It is now sadly time to come to a conclusion and unmask one
of the biggest ‘whodunit’ mysteries. In this blog I will be stating the most
important findings of this research, as well as delivering my own thoughts of
what I believe to be the most likely cause of megafaunal extinction. The outcome
of these blogs has revealed that climate and man are the two main culprits of extinction.
Man's Impact
The impact of man is one of the most popular reasons for the
extinction of megafauna during the Late Pleistocene. Growing support for this
theory is largely due to the arrival of Homo
sapiens coinciding with the demise megafauna. This was found in many
continents including Australia (Roberts’s et al 2001), North America and
Eurasia. It is important to note that human overkill was not the same in each
continent. Some regions may have experience blitzkrieg, whilst others might
have shown evidence of protracted overkill. Increased number of Homo sapiens is a key factor which would
have driven increased levels of hunting, and may have pushed megafauna to
extinction. Numerous findings of sophisticated hunting technology such as
spears, harpoons and nets (mostly used by Clovis hunters of North America) reinforce
evidence to suggest that overkill was responsible for the decline of these
great beasts. This is reinforced by Wong
(2012) who states how changes in technology were responsible for the
extinction of certain carnivores in East Africa. Bulte
et al (2006) provides another theory, suggesting that hunting of mini-fauna
would have increased chance encounters with megafauna leading to their eventual extinction.
Looking at man’s influence in Australia, it was found that the extinction of 60
faunal species coincided with the arrival of humans 65,000 years ago (Jonson
2006). Evidence of butchered animals in Cuddie Springs (New South Wales) is an
example which strengthens the overkill hypothesis. The extinction of animals resistant
to glacial/interglacial cycles is another reason that portrays man as the culprit
behind this controversial mystery. Hunting would have also selectively targeted
larger animals, which provides an explanation of why only megafauna became
extinct during the Late Pleistocene. The hunting of mega herbivores might have even
caused the decline of carnivores that relied of these food sources (Wong
2012), illustrating the detrimental impact man can have on megafauna. The
only continent that shows a co-existence between man and megafauna was Africa,
and consequently this region experienced much fewer losses then other areas. The
fire hypothesis has also shown to have a considerable effect of megafauna
through extreme temperatures and landscape modification. The studies by Rick
et al (2012) reveal that fire was of vital importance to humans as it was
used for light, cooking, warmth, and allowed the creation of new technologies. Human
induced fires were more common than lightning events, and therefore its effects
can be linked to man’s impact on megafauna. Similarly studies in Tight Eastern
Cave (South West Australia) found increasing charcoal concentrations coinciding
with the arrival of Homo sapiens,
suggesting that human induced fire was frequent. The impact of fire would have
restructured plant communities causing vegetation to change. This might not have
sustained megafauna and consequently led to their demise (Gill
et al 2009). Overall, whilst it is clear that fire had some impact of
megafaunal populations, it cannot be considered a key driver of extinction due
to lack of evidence. We also looked at the likelihood of the occurrence of an
extra-terrestrial event during the late Pleistocene (see Firestone et al 2007).
Whilst the impact of a comet would have caused the extinction of megafauna, the
lack of reproducible evidence (Haynes et al 2010) weakens
this hypothesis. Man can be seen to be responsible for the death of megafauna
through bringing hyper-disease (mostly carried by domesticated dogs). Megafauna
had weak immune systems due to not being exposed to diseases. Their inability
to withstand pathogens meant that hyper-disease is a mechanism of extinction. Rothschild
and Laub (2006) reinforce this believe by showing the extinction of a
particular type of mammoth through human carried tuberculosis. Evidence of this
was found in the disease being present in 52% of the 118 skeletons that were
surveyed. Whilst it is plausible in part, this theory lack much needed supporting
evidence.
Whilst there are many reasons to suggest that man played a
huge role in the extinction of megafauna, there is evidence which contradicts
this. The lack of kill sites is a large factor that weakens the overkill
hypothesis. Other evidence which disagrees includes the relationship between
technology and hunting. Many believe that the improvement of technology was
coupled with a varying diet as Homo sapiens had the newly found ability to
obtain alternative food sources such as fish. Agriculture during the late Pleistocene
may also reveal that man had access to an alternative food source, which would
suggest that other factors might be responsible for the extinction of megafauna.
Overall, poor quality fossil data sets make it exceptionally hard to determine whether primitive
man caused megafaunal collapse.
CLIMATE
There are many reasons why climate can be seen to be responsible
for the collapse of megafauna. During the late Pleistocene climate was subject to
large scale rapid oscillations between glacial and interglacial conditions. Such
transitions would cause landscape modifications which in turn would have
reduced the amount of suitable areas in which megafauna could survive. Climate changes
would have also altered ecosystems and resulted in large vegetation changes due
to the reduced growing season of plants. This would result in species with
small ranges to subsequently die out. This is corroborated by Wroe (2006)
and Dodson
(1998) who found that Australia experienced an expansion of arid areas. Evidence
which agrees with this hypothesis is also stated by Prescott et al (2012)
who stated that the most rapid episodes of population decline were associated
with the highest periods of temperature decrease. Such changes would have
caused species such as the Eurasian musk ox and the woolly rhinoceros to become
extinct (see Lorenzen
et al 2011).
However, there is much evidence which disagrees with this
hypothesis. The overall strength of the ‘man being responsible for extinction’
(mentioned above) severely weakens the climate hypothesis.
THE VERDICT
In my opinion I believe that the combination of both anthropogenic
and climate forcing’s caused the extinction of the majority of megafauna. This
belief can be strengthened because of the following reasons:
·
I believe that climate had the potential to
exacerbate human impact. Glacial periods could have caused increased levels of
hunting for survival.
·
Climate oscillations could have also been a
significant factor in the evolution of tools specifically designed to hunt prey
more efficiently. This resulting in increased numbers of megafauna being hunted
and consequently led to increased extinctions.
·
The best example which incorporates both human
and climate is the extinction of the woolly mammoth. Research by Nogues-Bravo
et al (2008) found that suitable
climate conditions for the mammoth reduced drastically between the Late Pleistocene
and the Holocene resulting in 90% of its geographical range disappearing.
Therefore climate would have significantly decreased the mammoth’s population
size, and consequently would make them more vulnerable to extinction when
hunting occurred.
Studies by Prescott et al (2012)
and Prideaux et al (2007)
found that the timing of megafaunal extinction is related to both climate and
human forcing factors. Overall I believe Climate change could have weakened megafaunal
populations, and with the combined presence of humans (which would have hunted,
caused fires, and brought diseases) megafaunal extinction would have been
inevitable. Hopefully with improved fossil records and data records the actual
reason behind megafaunal extinction will be revealed.
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