Many old school anthropologists and paleontologists reject the hypothesis that man overhunted the Pleistocene megafauna to extinction. Some of their arguments against the overkill hypothesis are so illogical they leave me astonished. For example 1 argument against the overkill hypothesis used to be that there was no archaeological evidence that paleo-Indians ever killed giant ground sloths, camels, horses, llamas, peccaries, glyptodonts, giant beavers, etc. Since that argument was made, evidence that paleo-Indians killed giant ground sloths, camels, and horses has been found. Nevertheless, in my opinion it is an unreasonable expectation to find such evidence. Large regions of the North American continent are almost completely devoid of Pleistocene fossils, let alone ones that show obvious evidence they were killed and butchered by humans. The odds against finding such evidence are astronomical. Most recent paleoecological studies of the late Pleistocene are consistent with the overkill hypothesis. Climate change models of extinction for this time period are becoming less tenable when all of the latest data are considered. One old school anthropologist who has not ignored the latest paleoecological data is Gary Haynes, a professor at the University of Nevada, Reno. Dr. Haynes uses the new data to speculate how man managed to wipe out most of the large American mammal species over a time period of a few thousand years. He suggests the megafauna suffered 3 stages of shock before man chased them into oblivion.
Man entered North America from Asia ~15,000 calender years BP (at the latest). A human turd found in an Oregon cave is the oldest definitive evidence of man in North America, and it dates to a few hundred years after the probable entrance date. Dr. Haynes refers to the initial contact between man and megafauna as the foreshock stage. When humans first encountered the megafauna, the hunters killed them opportunistically, and this fragmented the animal populations, eliminating some species from some areas. Humans likely followed big game trails and river valleys for the same reason the animals did–they were easier to traverse than hills and swamps. Because they followed the same paths, humans were more likely to encounter megafauna than not. Even low levels of hunting had a big impact on megafauna species with slow rates of reproduction. The foreshock stage may well be represented from studies of dung fungus spore abundance in 4 New York bogs and 1 kettle lake in Indiana. Below is an in depth explanation.
Scientists from Fordham University took cores of sediment from 4 ancient bogs in southeastern New York where fossils of mastodons and stag-moose had been found. They analyzed the sediment for pollen and charcoal content and carbon-dated the samples. Dung fungus spores, also known as sporormiella, live in the guts of megaherbivores. The abundance of sporormiella is used as a proxy for the presence of megaherbivores in the environment. When sporormiella levels fall below 2%, it means megafauna is absent in the local environment. The scientists found that megafaunal populations collapsed between 14,800 BP-13,700 BP. This time span is known as the Boling-Alerod warm phase. The composition of flora remained unchanged within this time span, so this finding rules out climate change as the cause of the initial population collapse. Moreover, the megafauna populations at each lake collapsed at different times, indicating humans wiped out all the game in 1 area, then moved on to the next location and extirpated them there later. A second study, this time of a kettle lake in Indiana, got similar results.
Appelman Lake, Indiana. This is a kettle lake formed when a partially buried piece of a glacier melted. A study of dung fungus spore abundance suggests megafaunal populations around this lake collapsed between 14,800 BP-13,700 BP.
Sporormiella–a dung fungus spore. Sporormiella levels rose to Pleistocene levels when Europeans introduced livestock to America.
Pollen graph from Appelman Lake. Sporormiella abundance is represented by the blue. Note how charcoal amounts increased after the megafauna populations collapsed. Forests replaced savannah environments after the megafauna were killed off. Forest fires increased in frequency because megaherbivores were no longer eating flammable material.
Dr. Haynes believes the megafauna suffered the main shock in the few centuries before and after the Younger Dryas cold phase which struck suddenly ~12,900 BP. Megafaunal populations had already collapsed, but they persisted in fragmented local refuges. Clovis hunters and their successors deliberately targeted these remaining populations. The Younger Dryas was an arid cold climate stage that caused water sources to shrink. Megafauna concentrated around the shrinking water holes where they were easy to ambush.
Dr. Haynes thinks the Pleistocene megafauna extinctions occurred during an extended aftershock when the last of the beasts were subject to many difficulties resulting from human activities. Humans continued hunting the now rare and declining populations; isolated populations were weakened by inbreeding; an ecology long dependent upon interdependence between different megafauna species was now completely disrupted as some species disappeared; and fire frequency changed as humans set fires at unusual times of the year. Humans didn’t have to kill every last individual of a species to render it extinct. Instead, anthropogenic changes, including hunting, raised the mortality rate above the reproductive capacity of each individual species.
There is no way of knowing exactly when each species became extinct. The latest terminal date for the mastodon is from a specimen found in Rochester, Indiana. It died ~10,032 BP. The last mastodon likely died centuries after this but didn’t become fossilized. SedaDNA in Alaska permafrost suggests horses didn’t become extinct there until 7600 BP. It’s probable that by 7500 BP humans had discovered and annihilated every population of Pleistocene megafauna in America.
Growth rings on mastodon tusks are another line of evidence consistent with overkill theories of extinction rather than climate models of extinction. Dan Fisher analyzed the growth rings from 10 mastodon specimens that date to close to the time of extinction. The growth rings on the mastodon tusks were similar to those from African elephants that had plenty of food but were under pressure from overhunting.
References:
Fisher, Dan
“Paleobiology and Extinction of Proboscideans in the Great Lakes Region of North America”
American Megafaunal Extinctions at the End of the Pleistocene 2009
Gill, Jacquelyn; et. al.
“Pleistocene Megafaunal Collapse, Novel Plant Communities, and Evidence of Fire Regimes in North America”
Science 326 November 2009
Haynes, Gary
“Extinctions in North America’s Late Glacial Landscape”
Quaternary International 2010
Robinson, Guy; Lida Burney, and David Burney
“Landscape Paleoecology and Megafaunal Extinction in Southwestern New York State”
Geological Monographs 75 (3) Jan 2005
Tags: dung fungus spore, Gary Haynes, mastodon tusk growth rings, megafaunal extinction, overkill hypothesis, sporormiella
GeorgiaBeforePeople 
January 30, 2013 at 11:36 pm |
I’ve read many of the theories for the big Pleistocene extinctions, and I’m firmly convinced that humans were the culprit. Of course it’s still going on now–there are remnants of the Pleistocene megafauna remaining. And what is causing their current destruction? The same thing that caused the earlier mass extinctions: Homo sapiens sapiens.