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PLEISTOCENE MAMMALS IN THE GREATER YELLOWSTONE ECOSYSTEM Christopher L. Hill Department of Anthropology and Environmental Studies Program, Boise State University, Boise, Idaho; Chill2@boisestate.edu

Introduction The Pleistocene, which generally corresponds to the Ice Age, is characterized by fluctuating climates that started around 3-2 million years ago and ended about 10,000 years ago, after a short, cold interval called the Younger Dryas. The Pleistocene is especially important in the application of ecological principles because it is associated with the evolution and extinction of a variety of mammals (Barnosky et al. 2004; Barnosky, 2005). In North America, the last part of the Pleistocene coincides with climate change, glacial advance and retreat, and the Rancholabrean land mammal age. The end of the Pleistocene also coincides with the earliest presence of humans in North America. Southwestern Montana, which includes the northwest part of the Greater Yellowstone Eco-system and adjacent areas, contains evidence for extinct Pleistocene mammals. These include herbivores such as mammoth, camel, and horse,

and, more rarely, carnivores such as scimitar cat, cheetah, and dire wolf. The Greater Yel-lowstone Ecosystem consists of parts of south-western Montana, northwestern Wyoming, and southeastern Idaho (fig. 1). The drainages of streams that are part of the Upper Missouri River basin (such as Red Rock River, Beaver-head River, Jefferson River, Ruby River, and Madison River) are part of this landscape in southwestern Montana (fig. 2). The broad char-acter of the Rancholabrean communities in this region is known from isolated discoveries in fluvial gravels and sands (chiefly of mam-moth), fossils collected from caves, and more detailed studies of late Pleistocene stratigraphic sequences. Besides fossil vertebrates, some localities contain evidence, based on the pres-ence of artifacts, for prehistoric human groups in the region by 11,000-10,500 radiocarbon (14C) years ago. The landscape of southwestern Montana is to a great degree the product of tectonic events and climatic change during the late Pliocene and Pleistocene (roughly the last 3 million years). Tectonic processes in the form of regional faulting have led to the formation of the basin-and-range physiographic character of the re-gion. Volcanism centered on the area of the Yellowstone Plateau over about the last 2 mil-lion years is connected to regional tectonic events extending over the last 15 million years or so on the Snake River Plain. Volcanism in the Pacific Range resulted in the deposition of several tephra (volcanic ash) deposits which serve as useful regional stratigraphic markers. Climatic fluctuations have also played an im-portant role, both in forming the present-day landscape and influencing the Pleistocene pa-leobiotic communities of the region. Late Plio-cene or early Pleistocene through Holocene glacial episodes have been documented. Most

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Figure 1. Location of Jefferson, Madison, and Gallatin Rivers in southwestern Montana in relation to Yellow-stone National Park.

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of the mountain ranges contain evidence for multiple glaciations during the late Cenozoic, while alluvial fans and terraces within the val-leys reflect the interplay between fluctuating climatic regimes and tectonic processes. Although Pleistocene fossils have been col-lected from the area for over a hundred years, extensively studied stratigraphic sequences containing Pleistocene vertebrate remains are relatively uncommon in southwestern Montana. Early collections include Mammuthus (mammoth) fossils found in the drainage of the Ruby River obtained as part of the Hayden Sur-vey in 1871. A significant Pleistocene locality is in Centennial Valley, east of Lima, Montana, along the Red Rock River. Mammal fossils in-

clude Mammuthus (cf. M. columbi), Homotherium serum (scimitar cat), canids (wolf and coyote), Equus (horse), Bison (bison), and Camelops (camel). Else-where in the Jefferson drain-age, in the vicinity of Black-tail Deer Creek, Equus, Camelops, Bison, Ovis (sheep), and Canis dirus (dire wolf) have been recov-ered from Sheep Canyon-Orr Cave, while Mammut-hus and Equus fossils have been recovered within the Ruby River drainage, and Acinonyx trumani (cheetah), Equus, Camelops and Ovis canadensis (mountain sheep) are known from the Sheep Rock Spring locality west of the Boulder River. Plio-Pleistocene Geologic Background Climate change and tectonic activity during the late Plio-cene and Pleistocene have affected the physical and

biotic environments of the region. A series of volcanic explosions occurred in the area cen-tered on Yellowstone National Park. The three major explosions date to about 2.0, 1.3 and 0.6 million years ago (cf. Hamilton, 1965; Walsh, 1971; Christiansen and Blank, 1972; Witkind, 1976; Weinheimer, 1979; Mannick, 1980; Christiansen, 1982; Sonderegger et al., 1982; Pritchett, 1993; Gansecki et al., 1998; O’Neill and Christiansen, 2004). These events resulted in the emplacement of igneous rocks. The prod-ucts of this local volcanic activity and volcanic ash beds originating from the Cascade region serve as useful local stratigraphic markers. For example, the late Pleistocene Glacier Peak ash dated to about 11,200 14C years B.P. and the early-middle Holocene tephras Mount Mazama ash dated to about 6,900 14C years B.P. are visi-ble in road cuts or natural exposures, and have

Figure 2. Location of major Pleistocene localities in south-western Montana.

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also been documented in stratigraphic cores. Both the Glacier Peak and Mazama volcanic ashes are present in a stratigraphic core col-lected from Kearns Basin, within the Beaver-head drainage in the southern Pioneer Moun-tains (Foit et al., 1993). The Glacier Peak and Mazama tephras are exposed along the Jeffer-son, Madison, and Gallatin Valleys (cf. Mon-tagne, 1965:51; Kellogg, 1992) and have also been documented in the Yellowstone Plateau area (cf. Whitlock, 1993), and elsewhere in the upper Missouri basin (Lemke et al., 1975; Davis and Greiser, 1992). The mountains within southwestern Montana supported glaciers at various times during the Pleistocene (Alden, 1953; Hall and McMannis, 1960; Paul and Lyons, 1960; Hall, 1961; Sloan, 1960; Montagne, 1960; Reshkin, 1963; Rich-mond, 1965; Hadley, 1969; Jacobs, 1969; Mon-tagne, 1972; Pierce, 1979; Gary, 1980; Roy and Hall, 1981; Hall and Heiny, 1983; Richmond, 1986a, 1986b; Locke, 1989; Hall, 1990; Locke 1990; Schneider, 1990a, 1990b; Locke and Schneider, 1990; Lundstrom, 1990; Pritchett, 1990; Ritter et al., 1990; Pritchett, 1993; Ritter et al., 1993; Sturchio et al., 1994; Bartholomew et al., 1999). Moraines within many of the tributary valleys show the extent of past glaci-ations. Alluvial fans and terraces on the flanks of the mountains and in the valleys are com-posed of sediments of glaciofluvial origin, de-posited as outwash from glacial meltwater. Late Cenozoic lacustrine, paludal, and spring (e.g. tufas) sediments are present in the valleys, as are aeolian silts (loess) and sands. Vertebrate remains have been recovered from some of these depositional contexts and have also been found in caves and rock shelters. Stratigraphic and geomorphic relationships of these various deposits can be linked to both paleoclimatic chronologies and tectonic events. This geochro-nologic-paleoenvironmental framework serves as a basis for evaluating the late Pliocene and Pleistocene paleobiotic communities of the re-gion. Pleistocene Mammal Localities The climate and physical environmental changes that occurred during the Quaternary

provided a variety of contexts that can be re-lated to paleobiotic patterns in southwestern Montana. Pleistocene mammal fossils have been recovered in the vicinity of the Red Rock River (the Merrell Locality), Blacktail Creek (Sheep Canyon Cave), South Everson Creek, Alder Gulch, Dry Boulder Creek, Sheep Rock Spring, and Point-of-Rocks Cave (fig. 2). These localities contain a record of biodiversity that can be related to changes in physical land-scapes and biotic habitats associated with re-gional Quaternary tectonic and climate events. The most extensively studied Pleistocene pale-ontological locality in the Greater Yellowstone Ecosytem is near Red Rock River, a major stream in the southern area of the Jefferson River drainage (fig. 3). The locality is east of Lima, which is about 45 miles south of Dillon. Red Rock River flows from east to west through the Centennial Valley, surrounded to the north by the Snowcrest and Gravelly Ranges and to the south by the Centennial Mountains. Four classes of animals have been recovered: Osteichthyes (bony fish), Aves (waterfowl), Amphibia (amphibians), and Mammalia (Dundas 1990, 1992; Dundas et al., 1996; Hill, 1999; Hill and Davis, 2005; Hill 2006a, 2006b). Table 1 provides a list of the mammals recovered from Centennial Valley, while table 2 is a list of radiocarbon dates. Fi-nite radiocarbon ages range from about 49,350 14C years B.P. (Beta-116519) to about 19,310 14C years B.P. (Beta-77826). Several measure-ments indicate some remains are older than 52,800 14C years B.P. The faunal assemblages are from several sedimentary units and appear to have been affected by a variety of ta-phonomic processes reflecting the dynamics of pre-burial deposition, burial, and post-burial events. Stratigraphic contexts and sedimentologic fa-cies associated with the Centennial Valley mammal fossils reflect a variety of depositional and post-depositional processes. These contexts provide information on the factors leading to the accumulation of the fossils. Five strata have been designated (figs. 4-7). The oldest set of deposits is stratum A which contains alluvial, lacustrine, and possibly colluvial sediments.

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TAXON STRATUM

Carnivora

Canis latrans (coyote) Stratum C

Canis lupus (gray or timber wolf) Unknown context

Ursus sp. indet. (bear) Unknown context

Homotherium serum (scimitar-tooth cat) Unknown context (beach)

Rodentia

Spermophilus sp. indet. (squirrel) Unknown context

Castor canadensis (Canadian beaver) Unknown context

Lemmiscus curtatus (sagebrush vole) Stratum C

Ondatra zibethicus (muskrat) Strata A-B or B

Perissodactyla

Equus sp. indet. (horse) Stratum C, D

Artiodactyla

Camelops sp. indet. Strata C, D

Cervidea sp. indet. (deer) Stratum C

Odocoileus hemionus or O. virginianus (mule deer or white-tailed deer)

Unknown context

Antilocapridea americana (pronghorn) Unknown context

Bison sp. indet.(bison) Stratum D

Proboscidea

Mammuthus columbi (Columbian mammoth) Strata A, A-B or B, C, D

Table 1. Mammal species from Centennial Valley, southwestern Montana.

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TABLE 2: Radiocarbon Measurements from Centennial Valley

Age Lab Number Material/Method Location Other

>52,800 SR-6012 Chem-6817

Mammuthus tooth, XAD-gelatin, KOH-collagen

ES-26-7 (Excavation E South ½, Level 26)

South Area: Either Stratum A or B

>52,800 SR-6013 Chem 6821

Mammuthus tooth, XAD-gelatin, HOH-collagen

ES-27-1 (Excavation E South ½, Level 27)

South Area: Stratum B

>52,800 SR-6016 Chem-6833

Equus upper mo-lar, XAD-gelatin, KOH-collagen

Ib#12, 95.2.155

North Area: Stratum D

>52,800 SR-6017 Mammuthus tusk, XAD-gelatin, KOH-collagen

Ib#21

North Area: Stratum D

49,350 +/- 1,500

Beta-116519 Mammuthus molar fragments

CS-21-1 LI94.5.277 154, MS686

North Area: Stratum A -19.2 C13/C12

43,970 +/- 370

Beta-110647 Cygnus-Olar, bone collagen

Not in stratigraphic context -11.1 C13/C12

>41,940 Beta-83614 Humates (HCl/NaOH/HCl)

East of Test Pit E, from backhoe trench, South Block

South Area: Stratum B -28.2 C13/C12

36,520 +/-710

Beta-74032 Organic sediments from Mammuthus rib

Excavation E South Area: Stratum B -26.0 C13/C12

>33,990 Beta-36206 Mammuthus fibula, bone collagen

Dundas specimen 10027 South Area: Stratum B

32,470 +/- 270

Beta 111325 Mamuthus (tusk, bone collagen, KOH)

97FS36 LI96.4.44 L3FS36 p. 137

South Area: Stratum B -25.2 C13/C12

30,400 +/-590

SR-6018 Chem-6839

Camelops, XAD-gelatin, KOH-collagen

Station E4 Hill specimen

North Area: Stratum C

26,630 +/- 190

SR-6015 Chem-6826

Equus, XAD-decalcified colla-gen

Ia#4

North Area: Stratum D

25,030 +/- 510

Beta-36205 Mammuthus, meta-tarsal, bone colla-gen

“Channel fill” re. Dundas specimen 10006 = debris flow

North Area: Stratum D

23,120 +/- 1190

SR-6014 Mammuthus tusk XAD-gelatin, KOH-collagen

K#29 Excavation K

South Area: Stratum B

21,530 +/- 100

Beta-118755 Bone collagen, KOH

ML-98-CLH97-C, Stratum D, fragment of bone in matrix above TL3 sand sample

North Area: Stratum D -20.9 C13/C12

19,290 +/- 90

Beta-77826 Collagen, KOH Debris flow = Stratum D -23.7

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Stratum B consists of dark, organic-rich sedi-ments deposited in a swamp or bog. Silts, sands, and gravels from stratum C mostly rep-resent alluvial deposition. Stratum D is chiefly composed of a debris flow. It overlies a sandy facies of stratum A. After strata A-D were de-posited, they were affected by soft-sediment deformation-liquefaction, and faulting, perhaps linked to local tectonic events. The youngest depositional unit, designated stratum E, con-sists of colluvium. There is evidence of exten-sive bioturbation (biologic mixing) in stratum E and in parts of stratum C. Vertebrate remains found within stratum A are usually rare and isolated, except near its upper contact with stratum B (fig. 4). One example of an isolated find within stratum A is a patella of a proboscidean (probably from Mammuthus). It is likely that some of the fossils found within stratum A, especially near its upper contact with stratum B, have been moved by post-depositional events. The first taphonomic context in which there are

higher frequencies of mammal fossils is along the interface of strata A-B and in the lowest part of stratum B (fig. 5). There are no articu-lated specimens, but there are concentrations of bones, tusk and teeth of mammoth (fig. 6). Other faunal materials from this taphonomic context include Ondatra zibethecus (muskrat) and bivalves. These may include bones that accumulated on the surface of stratum A and then were buried within stratum B, as well as elements that accumulated during the deposi-tion of the stratum B organic-rich sediments. Radiocarbon measurements, if reliable, suggest that this taphonomic context contains a tempo-rally mixed fossil assemblage. Fragments of mammoth teeth were dated at >52,800 14C years B.P. (SR-6012, SR-6013), while radiocar-bon ages on tusk fragments are 32,470 14C years B.P. (Beta-111325) and 23,120 14C years B.P. (SR-6014). These could reflect a ta-phonomic or formational context associated with surface exposure within a small basin, and burial in or incorporation into a marsh. The alluvial deposits of stratum C also contain

Figure 3. Location of Merrell Site in Centennial Valley.

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Figure 4. Stratigraphic profile in Centennial Valley showing Pleistocene strata A-C and Holocene colluvium.

Figure 5 (above). Stratigraphy at Centennial Valley verte-brate locality. Dark layer is stratum B. It over lies stratum A and underlies stratum C. Figure 6 (left). Mammoth tooth in stratigraphic context.

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vertebrate remains. These include including limb bone, tooth, and tusk fragments of mam-moth, and fragments from Camelops (camel), Equus (horse), Canis latrans (coyote), a large artiodactyl, Lemmiscus curtatus (sagebrush vole), Pices (fish), and Anatidae (duck). The radiocarbon age on camel is about 30,400 14C

years B.P. (SR-6018). These fossils are distrib-uted throughout the sequence of stratum C, within fluvial gravels and sands interbedded with silts. Thus, these vertebrate remains repre-sent a taphonomic context primarily associated with stream transport and burial. A third sedimentological setting is associated with the fossils from stratum D, consisting of a fine-grained matrix with limestone and quartz-ite cobbles and bones, interpreted as a debris flow (fig. 7). Most of the faunal material con-sists of remains of mammoth (tusk, teeth, and bones, fig. 8) as well as some elements of Equus (horse) and Bison (bison). Based on the radiocarbon ages, this assemblage is temporally mixed. Fragments of mammoth and horse bone have measurements indicating ages of >52,800 (SR-6016, SR-6017) and finite ages of 26,630 14C years B.P. (SR-6015) and 19,310 14C years B.P. (Beta-77826). Thus, the youngest fossils from Centennial Valley appear to date to around the Last Glacial Maximum.

The depositional variability reflected in the stratigraphic record indicates that the Centen-nial Valley vertebrate assemblages are the re-sult of at least three different taphonomic con-texts. The dispersal, scattering, and accumula-tion of bones associated with the strata A-B appears to have occurred in a marsh-pond ba-

sin. Transport, deposition and burial of skeletal parts recov-ered within stratum C was the result of hydraulic events asso-ciated with fluvial conditions. The concentration of mam-moth fossils in stratum D oc-curs within a debris flow. Sub-surface movements—post-depositional crushing by sedi-ment overburden along with liquefaction and faulting—have also affected the charac-ter of the fossil record. Horse remains are associated with both fluvial and debris flow deposits. Camel and wolf re-

Figure 7. Debris flow (stratum D) with mammal fossils in Centennial Valley.

Figure 8. Mammoth tooth within stratum D, Centennial Valley.

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mains have been identified from alluvial con-texts, while bison were recovered only in asso-ciation with the debris flow. All three sedimen-tologic contexts contain evidence of mammoth. Two terraces are present along the Red Rock River Valley southeast of Lima (Scholten et al., 1965); they have been interpreted as being con-nected with Pleistocene mountain glaciation. Red Rock River flows northwest, between the Tendoy Mountains to the southwest and the Blacktail Mountains to the northeast and merges with Horse Prairie Creek to form the Beaverhead River at the Clark Canyon Reser-voir, about 11 miles south of Dillon (fig. 2). Blacktail Deer Creek flows into the Beaverhead River from the east and is bounded by the Blacktail Mountains to the southwest, the Snowcrest Range in the southeast and the Ruby Range to the north. Along the south side of Blacktail Deer Creek valley, south of Dillon, Pleistocene vertebrate remains were recovered from Sheep Canyon Cave. The locality was excavated by P. Orr between 1925 and 1930 (Campbell, 1978). Faunal remains include Equus, Camelops, Bison and Ovis. The remains of Canis dirus (dire wolf) have been identified from Orr Cave (Kurten, 1984), which is proba-bly another designation for Sheep Canyon Cave. Southwest of Dillon, studies in the Horse Prai-rie Creek and Grasshopper Creek Basins and along the adjacent slopes of the Beaverhead Mountains indicate at least six pre-Bull Lake age glacial advances (Turner et al., 1988). Six-teen terraces are recognized near South Everson Creek (fig. 2), which flows from the foothills of the Beaverhead Mountains into Horse Prairie Creek (Bonnichsen et al., 1987, 1992). The lowest terrace contains what is probably Gla-cier Peak volcanic ash (ca. 11,200 14C years B.P.) as well as flaked mammoth bone (Bonnichsen et al., 1987). Possible fragments of mammoth bone were associated with sedi-ments consisting of cobbles and boulders em-bedded in clays (Bonnichsen et al., 1990; Bon-nichsen et al., 1992). The clays may be late Pleistocene paludal or lacustrine deposits (Turner et al., 1987; Turner et al., 1988).

Pleistocene vertebrate remains have been re-covered east of Dillon from the Alder Creek area, within the Ruby River drainage (fig. 2). The Ruby River flows northeastward into the Beaverhead-Jefferson Valley. It is bounded to the south by the Ruby Range and to the north by the Tobacco Root Mountains. F.V. Hayden obtained Pleistocene fossils from the vicinity of Virginia City, at Alder Gulch (Hayden, 1872; Merrill, 1999). The remains were assigned to Elephas (= Mammuthus) primigenius by Hay-den (1872). Later some of the proboscidean remains were identified as E. columbi (Hay, 1924). Other mammoth fossils from Alder Gulch were recovered during placer mining prior to 1894 and are in the collection of the Virginia City Museum and Library. Along the northern flanks of the Ruby Range, fossils of Pleistocene horse have been collected from gravels at the mouth of Dry Boulder Creek, and from silts near Dry Georgia Creek (Petkewich, 1972). A late Pleistocene vertebrate assemblage was collected west of the Boulder River on the flanks of the southern end of Bull Mountain, at the Sheep Rock Spring locality (Wilson and Davis, 1994; Davis, 1997). The (Northern) Boulder River flows southward from the Elk-horn Mountains and joins the Jefferson River near Whitehall and Cardwell, about 55 miles northwest of Dillon (fig. 2). At least three ter-races can be recognized in the Boulder River Valley north of Cardwell. These were assigned to the early to middle and late Pleistocene (“second and third sets”) by Alden (1953:80). Five stepped pediments levels were studied by Morgan and Hall (1982). Faunal remains in-clude cheetah (Miracinonyx trumani), horse (Equus sp.), camel (Camelops sp.), and large mountain sheep (Ovis canadensis catclawen-sis). The lowest part of the sequence has radio-carbon dates slightly older than 10,000 14C years B.P. (Hill, 2006a). Point-of-Rocks Cave (Davis and Johnson, 1988) is situated on the slopes of the Tobacco Root Mountains adjacent to the Jefferson River, south of Whitehall and east of Renova. Fossils

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recovered from the cave include a possible B l a n c a n a g e M e g a n t e r o n s p . (Machairodontinae) (personal comm. to D. Rasmussen from L.D. Martin, 1999) and Equus (Davis, 1997).

Evidence for Late Pleistocene Humans The earliest well-documented evidence for hu-mans in North America come from discoveries associated with Clovis and Folsom artifacts. These types of artifacts are considered to be time indicators for the end of the Pleistocene and have been discovered with extinct Ran-cholabrean mammals. Clovis artifacts have been found in stratigraphic contexts with mam-moths, while Folsom artifacts are associated

with extinct forms of bison. In eastern Idaho, Folsom artifacts have also been found with mammoth fossils (Miller and Dort, 1978). Clovis artifacts may date to about 11,100-10,800 14C years B.P. (Waters and Stafford, 2007), while Folsom artifacts may range from about 10,900-10,100 14C years B.P. (Holliday 2000). A stratified sequence at Indian Creek on the flank of the Elkhorn Mountains in western Montana contains a Clovis component (Davis and Greiser, 1992; Hill and Davis, 2005). Fol-som artifacts have also been found regionally. One example was found north of Lima Reser-voir in Centennial Valley (fig. 9). Slightly younger artifact forms dating to about the Pleis-tocene-Holocene transition have been discov-

ered in the region. These range in age from about 10,500-10,000 14C years B.P. for Agate Basin (fig. 10) as well as 10,200-8,800 14C years B.P. for Alberta, Scottsbluff and Eden artifact forms (fig. 11) (Holliday, 2000). These discoveries suggest that humans were present in this region of North America during the Younger Dryas (from about 10,900 to 10,200 14C years B.P.) or slightly earlier and appear to have persisted throughout the Pleistocene-Holocene transition. Ecological Interpretations and Conclusions Large and small mammals in the Greater Yel-lowstone Ecosystem include both carnivores

and herbivores (Bailey, 1930; Hadly, 1986; Streubel, 1989; National Research Council, 2002; Cannon and Cannon, 2004). Carnivores present to-day include Ursos arctos (grizzly bear), Ursus ameri-canus (black bear), Felis con-color (mountain lion), Canis latrans (coyote), and Canis lupus (wolf). Herbivores in-clude Cervus elaphus (elk or wapiti), Odocoileus hemionus (mule deer), Bison bison (bison), Alces alces (moose),

Ovis Canadensis (bighorn sheep), Antilocapra americana

Figure 9. Fragment of Folsom point found north of Red Rock River, Centen-nial Valley (from Hill and Davis, 2005).

Figure 10. Agate Basin points from Centennial Valley (from Hill and Davis, 2005).

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(pronghorn), and Odocoileus virginianus (white-tailed deer). Some of the smaller mam-mals include Erethizon dorsatum (porcupine), Lepus americanus (snowshoe hare), Castor canadensis (beaver), Ondatra zibethicus (muskrat), Gulo gulo (wolverine), Mustela (weasel), Mustela vison (mink), Martes Ameri-can (pine marten), Martes martes (fisher), Taxidea taxus (badger), Lutra canadensis (river otter), Ochotona princes (pika), Marmota flaviventrus (yellow-bellied marmot), Tamias minimus (least chipmunk), Spermophilus ar-matus (ground squirrel). The Pleistocene mammals for southwest Mon-tana fall into the two categories: those that are extinct and those that are still present. This seems to suggest some ecological relationships that exist today may have persisted in the re-

gion since the Pleistocene. It also implies that some aspects of the Greater Yellowstone Eco-system in southwestern Montana have changed since the Pleistocene. This pattern is illustrated by the carnivores. For the canids, Canis dirus is extinct, while Canis latrans (coyote) and Canis lupus (gray or timber wolf) appear to have been present in the region prior to the Last Glacial Maximum (centered on about 20,000 years ago). Other extinct carnivores include the felid Homotherium serum (scimitar cat) and Miraci-nonyx trumani (American cheetah), while Ur-sus (bear) has been present since the Pleisto-

cene. Herbivores show a pattern similar to the carnivores. Some, like Mammuthus (mammoth), Equus (horse), and Camelops (camel) did not survive the end of the Pleisto-cene, while other animals such as Odocoileus (mule or white-tailed deer), Ovis canadensis (bighorn/mountain sheep) and Antilocapridea americana (pronghorn), and Bison (bison) per-sisted regionally. In contrast to the larger mammals, rodents appear to have persisted without major extinctions during the last glacial to interglacial transition, although some range changes may have occurred. This is illustrated by the Merrell Locality in Centennial Valley where Castor canadensis (Canadian beaver), Lemmiscus curtatus (sagebrush vole), and On-datra zibethicus (muskrat) are found in late Pleistocene sediments. In terms of patterns of extinctions, there appears to be a dichotomy between some large mammals, regardless of whether they are herbivores or carnivores, and small mammals. The extinction of large mam-mals near the end of the Pleistocene has been linked to both climate change and interactions with humans (Barnosky et al., 2004). References Cited Alden, W.C., 1953, Physiology and glacial geology of western Montana and adjacent areas: United States Geological Survey Professional Paper 231. Bailey, V., 1930, Animal life of Yellowstone Na-tional Park: Springfield, Illinois, Charles C. Tho-mas. Barnosky, A.D., 2005, Effects of Quaternary cli-matic change on speciation in Mammals: Journal of Mammalian Evolution, v.12, p. 247-264. Barnosky, A.D., Koch, P.L., Feranec, R.S., Wing, S.L., Shabel, A.B., 2004, Assessing the causes of Late Pleistocene extinctions on the continents: Sci-ence, v. 306, p. 70-75. Bartholomew, M.J., Lewis, S.E., Russell, G.S., Stickney, M.C., Wilde, E.M., and Kish, S.A., 1999, Late Quaternary history of the Beaverhead Canyon, southwestern Montana: in Hughes, S.S., and Thack-ray, G.D., eds., Guidebook to the Geology of East-ern Idaho, Idaho Museum of Natural History, Poca-tello, p. 237-250.

Figure 11. Late Pleistocene and Early Holocene points (Alberta, Scottsbluff, and Eden) from Centennial Valley (Hill and Davis, 2005).

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...saw several bald Eagles and two large white headed fishing-hawks boath these birds were the same common to our country. From the number of rattle snakes about the Clifts at which we halted we called them the rattle snake clifts. This serpent is the same before discribed with oval spots of yellowish brown. The river below the mountains is rapid rocky, very crooked, much divided by islands and withal shallow. After it enters the moun-tains its bends are not so circuetous and it's general course more direct, but it is equally shallow les divided more rocky and rapid.

Capt. Lewis, August 10, 1805