Blame North America Megafauna Extinction On Climate Change, Not Human Ancestors

Blame North America Megafauna Extinction On Climate Change, Not Human Ancestors

Even such mythical detectives as Sherlock Holmes or Hercule Poirot would have difficulty trying to find the culprit that killed the mammoths, mastodons and other megafauna that once roamed North America.
Scientists have been picking over the bones and evidence for more than three decades but can not agree on what caused the extinction of many of the continent's large mammals. Now, in two new papers, a University of Washington archaeologist disputes the so-called overkill hypothesis that pins the crime on the New World's first humans, calling it a "faith-based credo" that bows to Green politics.

"While the initial presentation of the overkill hypothesis was good and productive science, it has now become something more akin to a faith-based policy statement than to a scientific statement about the past," said Donald Grayson, a UW anthropology professor

Writing in the current issue of the Journal of World Prehistory and in a paper to be published in a forthcoming issue of the Bulletin of the Florida Museum of Natural History, Grayson said there are dangerous environmental implications of using overkill hypothesis as the basis for introducing exotic mammals into arid western North America."

He looks askance at the idea of introducing modern elephants, camels and other large herbivores into the southwest United States. "Overkill proponents have argued that these animals would still be around if people hadn't killed them and that ecological niches still exist for them. Those niches do not exist. Otherwise the herbivores would still be there."

If early humans didn't kill North America's megafauna, then what did? Grayson points to climate shifts, during the late Pleistocene epoch, which ended about 10,000 years ago, and subsequent changes in weather and plants as the likely culprits in the demise of North America's megafauna. The massive ice sheets that covered much of the Northern Hemisphere began retreating.

In North America, this icy mantle prevented Arctic weather systems from extending into the mid-continent. Seasonal weather swings were less dramatic and didn't reach as far south as they presently do. But with this change, the climate became more similar to today's, marked by cold winters and warm summers.

As a result, an unusual patchwork aggregation of plant communities ceased to exit and there was a massive reorganization of biotic communities. At the same time, new data developed by Russell Graham, a paleontologist with the Denver Museum, shows that small mammals such as shrews and voles were moving about the landscape and becoming locally extinct. And there were the extinctions of some 35 genera of large North American mammals, including horses, camels, bears, giant sloths, saber-toothed cats, mastodons and mammoths.

The overkill hypothesis was proposed by retired University of Arizona ecologist Paul Martin in 1967 and its basic arguments haven't changed since. It claims large mammal extinctions occurred 11,000 years ago; Clovis people were the first to enter North America, about 11,000 years ago; Clovis people were hunters who preyed on a diverse set of now-extinct large mammals; records from islands show that human colonists cause extinction; therefore, Clovis people caused extinctions.

"Martin's theory is glitzy, easy to understand and fits with our image of ourselves as all-powerful," said Grayson "It also fits well with the modern Green movement and the Judeo-Christian view of our place in the world. But there is no reason to believe that the early peoples of North America did what Martin's argument says they did."

First of all there is no compelling evidence that the majority of the extinctions occurred during Clovis times, said Grayson. Only 15 genera can be shown to have survived beyond 12,000 years ago and into Clovis times.

For 30 years, overkill proponents have assumed that since some genera can be shown to have become extinct around 11,000 years ago, all the big North American mammals became extinct at that time, he said.

"That's an enormous assumption, even though there is no compelling evidence of it in North America," Grayson said.

He also said overkill proponents have consistently ignored the possibility that the Clovis people were not the first humans in the New World. They reject evidence from a site in Monte Verde, Chile, showing human occupation that dates some 12,500 to 12,800 years ago. Monte Verde also has yielded some material that may push human occupation back to 33,000 years before the present.

Well-accepted Clovis sites dating between 10,800 and 11,300 years ago have been found in North America, and distinctive, fluted projectile points mark this culture. Clovis artifacts have been found with mammoth remains in more than a dozen sites across the Great Plains and the southwestern United States.

Grayson said there is no reason to doubt that these people scavenged and hunted large mammals. But he cautioned that while mammoths, mastodons, horses and camels were the most common large mammals in the late Pleistocene - 10,000 to 20,000 years ago - only mammoths are found at kill sites associated with Clovis people.

As for the claim that human colonization of the world's islands resulted in widespread vertebrate extinction, Grayson said this did not occur simply because of human hunting.

"No one has ever securely documented the prehistoric extinction of any vertebrate as a result human predation, though it may certainly have happened. In virtually all cases, when people colonize an area many other changes follow - fire, erosion and the introduction of a wide range of predators and competitors.

"We do know that human colonists caused extinctions in isolated, tightly bound island settings, but islands are fundamentally different from continents," he added. "The overkill hypothesis attempts to compare the incomparable and there is no evidence of human-caused environmental change in North America. But there is evidence of climate change. Overkill is bad science because it is immune to the empirical record."

The South American Twist

Clovis First Doesn’t Fit the Rich Prehistory of the Southern Continent

by Ruth Gruhn

South America may hold the key to understanding the initial settlement of the New World. The Clovis First model simply does not explain the abundant and varied archaeological sites in South America that are at least as old as North America’s Clovis culture.

The South American evidence points to well-adapted populations with varied subsistence patterns who occupied all major environmental zones of the continent by at least 11,000 radiocarbon years ago (13,020 calendar years) — before Clovis had spread throughout North America. The diverse regional technological traditions of the south show no relationship to Clovis.

For South America, a model of mass-population movements into already-occupied territory is not necessary. Although invasions may be more dramatic than models of a slow, indigenous population growth and adaptation, the latter seems the best fit with the known archaeological record from South America. The best explanation is an initial entry into South America well back in the Late Pleistocene — thousands of years before the Clovis culture came to the north.

To illustrate the regional diversity that was found throughout South America by the time the Clovis complex was spreading across North America, I offer a sampling of sites with dates to Clovis age or several millennia earlier, plus two sites that apparently date to very early times:

• Taima-taima: In the Caribbean coastal zone of Venezuela, this site is at a water hole among low hills. The region is now a semiarid thorn forest, and paleoenvironmental evidence suggests roughly the same setting 13,000 years ago (15,350 cal BP), when hunters, using long, thick El Jobo points shaped like willow leaves, killed and butchered a juvenile mastodon there. José Cruxent initiated archaeological research at the site.

• Tibitó: High in the Andean uplands of Colombia, the Tibitó site revealed clusters of bone fragments and stone artifacts distributed in activity areas around a large boulder. Excavated by Gonzalo Correal and associates, it is radiocarbon dated to 11,740 years ago (13,700 cal BP). Faunal remains include extinct horse, mastodon, and deer. The stone artifacts are very simple, unifacial tools showing minimal retouching.

• Pachamachay: People may have lived even higher in the Andes. The cave of Pachamachay, excavated by John Rick, is at an elevation of 4,300 meters (13,000 feet) on the high, grassy puna of central Peru. The site provided evidence of camelid hunting with triangular and lanceolate (long, narrow) points and produced a radiocarbon age of 11,800 years (13,800 cal BP).

• Quebrada Jaguay: Evidence of a specialized maritime economy is found on the desert Pacific Coast of southern Peru. The oldest site known at present — labeled QJ-280 — produced a radiocarbon date of 11,105 years ago (13,025 cal BP). The site, excavated by Dan Sandweiss and associates, indicates intensive exploitation of fish, marine clams, crustaceans, and seabirds. Most of the tools, weapons, and utensils of the earliest occupants likely were made of perishable materials, as only flaking detritus and a few broken or unfinished stone tools were found.

• Monte Verde: In the very far south, the now-famous Monte Verde site, excavated by Tom Dillehay and associates, is in the temperate rain forest of south-central Chile. By 12,500 years ago (14,850 cal BP), there was a substantial settlement here, its organic remains preserved under a peat deposit. The abundant floral and faunal remains indicate a subsistence economy built primarily on collecting a wide variety of plants over a large area, with some exotic materials brought or traded from the coastal zone and the Andes range. While a number of wood items were found, most of the stone artifacts are quite simple: naturally sharp-edged pebbles or simple flakes.

• Los Toldos and Piedra Museo: East over the Andes mountains, people had moved into the grasslands of Patagonia in southern Argentina. Augusto Cardich reported a radiocarbon date of 12,600 years (14,900 cal BP) in 1973 on the lowest occupation level at the rock shelter site of Los Toldos, with a unifacial stone industry and remains of extinct animals. Recent excavations by Laura Miotti and associates at a rock shelter in the Piedra Museo locality, not far from Los Toldos, produced a radiocarbon date of 12,890 years (15,200 cal BP) for a small assemblage of flakes and artifacts with extinct fauna.

• Lapa do Boquete: More than half a dozen archaeological sites have been radiocarbon dated to 11,000 years ago (13,020 cal BP) or earlier in the interior uplands of eastern Brazil. One example is the Lapa do Boquete, a large rock shelter excavated by André Prous and associates. The site is in a semiarid savanna-woodland with a variety of game and edible plants. Four radiocarbon dates between 12,070 and 11,000 years ago (14,000-13,020 cal BP) were obtained on charcoal from the lowest occupation level, which yielded remains of palm nuts, freshwater mussels, fish, and bones of small- to medium-sized mammals in association with an assemblage of unifacial flake tools.

• Caverna da Pedra Pintada: Foragers had also adapted to the tropical rain forest deep in the Amazon Basin. The lowest occupation level in this large rock shelter just north of the Amazon River has two radiocarbon dates of around 11,100 years ago (13,025 cal BP). The site, excavated by Anna Roosevelt and associates, suggests a foraging economy exploiting a variety of tropical fruits and nuts, stream fishing, mussel collecting, and small-game hunting.

If a variety of well-adapted, regional populations had become established in every major environmental zone of South America by the end of the last Ice Age, how early did people first arrive on the continent? Two sites suggest the initial entry may have occurred as much as 35,000 years ago.

The first is Tom Dillehay’s Monte Verde site in Chile. A test pit, placed across a creek from the Monte Verde II settlement, found artifacts and features deeply buried in a sand stratum. The position of this stratum within the geological sequence in the region supports a radiocarbon age of 33,370 years on charcoal fragments from the features — lenses of clay within the sand that possibly represent hearths.

A total of 26 lithic (stone) specimens were recovered in direct association. One specimen is a basalt core with at least 11 flakes removed; close examination shows use-wear and a residue of mastodon blood. Of 20 flakes or faceted stones, six show use-wear. Further investigation is planned, but this is certainly a potential time bomb sitting under any model that maintains an initial entry of people into the Americas no earlier than 15,000 years ago.

The other South American archaeological site with comparable antiquity is the Toca do Boqueirão da Pedra Furada, a large rock shelter at the foot of a high sandstone cliff in northeast Brazil. It was excavated from 1978 to 1988 by Niéde Guidon and associates. Within the rock shelter, up to five meters (16.4 feet) of sediment have yielded approximately 600 simple stone artifacts, pebble tools and flake tools, and a long, stratified series of finite radiocarbon dates on charcoal that range back to about 32,000 years ago. Several indefinite dates from lower levels hint at an age of over 40,000 years.

Some believe the validity of Pedra Furada was buried by a critique published by several North American researchers who attended a field conference at the site in 1993, but it cannot be so easily discounted. The essential issue at Pedra Furada is whether any real stone artifacts came from the Pleistocene deposits within the shelter. Critics of the site have suggested that the specimens classified as artifacts could have been flaked naturally in a high-energy depositional environment — but no such environment existed within the sheltered area where the specimens were found, as the sediments are mainly derived from slow weathering of the sandstone overhang. I believe the site of Pedra Furada is not to be dismissed so readily.

The evidence from South America suggests the Clovis phenomenon was a regional North American development — and a rather late one at that, especially if the really early archaeological sites in Chile and Brazil prove to be valid.

For decades, North American archaeologists have discounted the South American evidence because it hasn’t met their expectations or fit their models. Now it is impossible to ignore the implications: A population with a simple lithic technology entered the Americas much earlier than is generally accepted.

RUTH GRUHN, Professor Emerita at the University of Alberta, Edmonton, Canada, has pursued the first settlements of the New World throughout North and South America.

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