the extinction of megafauna -- 7/27/22
Today's selection -- from Where The Wild Things Were by William Stolzenburg. With the arrival of man, the megafauna of North America -- giant camels, beavers as big as bears, and the giant saber-tooth cat -- disappeared:
"One wintry weekend outside Montreal in 1956, a young postgraduate ecologist found himself hunkered inside against the cold, pondering death. Paul S. Martin was preparing a seminar on the biology of the Pleistocene, an epoch beginning 1.8 million years ago with the onset of its signature glaciers, and ending -- as Martin was now reminded -- with the sudden and sweeping disappearance of so many great animals. Martin began the weekend thumbing through the time line of mammalian evolution leading up to the Pleistocene. With every advancing epoch, Miocene to Pliocene to Pleistocene, twenty-four million to five million to nearly two million years ago, the fauna had tumbled by the score over a cliff of extinction. Each die-off was followed with a resurrection of sorts, an evolutionary reconfiguration that restocked the empty niches with new and equally fantastic life-forms, large and small, a revolving canvas of bestiaries. And then, near the end of the Pleistocene, the pattern took a twist that brought a double take from Martin.
"Again the reigning fauna had collapsed, but this time with a blatantly heavy bias. This time, the reaper had apparently handpicked the mightiest among the beasts. In contrast to the more random assortments that preceded them, the animals that disappeared at the end of the Pleistocene were almost without exception the largest of the lot. The cast had included Columbian mammoths, thirteen feet at the shoulder, and herds of wild horses and giant bison. America had housed giant camels and a beaver as big as a bear. There was everybody's favorite Paleolithic monster, Smilodon, the saber-tooth cat, There was a dire wolf and a rocket-fast feline called the American cheetah. There was a bear the shoulder-height of a moose with the leg-speed of a quarter horse, a creation to give anthropologists the night sweats.
|Dire Wolf restoration with skeletal mount|
"And yet so suddenly they were all but gone, with only a skeleton crew surviving. Prior to that night in Montreal, Martin had once entertained notions of a career as an ornithologist. That would now have to wait for some other lifetime. The next year Martin moved his family to Tucson to take a research post at the University of Arizona's Desert Laboratory, where for the next fifty years he would work on solving the most contentious mass extinction since the dawn of humans
"The Pleistocene die-off in itself was nothing new to science. Charles Darwin had puzzled over it as a green, twenty-four-year-old naturalist circling the globe aboard the HMS Beagle. 'It is impossible to reflect on the changed state of the American continent without astonishment,' he wrote in his journal. 'Formerly it must have swarmed with great monsters: now we find mere pygmies.'
"Alfred Russel Wallace, Darwin's codiscoverer of evolution by means of common descent, had too marveled at the great bestiary whose remains had been unearthed in the Pleistocene beds not only of North America but around the globe. 'We live in a zoologically impoverished world, from which all the hugest, and fiercest, and strangest forms have recently disappeared,' he wrote.
"Surely, thought Wallace, in line with many of his contemporaries, the Pleistocene ice must have been the dagger that killed the megafauna. Yet even as he argued the case for climate's role, Wallace was subconsciously implicating a second party. 'This is certainly not a great while ago, geologically; and it is almost certain that this great organic revolution, implying physical changes of such vast proportions ... has taken place since man lived on the earth.'
"Since man lived on the earth. The point struck Martin a hammer blow. 'The glaciers had waxed and waned, climates had blown hot and cold with the wild swings of the Pleistocene, but the first arrival of humans on the continent had only happened once, and that, it appeared, had coincided all too suspiciously with the disappearance of the megafauna.
"Martin's suspicions had come at an opportune time. The field of paleoecology had recently entered the revolution of radiocarbon dating, a technological timepiece with which one could precisely age life-forms long dead by measuring an odd form of carbon in their bones. Carbon 14 is a rare and radioactive molecule, a trillion times less common than its ubiquitous cousin carbon 12, but nonetheless taken up in measurable quantities in the tissue of all living matter. Carbon 14 is an unstable molecule, steadily leaking neutrons like grains of sand from an hourglass. When life stops, carbon 14 starts vacating its host, dwindling by half every s 5,370 years. With a good sample, geochemists could date the death, to within a few centuries, of an animal that had died up to 40,000 years ago.
"What the radiocarbon had begun to reveal was a North American menagerie of some forty species of mammal, all weighing more than one hundred pounds, coming to an abrupt end. All but fourteen had disappeared, and most of the casualties indeed clustered around the arrival of humans.
"To those of the climatic persuasions, it was telling that 13,000 years ago -- the cliff in time over which most of the megafauna of North America tumbled -- the land was coming out of the latest glacial cycle, warming and drying and generally rearranging the continent's communities of plants. But to those leaning toward man as the smoking gun, it was more telling that most of these animals had already breezed through twenty-two such glacial cycles of the Pleistocene, some of them more severe than the latest.
"Whatever or whomever the phantom killer was, it visited South America shortly after cleaning out North America, removing 80 percent of that continent's large mammals. And strangely enough, the same sort of blight had apparently blitzed Australia some 40,000 years ahead of the American massacre, taking the island continent's giant marsupial mammals, its giant flightless birds, and a lizard sixteen feet long. It did so too on the heels of human arrival, with no glaciers in sight.
"In the Americas, the final years of the megafauna coincided with the first appearance of the Clovis culture and their exquisite spear points. Flaked from chert and flint and quartz, and sharp as broken glass, they turned up in brilliance and abundance in sites across the country. Some of them were recovered from between the ribs of fossil mammoths. The Clovis people, carrying the name of the dusty little town on the plains of eastern New Mexico where their artistic weapons were first uncovered, began showing up in North America around 13,400 years ago. They were the descendants of Siberian mammoth hunters who, during a period of low water, had walked across the Bering land bridge to Alaska. Southward they wandered, through an ice-free corridor, into a land of giant beasts that had never seen such odd creatures as these shifty bands of two-legged waifs wielding fire and hurling pointed sticks. To Martin, it was tantamount to a superpredator entering Eden. Spreading at a reasonable pace of 2 to 4 percent per year, cleaning out the naïve larder as they went, the Clovis colonists had in about two or three centuries laid waste to the continent's biggest mammals.
"More damning evidence indicting humans as the Pleistocene asteroid followed in the boat wakes of ancient mariners. In their explorations of the oceanic islands of the globe, humans eventually discovered New Zealand and Madagascar, and again megafaunal carnage followed. The massive moas of New Zealand, the elephant birds of Madagascar, both families characterized by the big, the meaty, and the flightless, disappeared soon thereafter.
"Whether by foul climates or foul play, the results of this pandemic of mass extinction were there for anyone to observe. In North America, the megafauna of the late Pleistocene had been extinguished by about 12,000 years ago. Which meant that by the time Columbus and company from Europe began their invasion 11,500 years later, the continent's fauna had already been thoroughly plundered. North America had been reduced to a tattered remnant of its Pleistocene grandeur. It had become Darwin's continent of pygmies.
"Nor were the pygmies particularly safe. 'When I consider,' wrote Thoreau from mid-nineteenth-century New England, 'that the nobler animals have been exterminated here -- the cougar, panther, lynx, wolverine, wolf, bear, moose, deer, beaver, turkey, etc., etc., -- I cannot but feel as if I lived in a tamed, and, as it were, emasculated country ... I should not like to think that some demigod had come before me and picked out some of the best of the stars.'
"The century following Thoreau amounted to a mop-up of the megabeasts. By midway through the twentieth century, the gray wolf and grizzly bear had been relegated to a class of loners, outlaws, and outcasts everywhere south of Alaska and the Canadian wilds. The secretive mountain lion survived in minimal numbers by keeping to the dark canyons and high crags, often operating under cover of night."
|Where the Wild Things Were: Life, Death, and Ecological Wreckage in a Land of Vanishing Predators|
|Copyright 2008 by William Stolzenburg|
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