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EXTINCTIONS OF BIG GAME 1365
EXTINCTIONS OF BIG GAME
Todd A Surovell, University of Wyoming, Laramie,
WY, USA
ã 2008 Elsevier Inc. All rights reserved.
Glossary
Blitzkrieg A specific form of the overkill hypothesis formulated
by Paul Martin with respect to Pleistocene extinctions in the
Americas. In blitzkrieg overkill, humans encounter faunas naı̈ve
to human predation making them extremely susceptible to
extinction by hunting. Rapid human population growth and
geographic spread are fueled primarily by hunting of large game,
and human colonization and faunal extinctions are complete
within a millennium.
Hyperdisease A hypothesis developed by Ross MacPhee and
Preston Marx to explain the extinction of Quaternary faunas.
The hyperdisease hypothesis argues that many prehistoric
‘‘first-contact’’ animal extinctions are explained by the
introduction of hyper-virulent and hyper-lethal diseases first
introduced to animal populations by colonizing humans and/or
their domesticates (e.g., domestic dogs).
Megafauna A term generally used to refer to the largest animals
present within an ecosystem, most often used with respect to the
array of large-bodied species which suffered extinction during
the Quaternary. A strict definition refers to animal species
weighing more than 44 kg (approx. 100 lbs).
Overkill hypothesis The hypothesis that most animal
extinctions of the Quaternary can be directly or indirectly
attributed to predation by humans.
Sitzkrieg A hypothesis developed by Jared Diamond to explain
the extinction of Quaternary faunas. The sitzkrieg hypothesis
refers to slow, drawn-out extinction events caused by secondary
human effects, such as deforestation, anthropogenic burning,
and general habitat modification.
humans and hominids lived side by side with the
woolly mammoth, rhinoceros, cave bear, giant deer,
and straight-tusked elephant for thousands of years.
They even left painted depictions of some of these
animals on cave walls (Figure 1). When humans first
arrived in Australia some 50 000 years ago, the island
continent was inhabited by a menagerie of marsupial
mammalian, avian, and reptilian megafauna. Yet by
comparison, the world’s large fauna of the modern
era are much reduced in diversity and geographic
extent. Surprisingly, though the extinctions of the
Quaternary are the most recent ‘mass extinction’ of
the fossil record, the issue of cause remains largely
unresolved.
The idea that humans caused Late Pleistocene
extinctions through over-hunting is known as the
‘overkill hypothesis’, but other explanations have
been proposed. For example, some argue that Quaternary extinctions may have been caused by climate
and ecological changes that have occurred during the
last two million years. Others suggest that extinctions
may have resulted from the introduction of novel and
highly lethal pathogens by humans to populations
of animals. Still other researchers have proposed
multi-causal explanations that point to both human
and natural causes. Of course, extinctions of all taxa
in all places and times in the Quaternary need not
have the same cause. Different factors may account
for animal extinctions over time and space, and
dauntingly any or all of these explanations could be
correct when viewed at a global scale.
Introduction
Over the last two million years, humans and our
hominid relatives have witnessed a broad wave of
animal extinctions deemed by some as the sixth mass
extinction to have affected the biological communities of the Earth. Mass extinctions are characterized
by dramatic increases in extinction rates in fossil
assemblages – large numbers of species disappear
from the fossil record over brief windows of geologic
time. Although the causes of recent extinctions
remain unresolved, some researchers argue that
humans were not mere witnesses to but were instead
directly responsible for the extinction of most taxa
that disappeared from the fossil record within the last
two million years.
There is little question that prehistoric peoples of
the New World coexisted with mammoths, mastodons, camels, horses, and a myriad of other nowextinct animals. In Europe and Asia, Palaeolithic
What Happened to the Megafauna?
The Overkill Hypothesis
The overkill hypothesis states: ‘‘the majority of animal extinctions that have taken place over the Quaternary have resulted directly or indirectly from
human hunting.’’ Proponents of overkill do not
claim that humans caused all animal extinctions of
the Quaternary; nor do they claim that all humancaused extinctions resulted from over-hunting of
extinct prey. For example, extinctions of large carnivores might have resulted from competition with
humans rather than direct human predation of carnivores. The argument is simply that prehistoric
human hunting dramatically modified animal communities, and had humans not colonized the planet, most
of the species that suffered extinction during the Pleistocene and Holocene would still exist today. Although
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1366 EXTINCTIONS OF BIG GAME
the origins of overkill can be traced to the nineteenth
century, overkill was championed in the latter half of
the twentieth century by Paul Martin, a palaeoecologist at the University of Arizona.
Figure 1 Line drawing reproductions of Upper Palaeolithic cave
paintings of extinct Pleistocene fauna. Irish elk, Lascaux cave a,
woolly mammoth, Rouffignac cave b, cave bear c, and two-horned
rhinoceros d, Chauvet cave.
The keystone to Martin’s argument was the apparent widespread occurrence of ‘first contact’ extinctions across the globe. With the important
exceptions of the continents of Africa, Europe, and
Asia, waves of animal extinctions immediately followed initial human colonization of many regions of
the world (Figure 2). In the 1970s, when considering
extinctions in the Americas, Martin developed his
most explicit formulation of the overkill hypothesis,
a model he called ‘blitzkrieg’. With mathematician
James Mosimann, Martin constructed a computer
simulation which showed how humans could have
colonized the entirety of the unglaciated New
World from southern Canada to Patagonia within
1000 years (Figure 3). Rapid population growth and
migration would have been fueled by hunting of nowextinct Pleistocene mammals. These animals which
had never experienced human hunters would have
been naı̈ve and easily killed.
Although the overkill hypothesis (or variations
thereof) applied to oceanic islands extinctions is
generally accepted today, whether overkill explains
extinctions on continents remains highly controversial.
The most serious obstacle to overkill is that in most
regions archaeological evidence for human exploitation of extinct taxa is scarce. In North America, for
Continents
Islands
Colonization by:
Archaic Homo
Modern Homo
1000
Years before present
Major extinctions
10 000
100 000
1 000 000
Australia
2 000 000
3 000 000
Europe
South
North America
America
Caribbean
Mediterranean
New
Zealand
Madagascar
Geographic region
Figure 2 The relative timing of human colonization and the major wave of animal extinctions for various continents (left) and islands
(right). Solid colors and lines indicate certainty about age. Dashed lines and colors indicate uncertainty about age. Age axis is log-scaled.
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EXTINCTIONS OF BIG GAME 1367
13
15
13
0B
P
400
BP
example, although 33 genera of large-bodied mammals suffered extinction during the Late Pleistocene,
fewer than five can be shown to have been utilized by
humans. If humans caused the extinction of North
American species by over-hunting, then they must
have killed thousands if not millions of animals,
which begs the question, ‘Where is the archaeological
evidence?’ Martin has argued that if blitzkrieg-type
overkill happened very quickly, little archaeological
evidence would be expected. For others, however, this
lack of direct evidence has meant that perhaps we
should be seeking explanations for extinctions elsewhere, such as in the dramatic swings in global
climate that have occurred during the Quaternary.
12
83
0
BP
13 050 BP
Climate Change
12 700 BP
12 600 BP
12 500 BP
12 400 BP
Figure 3 The Martin/Mosimann ‘blitzkrieg’ model of Pleistocene
extinctions. Humans enter North America via the ‘Ice-free corridor’
at approximately 13 400 BP, and rapidly colonize the New World
within 1000 years. Human range expansion takes the form of a
traveling wave. Along the wave front, naı̈ve Pleistocene fauna are
hunted to extinction. Redrafted from Figure 2 from Martin PS
(1973) The discovery of America. Science 179, 969–974.
Glacial
Climate:
Variations in the Earth’s orbit over the last two million years have caused climate to oscillate between
glacial and interglacial conditions. There were more
than 20 instances when continental glaciers expanded and contracted over the Northern Hemisphere
(Figure 4). As continental glaciers waxed and waned,
oceanic and atmospheric temperatures cooled and
warmed, sea levels fell and rose, precipitation
regimes were greatly modified, and plant and animal
species migrated and reorganized ecological communities. Because swings in climate had major impacts
on biological organisms, there is no doubt that animal extinctions could have resulted, but there is
considerable argument about how climate change
might cause mass extinctions, and whether climate
change explains the observed extinctions of the
Quaternary.
Interglacial
Less
δ18 O
3
4
5
Volume of glacial ice
2
More
6
0
100 000
200 000
300 000
400 000
500 000
Years before present
Figure 4 The last five glacial cycles recorded in stable oxygen isotopes from benthic foraminifera recovered from a core of the Pacific
Ocean floor. Oxygen isotopes of marine foraminifera record the isotopic composition of ocean water which is a direct reflection of the
volume of glacial ice in terrestrial settings. High values of d18O indicate glacial periods. Low values of d18O, like those observed in modern
times, indicate interglacials. Data from Mix AC et al. (1995) Benthic foraminferal stable isotope stratigraphy of site 846: 0–1.8 ma’.
In: Pisias NG et al. (eds.) Proceedings of the Ocean Drilling Program. Scientific Results 138, College Station, TX, USA. 839–854.
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1368 EXTINCTIONS OF BIG GAME
A handful of models have been proposed which
attempt to link Quaternary climate change to extinctions. Unlike overkill models, climate change hypotheses are typically constructed with reference to specific
geographic regions because extinctions occurred at
different times in different parts of the world. The
most explicit climatic/ecological extinction models
have considered North America. For example, Dale
Guthrie, a vertebrate palaeontologist at the University
of Alaska, has argued that the transition from glacial to interglacial climate in North America (20 000–
10 000 years ago), resulted in vegetational communities
that would have been detrimental to many species
of Pleistocene megafauna. Lower levels of seasonality
and longer growing seasons in Pleistocene ecosystems
produced high-diversity mosaics of vegetation that
would have permitted large herbivores to easily meet
their nutritional requirements. With the transition to
the Holocene, North American biomes were transformed into large-scale low-diversity patches wherein
generalist feeders with simple digestive tracts, such
as mammoths, mastodons, sloths, and horses would
essentially starve, or due to anti-herbivory toxins, be
poisoned to death by being forced to eat large quantities
of toxic foods, to which these animals had little physiological resistance. According to Guthrie, only large
mammals with specialized diets or physiologies, such
as bison, pronghorn, and moose, thrived in Holocene
ecosystems.
Climate-based hypotheses, like overkill, suffer
from many problems. Most commonly, it is questioned why it was a particular climate change that
caused the extinctions. For example, in the Americas,
extinction correlates with the most recent transition from glacial to interglacial climate, but this
was just one of many such transitions that occurred
during the Pleistocene. Proponents of overkill would
argue that this episode of climate change just happens to correlate with the first arrival of human
migrants; proponents of climate hypotheses would
argue that this period of climate change was uniquely severe. Also, proponents of climate hypotheses
must explain why extinctions seemingly always correlate with human colonization. If humans had no
causal role in Pleistocene extinctions whatsoever,
then the timing of extinction should be independent
of human global colonization, and yet human migration and animal extinction seem to be highly correlated (Figure 2).
Hyperdisease
Due in part to problems with overkill and ecologicalclimatic hypotheses, a third major contending explanation for Pleistocene extinctions has come to the
fore – hyperdisease. This idea, proposed by palaeontologist Ross MacPhee and virologist Preston Marx,
can explain two aspects of Quaternary extinctions
with which overkill and climate change struggle.
Climatic models fail to explain the global pattern
of ‘first contact’ extinctions, and overkill struggles
to explain the paucity of archaeological evidence
demonstrating human hunting of extinct fauna.
MacPhee and Marx propose that extinctions were
caused by the introduction of ‘hypervirulent, hyperlethal diseases’, which they call ‘hyperdiseases’, by
humans or domestic dogs to naı̈ve populations of
animals, naı̈ve in the sense of having no immunity to
such pathogens because they had no prior experience
with them. The hyperdisease hypothesis predicts that
extinction should follow a first contact pattern and
should produce little archaeological evidence of
human exploitation of extinct animals.
However, the disease model has yet to successfully
overcome a range of potential theoretical setbacks:
(1) Foremost, it is unclear whether a disease is capable
of driving any species to extinction under natural
conditions. (2) It is also unknown if a single disease
could infect such a broad range of species as those lost
during the Quaternary. (3) Finally, this hypothesis is
very difficult to test. Efforts are in progress to attempt
to recover pathogens directly from remains of extinct
animals or from their fecal matter, but even if pathogens are discovered, it will be difficult to determine if
in fact the identified pathogen is the sought-after
hyperdisease.
The Keystone Herbivore Hypothesis
South African ecologist Norman Owen-Smith, an
expert in ‘mega-herbivores’ (>1000 kg), recognized
that the extinction of the largest of the Pleistocene
fauna must have had dramatic effects on past vegetation. Extant terrestrial mega-herbivores, the African
and Asian elephants and rhinoceroses, through foraging and trampling can dramatically impact ecosystems, turning forests and woodlands into scrubland,
savannah, or grassland. The removal of mega-herbivores by hunting or climate change, therefore, could
have dramatic effects on the structure of vegetational
communities. If mega-herbivores served as keystone
species in Pleistocene environments, their removal
could have cascading effects causing the extinction
of numerous other animal taxa. Owen-Smith calls
this idea the ‘keystone herbivore hypothesis’. The
Achilles’ heel of the keystone herbivore hypothesis is
the prediction that mega-herbivore extinction should
have preceded the extinction of other taxa, and to
date there is very little evidence to indicate that this
actually happened.
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EXTINCTIONS OF BIG GAME 1369
fauna? When viewed from a global perspective, Quaternary extinctions show a number of patterns that
provide clues to cause(s): (1) Extinctions were asynchronous across the globe, but globally appear to
correlate to some degree with first human arrival
to regions (Figure 2). (2) Quaternary extinctions on
continents and large islands disproportionately and
severely impacted large-bodied taxa. (Figure 5).
(3) Fauna in some regions were more severely impacted than others (Figures 5 and 6). (4) In most regions,
archaeological evidence for the interaction of humans
and extinct animals is limited. The extinction records
in various regions of the world are discussed in the
following sections.
Sitzkrieg
Jared Diamond argues that most Pleistocene extinctions can be attributed to humans, but diverges from
traditional overkill models with respect to cause. Using
observations of historically recorded extinctions, Diamond notes that many human-induced animal extinctions are not caused by hunting, but have instead
resulted from secondary effects. Diamond contrasts
the traditional ‘blitzkrieg’ model to what he calls
‘sitzkrieg’. Diamond suggests that extinctions may
not have been a lightning-quick predatory assault on
Pleistocene fauna by humans, but instead a slow ‘war
of attrition’ where extinctions were by-products of
secondary impacts, such as felling of forests, anthropogenic burning, and the introduction of non-native
competitors. Like the disease model, the ‘sitzkrieg’
model predicts that extinctions should correlate with
or postdate human colonization, and that there should
be relatively little archaeological evidence for human
hunting of extinct fauna. As such, it remains a very
difficult model to distinguish from hyperdisease, but
some researchers find this idea very compelling for
explaining extinctions on oceanic islands.
Africa
Africa holds a unique position in the Quaternary
extinctions because it is the homeland of hominid
and modern human evolution (see Modern Humans,
Emergence of). In addition, a greater proportion of
large-bodied mammalian taxa survived here than in
any other region of the world (Figure 6). Proponents
of overkill do not see these two facts as independent.
Large mammal survival in Africa, they would argue
results from the co-evolution of African large mammals with bipedal hominids whose hunting prowess
gradually increased over time. Although many genera
of large-bodied mammals did suffer extinction in
Africa, extinctions do not show clear clustering in
time, and many extinct genera were replaced by similar taxa, indicating that many African extinctions
likely were caused by interspecific competition rather
than anthropogenic factors.
The first members of the genus Homo evolved in
Africa roughly 2.5 million years ago. However, it
The Global Record of Quaternary
Extinctions
Attempts to test extinction hypotheses typically focus
on a handful of key variables. Which species suffered
extinction, which survived, and was there a detectable and dramatic increase in extinction rate in the
Quaternary? What is the relative timing of initial
human colonization, climatic/ecological change, and
the major wave of extinctions? Also, what is the
archaeological evidence for hunting of extinct
Surviving
Extinct
100
100
Number of species
North America
South America
50
50
0
0
0
1
2
3
4
5
6
0
7
1
2
3
4
5
6
7
100
100
Africa
Australia
50
50
0
0
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
log body mass (g)
Figure 5 Body size distributions for extinct and extant Quaternary species in North America, South America, Australia, and Africa. In
all regions, extinctions were highly selective, disproportionately affecting large-bodied animals. Redrafted from Figure 1 of Lyons SK,
Smith FA, and Brown JH (2004) Of mice, mastodons and men: Human mediated extinctions on four continents. Evolutionary Ecology
Research 6: 339–358.
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1370 EXTINCTIONS OF BIG GAME
Percent megafaunal mammals
100%
75%
Extinct
Surviving
50%
25%
Australia
South
America
North
America
Eurasia
Africa
0%
Continent
Figure 6 The percentage of extinct and extant megafaunal (>44 kg) mammalian genera by continent. Data from Barnosky AD, Koch PL,
Feranec RS, Wing SL, and Shabel AB (2004) Assessing the causes of Late Pleistocene extinctions on continents. Science 306: 70–75.
is not until the evolution of Homo erectus roughly
1.8 million years ago or perhaps even hundreds of
thousands of years later that hominids had likely
developed the ability to effectively hunt large animals. Over this period, there is an absence of clear
temporal clustering in animal extinction in Africa,
although there are many cases of likely climactically
driven local extinctions (species survived in other
parts of the continent). The inability to detect waves
of extinction in Africa may be attributed either to a
true lack of clustering of extinctions in time, or to
poor chronological control on extinction events.
Among the extinct Quaternary fauna of the African
continent are many species of hominids including the
entire genus Australopithecus, three genera of proboscideans, and more than 24 genera of ungulates
and carnivores. Notably, many extinct genera have
been recovered from archaeological contexts, particularly in Early and Middle Pleistocene contexts,
but establishing predation of extinction species by
pre-modern hominids has proved to be exceptionally
difficult.
Eurasia
Like Africa, Eurasia suffered relatively few losses
of large mammals, and hominids and extinct
fauna coexisted for an extended period of time. The
Eurasian landmass lost two genera of proboscideans
including mammoths, at least three species of rhinoceros, hyenas, cave bears, hippopotamus, giant deer,
and others. Europe lost proportionately more large
mammals than Asia where mega-herbivores, like
Asian elephants and rhinoceroses, survived to the
present in tropical Southeast Asia. Unlike Africa,
which sustained a hominid presence across most of
the continent throughout the Pleistocene, large portions of high-latitude Eurasia remained uncolonized
by Homo until the Late Pleistocene, providing refuge
for many now-extinct taxa until the end of the last
Ice Age. During the Pleistocene, continental glaciers
expanded and contracted over most of northern
Europe many times causing dramatic ecological shifts
(see Paleoenvironmental Reconstruction, Methods).
Hominids and animals underwent repeated range
shifts in response to glacial oscillations.
The genus Homo first migrated out of Africa and
into the southerly latitudes of Eurasia approximately
1.8 million years ago, or slightly earlier. It is unclear
whether hominids maintained a consistent presence
in Eurasia during the Early Pleistocene (1.8–0.78
million years ago), but by the start of the Middle
Pleistocene c. 0.78 million years ago, Homo was likely to stay in Eurasia. By 50 000–45 000 years ago,
modern Homo sapiens had spread through most of
Eurasia. Precise extinction dates for many Eurasian
species are poorly known, especially for Asian species
and those species which suffered extinction prior to
50 000 years ago, but numerous now-extinct animals
coexisted with hominids for hundreds of thousands of
years before suffering extinction. Although numerous
mammalian extinctions occurred throughout the
Quaternary in Europe, extinction rates among large
mammals increased substantially in the Late Pleistocene between c. 50 000 and 10 000 years ago with
extinctions possibly occurring in two pulses.
Straight-tusked elephant and hippopotamus, species
common in temperate fossil assemblages, were the
first to suffer extinction, around 50 000–40 000 years
ago. At this time, not only were continental glaciers
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EXTINCTIONS OF BIG GAME 1371
expanding pushing these species southward, but modern humans made their first incursions into Europe.
Arctic species like woolly rhinoceros and mammoth,
well adapted to cold glacial conditions survived
through the Last Glacial Maximum (c. 20 000 years
ago) only to suffer extinction as the climate warmed
c. 10 000 years ago. It is also after the Last Glacial
Maximum that major human influxes into arctic
regions occurred. A case can be made of overkill
and/or climate change as the extinction causes
for Europe since extinctions seem to occur at times
when both humans and climate are on the move. Nowextinct mammal species did survive into the Holocene
in isolated geographic pockets. For example, dwarfed
mammoths survived until 4000 years ago on Wrangell
Island in high arctic northeast Asia, and the giant
deer, Megaloceros survived into the Early Holocene
in western Siberia and the Ural mountains.
Although human associations with extinct fauna,
like rhinoceros, elephant, and mammoth, are fairly
common in Lower and Middle Palaeolithic assemblages, direct associations are considerably less common in the Upper Palaeolithic when the majority of
extinctions occurred. There are more than a dozen
archaeological sites showing subsistence use of proboscideans (Elephas and Mammuthus) throughout
Eurasia spanning more than 600 000 years of prehistory. These sites gradually increase in latitude with
age, possibly reflecting slow human northward range
expansion with concomitant proboscidean range
contraction. Nonetheless, the causes of Eurasian
mammalian extinctions remain as unresolved as on
any continent.
Australia
During glacial phases of climate, sea levels dropped,
and the map of Australia was dramatically altered
because the island continent became connected to
the adjacent islands of Papua New Guinea and Tasmania, forming the Ice Age continent of Sahul (see
Oceania: Australia). Prior to human colonization,
Australia was home to 28 genera and 55 species of
vertebrate fauna that are now extinct (Figure 7). Australian extinctions were among the most severe of any
continent, having lost 88% of its megafaunal mammalian genera (Figure 6). The largest known marsupials, the diprotodonts, large browers weighing
perhaps up to 2000 kg, suffered extinction during
the Late Pleistocene, as did 24 species of macropods
(a family of marsupials which includes the kangaroos,
tree kangaroos, wallabies, and padmelons). Also lost
were a handful of carnivores including Megalania
prisca, a huge meat-eating lizard. The flightless
Genyornis newtoni was the largest of the five or six
birds to have suffered extinction. Genyornis left
Figure 7 Silhouettes of the extinct Pleistocene fauna of Australia drawn to scale. Reproduced from Murray in P. Martin and
R. G. Klein (1984) (eds.) Quaternary Extinction: A Prehistoric
Revolution Tucson: University of Arizona Press.
abundant eggshells in Australia’s fossil record that
can be readily dated and analyzed to determine the
animal’s diet. Studies of Genyornis eggshells have
produced critical data about timing of extinction
and ecological change in Australia.
Gifford Miller and colleagues dated more than 700
Genyornis eggshell fragments by the radiocarbon and
amino acid racemization methods and found that
the giant flightless bird went extinct between 55 000
and 45 000 years ago. The extinction date for Genyornis is unique because it is one of only very few
extinct taxa whose extinction date is well established.
Determining the precise timing of Australian extinctions has proved problematic. In some critical localities, it appears that extinct fauna were geologically
redeposited into younger contexts creating the appearance of survival into time periods long after
which the animals suffered extinction. Also, it is increasingly apparent that most Australian extinctions
occurred near the temporal limit of radiocarbon
dating (c. 50 000 years ago). One rigorous study of
extinction dates in Australia by Richard Roberts and
colleagues found that at least six genera of megafauna, in addition to Genyornis, suffered extinction at
approximately 46 000 years ago. Therefore, the time
period between 55 000 and 45 000 years ago appears
to be the key to solving the riddle of Australian
extinctions.
Although the precise date of human colonization of
Australia remains controversial, well-dated contexts
at Lake Mungo and Devil’s Lair both suggest a
colonization date between 50 000 and 45 000 years
ago. At other more controversial sites, colonization
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dates have been proposed in excess of 60 000
and even 100 000 years ago. Bearing in mind the
possibility for older sites, as Australian researchers
have done more work and improved dating of critical
localities, dates for extinctions and human arrival
seem to be converging at a 10 000 year period between 55 000 and 45 000 years ago. To many
researchers, this is strong albeit circumstantial evidence for human involvement in animal extinctions.
Of course, temporal correlation is not necessarily
causation, and it remains possible that climate change
could have played a major or minor role in Australian
extinctions. However, the climate change argument
does not fare well in Australia because this critical
time period, 55 000 to 45 000 years ago, was not a
period of dramatic climatic shift in Australia. However, a recent study of the prehistoric diets of Genyornis, emus, and wombats found that when Genyornis
went extinct, the diets of surviving emus and wombats shifted suddenly and permanently in multiple
regions of Australia. To Gifford Miller and colleagues, this dietary shift indicates a major reorganization of Australian ecosystems right at the time of
extinction, and they argue that this ecological change
cannot be explained by climatic forcing. Instead, they
hypothesize that burning of Australian environments
by humans caused this environmental change, thus
driving Genyornis and other species to extinction.
Others have suggested that maybe it was not the
ecological change that caused the extinction, but it
was the extinction that caused the ecological change.
Australia lost many species of large browsing marsupials, and their removal could have had dramatic
ecological consequences as Owen-Smith has proposed for the keystone herbivore hypothesis. Though
the precise cause remains unclear, many researchers
are convinced of a human involvement in Australian
Pleistocene extinctions. Not helping the overkill case
in Australia, there are no kill sites of extinct Pleistocene fauna, and direct evidence of human use of
megafauna is extremely rare.
The Americas
Extinctions in North and South America were similar
to those in Australia, except they occurred 30 000 years
later. In North America, 33 genera of megafauna were
lost including, mammoths, mastodons, horses, camels,
ground sloths, lions, cheetahs, dire wolves, giant shortfaced bears, and others. In South America, extinctions
were more severe, where 50 genera of large mammals
disappeared in the Late Pleistocene. These include
four genera of proboscideans, three genera of horses,
the great majority of large ungulates, and many genera
of ground sloths and giant armadillos. Extinctions
in North and South America disproportionately impacted the largest mammals, and a clear spike in
extinction rates occurred in the latest Pleistocene.
Though New World Pleistocene extinctions are
better dated than those in Australia, the precise timing
of extinctions continues to be a matter of contention.
Chronological control on North American extinctions is better than that for South America, but
extinctions on both continents appear to have been
more or less simultaneous occurring in a narrow time
interval between c. 13 300 and 12 500 years ago.
Extinctions in North and South America correlate in
time with both initial human colonization and a period of dramatic climate change, the most recent transition from glacial to interglacial climate. The best-dated
New World extinctions correlate well with the start of
Younger Dryas stadial (c. 12 900–11 500 years ago),
a 1300–1400 year long abrupt reversal to glacial conditions where global temperatures cooled and glaciers
readvanced (Figure 8). Humans entered the New
World from northeast Asia across the Bering land
bridge in the millennia preceding the Younger Dryas.
For more than six decades, it was believed that the
initial colonization of the New World was represented
by the Clovis complex characterized by the production of lanceolate basally intended, fluted projectile
points. Correlating very well New World extinctions,
the Clovis complex dates to a very narrow time interval
from c. 13 400 to 12 800 years ago. Recently, however,
a handful of sites that appear to predate Clovis have
been excavated, most notably Monte Verde, Childe,
dating to 14 800 years ago, more than 1000 years
before Clovis. The significance of pre-Clovis sites for
the extinctions debate is twofold. First, if these sites
truly predate Clovis, Martin’s blitzkrieg simulation,
which assumes colonization by Clovis, cannot be correct. Second, humans and Pleistocene fauna coexisted
in the New World for a slightly longer period than
previously believed. Whether the existence of preClovis sites is problematic or beneficial to the general
overkill hypothesis, however, is not clear because it has
important implications for the archaeology of overkill.
The thorn in the side of the New World overkill
hypothesis has been the paucity of archaeological
evidence demonstrating the exploitation of extinct
fauna. In North America, there is relatively abundant
evidence for hunting of mammoth during Clovis
times, and there is minimal evidence for hunting
of mastodon, horse, and camel. But considering
that 33 genera of large mammals suffered extinction in the Late Pleistocene of North America, the
overkill hypothesis is weakened by this scarcity of
evidence. However, if humans were in the New
World 1000–2000 years prior to Clovis and hunted
Pleistocene fauna to extinction, the Clovis period
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EXTINCTIONS OF BIG GAME 1373
−32
δ18 O
−36
Temperature
Younger Dryas
Warmer
−34
−38
Colder
−40
−42
20 000
15 000
10 000
5000
0
Years before present
Figure 8 The Younger Dryas stadial (highlighted in blue) recorded in stable oxygen isotopes of glacial ice in the GISP2 core from
Greenland. Oxygen isotopes of glacial ice record the isotopic composition of precipitation which is strongly related to air temperature. High
values of d18O indicate warm temperatures. Low values of d18O indicate cold temperatures. The Younger Dryas was a 1400 year reversal
to glacial-like conditions that punctuated the warming trend that occurred between 20 000 and 10 000 years ago. New World extinctions
appear to correlate with the onset of the Younger Dryas. Data from Grootes PM and Stuiver M (1997) Oxygen 18/16 variability in
Greenland snow and ice with 103 and 105 year time resolution. Journal of Geophysical Research 102: 26455–26470.
correlates only with the tail end of the extinction
event where many populations of extinct fauna
would have been highly depressed, and the majority
of hunting of extinct fauna might have occurred prior
to Clovis, a portion of the archaeological record of
which we have a tiny sample. Therefore, the archaeological evidence for overkill might be in the millennium just prior to Clovis, a portion of the record which
has remained virtually invisible. Despite claims that
the overkill hypothesis for North America has itself
perished, it lives on because it remains as likely an
explanation for Quaternary extinctions as any other
model.
Island Extinctions
Vertebrate extinctions on oceanic islands have
figured prominently in discussions of Quaternary
extinctions, and unlike continental extinctions virtually all researchers agree that human impacts were
responsible for the great majority of island extinctions, although precise mechanisms remain unresolved. Blitzkrieg-type overkill is advocated by some
researchers, while others argue island extinctions
were likely much more akin to Diamond’s sitzkrieg
scenario. For overkill advocates, islands serve as
important controls in the extinction debate. Many
oceanic islands were not discovered or colonized by
humans until well into the Holocene, and they show
the survival of many genera after the extinction of
their continental counterparts with extinction
occurring only after human arrival. For researchers
who advocate climatic/ecological hypotheses, island
fauna survived because islands are insolated from
climatic change, or island extinctions are irrelevant
to continental extinctions because island faunas are
much more vulnerable to human effects. Island animals live in small populations, within confined geographic ranges, without access to a pool of
conspecifics from which to recruit new individuals.
A repeated pattern is seen on oceanic islands; with
human colonization, a large range of species suffer
extinction (Figure 2). Island regions that have figured
prominently in extinction discussions are the West
Indies, multiple Pacific archipelagos, the Galapagos,
the islands of the Mediterranean, Madagascar, and
New Zealand. Unlike continents, island extinctions
typically impacted a broad array of vertebrate taxa
including small-bodied birds, reptiles, and mammals.
Among the first island extinctions were those of
the Mediterranean. Early Holocene human colonization resulted in the decimation of the mammalian
fauna of Mediterranean islands where only two
relict Pleistocene mammalian species remain. Prior
to human arrival, Mediterranean islands were home
to dwarf varieties of elephants, hippos, and red
deer which survived long after their nearby continental relatives; also lost were other species of ungulates,
rodents, insectivores, birds, and reptiles. In the
Caribbean, ground dwelling sloths, large rodents,
and a wide array of small mammals, lizards, and
birds suffered extinction with human colonization in
the Middle Holocene. Like Mediterranean hippos
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1374 EXTINCTIONS OF BIG GAME
and elephants, Caribbean sloths survived thousands
of years after the extinction of large North and South
American sloths.
The islands of New Zealand and Madagascar also
show waves of extinction at the time of human
colonization. Beginning around 2000 years ago,
Madagascar lost many species including seven genera
of giant lemurs, at least six genera of large flightless
birds, a pygmy hippo, an aardvark, a large viverrine
carnivore, and giant tortoises. Limited but clear archaeological evidence of human butchery of extinct
giant lemurs has been recovered from Madagascar,
as have a few specimens of human-modified bones
of other extinct fauna, such as a tibiotarsus from the
3 m tall, 500 kg elephant bird. The islands of New
Zealand were first colonized by humans only about
900–1000 years ago, but within a matter of centuries,
the large flightless moas and other species were decimated. New Zealand is particularly important in the
extinctions debate because clear and abundant
archaeological evidence for human predation of
moa species has been recovered there. More than
100 archaeological sites show evidence of human
subsistence use of moas. That humans hunted and
caused moa extinction is not disputed, but the relative
importance of hunting, anthropogenic burning, and
the introduction of non-native rats and domestic dogs
in moa extinction is a matter of debate.
Where Are We Now?
In recent decades, the amount of information available
to researchers studying Pleistocene extinctions has
grown substantially. With the exception of the development of a general consensus that human impacts,
whether hunting or otherwise, regularly caused island
extinctions, this dramatic increase in data has not led
to a dramatic increase in conclusions about the cause
(s) of Quaternary extinctions. The fundamental problem is that extinction hypotheses are very difficult to
test directly, and they tend to be incredibly flexible,
capable of accommodating virtually any evidence
brought forth. For example, does a scarcity of archaeological evidence support or refute the overkill hypothesis? Unfortunately, there is no simple answer to that
question. What has become increasingly clear is that a
strong circumstantial case can be made for a significant human role in Quaternary extinctions, not only
on islands but also on continents.
With the exception of Europe, Asia, and Africa, one
could determine the timing of human colonization of
virtually the entire world by studying only the palaeontological record. A wave of extinctions occurring
within the last 50 000 years would indicate that
humans had arrived. To many researchers, this evidence alone indicates clear human agency in Quaternary extinctions. If, however, islands are eliminated from
this scenario, this temporal correlation only occurs
on three large landmasses, North America, South
America, and Australia, and perhaps it becomes more
feasible to argue that these correlations are just coincidence. But extinctions on continents show consistent
trends with respect to body size, disproportionately
affecting the largest species, the preferred prey of hunter-gatherers. Yet if humans caused the continental
extinctions of dozens of genera of Pleistocene fauna,
must it have been the perfect crime? To kill these many
animals and leave so little evidence, to some researchers
seems like an impossible feat. To others, little evidence
is expected. Such disagreements highlight why it has
been so difficult to determine the causes of big game
extinctions in the Quaternary.
See also: Archaeozoology; Butchery and Kill Sites;
Migrations: Australia; Pacific; Modern Humans, Emergence of; New World, Peopling of; Oceania: Australia;
Paleoenvironmental Reconstruction, Methods; Siberia,
Peopling of.
Further Reading
Barnosky AD, Koch PL, Feranec RS, Wing SL, and Shabel AB
(2004) Assessing the causes of Late Pleistocene extinctions on
continents. Science 306: 70–75.
Diamond JM (1989) Quaternary megafaunal extinctions: Variations on a theme by Paganini. Journal of Archaeological Science
16: 167–185.
Grayson DK (2001) The archaeological record of human impacts
on animal populations. Journal of World Prehistory 15: 1–67.
MacPhee RDE (1999) Extinctions in Near Time: Causes, Contexts,
and Consequences. New York: Kluver /Plenum.
MacPhee RDE and Marx PA (1997) The 40 000-year plague:
Humans, hyperdisease, and first-contact extinctions. In:
Goodman SM and Patterson BD (eds.) Natural Change and
Human Impact in Madagascar, pp. 169–216. Washington, DC:
Smithsonian Institution Press.
Martin PS and Klein RG (eds.) (1984) Quaternary Extinctions:
A Prehistoric Revolution. Tucson: University of Arizona Press.
Miller GH, Fogel ML, Magee JW, Gagan MK, Clarke SJ, and
Johnson BJ (2005) Ecosystem collapse in Pleistocene Australia
and a human role in megafaunal extinction. Science 309:
287–290.
Owen-Smith N (1987) Pleistocene extinctions: The pivotal role of
megaherbivores. Paleobiology 13: 351–362.
Stuart AJ, Kosintsev PA, Higham TFG, and Lister AM (2004)
Pleistocene to Holocene extinction dynamics in giant deer and
woolly mammoths. Nature 43: 684–689.
Surovell TA, Waguespack NM, and Brantingham PJ (2005) Global
archaeological evidence for proboscidean overkill. Proceedings
of the National Academy of Sciences 102: 6231–6236.
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