North American views of Pleistocene mammal extinctions

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North American views of Pleistocene mammal
extinctions

• GEOG 4053
• Week 12

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Theories that explain global mass extinctions at
the end of the Ice Age

• Overkill
• Climate change
• Co-evolutionary disequilibrium
• Mosaics, allelochemics and nutrients
• The Zig-Zag theory
• Meteorite impact

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Arrival of humans
Humans presence
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Radiocarbon dates of animal remains associated
with human sites
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Overkill theory in NA
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Overkill group of theories

• Overkill
• Blitzkrieg (rapid kill)
• Sitzkrieg aka indirect kill (fire, introduction
  of exotic species and habitat fragmentation)

First author Paul Martin
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Climate change theory
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Climate change theory
Restructuring of predators
Climate change
Restructuring of herbivores
Vegetation change
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Co-evolutionary disequilibrium

• R. Graham and E. Lundelius
• The concept of disharmonious faunas

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Mosaics, allelochemics and nutrients

• R. Dale Guthrie (U. of Fairbanks, Alaska)
• Based on the existence of the mammoth steppe
• Highly complex theory, but quite possible. It
  dismisses the effects of humans

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New theories?
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The Zig-Zag theory

• It combines climate change and human hunting, but
  puts most of the blame on hunters.
• Developed for South America.
• It hasnt been tested in North America
• It is difficult to test it in North America.

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Differences in extinctions in N. and S. America

• North America
• Extinctions occur between 13,000 and 12,000 years
  ago
• They happened in less than 400 years

• South America
• Extinctions occur between 12,000 and 6,000 years.
  The majority occurred at the beginning of this
  period.
• It took about 6,000 years.

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Similarities between N. and S. America

• Humans arrive in the two continents almost at the
  same time, but obviously earlier in North
  America.
• Both areas had rapid climate change that may have
  stressed vegetation and fauna.

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Differences in vegetation change in N. and S.
America at the end of the Pleistocene

• North America
• Less influence from the tropics
• Vegetation opened up in the center and west, but
  became more closed in northern areas.

• South America
• More influence from the tropics
• Vegetation got more closed in most of the
  continent.

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The most recent theory

• The Meteroite Impact

Firestone, R.B. and a list of authors. 2007.
Evidence for an extraterrestrial impact 12,900
years ago that contributed to the megafaunal
extinctions and the Younger Dryas cooling.
Proceedings of the National Academy of Sciences,
104(41) 16016-16021.
National Geographic and PBS have a video on it!
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Analysis of extinctions
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Rancholabrean herbivore assemblages in North
America
Most common Holocene large herbivores (survivors)
Extinct after cal. 12,900 years BP
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Lubbock Lake Landmark Site, Lubbock, TX