<extinct.htm> <Archeology> <Index>
PLEISTOCENE EXTINCTION OF MAMMALS
IN
AMERICA
E. F. Legner Professor Emeritus, University of California (Contacts) Please CLICK on highlighted sections for detail: The magnitude of the dynamic forces that began in
the Western Hemisphere about 10,000 B.C. is truly astounding. Prior to that period many portions of the
Americas resembled some of the African scene of today, but with even more
species present. There were large
herds of herbivores and correspondingly smaller numbers of carnivores. Pleistocene animals in great abundance
were camels, guanacos, horses, mammoths, mammoths, mastodons, bovines, ground
sloths, saber-tooth cats, tigers, lions, etc. The recent construction of a reservoir in western Riverside
County, California turned up great quantities of the remains of the
herbivorous species, and provided good evidence of their large population
size. However, by 9,000 B.C. most of them had disappeared! Only the guanacos and tree sloths remained
in South America, and the bison in North America. There were few herds of bison west of the Rocky Mountains. Three hypotheses attempt to explain
this mass extinction. (1) The first
hypothesis assumes that Amerindians slaughtered them all: an imperceptive suggestion! An argument against this notion is that in
Southern California, Amerindians did not inhabit the region earlier than about
7,000 B.C. In other words, people
were present there no earlier than 2,000 years AFTER the animals had disappeared! Also when Europeans first ventured en masse to America in the
15th Century, the natives were found to live amidst vast herds of bison and
other herbivores, upon which they depended for food. Similarly, the Pleistocene mammals became
extinct inland from the 16,000 B.C. Monte
Verde site in Chile, although humans had rarely ventured far inland from
the coast by 10,000 B.C.
Nevertheless, Jared Diamond seems to support human
involvement in the extinction vicariously by suggesting that it did not occur
in Africa because of a longer period of co evolution with humans in the sub
Saharan region. (2) A second hypothesis points out that the
ice age had just ended abruptly and climates changed to a warmer, drier cycle
by 9,000 B.C., but this does not account for the vastness of the extinction
(from both North & South America).
At the same time, climates became warmer and drier in the Eastern
Hemisphere (Europe-Africa-Asia), but horses and camels, both of which
originated in the Americas, diversified and flourished. (3)
A third hypothesis proposes, without evidence, that some devastating
widespread disease decimated the animals, something uncharacteristic of
pathogens and unprecedented in all of the world’s history. Some of the extinctions in America seem
obviously associated with the reduction in plant cover with a drying of the
landscape. An example is that of the
saber-tooth cat that is believed to have stalked its prey from the cover of
tall grass and brush. When such cover
was reduced in the drier climate this hulking and heavy animal was less
efficient in surprising and capturing its primarily ungulate prey. There is evidence from the La Brea tar
pits in California that many of the saber-tooth cats had sustained great
physical injuries resulting from difficulties in capturing their prey. The
prey, such as bison and horses, also diminished in size and gained fleetness at
the same time. It has also been
suggested that dietary limitations on horses caused them to become extinct
under the drier conditions. However,
when horses were reintroduced during the European colonization, they
flourished in large wild herds, which have remained abundant to the 21st
Century, even under the increased pressure of human settlement. Dr. Dee Simpson, recently deceased, believed that Homo erectus could have made it to the
Americas (personal communication), and she suspected that the Calico,
California dig site was possibly a H. erectus camp. Could there have been large numbers of a
separate race of humanlike people present in Pleistocene America that stemmed
from Homo
erectus stock, which then eliminated itself as well as the animals? Well, that argument is weak also as there
is no archeological evidence for such a large population around the time that
the animals’ extinction occurred (10,000-9,000 B.C.). Finally, it is noteworthy that Plato
mentions the disappearance of a great civilization on the earth around 9,000
B.C.! As of 2009, available evidence to explain the mass
extinction has pointed to the crash of a massive asteroid in northeastern
Canada, which gave rise to widespread dust clouds and changes in Atlantic Ocean
currents. This in turn led to
excessive droughts and other ecological disruptions that greatly restricted
the available food supply for many large mammals. It also led to emigrations of humans from the Eastern portions
of North America to points west and southwest. |