these plant communities into arrangements for which there are no modern equivalents.
Northern North America probably lay covered by ice during the Last Glacial Maximum (about 18,000 to 20,000 years ago). The Laurentide ice sheet buried the land from the North Atlantic coast to the Rocky Mountain trench, south into Ohio. The Cordilleran ice sheet came out of the Coastal Range and Rocky Mountains, huge valley glaciers coalescing into a composite sheet, smaller than the Laurentide, covering northwestern North America. Temperatures in Greenland during the last glacial maximum were 41 degrees Fahrenheit cooler than today. A key issue for archaeologists is whether there was a corridor between the two sheets sufficiently benign to permit human migrations coming south out of Beringia. Textbook maps often show the two great ice-sheets conjoined. Glacier erratic trains (boulders carried by the glacial ice) on the foothills of the Northern Rockies indicate this was the case 18,000 years ago. But there is conflicting evidence. The Ice Free Corridor (IFC), and other pre-last glacial maximum routes between the ice sheets, could have been open much of the time during the past 30,000 years. The debate continues.
People moved around the edges of these glaciers, looking for food and shelter from the cold. The Greatest Adventure began whenever those bands of Siberian hunters moved east across Beringia into present day Alaska. That crossing could have taken place anytime beginning about 30,000 years ago. The Bering Strait land bridge was almost certainly open 10,000-27,000 years back. Dating for the last stages of the Ice Age is imprecise; the geography of ice in North America, which areas might have been ice-free, is not clear. Many archaeologists believe the far north of Late Pleistocene Siberia was too damn cold for people to live there. Since no sites dating between 30,000 and about 14,000 years ago have been found in northeastern Siberia, some scientists think these children of the ice retreated south to sub-Arctic central Siberia during this time. Similar claims about the inhospitable climate—bleak, frigid, uninhabitable—are made for the same period in Alaska.
Approximate extent of ice during the Last Glacial Maximum.
But even ice-ages have summer time. Just because we haven’t yet found an archaeological trace, that doesn’t mean hunters were not eking out a living in these frigid climes. In fact, plenty of big game, the Pleistocene megafauna, roamed Beringia before and during the Last Glacial Maximum (LGM) when glaciers blocked all routes south; the Arctic, though colder before and during the LGM, was, botanists think, more grassy than shrubby offering an abundance of food for mammoth and other grazers who were in turn stalked through the snows by their gigantic predators.
The fossil record of Alaska and Canada confirms the presence of these animals. Now-extinct species of camel, long-horned bison, tapir, deer, antelope and horse ranged the tundra and grasslands. Great herds of caribou gnawed the northern lichen and bison grazed the open plains. Hidden in the draws and breaks were huge American lions, big dire wolves and gigantic short-faced bears. The deglaciated valleys were wet, the high benches speckled with pothole lakes, springs and ponds frequented by giant beaver. Mastodon browsed the edges of boreal forests; small groups of mammoth roamed the open country.
•
A spectacular array of very large animals lived in North America during the Late Pleistocene. Most of this astonishing menagerie of megafauna, along with some smaller genera of creatures, vanished suddenly nearly 13,000 years ago. The bulk of these animals were unusually large. Here’s a sample bestiary:
Most iconic was the Columbian mammoth, monster of the plains, and its smaller cousin (they probably interbred) of the North, the woolly mammoth. Standing several feet taller than the largest elephant ever measured, these grazers no doubt traveled in matriarchal herds, like today’s elephants. Massive, long tusks spiraled to a point and sometimes crossed. These creatures, some believe, were the spiritual and material center of Clovis culture and show up in a dozen kill or butchering sites. A small population of woolly mammoth survived on Alaska’s Wrangell Island until about 4,000 years ago.
The American mastodon was also hunted by Clovis people, but perhaps not as frequently as mammoths. Shorter and stockier than the mammoth, this browser of spruce trees was a solitary animal often found in forests.
Clovis people also hunted a four-tusked cousin of the mastodon, the gomphothere, down in Sonora, Mexico about 13,000 years ago. This elephantine creature was found more commonly in South America and was, prior to the Sonoran discovery, believed to have gone extinct 30,000 years ago in the region.
Several kinds of giant ground sloth roamed the land and ranged in weight from about 200 to 6,000 pounds. The big ones had huge claws and one would think they would draw attention from anyone wandering the grasslands.
Early Americans no doubt hunted other American animals, for which we have no archaeological record of association. Chief among them would be horses, camels, tapir, peccary and, in the North, Saiga antelope.
A gigantic long-horned species of bison roamed the Pleistocene steppes and plains, along with herds of smaller buffalo. Bison, along with caribou and musk ox, important prey animals for Clovis as well as later human hunters, survived the great megafauna extinction around 12,900 years ago.
Smaller animals, but gigantic for their kind, included 350-pound beaver, armadillo and the glyptodont, a mammal almost ten feet long with armored shell, head and tail. Giant carrion birds teetered over the landscape, including condors with 20-foot wingspans. A deer called the stag-moose (slightly larger than a modern moose) displayed some of the biggest palmate antlers ever found on a mammal; these antlers are frequently preserved in fossil deposits. We don’t know anything of the relationships of such creatures with humans but the animals must have painted the Pleistocene landscape with shimmering colors scarcely dreamed of today.
Preying on the grazing and browsing animals were giant carnivores. The biggest was the North American short-faced bear weighing in at over a ton. This long-legged giant could have been an omnivore but others think it lived by exclusive scavenging and predation. More on Arctodus simus later in this chapter.
The most effective American predator might have been the Pleistocene lion, same genus as today’s African variety but eight-feet long with some of the biggest cat craniums ever measured, an animal that prowled North America and northwestern South America. The big brains, some suggest, indicate a highly social, pride-hunting predator.
The prototypical American Ice Age carnivore was the sabertooth cat, a stout, powerful predator with six-inch upper canines. The lovely name, Smilodon fatalis, says it all. This sabertooth was about the size of an African lion and is believed to have been a solitary ambusher of prey. Likewise, the scimitar cat had long, sharp serrated fangs perfect, they say, for slashing baby mammoths. As the second kind of sabertooth, the scimitar’s teeth were nowhere near as long as Smilodon. The American cheetah, twice as big as the one in Africa, was also on the scene.
Wolves functioned much as they do today but probably scavenged more. The dire wolf and Beringian gray wolf had unusually heavy jaws and crushing teeth; the paleontological guess is that they both scavenged and hunted in packs. Dhole dogs, coyote and fox followed the flocks of condors, buzzards, crows and ravens to the kill sites of big cats and, eventually, ice-age Americans.
Los Angeles’s La Brea tar pits hint at the spectrum of Pleistocene predators, unfortunate enough to mire in the tar. The Natural History Museum of Los Angeles lists these numbers: 4,000 dire wolves, 2,000 sabertooths (not scimitar), 80 lions, mostly male, and 30 short-faced bears. It’s theorized that the sabertooths came in for mired bison and dire wolves cleaned up after them. Of course, tar pit death traps are not the same as kill sites: Carnivore behavior and selection (death) might be atypical at La Brea.
