Ice Age Extinctions of the Megafauna Essay

This essay has a total of 3355 words and 14 pages.

Ice Age Extinctions of the Megafauna



Lisa Gantenbein
ANTH 365U
March 15, 2000


ICE AGE EXTINCTIONS OF THE MEGAFAUNA



During the last Ice Age before humans arrived, the North American continent belonged to
various forms of enormous, fantastic creatures. By the end of the Ice Age, most of these
large animals had become extinct. Numerous attempts have been made to explain the
disappearance of these animals, but there has yet to be a consensus. Among the theories
that have been debated, two are predominant. They are the climatic change theory, and the
overkill theory. The climatic change theory advocates the idea that the global warming,
which brought about the end of the Ice Age, caused the animals to die off. The other is
the overkill theory, which maintains that humans, by over hunting the animals, are
responsible for the extinctions. It is likely that many of these animals became extinct
at the end of the Ice Age due to a combination of climatic change and overkill.

The Ice Age, which began about one and a half million years ago, is also referred to as
the Pleistocene Epoch. Much of the Pleistocene falls within the geological time period
called the Quaternary stage. We are still in the Quaternary today. The Ice Age consisted
of a series of glacial advances and retreats called glaciations and deglaciations. There
have been a total of at least twenty glaciations, including four or five that were
significant, in the last 2.4 million years.

In the most recent glaciation, thirty percent of the earth was covered in sheets of ice
over two miles thick. The last glaciation in North America is called the Wisconsin. The
Wisconsin glaciaciation began 122,000 years ago. The advance of the Late Wisconsin began
35,000 years ago. The ice sheets, called the Laurentide and the Cordilleran glaciers
stretched southward to the middle of the continent, covering most of what is now Canada
and the area in the Pacific Northwest from Alaska to Tacoma. On the eastern half of the
continent, the ice covered the area to about the middle of where New York is today.
Diverse environmental conditions south of the ice sheets remained as they were, but in the
northern half of the continent, regions that had once been surfaced with dense forests,
fertile land, and abundant game, turned cold, and barren.

The expanding glaciers in the Ice Age forced sea levels to drop between 330 and 490 feet,
opening a passage between Siberia in northeastern Asia and Alaska in North America. This
passage was a strip of land, called the Bering Land Bridge. The land bridge still exists
today, but is immersed under water. When sea levels were lowered by 330 feet, a 1000 mile
wide strip of land was exposed. It surfaced and submerged many times throughout the Ice
Age, and is believed to have been exposed for much of the time between 75,000 and 14,400
years ago. New research shows that the land bridge may have even been exposed until as
late as 11,000 years ago.

This land bridge was the route of migration for a large variety of mammals crossing
between Asia and North America. Some of the animals arrived long before the glaciation of
North America. The animals that migrated to this continent adapted to their new
surroundings. Many of the animals living on the continent were herbivorous and extremely
large compared to the present fauna. These huge, plant eating animals are called the
megafauna.

Some of the most well known megafauna are the Probocidea. Animals with trunks, which
include the mastodon (Mammut) and the mammoth (Mammuthus) of the Ice Age, and the two
modern species of elephants, belong in the order Proboscidia. The mastodon probably
traveled alone rather than in a herd, browsing on Spruce limbs in open woodlands. The
mammoths migrated into North America by at least 1.7 million years ago (Haynes, 1991).
They traveled in herds and generally grazed in vast grasslands. The types of vegetation
that these animals consumed, can be determined bye observing the structures of their
teeth. A new mammoth species evolved from the original mammoths as they migrated from
Eurasia, over the Bering Land Bridge, leaving substantial populations in Beringia as they
progressed southward. This new species was called the Columbian mammoth (Mammuthus
columbi). The Columbian was a larger mammoth well adapted for the North American
grasslands.

While the Proboscidea originated in Asia and Africa and migrated to North America, other
animals evolved in the New World and traveled across the land bridge in the opposite
direction from North America to Eurasia. Among the genera that originated in the New
World was the horse (Equus). Horses migrated to Asia and Europe during a period when the
land bridge was exposed. Before the mass extinctions, the horse became one of the most
populous mammals in North America. By the end of the Ice Age, the horses had completely
died off in the New World, but survived in Eurasia. The horse exists, now and even
abounds in the New World, because it was reintroduced in the sixteenth century by
Europeans. Other Ice Age animals include such varied genera as the glyptodont
(glyptotherium), the ground sloth (Eremotherium), and the giant beaver (Castoroides
ohioensis). What is notable and extremely interesting about these animals is that they
have many similarities, but are much larger than their modern day counterparts. For
example, the glyptodont, similar to a turtle, would have been comparable in size to a
Volkswagen Beetle. The ground sloth reached weights of up to three tons, about the size
of a mammoth, and the giant beaver was about the size of a black bear (Grayson, 1993).

About 18,000 years ago, the Wisconsin glacier began its retreat. Buried lands began to
reveal themselves. Strong winds spread seeds planting various types of new vegetation
along the banks of the glaciers. By the time of 10,000 years ago, the glaciers retreated
to the size they are today. This point marks the end of the Pleistocene and the beginning
of the Holocene.

Such an extensive variety of animals, large and small, thrived on the continent until the
end of the Pleistocene. At this point most of the megafauna had vanished. Thirty-five
genera of mammals that once wandered this land, and nineteen genera of birds are now
extinct. Archeological research shows that none of these extinct animals existed after
10,000 years ago. Of the thousands of archeological sites in North America, not one has
contained the remains of any extinct animal that proves to be younger than 10,000 years
old (Grayson, 1993). It was once assumed by many people that all thirty-five genera
became extinct in the short period of time between 10,000 and 12,000 years ago. This
presumption emerged when six of the genera were proven to have disappeared in the span of
two-thousand years. That was in 1969, and since then, only the extinctions of three more
genera have been placed in the same time period (Grayson, 1993). It is possible that the
other twenty-six genera became extinct at the same time, but if that is the case, we have
a long way to go before it will be proven. The other feasible possibility is that the
extinction’s happened thousands, or even millions of years ago.

The climatic change brought about the end of the Ice Age. It resulted in a number of
physical environmental changes. The temperature of the earth grew increasingly warm,
resulting in a greater difference in seasonal temperatures. The glaciers melted away,
causing sea levels to rise and shore lines to recede. The general hypothesis of the
climatic change theory is that a mixture of factors, such as environmental and ecological
changes that resulted from the warming climate, wiped out the megaphone. Could this
climate change of the last glacial retreat be the cause of these extinction’s? For
decades, scientists have deliberated the question which is surrounded by controversy.
They have considered many different models of explanation that comply with the general
hypothesis of the climatic change theory. One idea comes from Peter D. Ward as follows:


As the glaciers receded, a profound reorganization occurred in hydrological, biological,
and sedimentological systems. The world’s ice coverage changed from 30% of its surface to
the current level of about 10%. This phase change of so much water from solid to liquid
was the driving force behind much of the subsequent geological, climatic, and biotic
transformation. As the ice melted, water and sediment choked the rivers; they altered the
drainage of great lakes and, in breaking the ice dams that had formed some of these lakes,
caused cataclysmic floods that themselves changed the face of North America (the channeled
scab lands of Washington State and Idaho are examples). The continental shelves changed
positions and depth as the shorelines migrated inward under rapidly rising seas. Rainfall
patterns shifted; the seasons themselves were lengthened or shortened. Temperatures rose
all over the earth. And of course, in the wake of so much physical perturbation to the
environment, biotic systems changed. These great changes in the physical environment are
at the heart of many scientists’ belief that the large-animal extinction at the end of the
Ice Age was brought about by physical or environmental changes, not by human hunting. The
extinction of many species in a broad environment must involve many variables in both
biotic and physical spheres, because ecosystems are complex. Physical changes may bring
about the death of one species, and its disappearance then affects other species, such as
its predators, prey, and parasites. In this way even a single extinction causes effects
that ripple through the ecosystem. At the end of the age of glaciation, many species
faced environmental changes, and surely many succumbed before they could adapt or migrate.
Habitat destruction is probably the major cause of physically induced extinction.

(Ward, 1997:155-156)

One may wonder why, if the climatic change ended the existence of the megafauna, did it
not affect the smaller animals in such dramatic ways. The likely answer that large
animals have more difficulty adapting to new environments than do smaller animals. Larger
animals are safer from predators than small animals are, but it is also harder for them to
sustain in trying conditions. Many of the larger animals such as mammoths and bison
travel in herds, and that, along with their large size, protects them from predators.
However, when the predator is Mother Nature, there is virtually no defense. For modern
day elephants, drought is the biggest concern. It can take twenty percent of a herd every
year, but the elephants continue to exist (Ward, 1997). It would have been harder though,
for the mammoths and mastodons to survive a drought. Because of their size and weight,
the Ice Age Proboscidea had longer gestation periods, which meant lower birth rates. If
Continues for 7 more pages >>




  • Ice Age Extinctions of the Megafauna
    Ice Age Extinctions of the Megafauna Lisa Gantenbein ANTH 365U March 15, 2000 ICE AGE EXTINCTIONS OF THE MEGAFAUNA During the last Ice Age before humans arrived, the North American continent belonged to various forms of enormous, fantastic creatures. By the end of the Ice Age, most of these large animals had become extinct. Numerous attempts have been made to explain the disappearance of these animals, but there has yet to be a consensus. Among the theories that have been debated, two are predom
  • Fossils
    fossils Fossil Project On Saturday 12th 2000, my family and I went on a float trip on the Huzzah River in Steelville, Missouri. The Huzzah River and its surroundings were a perfect location for me to look for my fossil. Since the water level was shallow, that enabled me to look to the river bottom. Almost immediately after I began my search near the edge of the river, I spotted a rock that appeared to have some sort of shell embedded in it. I decided this would be a good specimen for me to try t
  • COEXISTENCE OF HUMANS AND MEGAFAUNA IN AUSTRALIA
    COEXISTENCE OF HUMANS AND MEGAFAUNA IN AUSTRALIA Troublesome Questions In 1830 Mr. Rankin tied a rope around a projection out of a rock face in order to lower himself into Wellington Cave (Horton, 1980). The projection turned out to be the bone of a giant extinct marsupial. It was to be the first discovery of a great range of giant marsupials. Were these animals extinct?? Horton (1980), describes how Leichhart believed that on his journeys to northern Australia he would find Diprotodon still roa
  • The west
    the west On Jan. 24, 1855, Henry David Thoreau sat down to his journal to reflect on all the ways his homeland had changed since the first English colonists had arrived on the shores of Massachusetts two centuries earlier. For several days, Thoreau had been reading the accounts of some of the earliest settlers. Compared to the America they had found, Thoreau reflected, his experience in the forests was like listening to a symphony played without most of the instruments. As he further considered
  • The west
    The west The West that was, and the West that can be by Dan Flores On Jan. 24, 1855, Henry David Thoreau sat down to his journal to reflect on all the ways his homeland had changed since the first English colonists had arrived on the shores of Massachusetts two centuries earlier. For several days, Thoreau had been reading the accounts of some of the earliest settlers. Compared to the America they had found, Thoreau reflected, his experience in the forests was like listening to a symphony played