John Robison

April 25, 1998

Pleistocene Extinctions Annotated Bibliography

Massive extinctions have punctuated the history of life on earth.

Often overlooked in the drama of the large extinctions are the Pleistocene

extinctions in which 75% of the megafauna in North America (and lesser

amounts around the world) perished. Because the smaller herbivores and

individual plant species survived, the pattern of this demise is somewhat

mysterious. Instead of a disruption occurring at the bottom of the food

chain and affecting organisms along this trophic chain, this event seemed

to affect only large herbivores in the middle of the food chain and their

predators. The 15 articles and books reviewed hypothesize on mechanisms

for processes, primarily human overkill and climate change.

The following ten articles were compiled in Martin and Wright, 1967.

Pleistocene Extinctions. Volume 6 of the Proceedings of the VII Congress

of the International Association for Quaternary Research. New Haven and

London, Yale University Press.

Martin, Paul S. 1967. "Prehistoric Overkill"

Martin describes how the pattern of extinctions of large animals coincides

with human expansion and development of technologies to hunt big game.

Terrestrial and marine flora and fauna were not affected, distinguishing

these extinctions from those of the Permian, Triassic and Cretaceous. The

niches of the organisms that died were not replaced or maintained by other

species, contrasting with other episodes of both extinction and expansion.

Martin points out that previous glaciations did not result in such

ecological catastrophes. Martin believes that the animals' ability to

migrate to suitable areas precludes theories of climate change adversely

impacting the fauna..

Guilday, John E. 1967. "Differential Extinction During Late-Pleistocene

and Recent Times."

I particularly enjoyed Guilday's introductory quote that "To single out a

particular predator or a set of circumstances is fun but futile".

The coincidence of this extinction event throughout the globe assures that

one primary factor, climate, was indeed the cause. Guilday states that

climatic changes led to desiccation and shrinkage of Parkland type

habitats, which led to intense competition among herbivores. The geography

of North America precluded migrations to more suitable terrain. The

greater food and space habitat needs of larger animals made them more

vulnerable than smaller species. Contrary to Martin, Guilday suggests that

previous glaciations also caused similar extinction events, but these are

not preserved as well within the fossil record. Guilday acknowledges the

influence of man under certain specific circumstances, but dismisses the

overkill hypothesis as the primary impetus for the extinctions.

Edwards, William E. 1967. "The Late-Pleistocene Extinction and Diminution

in Size of Many Mammalian Species."

Edwards notes that the hunting selection of larger organisms, differential

intensity of extinctions and rapidity of the extinctions could be caused

by several factors, including climatic change, human hunting and parasitic

disease. The spread of disease through reconnected populations of

gregarious mammals is a new theory for discussion. As animals populations

were separated during the glaciation, diseased continued to evolve and

when these mammals were reunited with the ice retreat, large epidemics may

have occurred. Disease may have depleted the populations of larger,

slower-breeding and more gregarious mammals. However, diseases rarely

result in total extinction as populations become isolated and gain

resistance. Edwards goes on to discount Guilday's competition theory

because only bison replaced the camels, horses, mammoths and larger bison.

Edwards also states that the shift in climate was so gradual that it would

be imperceptible to a single generation of mammals, precluding the need

for major migration adjustments.

He invokes preferential hunting of larger individuals as an explanation of

the decrease in body size of the Pleistocene mammals because previous

glaciations had no such effect.

Slaughter, Robert H. 1967. "Animal Ranges as a Clue to Late-Pleistocene

Extinction."

Slaughter suggests that larger temperature ranges at the end of the

Pleistocene disrupted entrenched mating habits. He states that

long-gestation periods rather than body size was the common denominator of

the extinct mammals. Animal species normally giving birth in a narrow time

period in the spring would experience poor success due to unpredictable

extreme cold snaps or heat waves which reduce sperm amounts. Slaughter

disregards the evidence for desiccation, citing simultaneous increases in

rainfall amounts in nearby locations. In addition, the geography of North

America served to isolate species and restrict migration. I found this

essay to be particularly unconvincing.

Hester, James J. 1967. "The Agency of Man in Animal Extinctions."

Hester examines known human-caused extinctions and concludes that

prehistoric man was too few in numbers and lacked the means to exterminate

a species. Climatic changes and the associated habitat losses were cited

as the primary force behind the extinctions. In North America only mammoth

and bison were hunted significantly by early man. Other common prey

species in Europe such as reindeer and wild horses survived whereas

unknown known prey such as camels perished. He concludes that most species

were already spiraling toward extinction before man arrived in North

America.

Jelinek, Arthur J. 1967. "Man's Role in the Extinction of Pleistocene

Faunas."

Extensive vegetation available in Africa allowed a more omniverous

subsistence pattern for humans while in Northern regions meat was a

primary food source. As others have mentioned, previous glaciations did

not result in such extinctions. Because old world mammals were accustomed

to human hunting, the horses, elephants, pigs and camels in Europe

survived, while their naive counterparts in North America were caught

unawares by early hunters. He also cites climate stress as another factor,

but dismisses Slaughter's range analyses.

Mehringer, Peter J. "The Environment of Extinction of the Late-Pleistocene

Megafauna in the Arid Southwestern United States."

Based on paleobotany, the time period following the glaciation should have

seen an increase in animal habitat and populations. Pollen records show no

reduction in habitats. Because the habitats occupied by the now extinct

fauna were variable, some should have survived shifts in climate. He also

cites the success of reintroduced horses in extremely dry areas that

extinct horses also inhabited and perished from. In addition, the

temperature tolerances of animals was variable, and he finds that there

were no barriers for animal movement An additional reason must be sought.

His reason for the extinction following this last glaciation is the

extremely variable temperatures. Such extremes may have gradually led to

extinctions in several thousand years. I found the support for this idea

to be rather thin.

Irwin-Williams, Cynthia. 1966. "Associations of Early Man with Horse,

Camel an Mastodon at Hueyatlaco, Valsequillo."

This paper is a detailed analysis of fluvial deposits housing a variety of

Pleistocene fossils. Evidence of hunting and butchering argues that early

man did not prey exclusively on mammoths and mastodons, but included

horses and camels in his diet. Irwin then describes in great detail the

archaeological process of excavation, stratigraphy and discusses various

artifacts.

Kowalski, Kazimierz. 1967. "The Pleistocene Extinction of Mammals in

Europe."

Based on the small size of refugia in southern Europe where animals

survived the Pleistocene, human hunting does not confer overkill, Animals

extensively hunted such as reindeer, wild horse and red deer survive to

this day while more difficult prey such as woolly mammoths, woolly

rhinoceros, cave bear lions and hyenas died out. He concludes that the

extinction of the woolly mammoth, woolly rhinoceros and Irish elk were due

to climatic changes

Vereshchagin, N. K., 1967. "Primitive Hunter and Pleistocene Extinction in

the Soviet Union."

The author joins many other researchers in claiming that climatic changes

were the primary cause, but that human influence helped push them over the

brink. Evidence has been found for hunters using the meat and the skins of

23 different mammals. Man's carnivorous habits enabled him to expand into

harsh steppe land. There is ample evidence for massive cliff drives in

which much of the animal was wasted. Spring floods, ice storms, and the

expansion of coniferous forests also had negative impacts on the

megafauna.

Martin, Paul S. 1973. "The Discovery of America." Science vol. 179:

969-973.

In the article we used for discussion, Martin describes the wave and

consumption rate of early man. Martin expounds on his theory of overkill

but overlooks several important questions. As Martin describes the

continued naivet of the North American fauna, I can't help but imagine

that some prey species would have learned to defend themselves. However, I

am partially convinced by his arguments, particularly the straightforward

logic of associating large mammalian losses with the arrival of a

specialized big game hunter.

Beck, Michael W. 1996. "On Discerning the Cause of Late Pleistocene

Megafaunal Extinctions." Paleobiology, 22(1): 91-103.

Beck attempts to solve the debate by analyzing a testable hypothesis that

large animals should have gone extinct along the front of human hunters.

According to the Blitzkrieg hypothesis, the most recent fossils should be

found farther south. Beck's research finds just the opposite pattern. Beck

confirmed that the extinctions occurred within a time period, consistent

with both climate and overkill theories. Beck calls for a set of new,

testable, hypotheses to end the stalemate of rhetoric versus rhetoric.

Alford, John J. 1973. "The American Bison: An Ice Age Survivor."

Proceedings Ass. Am. Geog.: 1-6.

Alford notes a decrease in prehistoric bison populations at the same time

period of the Pleistocene extinctions and rejects both the climate and the

overkill hypotheses. In his analysis, Alford calculates animals numbers

from fossil frequencies, a correlation I feel is unsubstantiated. He uses

these numbers to show that bison were expanding just when they should be

experiencing hunting pressures from humans. He summarily dismisses

changing climate on a handful of contradictory pollen results. I found

this report oversimplistic and lacking in fresh theories to replace the

ones dismissed.

Martin, Paul S. 1992. "The Last Entire Earth." Wild Earth. Vol. 2. Number

4. 29-32.

This popular article begins with Martin musing about our conceptions of

extinct megafauna. After exploring dating methods, Martin proposes his

blitzkrieg theory, while acknowledging other explanations such as climate,

disease and competition. This article echoes with philosophy and excerpts

from Thoreau.

Haynes, Gary. 1991. Mammoths, Mastodonts and Elephants. Cambridge

University Press, New York.

In this excellent review, Haynes adds his own knowledge of proboscidean

ecology to the current debates. His summary of Pleistocene extinctions is

a treasure trove of relevant articles and opinions. Haynes believes that

climate change led to a die off and that human hunting amplified the

losses to a die out. I find myself most drawn to his arguments.

Ward, Peter D. 1997. The Call of Distant Mammoths. Copernicus Press, New

York.

Ward spends a large amount of time introducing basic ecological and

geological concepts before finally examining the Pleistocene extinction

events. Topics range from time travel to natural selection. Toward the end

of the book, he explores new analysis techniques but does not reference

them. I found this text to be a good overview of the literature, but not a

very efficient one.

Lister, Adrian and Bahn, Paul. 1994. Mammoths. Macmillan, New York.

In this coffee table text, a description of mammoth fossils and natural

history is followed by a discussion of the extinction theories. The last

chapter provides a good overview of this debate along with lots of glossy

photos.