A TALE OF THREE CAVES: LATE PLEISTOCENE TO MIDDLE HOLOCENE FAUNAL CHANGES IN THE GREAT BASIN
by Bryan Scott Hockett
Paper Presented at the Sundance Workshop
February 24, 2000
Interest has been shown in behavioral relationships between early residents of the Great Basin and extinct, Pleistocene-aged megafauna for over a century. In his 1933 Gypsum Cave report, Mark Harrington published a review of Great Basin sites producing Pleistocene megafauna, and argued that several sites demonstrated good evidence for human exploitation of extinct megafauna. Many subsequent reviews related to Pleistocene megafauna have been published since 1933, the most recent of which is Don Grayson’s review in 1994 in the "Natural History of the Colorado Plateau and Great Basin" volume. In addition, George Jefferson and others are currently working on a catalogue list of Late Pleistocene locales in Nevada similar to the volumes previously published for southern California and Utah by the Natural History Museum of Los Angeles County.
Rather than simply repeat these efforts, in this paper I wish to first list seven research themes important to understanding Late Pleistocene to Middle Holocene faunas in the Great Basin. This list is not intended to be exhaustive, rather it highlights several important issues regarding the study of faunal remains, ancient Great Basin ecosystems, and the place of early peoples in those ecosystems. Second, I would like to present data from three on-going research projects that are addressing many of these themes. These three sites are all caves. Each cave contains Late Pleistocene and Holocene deposits, each is relatively well-dated with multiple radiocarbon dates, and each is located in a different part of the hydrographic Great Basin. These three caves are the following: (1) Homestead Cave is located in the northern Great Basin; (2) Mineral Hill Cave is located in the central Great Basin; and (3) Pintwater Cave is located in the southern hydrographic Great Basin near the boundary of the northern Mojave and southern Great Basin deserts.
After a century of research, seven themes come to mind that are critical to advancing our understanding of Pleistocene to Middle Holocene-aged faunas and their relationship to prehistoric cultures: (1) human exploitation of extinct megafauna in the Great Basin remains equivocal; (2) because no site has been found that behaviorally associates early people with extinct megafauna in the Great Basin, there currently is no support for the ‘Blietzkrieg’ or ‘Overkill’ model to explain the disappearance of many animal species during the Late Pleistocene and Early Holocene in the Intermountain region; (3) we have learned a great deal about general changes in animal species composition in the Great Basin over the past 20,000 years, but few well-dated Late Pleistocene faunal assemblages have been reported from the region; (4) there are similarities and differences between the northern and southern Great Basin in the nature and timing of faunal changes between the Late Pleistocene and Middle Holocene; as a result, we are just beginning to understand the climatic implications of these data, and by extension, the precise effects these changes may have had on the earliest inhabitants of the Basin; (5) we do not yet know the overall health of the latest Pleistocene populations of now-extinct megafauna, carnivores, and birds which were present at the time of early human occupation in the Great Basin; (6) relatedly, we know much more about the Great Basin ecosystems of the last 20,000 years than we do about the ecosystems of pre-Glacial Maximum times; and (7) our knowledge of the anatomical and behavioral similarities and differences between Pleistocene-aged animals and their Holocene-aged counterparts is insufficient for meaningful archaeological and paleoecological analyzes.
I would like to present brief overviews of the research programs at Homestead, Pintwater, and Mineral Hill caves, and then present data from these sites that are pertinent to addressing the seven research themes just mentioned.
A TALE OF THREE CAVES
Homestead Cave is located in the northern Great Basin near the western flank of modern Great Salt Lake. The cave is located at an elevation of 1406m (4,640 ft.). Vegetation growing near the cave includes shadscale, horsebrushes, bud sagebrush, rabbitbrush, greasewood, and scattered Utah juniper trees. Dave Madsen led excavations in the site in 1993 and 1994 as part of his Silver Island Expedition. Homestead Cave contains stratified deposits spanning the period 11,300 to 1,000 BP. A total of 21 radiocarbon dates have been obtained from the 18 recognized strata. The lowest stratum lies on bedrock. Artifacts were scanty in the cave, but a rich deposit of hundreds of thousands of faunal remains was recovered during the excavations. Most of these bones were deposited in the cave via owl pellets, and when I visited the cave in the summer of 1994, I photographed a western screech owl inside the cave.
Don Grayson has been studying the mammal bones from Homestead Cave. He presented preliminary results of his analysis at the GBASH meetings held in Salt Lake City in 1997. Since then, Don has completed the manuscript for a chapter in a conference volume to be published by the Smithsonian Institution. Don graciously sent me an advanced copy of his chapter several months ago while I was finishing my analysis of the Pintwater Cave fauna. Don’s results will be incorporated into my discussion here today.
Pintwater Cave is located in the southern hydrographic Great Basin, and the northern reaches of the Mojave Desert, in southern Nevada. The cave is situated at 1268 m (4,185 ft.) in elevation. Pintwater Cave is only 500 feet lower in elevation than Homestead Cave. Vegetation growing within several hundred meters of the cave is typical of a Mojave Desert scrub community: white bursage, creoste bush, shadscale, Mormon tea, desert needle grass, Mojave yucca, and California barrel cactus. Trees, found only in the extreme northern portion of the Pintwater Range, are mainly scattered pinyon pine and Utah juniper.
Paul Buck of the Desert Research Institute guided excavations in the cave during the summer of 1996, and I participated in these excavations. Similar to Homestead Cave, Pintwater Cave produced few buried artifacts. A rich and diverse assemblage of arrow and dart shafts, as well as projectile points, was recovered from the surface of the cave and from the top 5cm of cave deposit.
Five test units were excavated in Pintwater Cave in 1996. The faunal remains recovered from Unit 3 will be discussed here because approximately 80% of the 70,000 bones recovered were found within this single unit. As was the case at Homestead Cave, most of the bones in Unit 3 were from degraded owl pellets.
Unit 3 was situated beneath a ledge repeatedly used by roosting owls between the Late Pleistocene and middle Holocene. As a result, much of the sediment in Unit 3 consisted almost entirely of degraded raptor pellets mixed with lesser amounts of silt, roof spalls, and mountain sheep dung. Bedrock was estimated to lie several meters below the base of the excavated unit: therefore, the degraded raptor pellet debris probably represents an upper stratum separated by deeper, unexcavated strata below.
Because the raptor pellet stratum was at least 65 cm thick, it was sampled by excavating arbitrarily at 10 cm levels to gain more precise vertical and temporal control within the stratum. Radiocarbon dates were obtained from six of the eight levels excavated within Unit 3, producing a chronologically ordered suite of dates. These dates range between 32,000 and 7,350 BP, with a large gap in time between 32,000 and 15,000 BP.
Faunal remains were regurgitated by owls at both Homestead and Pintwater Caves during the latest Pleistocene into the Middle Holocene, which allows a unique comparison of changes to small fauna during the Pleistocene to Holocene transition in the northern and southern Great Basin.
Mineral Hill Cave
Mineral Hill Cave is located approximately 55 miles southwest of Elko in southern Pine Valley. The cave rests at 2,121m (7,000 ft.) in elevation along the southern flanks of the Sulpher Springs Range. The topography and vegetation surrounding the cave are typical of the central Great Basin: limestone ranges blanketed by big sagebrush and rabbitbrush on the lower foothill slopes, big sagebrush and Utah Juniper on the upper foothill slopes, and pinyon-juniper together with big sagebrush, mountain mahogany, snowberry, serviceberry, balsam root, and a host of grasses above 6,500 feet.
Kelly McGuire excavated a 1m by 2m unit in the first chamber of Mineral Hill Cave in 1975. In 1980, he reported finding extinct horse, big-headed llama, and shrub ox from the cave. He also identified a number of extant species, including pronghorn, mountain sheep, coyote, fox, marmot, squirrel, woodrat, cottontail, and hare. McGuire also reported finding charcoal throughout his excavation unit, although he did not find a single artifact. This prompted Kelly to do two things: (1) he argued that the sediment in his excavation unit had been thoroughly mixed by natural processes, and therefore he did not obtain radiocarbon dates from his charcoal samples; and (2) he argued that the presence of charcoal with extinct megafauna did not necessarily imply a behavioral association between the two types of ecofacts. Kelly published his results in 1980 in Quaternary Research, which prompted Allan Bryan to submit a rejoinder paper which essentially argued that archaeologists should not write-off the cave just yet, and Mineral Hill Cave might exhibit a behavioral association between humans and extinct Pleistocene megafauna.
I relocated Mineral Hill Cave in 1996. Using a Trimble Global Positioning System unit, I determined that Mineral Hill Cave was located 60m from private land on public land managed by the BLM Elko Field Office. Kelly’s original 1m by 2m unit was still quite intact 20 years after it was excavated, and someone had dug a looter’s pit approximately twice that size next to Kelly’s unit. After finding a horse phalanx and a llama phalanx protruding from the side walls of the looter’s pit, I decided that additional research at Mineral Hill Cave was warranted.
In the summer of 1997, with the help of Dave Rhode, Dave Madsen, Bill Shaver, Paul Buck, and Bob Elston, we excavated a small 1m by 25cm trench in the face of the looter’s pit to determine the stratigraphic integrity of the cave. In addition, although Kelly’s 1980 article mapped Mineral Hill Cave as a single chamber, the cave actually consists of 5 chambers, the last of which is not penetrated by sunlight. During my visits to the back chambers, I discovered several horse phalanges lying on the surface, prompting me to propose placing a unit against the far wall of the 5th chamber.
With the help of Bob Elston, Paul Buck, and Dave Madsen, we mapped what looked like possible strata in the first chamber of the cave. As we excavated, bones of extinct and extant animals were recovered, including a complete first phalanx of a camel. Similar to McGuire’s findings 20 years earlier, each of our possible strata contained charcoal. Samples of bone and charcoal from each of our recognized strata were submitted to Tom Stafford for AMS analysis.
In short, Kelly was correct: the sediment in the first chamber had been thoroughly churned, probably by marmots. Marmot remains are the most common bones identified from Mineral Hill Cave, and subsurface marmot burrows are numerous throughout the cave sediment. All of the charcoal from the first chamber dated to the last 1200 years, and one specimen was dated to 600 BP at a depth of 1.5m below present ground surface. A pronghorn calcaneus dated at about 30,000 BP was stratigraphically above a marmot mandible dated at 13,000 BP.
However, one portion of the sediment in the 5th chamber preserves thinly laminated clays clearly deposited by water. Several bones, including another complete first phalanx of a camel , were found in these stratified clays. Nevertheless, these stratified clays overall were found to contain few bones, although they did provide the main piece of evidence for the water deposition of sediment and debris at various times in the past. While some bones may have been flushed into the cave from the surface over the millenia, taphonomic analysis shows that the 5th chamber likely served as a carnivore den between at least 30,000 and 50,000 BP, and perhaps as long ago as 75,000 to 100,000 BP. The cave currently contains a single entrance directly into Chamber 1, but I think that a second entrance, now collapsed, once existed between the surface and the back portion of the cave.
The organic component of the bones is excellent. I was a bit excited to find out from Stafford that not only did some of the bone date to 40,000 BP or older, but that the bones of that age were so well preserved that they chemically looked similar to modern bone. Jennifer Leonard, a biology graduate student at UCLA is attempting to extract DNA from some of the Mineral Hill Cave bones.
As a result of the stratigraphic analysis and the first series of AMS dates, I concluded that stratigraphic interpretations of the cave sediment could not be trusted to produce chronological sequences. I embarked on a program of additional excavations and procuring as much funding as possible for AMS dating of the bones themselves.
Excavations subsequently were carried out in chambers 1, 2, and 5 in the cave during the summers of 1997, 1998 and 1999. Two units in Chamber 1 and one unit in Chamber 5 produced an abundance of faunal material.
To date, we have received a total of 53 AMS dates from the cave, and seven dates are currently "banked" at Beta Analytic: 43 dates have been returned on bone, six on charcoal, and four on plant macrofossils. In addition, Rhawn Denniston from the University of Iowa has obtained 18 Uranium-Thorium dates from speleothems collected throughout the cave. The results to date show that the bone dates cluster in or near three general time periods: (1) Neoglacial - 2,000-4,000 BP; (2) Pleistocene-Holocene boundary - 9,000-13,000 BP; and (3) significantly older than pre-Glacial Maximum - 30,000 BP+. A total of 31 of the 43 bone dates are Pleistocene-aged, while 12 are Holocene-aged. The vast majority of the speleothems dated beyond 350,000 BP, the limit of the Uranium-Thorium dating technique, indicating that the cave was actively forming stalagmites and stalagtites during or before the Middle Pleistocene. In Don Grayson’s recent review of 34 Late Pleistocene faunal assemblages from the Great Basin, he argued that only five sites have reliable radiocarbon dates associated with them. Of these, only one site has produced a single AMS date on an extinct animal. At a minimum, the Mineral Hill Cave project will produce 50 AMS dates on bone from a minimum of 30 different mammalian, avian, and reptilian species, including 17 AMS dates on extinct animals.
I would now like to present a brief overview of the results to date from analyzes of the fauna from Homestead, Pintwater, and Mineral Hill caves. To do this, I will refer to the seven themes mentioned earlier, and present data which address each of these themes.
(1) Human exploitation of extinct megafauna in the Great Basin remains equivocal.
There is no evidence for human exploitation of extinct megafauna at Homestead, Pintwater, or Mineral Hill caves.
(2) Because no site has been found that behaviorally associates early people with extinct megafauna in the Great Basin, there currently is no support for the ‘Blietzkrieg’ or ‘Overkill’ model to explain the disappearance of many animal species during the Late Pleistocene and Early Holocene in the Intermountain region.
There is no evidence to support the model that humans overhunted extinct Pleistocene megafauna near Homestead, Pintwater, or Mineral Hill caves.
(3) We have learned a great deal about general changes in animal species composition in the Great Basin over the past 20,000 years, but few well-dated Late Pleistocene faunal assemblages have been reported from the region.
Homestead, Pintwater, and Mineral Hill caves represent three of the best dated Pleistocene faunal assemblages in the Great Basin. In addition, all three caves contain significant Holocene faunal assemblages.
Corroborating previous research, all three caves show significant changes in faunal composition through time. At Homestead Cave, a low elevation site in the northern Great Basin, cool and mesic species such as the mountain vole, bushy-tailed woodrat, marmot, and pygmy rabbit were common in the Late Pleistocene strata. These animals suggest a cool and moist Late Pleistocene environment for the northern Great Basin. Additionally, these species persisted in the Homestead Cave area until 8,300 BP, suggesting that the early Holocene of the northern Great Basin was also cool and moist, although as Grayson argues, not as cool or moist as the Late Pleistocene.
At Homestead Cave, the end of the relatively cool and moist early Holocene occurs rather dramatically at 8,300 BP. The local extinction of marmots and pygmy rabbits, the dramatic decline of voles, and the dominance of bones of the desert woodrat compared to the numbers of bushy-tailed woodrat bones all suggest warmth and aridity in the northern Great Basin by 8,300 BP.
Previous faunal records established the presence of pika and marmot, as well as a host of extinct megafauna including jaguar, mammoth, sloth, horse, and camel in the Pleistocene Mojave Desert of the southern Great Basin. Pika was also present in the Pintwater Cave faunal record during the Late Pleistocene and Early Holocene. Pintwater Cave provides the first Late Pleistocene paleontological record of the northern pocket gopher from the region. Short-tailed weasel and grey wolf were also present in the Late Pleistocene deposits of Pintwater Cave, providing the first Pleistocene regional record of the wolf. The largest animal identified from Pintwater Cave was mountain sheep. Mountain sheep bones and dung were found in the lowest level of Unit 3, dated to 32,000 BP.
Similar to Homestead Cave, the Late Pleistocene deposits of Pintwater Cave contained cool and mesic-adapted species. At Pintwater Cave, these species included pika, northern pocket gopher, and mountain voles. These data suggest that the southern Great Basin was also cool and moist during the Late Pleistocene. In addition, these species persisted until 8,300 BP at Pintwater Cave, suggesting a somewhat cool and wet climate for the Early Holocene. However, at about 10,000 BP the chuckwalla appears in the faunal record at Pintwater Cave. This lizard was absent in the Pintwater faunal record before 10,000 BP. Chuckwalla require predictable summer precipitation for survival. Thus, the presence of chuckwalla at 10,000 BP indicates that the southern Great Basin had become warmer with predictable summer precipitation by the beginning of the Early Holocene.
Pintwater Cave continued to show significant faunal changes into the Middle Holocene. At 8,300 BP, pika and the northern pocket gopher became locally extinct. In addition, bones of voles dropped dramatically, and warm, arid species such as desert kangaroo rats dramatically increased in numbers. The most heat tolerant of all North American lizards, the desert iguana, first appears in the Pintwater faunal record after 8,300 BP. Importantly, numbers of chuckwalla continued to increase after 8,300 BP, suggesting that the southern Great Basin was warm with continued summer precipitation during the Middle Holocene, not warm and dry as the faunal data suggest for the northern Great Basin.
Mineral Hill Cave also records significant changes in faunal composition from the Late Pleistocene to the Holocene. During pre-Glacial Maximum times, the central Great Basin supported populations of camel, big-headed llama, at least two species of horse, Bison antiquus, mountain deer, mountain sheep, pronghorn, and, tentatively, American cheetah. Other extralocal and extant animals living in the central Great Basin at this time included marmot, red fox, bobcat, golden eagle, short-eared owl, prairie falcon, pika, coyote, raven, and tundra swan.
None of the extinct large ungulates or carnivores from Mineral Hill Cave date any later than about 30,000 BP, except for a possible short-faced bear phalange. This phalange matches the morphology of short-faced bear phalanges recovered from La Brea. This bone was first submitted to Tom Stafford for AMS dating, and it returned a date of 9,960 +/- 50 BP. Thus, this date would suggest that we can be confident the bone dates no earlier than 10,060 BP. Because of the possible Holocene age of this bear, the bone was subsequently submitted to Beta Analytic for dating. Beta’s date was 9,710 +/- 40 BP, which would place the bear unequivocally in the Early Holocene. If this unequivocal bear bone can be confidently identified as short-faced bear, then there is a good chance that this animal survived in the central Great Basin several millenia after the first arrival of people to the Intermountain region. It would also represent one of the few cases of extinct megafauna surviving past 10,000 BP in North America. We are currently joking that the presence of short-faced bears in the central Great Basin during the early Holocene is the reason why Dave Thomas could not find sites dating before 7,000 BP in this region.
(4) There are similarities and differences between the northern and southern Great Basin in the nature and timing of faunal changes between the Late Pleistocene and Middle Holocene; as a result, we are just beginning to understand the climatic implications of these data, and by extension, the precise effects these changes may have had on the earliest inhabitants of the Basin.
As mentioned earlier, the presence of pika and northern pocket gopher, the abundance of vole specimens, and the absence of warm-adapted species such as the desert kangaroo rat, chuckwalla, and desert iguana in the Pleistocene deposits of Pintwater Cave all suggest a cool and wet climate for the southern Great Basin before 10,000 BP. Barring a lengthy lag time for the migration of the chuckwalla from its presumed full-glacial homeland to the south, the absence of this lizard until the latest Pleistocene is consistent with the predominantly winter precipitation model for the southern Great Basin during late-glacial through Younger Dryas time, or from approximately 18,000 to 10,500 BP. These data are consistent with paleovegetation records, pluvial lake cycles, and paleohydrologic studies for the region. Grayson’s work with the fauna at Homestead Cave also indicates a cool and wet Late Pleistocene for the northern Great Basin. The presence of numerous large grazers and browsers, together with small mammals such as pika from Mineral Hill Cave, also suggest a cool and moist Late Pleistocene environment for the central Great Basin.
Based on the 10,000 BP date for the earliest chuckwalla remains in Pintwater Cave, the switch from predominantly winter precipitation to a more summer monsoonal flow in the southern Great Basin likely occurred between 11,000 and 10,000 BP., which accords with Barbara Woodcock's paleovegetation study from the Death Valley region. A relatively warm latest Pleistocene and Early Holocene climate, coupled with increased sand dune activity, is indicated by the presence of the desert kangaroo rat in the Pintwater record between approximately 10,000 and 9000 BP.
The timing of the onset of the present summer monsoonal regime in the southern Great Basin and the possible extension of these summer rains into the northern Great Basin during the early and middle Holocene have been a matter of debate. Bob Thompson argued that the Great Basin experienced increased summer monsoonal flow during the early Holocene, whereas Grayson’s work at Homestead Cave shows that the northern Great Basin was cool and wet, not warm and wet, during this time. Based on recent research at Homestead and Pintwater Caves, the northern Great Basin appeared to be relatively cool and wet during the Early Holocene between 10,000 and 8,300 BP, while the southern Great Basin was relatively warm and wet during this same time period.
Interestingly, while the Early Holocene climate of the northern Great Basin appears to have been cooler than the southern Great Basin, both regions seem to show a nearly synchronous onset of the warmer temperatures of the Middle Holocene at 8300 BP. However, while the northern Great Basin probably was warm and dry during the Middle Holocene, the Pintwater Cave data suggest a continuation of monsoonal rains in the southern Great Basin, as the remains of chuckwalla became increasingly abundant beginning 8300 BP., and they remained abundant at 7350 BP. Spaulding, however, argued for relative aridity in the southern Great Basin by 6800 BP.
It is becoming increasingly clear that the changeover from Pleistocene ecosystems to more modern ecosystems did not occur in the northern or southern Great Basin until the middle Holocene, and the Homestead and Pintwater Cave data corroborate these interpretations. It is also becoming increasingly clear that climatic interpretations for the northern Great Basin cannot be assumed to hold true for the southern Great Basin, and vice versa.
(5) We do not yet know the overall health of the latest Pleistocene populations of now-extinct megafauna, carnivores, and birds which were present at the time of early human occupation in the Great Basin.
This problem continues to be true today. Several years ago Dave Meltzer and Don Grayson noted that while 10,000 BP marked the end of the Pleistocene extinction process, these data by themselves do not inform on the tempo and mode of that process. Thus, we need well-dated faunal assemblages from the post- and pre-Glacial Maximum periods to determine the relative health of extinct species that were present at the time of first contact with humans.
Mineral Hill Cave helps fill a gap in our knowledge of pre-Glacial Maximum faunal composition in the central Great Basin. With many large grazers and browsers such as sheep, deer, pronghorn, camel, llama, bison, and horse dating between 30,000 and 50,000 BP, these data may suggest a very productive ecosystem filled with healthy herds of hooved animals before 30,000 BP. It may be significant that of the two Pleistocene dates on hooved animals that post-date 18,000 BP, both are from the extant pronghorn. More dates are needed, but it is possible that Mineral Hill Cave documents a reduction in large mammal biomass sometime between 30,000 and 20,000 BP.
(6) We know much more about Great Basin ecosystems of the last 20,000 years than we do about the ecosystems of pre-Glacial Maximum times.
This still holds true today, but Mineral Hill Cave helps fill this gap. The Homestead Cave faunal record ends at about 11,000 BP, and the the vast majority of the Pintwater Cave faunal record is from the past 15,000 years. The vast majority of the Pleistocene specimens from Mineral Hill Cave date before 30,000 BP. Interestingly, of the 43 AMS dates on bone thus far, none date between 20,000 and 30,000 BP. A total of 28 dates range between 30,000 and >50,000 BP, while only 5 dates range between 9,000 and 17,000 BP. As just mentioned, Mineral Hill Cave indicates a very productive ecosystem filled with a high diversity of large mammals before 30,000 BP.
(7) Our knowledge of the anatomical and behavioral similarities and differences between Pleistocene-aged animals and their Holocene-aged counterparts is insufficient for meaningful archaeological and paleoecological analyzes.
Previous studies have indicated that the habitat requirements of modern mammal species may not always be appropriate analogues for their pre-Middle Holocene distributions. For example, Jim Mead has argued that Pleistocene-aged pika remains are found in more diverse habitats than their Holocene-aged counterparts. Pintwater Cave records similar information for the chuckwalla. The chuckwalla is today closely associated with rocky habitat and creosote vegetation in the northern Mojave Desert, yet this lizard migrated into the Pintwater region ca. 10,000 BP., perhaps 3000 years before the establishment of creosote in the region.
Additionally, many of the Pleistocene-aged mammal bones from Mineral Hill Cave are much larger than the bones of their modern counterparts. For example, I have been correctly determining the relative age of mountain sheep bones from Mineral Hill Cave based on size alone. Many of the Pleistocene-aged postcranial bones of mountain sheep are nearly double the size of their modern counterparts. Size reduction in mountain sheep at the end of the Pleistocene has been noted in specimens recovered from Arizona and Colorado. The Mineral Hill assemblage shows that this phenomena also occurred in the Great Basin. If modern mule deer evolved from the Pleistocene mountain deer, then deer went through a similar reduction in body mass as did mountain sheep in the Great Basin. Larger, Pleistocene-aged postcranial bones are also evident in the Bison remains from Mineral Hill Cave.
However, the Mineral Hill Cave data indicate that pronghorn did not follow this same process. The pronghorn bones of 50,000 BP are about the same size as their modern counterparts. If ancient populations of pronghorn subsisted largely on sagebrush, as is the case with modern pronghorn, then an unchanged diet from the Pleistocene into the Holocene may help explain this phenomenon. Grass constitutes less than 5% of the modern diet of pronghorn anywhere in the west, so pronghorn probably were not faced with switching a diet based on C3 grasses to the less nutritious C4 grasses which came to dominate the Holocene-aged understory in many areas of the Great Basin. Sagebrush probably was relatively common throughout much of the Great Basin over the past 50,000 years, and probably supported populations of pronghorn that underwent little or no dietary change. Additionally, pronghorn are built for speed, and any increase in body mass may have placed those animals at a selective disadvantage on the open ground in which they feed, particularly if they were being pursued by cheetah-like cats.
The most common large mammal bones from Mineral Hill Cave were from horses, but like the rest of North America, horses appeared to have been extinct in the central Great Basin before the close of the Pleistocene.
In conclusion, Homestead Cave, Pintwater Cave, and Mineral Hill Cave fill important gaps in our knowledge base of Pleistocene to Middle Holocene-aged faunal assemblages in the Great Basin. Many publications are forthcoming on these sites. More data are needed from new sites to continue research about the extinct ecosystems of the Great Basin and how early people adapted themselves to these ecosystems.