The terminal radiocarbon dates for North America’s Pleistocene megafauna consistently translate to about 12,000 calendar years BP. Because these dates are so consistent for so many different species, scientists assume Pleistocene megafauna became extinct 12,000 years ago. I hypothesize this date reflects when these species became rare and local in distribution and not when these species actually became extinct. The chance that bones will become preserved in the environment for thousands of years is low and depends on unlikely circumstances. For example a flood has to rapidly cover remains of an animal with sediment before scavengers consume the carcass, and the soil chemistry has to have anti-bacterial qualities that prevent microbial consumption. Then, a man has to be lucky enough to even find it. An animal had to have been abundant in its environment to appear in the fossil record. I believe most species of Pleistocene megafauna continued to exist more recently than 12,000 years ago, but most more recent populations happened to live in areas where the process of bone preservation was uncommon.
There is evidence supporting my hypothesis. The discovery that mammoths lived on the Pribiloff Islands until 5000 years ago is well known. Some suppose the geographical isolation of the island temporarily sheltered the mammoths from the continental extinction event (caused by anthropogenic activity or environmental change) of 12,000 years ago. But DNA evidence in Alaskan permafrost shows that mammoths and horses survived on the North American continent as recently as 9000 years ago. Though there are no known fossil remains this young, the sedaDNA in frozen soil is evidence mammoths and horses were shedding hair, shitting, and pissing in Alaska several thousand years past the commonly accepted extinction date. A less well known specimen, the Kenora bison, also supports my hypothesis.
Kenora is in the western part of Ontario. This region supported a relic population of Bison antiquus as late as 4830 BP.
Size comparison between modern day bison on the left and Bison antiquus on the right. DNA evidence suggests modern bison evolved from Bison antiquus, but apparently, there was a relic, geographically isolated population of the Pleistocene bison in Canada as recently as 4830 years ago.
Jerry McDonald identified the Kenora bison as Bison antiquus, an extinct species formerly known from just the Pleistocene. Carbon dating of the bones yielded a calendar year date of 4830 BP. The bones of the specimen were found by a man excavating a peat bog near Kenora, Ontario, Canada. This specimen apparently died of old age in a pond and was later covered by 14 feet of sediment. It survived a broken jaw and suffered from malnutrition. This individual was not getting enough calcium in his diet, but neither the broken jaw nor deficient diet caused his demise. The Kenora bison lived in an environment interpreted as a pine/oak woodland. (I studied the pollen graph included in Dr. McDonald’s paper and determined the trees in order of abundance were pine, birch, alder, oak, and spruce.) Lily pads covered the pond the bison died in. Perhaps, he was enjoying a last meal of lily pads before he collapsed. This specimen is the northeasternmost known occurrence of this species.
Bison antiquus evolved from Bison latifrons, an even larger, longer-horned species, about 24,000 years ago. Bison antiquus averaged 30% larger than modern bison (Bison bison) and had significantly larger horns and longer limbs. However modern bison have bigger thighs and are better runners. Scientists believe human hunters shaped the evolution of Bison antiquus to Bison bison. During the Pleistocene big cats preyed upon Bison antiquus. In response to this environmental pressure Bison antiquus were large and powerful, enabling them to fight off lions and saber-tooths when in prime condition. But humans presented a different challenge. In response to human hunting pressure smaller bison that reached sexual maturity at a younger age were more likely to survive and reproduce. Smaller, more rapidly reproducing bison replaced the larger more powerful bison. This is an excellent example of natural selection. Human hunting pressure also selected for bison that tended to migrate long distances. Bison antiquus already had migratory tendencies, but the presence of human hunters intensified this habit. Bison that traveled for many miles away from humans were more likely to survive.
DNA evidence supports the assumption that modern bison evolved from Bison antiquus beginning about 12,000 years ago. Bison antiquus was genetically much more diverse than modern bison. Every clade became extinct, except for the 1 that led to modern bison. This clade was well adapted to survive in an environment with human hunters and soon spread throughout western North America. Some scientists regard the species of bison that lived from 12,000 BP-5,000 BP to be an intermediate form between Bison antiquus and Bison bison. It’s known as Bison occidentalis.
The Kenora bison must have been from a relic population of Bison antiquus, geographically isolated from the clade that evolved into Bison bison. Perhaps the 2 populations were separated by dense forest, unsuitable for bison. This population of Bison antiquus lived in a region with a low density of human hunters. Some time after 4830 BP, this population became extinct. They were either overhunted by man or became genetically swamped by interbreeding with Bison bison as the newer species expanded its range east.
Incidentally, I believe megafauna in southeastern North America were probably the first to be wiped out by humans. This region has the best climate and year round food resources in North America, and therefore supported the earliest population of Indians dense enough to impact megafauna populations.
References:
McDonald, Jerry; and George Lammers
“Bison antiquus from Kenora, Ontario, and notes on Evolution of North American Bison”
Tributes to the Career of Clayton Ray: Smithsonian Series Publication 2002
Wilson, Michael; Leonard Hills, Beth Shapiro
“Late Pleistocene Northwest Dispersing Bison antiquus from the Bighill Formation, Gallelli Gravel Pit, Alberta, Canada, and the fate of Bison occidentalis”
Canadian Journal of Earth Science 45 2008
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