendicular to the shaft, and the pit on the internal side below the pisiform process is separated from the intermetacarpal space by a distinct raised area (Woolfenden, 1961). Woolfenden (1961) noted that he could not find qualitative morphological details in the carpometacarpus to distinguish the genera of geese, including Anser, Branta, Chen, and others. However, the element is much larger than the carpometacarpus in Chen caerulescens and Anser albifrons. Size of the carpometacarpus is most similar to, or somewhat larger than, that of four available modern Branta canadensis from Oklahoma in the OMNH avian osteology collection. Records of Canada geese are fairly common and widespread in late Pleistocene localities across much of the United States and northern Mexico (Lundelius et al., 1983; Steadman and Mead, 2010), although we know of none within 200 km of the rockshelter in Cimarron County.

Class Mammalia

Order Rodentia

Family Sciuridae

Cynomys species indeterminate (prairie dog)

Material--OMNH 74707, partial skull (Figs. 3f-h); 74708, right dentary fragment with i1 and p4-m3 (Figs. 3i and 3j); 74709, left dentary fragment with i1 and worn partial p4.

Discussion--Measurements (in mm) of the cranium are: rostral depth, 12.2; interorbital constriction (somewhat broken), 9; length of left maxillary toothrow, 16.2; and width across M1s, 19.6. For the dentary, length of lower row of cheekteeth is 15.7 mm. Remains of prairie dogs from the Pleistocene can be difficult to assign to species, but sometimes specimens can be separated more easily into two subgenera, Cynomys (Cynomys black-tailed prairie dogs) and Cynomys (Leucocrossuromys white-tailed prairie dogs), according to Semken (1966), Dalquest (1988), and Goodwin (1993a, 1993b, 1995a, 1995b). In C. (Leucocrossuromys), the m3 has a stylid that joins the ectolophid and divides the anterior-posterior talonid valley like a bridge, whereas in C.(Cynomys), the stylid usually is absent. Semken (1966) and Goodwin (1993 a) noted that this character is variable; Semken found the m3 stylid present in 53 of 58 Leucocrossuromys and absent in 45 of 50 C.(C.) ludovicianus, which is the recent blacktailed prairie dog. Although the lower teeth in OMNH 74708 are worn moderately, the m3 retains enamel showing a separation of the talonid valley by a relatively narrow dividing bridge of dentine (Fig. 3i). This resembles the condition often seen in white-tailed prairie dogs and usually not seen in black-tailed prairie dogs. However, we examined 13 recent comparative specimens of black-tailed prairie dogs with m3s from western Oklahoma and found 11 of them with no division of the talonid valley and two specimens with a stylid dividing the valley (in one of these two specimens, there actually were two bridges present). Moreover, in five of the recent specimens in which the valley was not divided, there was a low connection in the valley that would have created a bridge with the ectolophid later in wear. The latter condition is replicated in the heavily worn teeth of the specimen from the rockshelter. One recent jaw we found on the surface of the floor in a different rockshelter in Tesesquite Canyon also showed an incipient connection in the m3.

Goodwin (1993a, 1995b) further noted that C.(Leucocrossuromys) could be distinguished from C.(Cynomys)in having a more distinct m3 mesolophid and a weaker anterior deflection of the hypoconid on m3. In the dentary from the rockshelter, toothwear again interferes, but it appears the m3 has a strong rather than a weak anterior deflection of the hypoconid as in subgenus Leucocrossuromys and a weak mesolophid as in subgenus Cynomys. Among late Pleistocene-to-recent prairie dogs, Goodwin (1995b) recognized two species of C.(Cynomys; C. ludovicianus and C. mexicanus)andfourofC. (Leucocrossuromys; C. gunnisoni, C. parvidens, C. leucurus, and C. niobrarius; the last including the named forms C. churcheri and C. spispiza). Thus, we believe the single worn dentary presently available is insufficient to establish a subgeneric identification of the fossil prairie dog.

The partial skull (Figs. 3f-h; OMNH 74707) consists of the anterior one-half of the cranium broken through the interorbital region. it retains most of the upper teeth, although several are broken or covered with hard matrix. in association with the rostrum, a small fragment of one of the dentary bones with one or more cheek teeth is accreted onto the palate and is mostly covered in matrix, obscuring the contained lower teeth as well as some maxillary teeth.

Dalquest and Stangl (1989) reported C. ludovicianus from a late Pleistocene assemblage in Tesesquite Canyon, Oklahoma, associated with a date on snail shells of 31,360 [+ or -] 570 years before present. Prairie dogs were eliminated from Tesesquite Canyon in recent times, although they still occur elsewhere within 50 km of the rockshelter (Dalquest and Stangl, 1989; Dalquest et al., 1990). Two species, Cynomys cf. C. ludovicianus and C. cf. C. gunnisoni (one black-tailed and the other a white-tailed prairie dog) were reported in the Mesa de Maya local fauna, southeastern Colorado, of Sangamonian (last interglacial) age (Hager, 1974).

Family Cricetidae

Neotoma species indeterminate (woodrat)

Material--OMNH 74701, left dentary with i1 and empty alveoli for molars.

Discussion--Openness of the molar alveoli indicates the jawbone came from a subadult woodrat. The absence of molars precludes identification beyond the genus Neotoma

Order Lagomorpha

Family Leporidae

Lepus species indeterminate (jackrabbit)

Material--OMNH 74702, right p3.

Discussion--The p3 is 4.7 mm long by 4.3 mm wide. Size and occlusal pattern (Fig. 3e) of this premolar match those of jackrabbits, but intraspecific variability in occlusal patterns of p3 does not allow us to identify the species.

Sylvilagus species indeterminate (cottontail rabbit)

Material--OMNH 74703, right I1; 74704, left partial dentary with i1, p3-p4; 74705, distal right tibiofibula; 74706, midportion of shaft of left tibiofibula.

Discussion--In the dentary fragment (Fig. 3c), p3 is 3.3 mm long and 3.0 mm wide. Size and occlusal pattern of the p3 are typical for Sylvilagus (Fig. 3d); available material is insufficient for a specific identification.

Order Carnivora

Family Canidae

Vulpes velox (swift fox)

Material--OMNH 74712, right femur.

Discussion--The femur (Figs. 4e and 4f) is complete and represents a small fox. Greatest length of the bone is 103 mm, proximal width is 21 mm, distal width is 18 mm, and diameter at midshaft is 6 mm. By comparison, the range (in mm) in length of femur in a few available comparative specimens of recent foxes was: Urocyon cinereoargenteus, 112-122 (n = 3); Vulpes vulpes, 115-130 (n = 2); Vulpes velox, 101-108 (n = 3); Vulpes macrotis, 94-96 (n = 2). Among these small samples, size of the femur matches that of the swift fox, Vulpes velox. Swift foxes were distributed widely across the short and mixed grasslands of central North America, but are uncommon to rare today. There are few fossil records of swift foxes, and most ancient records are within the historical range of the species (Faunmap Working Group, 1994). The nearest Pleistocene records are from the Jones local fauna, Meade County, Kansas, with radiometric dates of ca. 26,700 and 29,000 years before present (Davis, 1987), and Blackwater Draw Locality 1, Roosevelt County, New Mexico, in the gray sand bed dated > 13,000 years before present (Hester, 1972; Graham, 1987).

Canis latrans (coyote)

Material--OMNH 74713, proximal right femur; 74714, distal right femur; 74715, left femur ball; 74717, distal left femur; 74720, right calcaneum.

Discussion--Except for the femoral heads, which are intact, the other portions of femurs show the exploded preservation previously mentioned. As a result, their measurements might be misleading and they appear somewhat larger than recent comparative femurs from coyotes. Accounting for this expansion, femurs are similar in size to those of recent coyotes from western Oklahoma. For the two fragments of proximal femurs, diameters of the head are 18 and 18.5 mm. Proximal width of the more intact specimen is 41 mm. For the two distal femurs (Figs. 4c and 4d) OMNH 74741 and 74717, respectively, distal width (in mm) is 36 and 35; distal depth 37 and 37.5; and diameter at midshaft (only preserved in 74717) is 12. The calcaneum (Figs. 4a and 4b) is not exploded and is smaller than typical coyotes from western Oklahoma, with a greatest length of 37 mm. Late Pleistocene records of coyotes are relatively common in the central and western United States (Faunmap Working Group, 1994).

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Canis lupus (gray wolf)

Material--OMNH 74684, partial sacrum (Fig. 4j); 74685, partial right innominate (Fig. 4k); 74686, right metatarsal III missing distal end (Figs. 4g-i).

Discussion--These bones, like several others in the deposit, are fractured by internal swelling (Figs. 4g-k). Fractured pieces retain their original relative positions, but the internally expanded bones give the impression of being from a larger animal than modern comparative examples of the same species. A few measurements (in mm) that can be made on the specimens include anteroposterior diameter of acetabulum, 27; proximal anteroposterior diameter of metacarpal III, 17.5; and proximal transverse diameter of metacarpal III, 14.

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Pleistocene fossils of the gray wolf are uncommon in the United States. The nearest record to the rockshelter appears to be from the Brown Sand Wedge at Blackwater Draw Locality 1, near Clovis, Roosevelt County, New Mexico, which is nearly 300 km distant, and is dated ca. 11,500 years before present (Hester, 1972; Graham, 1987).

Family Felidae

cf. Lynx (bobcat or lynx)

Material--OMNH 74716, distal fragment of right humerus.

Discussion--Although it lacks the distal articular surface and is incomplete and poorly preserved, the fragment retains the matrix-filled entepicondylar foramen. No meaningful measurement can be made on the fragment, which is expanded like several other bones from this locality. However, in size, it is similar to intact humeri of the bobcat and Canadian lynx (Lynx canadensis).

Order Proboscidea

Family Elephantidae

Mammuthus cf. M. columbi (Columbian mammoth)

Material--OMNH 74677, fragment of cheek tooth; 74678, distal left tibia.

Discussion--Schoff and Stovall (1943:122) noted only a fragment of the pelvis of an elephant" from this rockshelter, but the specimen cannot be found today in the OMNH VP collection. Schoff and Stovall (1943) did not mention the fragment of cheek tooth and partial long bone (tibia) that are included in the collection. Possibly one of these two elements was an early find during excavations by Tate or Stovall and represents the piece found near the shelter entrance where an X-mark on the original sketch is labeled "Fragment of Elephant Bone" (Fig. 2a). The fragment of cheek tooth includes only parts of four of the enamel plates (Figs. 5a and 5b); although no meaningful measurement can be made, the thickness of enamel and spacing of plates resembles that in M. columbi. The distal portion of a tibia is preserved poorly and is not diagnostic to the species level, but it is referred to M. cf. M. columbi because it is the only other element of a proboscidean besides the more easily identified fragment of cheek tooth.

Schoff and Stovall (1943:129-130; Wyckoff and Czaplewski, 1997) listed nine localities for occurrence of remains of mammoths in Cimarron County. Stovall plotted these other localities of mammoths in Cimarron County on an unpublished map that is now in the archives of OMNH Vertebrate Paleontology. Schoff and Stovall (1943) identified some of the mammoths from Cimarron County as Elephas (=Mammuthus) columbi and others as Archidiskodon (Elephas) imperator (=Mammuthus imperator). Mammuthus imperator is dentally more primitive than M. columbi and usually is in older faunas (late Irvingtonian and early Rancholabrean, rather than late Rancholabrean land mammal age; Morgan and Lucas, 2005). No specimen from these nine localities is in the OMNH VP collection, so it is not possible to re-examine the other specimens from Cimarron County and confirm identifications as currently recognized (based on morphology and measurements of third molars; Maglio, 1973; Graham, 1986; Agenbroad, 1994). Other records of mammoths in the region of Cimarron County include M. columbi and Mammuthus unidentified species at Tramperos Creek and Perico Creek, respectively, in adjacent Union County, New Mexico (Schumacher, 2001; Lucas and Morgan, 2005; Morgan and Lucas, 2005), and M. imperator at Mesa de Maya, Las Animas County, southeastern Colorado (Hager, 1974).

Order Perissodactyla

Family Equidae

Equus cf. E. conversidens (extinct small horse)

Material--OMNH 74658, right distal humerus.

Discussion--This partial humerus (Fig. 6a) is from a small horse about the size of a recent burro (Equus asinus). Using the method of numbered measurements defined and illustrated by Harris and Porter (1980:figure 1D), dimensions (in mm) of this bone fragment are: D8, 54; D9, 57; D10, 33; D11, 32; D12, 26; D13, 24; and D14, 48. The humerus is not a particularly diagnostic element for identification of species. However, skulls, mandibles, and metapodials, which often are used in studies of Pleistocene horses, are unavailable in the assemblage from the rockshelter. Schoff and Stovall (1943) did not list bones of the horse from the rockshelter that they identified as Equus complicatus, but two species probably are represented. We tentatively refer the humerus to the small late Pleistocene horse E. cf. E. conversidens.

Dalquest and Stangl (1989) listed E. cf. E. conversidens in the nearby Tesesquite Canyon local fauna. Hager (1974) identified E. conversidens in the Mesa de Maya local fauna of southeastern Colorado, and noted that at least one and possibly two other species of Equus occurred in that fauna.

Equus cf. E. niobrarensis (extinct large horse)

Material--OMNH 74660, partial upper cheek tooth (deciduous premolar?); 74661, fragment of upper cheek tooth; 74662, right lower cheek tooth (Figs. 5g and 5h); 74659, lumbar vertebra; 74663, left proximal ulna; 74664, left lunar; 74665, left magnum; 74687, ball epiphysis of femur; 74666, fragment of left patella; 74667, left patella; 74668, left distal tibia; 74669, left cuboid; 74670, left ectocuneiform; 74671, fragment of distal metapodial; 73854-73856 and 74672, first phalanges of digit III (Figs. 6b-d); 74673, fragment of proximal phalanx 1 of digit III; 74674, fragment of distal phalanx 1 of digit III; 74675, phalanx 2 of digit III (Fig. 6f); 74676, ungual phalanx of digit III (Fig. 6e).

Discussion--Some of the larger bones of horses probably include those found near the back of the rockshelter on the original sketch (Fig. 2a) where it is labeled Horse and Camel." Three of the proximal phalanges were sampled for ancient DNA (aDNA; Figs. 6c and 6d) for a separate project, but they did not contain any aDNA (E. Willerslev, pers. comm.). The lower tooth (Figs. 5g and 5h), possibly m2, is 28 mm in anteroposterior length and 14 mm in transverse width; it seems small and may belong to the smaller of the two species from the rockshelter identified above as E. cf. E. conversidens. The remaining bones are all from a large species. Using numbered measurements for various postcranial bones in Harris and Porter (1980:figures 1-3), the following dimensions (in mm) can be reported for specimens of the large horse: tibia: C9, 74; C10, 57; C11, 31; C12, 45; ulna: B3, 78; phalanx 2 of digit III: C1, 50; C2, 55; C3, 45; C4, 47; C5, 34; C6, 29; phalanx 3 of digit III: B1 (maximum breadth of Hager, 1974), 72; B4, 23; B5, 26; B8, 33; B9, 55; B10 (maximum depth of Hager, 1974), 56; phalanx 1 of digit III (Table 1).

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Several authors have attempted to sort the confused systematics of North American Pleistocene horses (Winans, 1989; Azzaroli and Voorhies, 1993; Azzaroli, 1995, 1998; Scott, 2004; Weinstock et al., 2005), but the taxonomy of these animals remains elusive. Based on the morphometric analysis of Harris and Porter (1980), three Pleistocene taxa (Equus conversidens, E. niobrarensis, and E. scotti) from Dry Cave, Eddy County, New Mexico, none of the specimens from the rockshelter is as large as E. scotti, a Blancan and Irvingtonian species (Morgan and Lucas, 2005). However, specimens from the rockshelter are either between the smaller E. conversidens and larger E. niobrarensis from New Mexico (both Rancholabrean species) in some measurements, or they overlap both of these species in other measurements. Thus, the assignment of these specimens to species necessarily is tentative.

Equus niobrarensis iscommoninlatePleistocene vertebrate faunas in western North America. In the general area of the rockshelter in Cimarron County, other records are at Perico Creek, Tramperos Creek, and Casados Ranch in Union County, New Mexico (McMullen and Zakrzewski, 1972; Morgan and Lucas, 2005). Hager (1974) noted several specimens of a large horse in the Mesa de Maya local fauna, Colorado, but had insufficient material for identification to species. The sole specimen of digit III phalanx 3 from the rockshelter in Cimarron County is larger than the sole phalanx III-3 from Mesa de Maya measured by Hager (1974).

Order Artiodactyla

Family Camelidae

Camelops hesternus (giant llama)

Material--OMNH 74651, fragment of right proximal radius-ulna; 74652, right unciform; 74653, left proximal femur (Fig. 5i); 74654, distal metapodial (Fig. 5k); 74655, distal epiphysis of a metapodial (subadult); 74656, 74657, two first phalanges (Fig. 5j).

Discussion--Selected measurements (in mm) of some of the specimens are: proximal width of femur, 156, and diameter of ball of femur, 70; proximal phalanges (OMNH 74656 and 74657, respectively): maximum length 133 and 134, proximal width 52 and 52, distal width 41 and 44. The large proximal femur OMNH 74653 is probably the "Femur (prox. end) sect." labeled at the back (north end) of the shelter in the original sketch (Fig. 2a).

Camelops are relatively common camelids in late Pleistocene faunas in western North America (Kurten and Anderson, 1980). Several species of Camelops have been named and are distinguished mainly by cranial and dental characteristics. Most late Pleistocene occurrences, like this one, are referred to C. hesternus, whereas earlier (Blancan and Irvingtonian land mammal ages) records are of several other nominal species whose taxonomic and morphological limits are poorly known. Other occurrences of C. hesternus <200 km of the rockshelter in Cimarron County are at Mesa de Maya, Colorado (Hager, 1974); Elm Creek, Beaver County, Oklahoma (Dalquest and Baskin, 1992); and in New Mexico at Tramperos Creek, Perico Creek, and Badlands Ranch near Tucumcari (Morgan and Lucas, 2005).

Family Antilocapridae

Genus and species indeterminate (pronghorn)

Material--OMNH 74700, right M2; 74695, proximal end of left radius; 74694, fragment of proximal right radius; 74696, right astragalus; 74697, distal end of metapodial; 74698-74699, fragment of proximal phalanx 1.

Discussion--The M2 is 13.5 mm in anteroposterior length, 12 mm in anterior width, and 10.5 mm in posterior width. This specimen is well worn and the internal fossettes are absent (Fig. 5e), but it is obviously high-crowned and slightly tapering from occlusal surface to base. In this condition, the tooth differs from the abruptly tapering low-crowned molars of deer (e.g., Odocoileus). The M2 retains well-developed but fused roots that are longer than the remaining height of crown (Figs. 5d and 5f). Loss of the infundibula with wear and concomitant great development of the root indicate an old individual. Pronghorns have strongly hypsodont molars early in life, but in advanced age roots develop. In living Antilocapra americana, loss of infundibula in molars occurs by ca. 7 or 8 years of age (Dow and Wright, 1962). In late Pleistocene pronghorns (e.g., Capromeryx, Tetrameryx, Stockoceros, Antilocapra), a similar phenomenon likely occurred. Size of the M2 is similar to that of Stockoceros, Tetrameryx, and Antilocapra; it is larger than M2 in Capromeryx. Other characteristics that would allow us to distinguish between Stockoceros, Tetrameryx, and Antilocapra are absent. Horn cores usually form the basis for identification of these antilocaprid genera, but none was found in the rockshelter.

Postcranial elements tentatively are identified as Antilocapridae using criteria of Lawrence (1951). There is considerable osteological variability within, and overlap between, the postcranially similar-shaped and similarsized artiodactyls, pronghorns (including Antilocapra, Tetrameryx, and Stockoceros), mule deer (Odocoileus hemionus), white-tailed deer (Odocoileus virginianus), and bighorn sheep (Ovis canadensis). This variability and the incompleteness due to breakage and poor preservation of bones from the rockshelter preclude definitive identification.

By comparison with recent species, the proximal radius matches best in its proportions and in some but not all details with Antilocapra; some details are closer to Odocoileus (Lawrence, 1951:Fig. 17). The smaller fragment of radius (OMNH 74694) is too incomplete for identification but is listed here for convenience. The astragalus fits well with morphological details of Lawrence (1951:Fig. 8) for Antilocapra and differs from those for Ovis and Odocoileus. The distal metapodial, if it represents a metatarsal, also compares more favorably with criteria of Lawrence (1951:Fig. 10) for Antilocapra than for Odocoileus and definitely is not Ovis, which lacks an anterior vascular foramen in a pit and a shallow anterior groove. However, shallowness of the anterior groove on the short preserved section of the bone indicates that it probably is a metacarpal rather than a metatarsal. When compared to a metacarpal of Stockoceros onusrosagris from Arizona (OMNH 51458), the metapodial fragment from the rockshelter is somewhat larger, especially in width of shaft. Part of the apparent difference in size could be because the epiphysis is not fused completely and, thus, is somewhat swollen in the fossil from the rockshelter. Although the genus of pronghorn is uncertain, two proximal fragments of two first phalanges are consistent in a few details with phalanges of pronghorns. Available skeletal elements are insufficient to distinguish among the pronghorns Stockoceros, Tetrameryx, and Antilocapra of the late Pleistocene. No other late Pleistocene antilocaprid has been reported <200 km from the rockshelter in Cimarron County.

Family Bovidae

Bison species indeterminate (bison)

Material--OMNH 74679, one-half of upper molar; 74691, extremely worn remnant of an upper cheek tooth with root bases; 74680, cervical vertebra; 74681, lumbar vertebra; 74682, partial right innominate.

Discussion--The most diagnostic of these elements is the partial upper molar (Fig. 5c). The tooth is moderately worn with ca. 25 mm of height of the crown remaining labially. It retains a portion of a prominent labial style (protostyle) and is broken lingually, but its transverse width can be estimated to have been ca. 29 mm. Presence of a protostyle indicates the tooth represents a Bovinae such as Bison rather than a Caprinae such as Bootherium. Postcranial elements also pertain to a large bovid and additionally are considered to represent a large Bison, although they are less diagnostic. The partial innominate bone (OMNH 74682) is possibly the "Pelvic section" labeled on the original sketch along the north wall at the back of the rockshelter (Fig. 2a). If these postcranial bones represent Bison, it was a big bison; the partial pelvis is large, and so are the vertebrae. Even the partial cheek tooth seems large. These elements probably represent an extinct form such as B. latifrons, B. antiquus, B. occidentalis, B. chaneyi, or other named forms (Wyckoff and Dalquest, 1997), but crania with horn cores, usually considered the definitive skeletal element for bison, are lacking in the assemblage from the rockshelter.

Bison are abundant and widespread as fossils in the late Pleistocene of North America, including the area of Cimarron County. Some published records <200 km from the rockshelter include, in northeastern New Mexico: B. latifrons near Raton, Colfax County, B. antiquus near Folsom, Union County, B.cf. B. priscus near Wetherly, Union County, and Bison unidentified species at Tramperos Creek (Morgan and Lucas, 2005); in southeastern Colorado: Bison unidentified species near Mesa de Maya (Hager, 1974); in the Oklahoma Panhandle: B. latifrons near Hardesty, Texas County (Wyckoff and Dalquest, 1997), and Bison unidentified species at Elm Creek, Beaver County (Dalquest and Baskin, 1992); in southwestern Kansas: B. willistoni at Osbun Exposure, Finney County, B. bison at Jones, Meade County, Bison unidentified species at Jinglebob, Meade County; and in northern Texas: B. occidentalis at Palo Duro Creek, Randall County (Wyckoff and Dalquest, 1997).

Family indeterminate (unidentified mammals)

Material--OMNH 74688-74689, sesamoids; 74690, coprolite; 74692, fragment of radius-ulna with partial semilunar notch; 74693, vertebral centrum.

Discussion--These miscellaneous specimens generally represent large ungulates, and some probably belong to the species identified above (Bison, Camelops, or Equus)by more complete or diagnostic skeletal elements. However, none is identifiable based on their preserved morphology. The coprolite is much too small to represent a large ungulate; it likely came from a small-to-medium-sized carnivore. It is ca. 20 mm long and 17 mm in diameter and contains at least one small fragment of bone visible on the surface. In many places, it shows fibrous-like structures that might be impressions of hairs or represent natural casts of small clumps of hair within the otherwise amorphous fecal matrix, but these would require detailed microscopic study to confirm or exclude that determination.

DISCUSSION--As is common in paleontological studies, the inadequacy or incompleteness of specimens together with unknown interspecific and intraspecific morphological variability of fossil taxa precludes specific identification of specimens of several genera from the rockshelter in Cimarron County (Mammuthus, Lepus, Sylvilagus, Neotoma, Cynomys, Equus, and Bison). Wyckoff and Dalquest (1997) discussed many problems in recognizing variation and taxonomy in late Pleistocene Bison in the southern Great Plains. In fact, the same problems pertain to all taxa of vertebrates found as late Pleistocene fossils. Identification to species is the exception rather than the rule for most vertebrate paleontological specimens, which usually are incomplete. Nevertheless, even generic identifications can add to a partial picture of the late Pleistocene vertebrate life of the region. Moreover, late Pleistocene occurrences of vertebrates can lend a deeper time perspective and support to studies and projects attempting to address the conservation of biological communities, as do some zooarcheological studies (e.g., Lyman and Cannon, 2004), especially in progressively degraded and converted ecosystems.

In general, vertebrates from the Pleistocene portion of the rockshelter paint a picture of an open-country assemblage of animals, differing from the Anthropocene of today (Ellis, 2011; Zalasiewicz et al., 2011), primarily in the presence of extinct forms, the mammoth and the two horses, an historically extirpated form, the gray wolf, and the absence of remains of humans, human-produced artifacts, and remains of historically introduced livestock and other domestic animals. Additional species such as the swift fox and prairie dog presently are dwindling in the area, but were present at least as far back as the late Pleistocene. The mammoth and bison represent probable grazing specialists indicative of grasses, while the horses and pronghorn likely were mixed feeders that suggest presence of shrubby country with plenty of grasses (Hofmann, 1989). Although they vary in environmental preferences, woodrats indicate presence of woody or brushy vegetation; many species of woodrats also inhabit relatively arid areas. Of course, the late Pleistocene environment and ecological community relationships were far more complex than these few bones of vertebrates from the rockshelter can possibly reflect. However, they do provide additional records of occurrence of taxa in the late Pleistocene, if not insight into changes in climate and physical and biological habitats.

Relatively few other late Pleistocene vertebrate faunas are known from the region [less than or equal to] 200-km radius of the rockshelter in Cimarron County (Faunmap Working Group, 1994; Smith and Cifelli, 2000). Thus, the fauna of the rockshelter adds important records documenting how species were distributed across the landscape. Elsewhere in Cimarron County, Dalquest and Stangl (1989) and Dalquest et al. (1990) described the Tesequite (or Tesesquite) local fauna, a collection with 12 small mammals, a horse Equus cf. E. conversidens,andan indeterminate large proboscidean. The Tesesquite local fauna was collected ca. 4 km southwest of the rockshelter in Cimarron County. A radiometric date on snail shells from the deposits gave an age of 31,360 [+ or -] 570 years before present. At least four members of the Tesesquite local fauna are shared with the assemblage from the rockshelter: Sylvilagus; Cynomys; Neotoma; Equus cf. E. conversidens. Noteworthy among the small mammals from the Tesesquite local fauna were the water shrew Sorex palustris, a species of high-mountain streamside habitats today, and the desert shrew Notiosorex, a eurytopic shrew often of dryland and scrub habitats today. If sediments from this rockshelter had been screenwashed when the shelter was excavated, it is likely that fossils of more small vertebrates would have been revealed. Wilson (1972:202) noted elephant and bison bones" in basal clay deposits that had been dated to ca. 21,360 and 11,200 years before present along Tesesquite Creek, Cimarron County, Oklahoma, but he commented (Wilson, 1972:205) that the bones had been redeposited and did not give any details about the vertebrates.

About 200 km east in Beaver County, Oklahoma, the Elm Creek local fauna is comprised of two sublocalities separated by ca. 2 km (Dalquest and Baskin, 1992). Each of these was dated byradiocarbon using mollusc shells; the Prairie Dog Town Site yielded an age of 11,410 [+ or -] 110 years before present and the Gregg Ranch Site was aged 11,630 [+ or -] 90 years before present. Interestingly, the water shrew S. palustris occurred in this local fauna as it did farther west in the Tesesquite local fauna. Unfortunately, as previously noted, no specimen of microvertebrate (small enough to require a microscope to see) was collected at the rockshelter in Cimarron County. The Elm Creek local fauna shares with the rockshelter a prairie dog (C. ludovicianus), a woodrat (Neotoma cf. N. micropus), Mammuthus columbi, Equus, Camelops, and Bison.

In Las Animas County, Colorado, ca. 60 km to the northwest of the rockshelter, Hager (1974) described the Mesa de Maya fauna, a late Pleistocene assemblage from an excavation for an irrigation ditch. The same trench also produced a late Pliocene assemblage, the Donnelly Ranch fauna. The Mesa de Maya fauna was believed by Hager (1974) to represent the Sangamonian interglacial stage and the Rancholabrean land mammal age. The Mesa de Maya fauna comprises vertebrates indicative of grassland and marsh communities and shares about five vertebrate taxa with the assemblage at the rockshelter in Cimarron County (Cynomys, Canis latrans, Equus conversidens, Camelops hesternus, and Bison).

Morgan and Lucas (2005) documented several Pleistocene sites in northeastern New Mexico preserving molluscs and various taxa of vertebrates. These localities include Folsom, Wetherly, Tramperos Creek, and Perico Creek. Some of these sites reflect a Rancholabrean age based on presence of Bison, while others cannot be biostratigraphically assigned. The Wetherly site yielded only Bison cf. B. priscus, whereas the other three sites produced sizeable assemblages. The well-known Folsom site, the type site for the Paleoindian Folsom culture, has associated radiometric dates between ca. 10,890 and 10,260 years before present. It preserves one extinct form (Bison antiquus occidentalis) and five extant forms (Lepus californicus, Cynomys ludovicianus, Spermophilus, Thomomys bottae, and Odocoileus hemionus; Morgan and Lucas, 2005). The Tramperos Creek locality to date has produced a diverse fauna with 30 taxa of vertebrates, including many aquatic microvertebrates (fish and amphibians) as well as the terrestrial mammals Bison, Equus niobrarensis, Camelops hesternus, Capromeryx minor, Mammuthus columbi,and several small terrestrial vertebrates (Morgan and Lucas, 2005). Among the small vertebrates of Tramperos Creek are a few taxa or close relatives shared with the rockshelter in Cimarron County such as Sylvilagus audubonii, Lepus, and Cynomys ludovicianus. The Perico Creek site, Union County, New Mexico, is ca. 65 km southwest of the rockshelter in Cimarron County. Large mammals at the Perico Creek site include Camelops hesternus, Platygonus compressus, Equus niobrarensis, Mammuthus, Capromeryx,and Odocoileus (Schumacher, 2001; Morgan and Lucas, 2005). Small mammals at Perico Creek include Spermophilus, Geomys bursarius, Ondatra zibethicus, and Microtus, none of which is shared with the rockshelter in Cimarron County.

A question remains about how the moderately diverse assemblage of late Pleistocene vertebrates came to be in the rockshelter. Stovall (Schoff and Stovall, 1943:121) believed that the rockshelters, caves, and recesses in the Black Mesa area were themselves cut into the sandstone bluffs along the canyon walls by tributaries of the Cimarron River when their channels were at the level of the caves. He interpreted the rockshelter bed including the vertebrate fossils as stream-laid deposits of sand and mud. He also believed the breakage of bones and stratification of sediments indicated that the Pleistocene streams that carved the rockshelters also had deposited the bones and sediments. Sedimentary layers from which the bones were taken are gone and, thus, it is not possible to re-examine the deposit for taphonomic evidence. The bones themselves show no evidence of abrasion caused by prolonged exposure to high-energy flowing water. If the bones were water-transported and water-deposited, they neither traveled far nor in fast-flowing water. This explanation seems plausible to us.

Evidence of other taphonomic agents seems absent from the bones. The relatively high number of carnivores in the assemblage at the rockshelter (three canids and a felid out of 14 mammalian taxa) brings to mind the possibility that the bones were transported to the shelter by one or more of the carnivores. However, even considering the poor state of preservation of fossils and the preparation-tool marks on some of them, there is no obvious evidence of modification of bones such as gnawing by carnivores or scavengers, spiral fracturing, or tooth-puncture marks. Accumulation of some of the smaller bones by rabbits or rodents, especially woodrats, which gather and transport objects including bones to their dens, is possible. Yet, no bone showed tooth marks typical of gnawing by rodents (Behrensmeyer and Hill, 1980; Andrews, 1990). Possibly, several agents of accumulation, including some or all of those mentioned, acted to bring the fossils into the rockshelter.

We thank G. S. Morgan for providing measurements of femurs of kit and gray foxes. T. Yuri kindly gave access to the avian osteology collection of oMNH. For allowing us to access the rockshelter in Cimarron County, we thank landowners B. and J. Apple. R. Newman kindly provided logistical support. We extend a special thank you to R. Whitten of the Whitten-Newman Foundation for funding our visit to the locality. L. Bement kindly read and commented on an early draft of the manuscript. D. G. Wyckoff helped secure funding for dating specimens and A. Coldiron provided funds for radiocarbon dating of a sample.

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Submitted 26 September 2011. Accepted 14 July 2012.

Associate Editor was Troy A. Ladine.

NICHOLAS J. CZAPLEWSKI * AND KENT S. SMITH

Oklahoma Museum of Natural History, 2401 Chautauqua Avenue, Norman, OK 73072 (NJC, KSS)

Oklahoma State University Center for Health Sciences, 1111 West 17th Street, Tulsa, OK 74107 (KSS)

* Correspondent: nczaplewski@ou.edu
TABLE 1--Measurements (in mm) of first phalanges of digit III of
Equus from Rockshelter, Cimarron County, Oklahoma. Measurements
follow those of Harris and Porter (1980:figure 2) and are labeled
as theirs were labeled. Brackets indicate estimated measurement of
broken specimen.

OMNH        A1   A2   A4   A6   A7   A8   A9   A10   A11   A12   A13

73854 (a)   73   66   63   35   20   26   20   46    44    35     50
73855       86   75   75   33   20   23   19   40    45    34     51
73856       85   76   72   31   20   21   19   42    43    34    [53]
74672       81   75   73   37   20   24   20   39    40    30     49

(a) This specimen might be from a young animal, and it is missing its
proximal epiphysis.
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