North American v. World Extinctions
charts used by Connie Barlow for telling
The Story of the North American Continent
5,000,000 years ago, rhinos (which had been present in North America for 50 million years) went extinct on this continent. Somewhat earlier ginkgo and dawn redwood trees vanished from North America, after having been present here since the Jurassic. Cause is unknown, but perhaps correlated with volcanic activity of the Columbia flood basalts, Mount Rainier, and the uplift of the Colorado Plateau (through which the Grand Canyon was carved).
3,000,000 years ago, the Isthmus of Panama rose, connecting South America with North America for the first time since the dinosaur era. This prompted "The Great Biotic Interchange" of animals expanding their ranges in both directions. Possums, porcupines, armadillos, glyptodonts, and ground sloths successfully expanded into N.A. from their home of origin in S.A. But success was much greater in the other direction: bears, deer, horses, felids (jaguar, puma), canids (foxes and wolves), bears, raccoons, camels (llamas), and rabbits (preceded by mice and squirrels) "invaded" South America with such ecological force that most of South America's large endemic species went extinct, including all its marsupial "cats," like the one pictured. Its liptoterns that had evolved horse-like (pictured) and camel-like forms also were devastated.
beginning 2,000,000 years ago, glaciers advanced over Europe and North America for the first time in hundreds of millions of years. Vegetation of the lush deciduous forest that was shared by eastern North America, Europe, and China was forced to move south. Refuges were available for the plants to wait out the Ice Age in southeast Asia and along the Gulf of Mexico, but southward retreat in Europe was blocked by the Mediterranean, the Carpathian Mountains, and the Black Sea. Sweet gum (Liquidambar), tuliptree (Liriodendron), and hemlock vanished from Europe, but were able to recolonize the Appalachian Mountains of America and much of eastern Asia after the last glacial retreat. Extinctions of "the massive" (large animals) in "Near Time", the past 30,000 years, are regarded by a majority of scientists (e.g., Paul Martin, Jared Diamond) to have been caused by the influx of spear-throwing humans arriving on distant continents and islands for the first time:
30,000 years ago in Australia, 15 of the 16 species of animals (marsupials, a giant lizard, and a giant snake) weighing 100 pounds or more went extinct, plus a host of smaller animals. Radiocarbon dates of last fossils and first human hearths are scarce, however, and the climate was also drying, so the role of overkill and fire alteration of habitats by humans is contested.
13,000 years ago in the Americas, 2/3 of N.A. animals weighing >100 pounds vanished, as did 3/4 of those in South America. Extinction is well correlated with "Clovis" (mammoth hunter) artifacts, and appears to have run its course in about 300 years. If other peoples preceded the Clovis, their interaction with the landscape would have been less severe than were the Clovis. [from top left: giant capybara, toxodon, dung beetle, horse, long-horned bison, American lion (as well as sabertooth and scimitar cats, and cheetah), woolly mammoth (as well as Columbian mammoths and American mastodons), dire wolf, short-face bear (twice the size of a grizzly), camel, glyptodont, ground sloths (several genera). Not pictured: hyena, shrub ox, stag moose, Harriman's mountain goat, 4-horned pronghorn, giant beaver, giant peccary, carrion-feeding giant storks and teratorns, large tortoises.]
10,000 years ago on the island of Cypress in the Mediterranean, the arrival of the first humans is correlated with extinction of pygmy hippos and dwarf elephants. Because the skulls of these elephants have a single hole in the front of the face, where the trunk goes, a myth evolved that one-eyed giants (cyclops) inhabited the islands in the days of Odysseus.
6,000 years ago the islands of Cuba and Hispaniola finally lost their ground sloths, as well as giant flightless owls. These grounds sloths were smaller than those found on the continents, but because they went extinct a full 7,000 years after the mainland ground sloths vanished, this presents a strong argument for human cause, rather than climate change.
4,000 years ago, a type of dwarf woolly mammoth went extinct on an island north of Siberia, in the Arctic Ocean. Because this extinction happened 9,000 years after mammoths went extinct everywhere else in the world, this is strong argument that human impact rather than climate change was the cause everywhere in the world. Muskox went extinct along its last stronghold in Asia, Siberia, perhaps several thousand years earlier. The only reason muskox did not go extinct globally is that a population persisted in the remote Canadian Arctic, and has since been tapped for successfully re-starting muskox populations in Asia.
2,000 years ago, Madagascar suffered huge losses in its large animals. All of its largest lemurs went extinct, including one the size of a gorilla that had become too large to climb trees. The largest herbivorous, flightless bird of all time also went extinct: theelephant bird. So did tortoises that rivalled in size those of the Galapagos Islands. Dating of first human artifacts and hearths is difficult on Madagascar, but there is no other cause that is more plausible than overkill by humans.
1,500 years ago, Hawaii lost many birds, especially flightless birds such as flightless geese and flightless ibises. Hunting by the newly arrived first humans would have been exacerbated by the egg predation of feral pigs that they brought to the islands with them. Evidence linking these extinctions with the arrival of the first humans is very strong.
800 years ago, New Zealand began to lose all dozen of its species of flightless moa birds. The largest were just a bit smaller than the giant elephant birds of Madagascar. Loss of the moa is thought to be the reason that the largest eagle of all time, which surely preyed on the moa, went extinct too. Hearths associated with vast assemblages of egg shells provide strong evidence that the first humans to sail to such remote islands were the cause of extinction.
Scientists generally regard "THE SIXTH MAJOR MASS EXTINCTION" to have begun not with the spread of industrial humans, but with the spread of humans newly arriving on continents and islands in which the wildlife had not co-evolved with spear and fire technologies. For a playful and reverential experiential process for learning the 65 million year story of the North American Continent, visit our web page: "Coming Home to North America".
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