Itt

>35,000

Driftwood at base

of section below 65 cm; grid I-I, east trench of section below 65 cm; grid I-I, east trench source: See Robins, Martin, and Long pp. 117-30 in Euler, ed., 1984.

extinct goats ate a variety of shrubs, forbs, and grasses (Robbins, Martin, and Long 1984). Data from other sites confirm this. According to Jim Mead, Mary Kay O'Rourke, and Terri Foppe (1986), grasses, including Sporobolus, Festuca, Orizopsis, and Agropyron, were a major part of the diet of the extinct goats, along with Ceanothus (buck-brush) at certain times. On occasion the extinct goats ate Douglas fir (Pseudot-suga) (Mead and others 1987). Harrington's goats at Rampart Cave ate a good deal of juniper (Clark 1977). Rocky Mountain goats dine in the subalpine zone of the northern Rockies, browsing on mountain conifers such as spruce (Peek 2000).

At Stanton's Cave, as at Rampart, packrat middens yielded abundant juniper and other plant remains. Juniper trees must have ranged much closer to both caves than they do at present. The closest junipers I found to Stanton's Cave were far beyond packrat-foraging range. Judging by the fossil pollen record as well, the dominant woody plants outside Stan-ton's Cave over 10,000 radiocarbon years ago were probably sagebrush, shadscale, and juniper (Robbins, Martin, and Long 1984). The packrat middens indicate some reduction in juniper and sagebrush in the inner gorge of the Grand Canyon around 11,000 radiocarbon years ago, when the goat went extinct. However, a vast area of juniper and sagebrush persists in Arizona and Utah today. As far as one can determine from the remarkable midden records, the habitat and food plants of Harrington's goat persist, even if the animals do not.

Stanton's Cave also harbored other fossil evidence of the late-Quaternary change in climate: a quantity of ancient driftwood. In earlier times an archaeological team might well have tossed it out. Fortunately, as we have seen, Bob took a wide view, and he invited Wes Ferguson of Arizona's Tree Ring Laboratory to examine the wood. Wes (Ferguson 1984) identified it as mainly Douglas fir and cottonwood (Populus). Radiocarbon dating put the age of some samples at more than 40,000 years (Hereford 1984, 105). Cottonwood presently grows wherever it finds slack water along the Colorado River. Thus its occurrence in the more than 40,000-year-old driftwood provides little ecological insight. On the other hand, Douglas fir is presently found upstream in Utah at elevations of 7,000 to 8,500 feet. In Stanton's Cave, the abundance of Douglas fir, combined with the absence of pinyon (according to Ferguson; personal correspondence), the main conifer presently found in beach wrack along the Colorado in the Grand Canyon, at least until the construction of Lake Powell, indicates cooler times when Douglas fir rather than pinyon grew closer to the cave and would have been a major component of its driftwood. Still, it must have taken an extraordinary event, a discharge 33 times the largest historic flood of the Colorado River, to deposit driftwood in Stanton's Cave (Richard Cooley in Hereford 1984, 102).

Stanton's and other caves in the Grand Canyon yielded important records bearing on the mysterious megafaunal extinctions. Grand Canyon caves contained bones not only of large mammals, but also of two giant avian scavengers of those mammals: condors and the even larger tera-torns. Stanton's Cave held more than 68 bones of the California Condor (Gymnogyps californianus, mainly the large extinct taxon, Gymnogyps californianus amplus). Perhaps as many as eight individual condors are represented (see Rea and Hargrave 1984). Elsewhere in the Grand Canyon, a cave exploration team found not only more bones, but also the remains of a fossil nest of a Quaternary condor, revealing what the young birds were fed.

Early investigators believed that the condor fossils they discovered in the Southwest were quite young. Based on their superficial position, in some cases seemingly associated with Anasazi artifacts roughly 1,000

years old, and their fresh appearance ("not petrified"; Phillips, Marshall, and Monson 1964), ornithologists concluded that condors had inhabited the Southwest, including the Grand Canyon, not long ago, during the last millennium or two. This conclusion appeared to be in accord with seven sight records in Arizona and southern Utah reported from the late nineteenth and early twentieth centuries. In March of 1881, for example, a condor was reported from Pierce's Ferry on the Colorado River just west of the Grand Canyon. Alan Phillips and other ornithologists assumed that the birds reported historically were the last representatives of a late-prehistoric population.

Logical as this reasoning seemed, in the end it was to prove once more the importance of radiocarbon dating. Dates on the youngest condor fossils in the canyon were around 11,000 radiocarbon years old. With three exceptions, their dates coincide with those obtained from remains of extinct mammoths, horses, bison, and Harrington's goats (Emslie 1987), and with the association of Clovis points with mammoths in southern Arizona. In 1984, in a remarkable search involving cliff-climbing into otherwise inaccessible caves, Emslie, Mead, and Coats located condor remains in eight such caves in the inner gorge. The youngest in a suite of 18 dates on fossils from New Mexico and West Texas as well as the Grand Canyon was 9,580 ± 160 (AA-790, Emslie 1987). On the surface of a cave much smaller than Stanton's, Emslie found a condor skull so well preserved that it looked fresh (see plate 11), its keratinous beak still attached and its soft parts as hard and dry as beef jerky. An accelerator sample on the soft parts showed the skull to be 12,540 ± 790 (AA-692, Emslie 1987; Martin 1999, 272). The oldest date obtained by Emslie was over 22,000 radiocarbon years. On a preserved condor feather, Larry Coats subsequently obtained a date of over 42,500 years (Coats 1997). California Condors nested in the Grand Canyon during the late Pleistocene, ending at least 9,000 years ago, with no irrefutable evidence (radiocarbon dates on condor remains) of their nesting since, until reintro-duced birds began nesting in the twenty-first century.

The dates suggest that after extinction of the mammalian megafauna in the Southwest, condors did not linger very long. In addition to the Pacific Coast, with its rich supply of dead cetaceans, pinnipeds, and salmon, perhaps they persisted in regions that supported large herds of bison. However, there is every reason to suspect that with the disappearance of mountain goats, equids, mammoths, and bison from the Colorado Plateau, the largest avian scavengers such as condors and teratorns lost much of their food supply. Apparently mule deer were the main surviv-

Plate 11. Skull of i3,ooo-year-old California Condor from small cave downstream from Stanton's Cave, ca. 1985. Photo by the author.

ing large herbivores in the region. There may not have been enough mule deer and rabbit carrion to support any avian scavengers larger than Turkey Vultures.

If the fate of condors was tied to that of large animals, here was more evidence for the extinction of North American megafauna close to or possibly 1,000 years later than that magic number of 11,000 radiocarbon years ago. The three younger dates on condors reported by Emslie (1987) could reflect lingering opportunities for scavengers feeding on remains of bison or lesser beasts that survived the extinctions.

Another of Steve Emslie's 1984 discoveries further supports this conclusion regarding condor food supply. In a packrat midden in the richest cave, Sandblast, Emslie found bones of at least five condors. Bone porosity indicated that some birds were fledglings still in the nest. Food scraps, feathers, and eggshell fragments also indicated nesting. Near a nest were bone fragments of extinct animals: bison, camel, horse, mammoth, and Harrington's goat. According to Emslie, "The bones of large mammals associated with condor remains possibly represent food bones brought to the cave by the condors. Bone fragments of similar size and skeletal elements including phalanges, carpals, tarsals, teeth, and mandibles of horses, cows, sheep and deer, are found in nests of G. californi-anus today" (1987). Despite his caution, there is good reason to believe that Emslie had made an extraordinary discovery of what condors fed to their young before extinction of the late-Quaternary megafauna. How else would such bones have found their way to a condor nest in an in

accessible cave? Bone fragments of cattle, Bos taurus, are the most common item in modern condor nests (Collins, Snyder, and Emslie 2000). Bones and teeth supply calcium phosphate to meet the dietary needs of the young.

How, then, to explain the historic sightings of condors in the Southwest, at least 8,000 years after any fossil record of their presence? In the absence of any specimens, the sight records are unsubstantiated. If they are valid they might represent occasional vagrant condors from the Pacific Coast. Condors may also have spread briefly eastward from California as a result of European settlement. Diseases accompanying European contact (Diamond 1997) devastated Native American populations, thus potentially relaxing predation on wildlife and increasing the number of carcasses, to the benefit of predators and scavengers, including condors. Later, the development of Spanish ranching in California in the 1700s and the overstocking of an unfenced range by early Anglo ranchers in the Southwest in the 1880s would also have yielded an ample food supply for condors and other scavengers, more ample than any since the late Quaternary. Under these circumstances condors might have increased in number and perhaps spread eastward, accounting for historic sight records. Nevertheless, in the absence of specimens, these may be questioned. In the twentieth century, fencing and improved range management reduced livestock mortality and thereby diminished resources for scavengers, including condors.

As for the teratorn, that was a discovery I was privileged to witness. In September 1970, toward the back of Stanton's Cave, beyond the zone of artiodactyl pellets and thus beyond that part of the cave with enough light to be frequented by goats and mountain sheep, graduate students Martha Ames and Barney Burns helped me sample cone-shaped fossil packrat middens. The middens were in an unusual spot, in the middle of the cave floor. Perhaps the rats felt safe in the dark from their visually dependent predators and relied on their scent-marked pathways to return to their nests.

One of the middens incorporated a large bird bone. The Los Angeles County Museum identified it as a humerus (wing bone) of the giant scavenger-predator Teratornis merriami. Not known previously from Arizona, the species had twice the mass of living condors, with a wingspan (including primary feathers) of about 12 feet, 2.5 feet more than that of a condor (Mawby 1967).

Fossil pollen in matrix scraped from the teratorn bone proved to be 33 percent sagebrush (Artemisia), a higher count than that found in

Holocene cave earth from Stanton's (Robbins, Martin, and Long 1984) or in the modern pollen rain in the inner gorge of the Grand Canyon (King 1973; Mead, O'Rourke, and Foppe 1986). In other words, on the basis of pollen analysis we could expect a pre-Holocene radiocarbon date. Accelerators had yet to be developed, and a large sample, in this case the entire humerus, was needed to provide enough carbon for age determination. After preparation of a plaster cast copy, the humerus was combusted and radiocarbon dated at 15,230 ± 240 (A-1238). This date fell within the range of radiocarbon measurements on other extinct animals, including condors. If condors had difficulties in opening the body cavity of mammoths, bison, or other large carcasses, perhaps the teratorns helped solve the problem. Ecologist David Burney tells me he has seen Lappet-faced Vultures in East Africa rip open carcasses, to the benefit of less powerful scavenging birds.

Quaternary-age fossils of equids, including extinct species, are also found in caves in the West (Harris 1985), though less commonly than fossils of Shasta ground sloths, Harrington's goats, or condors. They include not only bones but also keratinous hooves the size of those of burros—and, provocatively, they first turned up at a time when living wild burros were scheduled to be eliminated from the Grand Canyon (see chapter 10). Fossil equid hooves are known from several caves in Arizona, including Rampart, Stanton's, and Sandblast; from Gypsum Cave and the Eleana Range in Nye County, Nevada; and from sites farther north.

Radiocarbon dates on well-preserved horse metapodials (foot bones) from Alaska range from 20,000 to 12,000 years. Mitochondrial DNA analysis has identified these fossils as Equus caballus, the same species at present found in Eurasia and wild in the lower 48 states (Vila and others 2001). Direct dates on two hooves associated with the ground sloth dung deposit in Gypsum Cave yielded the following results: large (quarter horse-size) hoof (A-1271), 25,000 ± 1,300; small (burro-size) hoof (A-1441), 13,310 ± 210. A date on an Equus hoof associated with a stratified sequence of packrat middens from the Eleana Range is 11,210 ± 400, presumably close to the time of equid extinction (Spaulding 1990). Two horse bones collected by Emslie from the fossil condor nest at Sandblast Cave are very likely of the same age as the immature condor bones, 9,580 ± 160 to 13,110 ± 680 (Emslie 1987). According to Emslie, they were among the food scraps brought to the young by their parents. In at least one case, a pair of condors now nesting in Grand Canyon National Park reoccupied a site with evidence of prior, I would suggest late-Pleistocene, occupation.

By 1982 I had almost given up hope of finding my dream: an unstudied cave rich in paleoecological treasure. Then the sun god, Ra, finally delivered on the prayers I had sent up at Bat Cave in 1958. Zoologist Steve Carothers and his friend Loren Haury (the son of Professor Emil Haury, who excavated the first Clovis sites in Arizona), along with National Park Service rangers Larry Belli and Charles Berg, made a monumental discovery. Searching for wild cattle in the Glen Canyon National Recreation Area in southern Utah, they came upon a relatively undisturbed cave, a huge dry rock shelter like a cathedral, with one side open to the sky. Inside, in the spoil of a pit dug by pothunters, were the trampled remains of a bolus that clearly had been of unusual size. Its coarse texture did not resemble that of cow or horse manure. Loren Haury thought it might be dry dung of a ground sloth. Maybe, he thought, it would interest those weird devotees of extinct animal manure at the Desert Lab, who still had not stopped complaining about the sloth shit lost six years before in the Rampart Cave fire.

For weeks a plastic bag containing the precious sample bounced around, along with other field trip leftovers, in the back of Steve's truck. Eventually Steve passed the bag on to Art Phillips at the Museum of Northern Arizona in Flagstaff. Art sent it down to the Desert Lab with a note to the effect that it did not look right for dung of the Shasta ground sloth. It contained what appeared to be masticated segments of coarse grasses, which (except for tall aquatics such as Phragmites) the ground sloth rarely ate. Also, the grass stems were up to 5 centimeters (2 inches) in length, longer than the clipped, short plant stems seen in ground sloth dung. The latter, like horse dung, is uniform in texture, and only 50 to 60 percent, rather than 80 to 90 percent, of the fragments are over a centimeter in length (Mead, Agenbroad, and others 1986).

None of the group of Quaternary ecologists at the Desert Lab at the time, including Julio Betancourt, Owen Davis, Pat Fall, Emilee Mead, Jim Mead, Mary Kay O'Rourke, Bob Thompson, Ray Turner, Tom Van Devender, and Bob Webb, could claim to have seen anything like it before. None of the specimens in our sizable reference collection of scats, fossil or modern, resembled the mystery dung sample, with one striking exception: dung samples from African elephants (Loxodonta africana) that I had collected in Tsavo Park in Kenya in 1965.

In February 1983 Jim Mead and Larry Agenbroad, a geology professor and proboscidean specialist at the University of Northern Arizona, received National Park Service approval to visit the cave, evaluate its contents, and, if warranted, dig a small test pit. They were guided by Larry

Plate 12. Mouth of Bechan Cave with riparian vegetation in foreground, March 1983. Photo by the author.

Plate 12. Mouth of Bechan Cave with riparian vegetation in foreground, March 1983. Photo by the author.

Belli and accompanied by Utah State Archaeologist Dave Madsen and Utah State Paleontologist Dave Gillette. They returned bursting with enthusiasm. From a test pit near the north wall they had extracted two large dung balls. One, designated M-i, measured 230 by 170 by 85 millimeters (9 by 7 by 3 inches); the other, M-2, was 225 by 175 by 80 millimeters.

According to Joe Dudley (1999), mature African elephant bulls produce the largest dung balls of any elephant, 190-230 millimeters (7 to 9 inches) in diameter. The dung balls from the locality to be known as Bechan Cave (derived from a Navajo word for "big feces") were somewhat flattened from trampling or from the weight of overburden. But their size greatly exceeded that of our Shasta ground sloth samples and approximated those of samples from female African and Asian elephants. Also unlike our ground sloth samples, the Bechan Cave boluses were not segmented, were not encased in a dried mucosoid coating, and with rough handling threatened to fall apart. We began to suspect that this was the spoor of America's second-largest extinct mammal—the Columbian mammoth. (The largest, the imperial mammoth, is very rare or absent from the fossil record in Arizona.)

The first two radiocarbon measurements on the dung yielded the following results: M-i (A-3212), 11,670 ± 300, with a delta carbon 13 of 23.2 percent; M-2 (A-3213), 12,900 ±160 with the same delta carbon

13, 23.2 percent (Davis and others 1984). Although the dates were close to being significantly different, the carbon 13 values of the dung balls were identical. Pollen samples from the two, analyzed by Owen Davis, were also similar, within expected statistical error. The pollen and delta carbon 13 similarities, plus the fact that both dung balls came out of the same small test pit, led me to suspect that both were dropped at the same time by the same individual.

In the spring of 1983 Owen and I returned with Larry and Jim to help them plot an isopatch (thickness of deposit) map based on the contents of 49 auger holes. The probes disclosed a buried organic layer, mainly mammoth dung, up to 16 inches thick (Agenbroad and Mead 1996) and estimated to contain 14,000 cubic feet of dung, more than the deposit at Rampart Cave before the fire.

Fourteen accelerator radiocarbon dates on boluses collected that spring range from 11,870 ± 140 to 12,880 ± 140 and average 12,450 years. It is possible that part of the dung blanket was deposited rapidly, perhaps in no more than a few days, by a small matriarchal herd seeking shade in the hot season. Larry Agenbroad and Jim Mead (1996) accept the maximum and minimum dates as valid, which would indicate occupation of Bechan Cave by mammoths at least sporadically over 1,800 years, ending 11,600 years ago. In either case, the data suggest abandonment of the cave shortly before 11,000 radiocarbon years ago, unless we failed to notice and date a younger layer. In Bechan Cave the last boluses deposited were not as obvious as in the case of the surface dung balls at Rampart, a much smaller collecting surface to sample. I am not confident that we can determine the time when mammoths last entered this cave.

Beyond one tooth of a medium-sized bovid, probably the shrub ox Euceratherium, we found no bones of extinct megafauna at Bechan Cave. We did find coarse hairs matching those from woolly mammoths in Siberia and Alaska. While it seems certain that all the dung we examined came from the Columbian mammoth, there is a remote possibility that some other megaherbivore, perhaps a medium-large ground sloth, such as Paramylodon, was responsible for part of the deposit. A Shasta ground sloth could have been the source of a small dung ball containing an acorn.

Nearly one-third of the plant macrofossils Owen Davis found in the dung samples were sedge (Carex) seeds (achenes) from marshy habitats or standing water. These were followed in abundance by cactus spines (17 percent)—the first evidence, to my knowledge, that American mammoths ate cactus—and grass florets (12 percent). Wood fragments in-

eluded birch (Betula, 12 percent), rose (Rosa, 11 percent), saltbush (Atri-plex, 5 percent), sagebrush (Artemisia, 3.5 percent), and smaller amounts of blue spruce (Picea pungens), snowberry (Symphoricarpos), and red osier dogwood (Cornus stolonifera). The fossil deposit even yielded the spruce cone gall, Chermes cooleyi (illustrated in Davis and others 1984). Associations of some of the plants indicated in the dung samples, including blue spruce and water birch, are found today along streams in the Henry and other mountains in southern Utah at elevations of 7,300 to 8,000 feet, 3,000 feet higher than Bechan Cave. Some of the plant fossils associated with the Bechan Cave dung are also extralocal. Evidently, the deposit accumulated at a time when the climate was cooler than at present and trees or shrubs such as blue spruce, water birch, and red osier dogwood grew in riparian habitat outside the cave.

Not all the twigs and sticks from the dung unit necessarily came from the mammoths. Several other kinds of animals, especially the large packrat Neotoma cinerea, very likely introduced twigs and branches. Nevertheless, African elephants can switch from grazing to browsing according to season and habitat. Possibly some of the woody material in the dung blanket represents the digestive residue of browsing Columbian mammoths.

To obtain a better estimate of the mammoths' diet, Owen Davis dissected 25 fragments of boluses under 7X magnification (Davis and others 1985). The identifiable plant remains were removed from the matrix and weighed. Over 95 percent of the boluses constituted a graminoid (grassy) matrix composed of crushed culms (stems) and leaves of grasses, sedges, and rushes (Juncus), along with small amounts of sand. The remainder was dominated (88 percent) by saltbush wood and fruits, followed by sedge achenes (5 percent), cactus parts (4 percent), and wood of sagebrush (1 percent).

The presence of saltbush, cactus, and sagebrush indicates dry upland vegetation when the dung layer was being deposited. Pollen analysis supports the interpretation that upland vegetation at the time was sagebrush steppe with blue spruce and water birch along the drainages (Agenbroad and Mead 1996; Davis and others 1984). At present the upland supports xerophytic shrubs, especially blackbrush. Wetlands harbor cottonwood, willow, sedges, and other aquatic herbs. In Davis's words, "The abundance of aquatic plants [especially sedges and rushes] in the dung demonstrates the importance of the riparian community to the diet of the mammoths. . . . Riparian vegetation near Bechan Cave may have attracted mammoths to the site. At the time Paleoindians reached southern Utah, mammoths and other megafauna may have been concentrated along streams and other mesic sites in an otherwise arid landscape" (Davis and others 1985).

Bechan Cave also offered an opportunity to test another analytical technique. In large numbers, herbivores may leave a trace in the fossil record not only of pollen, but also of spores. Ponds surrounded historically by heavily grazed land capture runoff rich in manure. This is the substrate for a distinctive fungal spore type known as Sporormiella, a small, smooth-walled spore in the shape of a pistol bullet with a sigmoid aperture. Davis and Pete Mehringer first reported Sporormiella from Wildcat Lake in eastern Washington, near a historic sheep pasture. Then Davis found it in fossil deposits of 16,000 to 12,000 radiocarbon years ago, just predating the megafaunal extinctions. At Bechan Cave he recovered large numbers of Sporormiella spores from the mammoth dung boluses themselves: 2,390 spores per cubic centimeter, equivalent to 16 percent of the pollen count (Davis 1987). Robinson (2003) is finding Sporormiella in lake muds associated with fossil bones of mastodon and stag moose (Cervalces). After mastodon extinction the spores decline, as Davis (1987) anticipated.

It turns out that all of the Colorado River drainage was mammoth country, from low elevations in southwestern Arizona near the Sea of Cortez to high elevations (9,000 feet) at the headwaters of the Colorado River in northern Utah. Larry and Jim found fragments of mammoth dung in four other Utah rock shelters. The youngest samples dated at 9,000 to 11,000 radiocarbon years, the oldest at 26,140 ± 670 and 28,290 ± 2,100 years (Mead and Agenbroad 1992). (Because mammoth dung is spongy, not compact, there are a variety of ways it might be contaminated by younger organic material, which would account for dates of less than 11,000 radiocarbon years.) Meanwhile, Dave Madsen and Dave Gillette had jurisdiction over the Huntington Canyon site, near the crest of the Wasatch Plateau in central Utah. At 9,000 feet, this is to my knowledge the highest elevation at which extinct megafauna have been found anywhere in the United States. Reliable radiocarbon dates on bone or-ganics of 11,200 and 10,800 years ago dated an old mammoth, suffering arthritis and fused vertebrae, and a giant short-faced bear.

Spectacular as the Bechan Cave finds were, it was Dick Hansen (1980) who had first identified fossil dung of a mammoth. In the summer of 1975 Jesse Jennings led a University of Utah field school at Cowboy Cave in Wayne County, Utah. Located at 5,800 feet in a short, nameless box canyon near Canyonlands National Park, the cave harbored a stratified cultural deposit up to 5 feet thick. The deposit proved to be rich in perishable artifacts such as sandals, basketry, medicine bags, and prehistoric shelled corn, suggesting seed stock. A test pit also revealed chopped plant remains in a culturally sterile unit at the base. Radiocarbon dating proved these to be at least 3,000 years older than the oldest cultural remains in the cave. Five dates on the material ranged from 11,020 ±180 (A-1660) to 13,040 ± 440 (A-1654) years. Although in reverse stratigraphic order, the values are conformable with the end of the reign of the late-glacial megafauna. Geof Spaulding and Ken Petersen (1980) suspected a clerical error was responsible for the reversal. The portion of the deposit associated with the dated material yielded both pollen and macrofossil evidence of spruce and Douglas fir, trees now found only at higher elevations.

Most of the identifiable residue, rich in finely chewed and digested grasses, looked like cow manure and was attributed to bison. Jennings sent samples of the dung to Dick Hansen's lab. It reported 73 percent dropseed (a grass in the genus Sporobolus) and 12 percent sedge. Modern bison eat almost exclusively grasses and sedges (Shaw and Meagher 2000). Three large boluses that Hansen believed to represent mammoth yielded even more dropseed, 95 percent. Two samples identified tentatively as horse also yielded 95 percent dropseed, suggesting that instead of horse they too might be mammoth dung. A broken piece of tusk roughly 4.5 inches in length, recovered from the base of the dung blanket, supported Hansen's identification of mammoth dung. Hansen also suspected the presence of Pleistocene Equus. The samples in storage at the University of Utah deserve DNA testing for the kinds of extinct animals once present in Cowboy Cave.

Many more fossil sites in Arizona and adjacent states feature mammoth remains. Others provide support for the overkill theory by linking the mammoths to the earliest hunters in America, the Clovis people. Nevertheless, some archaeologists have claimed that there should be more than are known. As I learned in the 1950s in Canada, many archaeologists search for the oldest. Recently some have proposed that the First Americans crossed the Atlantic in relatively quiet water between icebergs of glacial age. Others propose migration down the west coast of North America to South America. The traditional view of entry from Siberia through Beringia and into Alaska, with eventual passage through an icefree corridor during deglaciation, is considered passé in some circles, whose members favor a coastal entry past melting glaciers on the Pacific coast of southern Alaska and Canada.

The heart of the argument for me is that late-Quaternary climatic change, while impressive, is essentially no different from what we see in many, many swings from cold-dry to warm-wet and dusty to dust-free climates in the last 700,000 years or so. Unless oceanographers, ice-core stratigraphers, and climatologists find some unique event, the classic approach to explaining Quaternary extinctions by some physical means is inoperable.

Human involvement in the extinction process also encounters objections. Is the chronology tightly timed to the spread of Clovis hunters? Why are there not more kill sites? We will return to these issues in the latter half of this effort at following John Alroy's call.

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