“Science” programs on cable networks are often idiotic. I suppose the television producers want to boost ratings and make their presentation dramatic for entertainment value. But for those of us who know a good bit more about the subject than the average couch potato, these programs are laughable. I think it was the History Channel that featured a special about the Pleistocene megafauna that concluded the beasts became extinct because of global warming. The imbecilic producers actually showed computer images of the beasts dropping dead due to a heat wave. They made no mention of overhunting by humans which is a much more plausible cause of extinction. Instead, they wanted to jump on the bandwagon of global warming phobia, unware that all of these “Ice Age” species survived the Sangamonian Interglacial which was on average warmer than present day temperatures.
Another program about megafauna extinction (either on Discovery or PBS) did give equal time to overkill, climate change, hyperdisease, and comet impact. The latter two, in my opinion, are crackpot theories. While it is clear that an extraterrestrial impact probably led to the extinction of the dinosaurs, the evidence that a comet caused the recent megafauna extinction event is not at all convincing. Supposedly, the comet hit a glacier–explaining why there’s no impact crater. The theory is on shaky legs to start, if it’s proponents have to make an excuse for the lack of a smoking gun. Other independent scientists have been unable to replicate their findings, perhaps relegating the comet impact theory to the trash can of illogical ideas. When interviewed for the above mentioned program, one of the comet impact proponents made an astoundingly illogical comment. He stated that the overkill theory didn’t make sense to him because he couldn’t believe humans could kill every last individual of a species.
His statement demonstrates a remarkable ignorance of basic ecology. Humans would not have to kill every last individual of a species to render it extinct. All wild species of animals already have high rates of natural mortality. Let’s take the mastodon for example. Mastodons had a long lifespan and low birthrate. Saber-tooths and scimitar-toothed cats caused a certain amount of mortality. Diseases, such as tuberculosis, took a percentage more. Accidents (falling into quagmires, males killing each other in battles for mates, etc.) took a toll as well. But this was mortality the mastodon birthrate could keep up with, and they maintained their existence for millions of years. However, the addition of human hunting was a variable that increased a mortality rate that exceeded their birthrate. So man + natural mortality = extinction. Remove man from the equation and it would be natural mortality = a still extant species.
In my opinion overhunting by man is the only cause of the demise of the Pleistocene megafauna. There is no other logical solution to this mystery. But I don’t agree with Paul Martin’s blitzkrieg model of extinction. I believe the process took thousands of years rather than hundreds. A recent study supports my belief in a protracted overkill scenario.
Researchers taking cores of permafrost in Alaska’s north slope. There is forensic evidence of extinct Pleistocene megafauna in some of these cores. This forensic evidence dates thousands of years later than the most recent dated fossil evidence of these species. That means these animals lived more recently than previously thought. Photo from google images.
A group of scientists led by James Halle examined cores of permafrost found in Alaska. They were looking for megafauna DNA. The cores were dated using carbon dating and optically stimulated luminescence (see http://crustal.usgs.gov/laboratories/luminescence_dating/technique.htmlxplanation for an explanation of OSL dating). The dates of the cores with the megafauna DNA ranged from 11,000 to 8,000 years old. This sediment is more recent than the youngest known dated megafauna fossils from the interior of Alaska. (A population of dwarf mammoths is known to have survived on the Pribiloff Islands until ~4000 BP.) These cores harbored DNA from mammoth, horse, bison, moose, and snowshoe hare. This DNA is referred to as sedaDNA and comes from hair, feces, and urine. It proves the existence of these species in the environment, even though they left no fossil evidence from this time period. The mammoth DNA is 2600 years younger than the youngest known mammoth fossil from the interior of Alaska; the horse DNA is 3700 years younger than the youngest known horse fossil from this region. Using sedaDNA is uniquely possible in Alaska, thanks to permafrost conditions, and it’s a technique probably not possible anywhere else.
The scientists concluded that the continued existence of megafauna until ~7500 BP rules out climate change, the blitzkrieg model of overhunting, comet impact, and hyperdisease as the ultimate causes of megafauna extinction, though they do concede that anyone of these factors could’ve caused an initial population collapse. Curiously, they made no mention of a protracted overkill model of extinction, which in my opinion this study strongly supports.
It occurs to me that previously disregarded recent dates of megafauna fossils my not be in error. For example the Devil’s Den fossil site in Levy County, Florida yields remains of Jefferson’s ground sloth, dire wolf, Florida spectacled bear, southeastern lemming, saber-tooth cat, mastodon, horse, and flat headed peccary. The fossils from this site were radiocarbon dated to be 7,000-8,000 years old–several thousand years later than when scientists believe these species became extinct. Therefore, scientists disregard these dates as inaccurate due to some kind of contamination or obsolete carbon dating techniques. I suggest scientists redate these fossils, as well as those from other sites with unusually young dates, using the more updated and improved methods of carbon dating. It seems likely the Pleistocene megafauna may have survived in southeastern North America for several thousand years longer than previously thought.
References
Halle, James et. al.
“Ancient DNA reveals late survival of mammoth and horse in interior Alaska”
http://www.pnas.org/content/early/2009/12/16/0912510106.full.pdf
GeorgiaBeforePeople 