My next blogs will be focused on:
1. Possible causes of megafaunal collapse in
different continents e.g. Africa, Eurasia etc.
2. Specific examples of species e.g. woolly mammoth
etc. and their likely cause of extinction.
3. Other topics related to the debate e.g. Sporomiella Proxy etc.
Before I embark on these, I would like to take this opportunity
to briefly review the main findings of what we have learnt so far:
· There are various mechanisms that could have
caused the extinction of megafauna during the late Pleistocene (roughly
60,000-11,000 years ago). Mechanisms include: climate change, disease, humans,
fire, and the impact from an asteroid/comet.
·
Whilst there has been a large degree of research
conducted, conclusions remain deeply controversial.
·
Human overkill is a likely cause of extinction
through hunters preying on large mammals leading to their demise (see
Bulte
et al 2006 & Roberts et al 2001). However evidence which disagrees with
this includes the availability of alternative food sources from agriculture.
·
It is plausible that humans could have caused
the extinction of megafauna in Australia (see
Johnson 2006). The decline of
species such as G.newtoni immediately after initial human colonization as well
as mild climatic variability in this region, reinforces evidence to support the
human overkill theory. However lack of evidence weakens this hypothesis.
·
Climate can be seen to be responsible through
exacerbating human impacts
(wroe
et al 2006), or through habitat
modification. Evidence of extreme climatic changes are present, but linking
this to megafaunal decline is difficult (
Lorenzen
et al 2011). Similarly, the demise
of species that were able to adapt to climate change weakens this hypothesis.
·
Fire can be seen to be responsible for the extinction
of megafauna through; extreme temperatures as well as altering landscapes so
that megafauna are unable to sustain themselves (see
Gill
et al 2009). However lack of
fossil evidence and uncertainties in dating have made it exceptionally hard to
test this hypothesis.
·
It is unquestionable that a comet hitting the earth
would have ultimately led to megafaunal decline (
Firestone et al 2007). However many are
sceptical about this due to severe lack of reproducible evidence.
·
Disease is credible mechanism as megafauna might
have had weak immune systems and were unable to withstand pathogens (see
Rothschild
& Laub 2006). However there is lack of evidence uncovering a pathogen
that has the capability to cause such widespread extinction.
·
Poor quality fossil datasets make it
exceptionally hard to discover what caused megafaunal collapse. Similarly, it
is highly unlikely that extinctions across the globe were a result of a single
cause. It is more likely that different species or continents were subject to different
forcing mechanisms e.g. continents that experienced dramatic climate variability
suffered majority of extinctions because of climate change, whilst the early
colinization of man in other continents might have caused megafunal demise.
·
In the majority of cases perhaps combining
multiple causes of extinction might be the most likely cause of megafaunal
extinction.
Some examples of megafauna becoming extinct (going down): woolly mammoth, woolly Rhino, Irish Elk, Diprothodon, Giant sloth, Cave lion, G.Newtoni, Giant Kangeroo, Glytodon, Smilodon.