Lecture 14: Pleistocene Extinctions

When did the extinction of large animals occur in the Americas?

during the late Pleistocene-Early Holocene

What did Comte Buffon criticize the New World fauna as?

“diminutive” and “degenerated” (1766)

What would fossil evidence lead A.R. Wallace (1876) to state?

“We live in a zoologically impoverished world, from which all the hugest, and fiercest, and strangest forms have recently disappeared”

Why did Thomas Jefferson, then president, initiate the Lewis and Clark expedition to cross North America overland in 1804?

in part to search for megafauna to prove Comte Buffon wrong

What did late Pleistocene conditions in Las Vegas Valley during the LGM show evidence of?

no evidence of humans in the valley

Tule Springs Fossil Beds National Monument

held lots of fossils, which were evidence of Megafauna

What were some Late Pleistocene large mammals found in southern Nevada?

Columbian Mammoths (~14.6kya)

Two species of Bison

Three species of Horses:

Yesterday’s Camel

Two species of Ground sloths:

American Lion (Panthera atrox)

Dire Wolf (Canis dirus)

Saber-tooth cat (Smilodon fatalis)

What were the two species of Bison found in Southern Nevada?

Bison latifrans

Bison antiquus

What were the three species of Horses found in Southern Nevada?

Large stout-legged horse (Equus scotti)

Small stout-legged horse (Equus sp.)

Small stilt-legged horse (Haringtonhippus)

What was Yesterday’s Camel?

Western Camel (Camelops westernus)

What were the two species of Ground sloths found in Southern Nevada?

Jefferson’s (Megalonyx jeffersoni)

Shasta (Nothrotheriops shastensis)

What were three of the general theories to the extinction of Megafauna?

1. As classically interpreted, the ‘arrival’ of Clovis people in North America from Asia

2. Erratic swing in climate towards the end

3. Combination of the two

What did erratic swings in climate towards the end mean?

animals simply couldn’t deal with the abrupt change in climate that was too fast for them to adapt to

What was the arrival of Clovis people in North America marked by?

abundant sites across the Americas

When does the arrival of Clovis people in North America date to?

13,400 years ago

Were there any close sites in Siberia?

No

What does genetic data suggest about Clovis people?

only one single colonization event occurred

What was the Clovis First Hypothesis?

the classical interpretation where Clovis people, or “big game hunters”, followed herds through Beringia and then south through an ice-free corridor sometime between ~13,000 years ago

When did evidence of Clovis tools in N.A. date back to?

13,400 years ago

What was the Overkill Model of Megafauna extinction?

Modern Homo sapiens were novel predators that overkilled animals

How were modern Homo sapiens thought to be novel predators?

by being ecosystem engineers: through fires and built traps

Who developed the Overkill Model of Megafauna extinction?

Paul Martin in 1973

Why were extinctions not limited to N.A.?

• not temporally linked to specific climatic periods across continents (extinction occurred from 50-10ka across continents)

• not observed during previous glacial-interglacial transitions

  • strong correlation with the arrival of novel predator species, modern Homo sapiens

Why did size matter in terms of extinction?

the bigger the species was, the more likely they were to go extinct

the smaller the species was, the less likely they were to go extinct

Why did size not impact Africa Megafauna similarly?

they coevolved with humans as they figured out how to deal with humans to avoid being hunted

Spatial-temporal correlation

• percent of Megafauna extinction

• distributions of Homo sapiens

• change in temp

  • there is some correlation

What were some Pleistocene hunting technology?

atlatl

clovis point

What is an atlatl?

a spear-thrower (tool) used to provide leverage for greater velocity and distance

What is a Clovis point?

fluted stone projectile points; ~14Kya

What did technology evolve for?

hunting and big game

What were some support for human impacts in the Americas?

• Indisputable hunting of some extinct species

• Clustering of extinctions around first contact with Clovis people

• Widespread distribution of Clovis people

• Support from simulations of hunting impact

• Extinctions during the latest glacial-interglacial transition were more pronounced than during any of the earlier climate changes throughout the Pleistocene

• At the end of the last glaciation, the Northern Hemisphere plunged back into and then out of glacial conditions for decades

What were some problems with the Overkill hypothesis?

• Evidence of humans as the primary driver is predominantly correlative

• Argument uses "untested" assertions about human-environment interactions: can't test interactions with extinct organisms

• Direct evidence of megafauna hunting by Pleistocene humans is rare despite a rich fossil record: lots of evidence that humans hunted

• The argument has a political connotation that supports common environmentalist perspectives of humans as a wholly destructive species

• Data accumulating that humans may have arrived earlier in the Americas (south of Alaska)

Evidence of humans as the primary driver is predominantly?

correlative

Argument uses "untested" assertions about human-environment interactions:

can't test interactions with extinct organisms

Direct evidence of megafauna hunting by Pleistocene humans is rare despite a rich fossil record:

lots of evidence that humans hunted

The argument has a political connotation that supports common environmentalist perspectives of humans as?

a wholly destructive species

Data accumulating that humans may have?

arrived earlier in the Americas (south of Alaska)

What was the Coastal Migration Hypothesis?

Modern humans arrived much earlier in the Americas, following a coastal route by boat to jump from one ice-free patch in another until arriving south of the glaciers

Why was there no evidence for Coastal Migration Hypothesis?

evidence was washed away by coastlines/oceans

What does the Coastal Migration Hypothesis assume?

that Pre-Clovis people had their own technology and a more coastal lifestyle

There was not a lot of evidence of humans in the Americas before Clovis people, but:

• Non-Clovis style spear points and tools dating to 14 - 16 Ka

• In Paisley Cave, Oregon, human mtDNA extracted from coprolites dating to 14,300 years ago matched with common haplotypes found in modern Native Americans

• In White Sands, New Mexico, ancient fossilized footprints were found, 21,000 - 23,000 years old (children's and teenagers’ footprints)

• Several other sites with non-Clovis lithic artifacts beneath Clovis artifacts

When did Non-Clovis style spear points and tools date back to?

14 - 16 Ka

In Paisley Cave, Oregon, human mtDNA extracted from coprolites dating to 14,300 years ago:

matched with common haplotypes found in modern Native Americans

In White Sands, New Mexico, ancient fossilized footprints were found:

21,000 - 23,000 years old (children's and teenagers’ footprints)

What is the genetic data and other observations beginning to support?

the perspective that Clovis people did not migrate south from Beringia, instead their culture may have evolved in the Americas from people already here

Novel technology and culture:

allowed Clovis people to hunt Megafauna, gaining access resources not generally pre-Clovis people

Clovis populations spread

Where does this leave us?

• Evidence now seems to dispute the traditional Clovis First Hypothesis

• However, it is fairly clear that the Clovis People played a role in hunting, changing fire regimes

How does speculation remain regarding climate change?

the erratic swings in temperature would have been difficult to tolerate

Lots of evidence that both humans and climate were?

synergistic