History of Megafaunal Loss

What are we talking about?

Before embarking on this exploratory journey in earnest, let’s first establish some loose definitions for the temporal and descriptive characteristics that will be referenced moving forward.

What: Fundamentally derived from the Greek megalo (meaning large), and the Latin fauna (meaning animal), megafauna are simply defined as large animals. Defining ‘large’ in this context is then where complexity arises. Delimitation of megafauna tends to be according to some threshold mass of the adult animal, commonly >44 kg but varying greatly between >5 kg and >1000 kg in different studies. Elsewhere, megafauna are defined and stratified according to a trophic (relating to feeding and nutrition) herbivore-carnivore cascade. Malhi et al. divide megafauna into megaherbivores (>= 1000 kg), megacarnivores (>=100 kg), large herbivores (45-999 kg), and large carnivores (21.5-999 kg) in order to incorporate intra-megafaunal trophic interactions.

When: The timeframes to be dealt with are likely to be variably and sometimes interchangeably referred to as the late Pleistocene (from ~60,000 years ago to the beginning of the Holocene (~11,700 years ago)), the late Quaternary (from ~60,000 years ago to the present), or in terms of thousands of years before present. For the uninitiated (including myself until very recently), the following table may be of some help: 

Having, in characteristically (and arguably unnecessarily) loquacious fashion, established that megafauna are large animals and that we’re dealing with a timeframe of ~60,000 years to the present, let’s get stuck in.

History of Megafaunal Loss

Aside from the Cretaceous-Tertiary mass extinction event, infamous for its termination of the dinosaurs ~65 million years ago, megafauna experienced no significant losses until ~1 million years ago in Early Pleistocene Africa, when, coincident with the evolution of Homo Erectus into the carnivore niche space (increased human consumption of meat, perhaps in relation to expanding brain size), several carnivore lineages were locally cut short (some continued to flourish elsewhere for thousands of years) and there was a substantial decrease in proboscidean (order of mammals containing Elephants, Mammoths, similar) diversity.

The speed and magnitude of these losses was to be dwarfed by the ~1 billion land megafauna individuals lost globally in the late Pleistocene. ~50,000 years ago (50 kya) the earth hosted more than 150 genera of megafauna greater than or equal to 44kg. By  ~10 kya, at least 97 were extinct. The figure below, from Barnosky et al summarises the number and suspected causes of megafaunal extinctions on each continent in the context of human arrival and climate change by genera:

In Eurasia (northern Europe, Siberia and Alaska), megafaunal extinction occurred in 2 pulses:

•          From 45-20 ky RCBP (thousands radio carbon years before present), coincident with decreasing temperatures and dispersion of Homo Sapiens
•          From 12-9 ky RCBP, coincident with increasing temperatures and increasing Homo Sapiens populations

In North America, megafaunal extinction coincided with climate change and the arrival of advanced Homo Sapiens armed with a repertoire of advanced stone hunting tools between 11.5-10 ky RCBP, with more than 15 species becoming extinct during the Younger Dryas (a shift from cold glacial to warmer interglacial state) between 11.4 and 10.8 ky RCBP.

In the southern hemisphere (where a very significant proportion of the extinctions occurred), pending further research, chronology is less certain. Current indications point to megafaunal extinctions loosely around 45 kya in Australia, coincident with believed timeframe of Homo Sapiens expansion in the region but interestingly predating regional Last Glacial Maximum climate change. In South America, the current consensus is that humans arrived between 12.5-12.9 ky BP and that megafaunal extinction occurred sometime thereafter, probably coincident with changing climate.

Outside of these major regions, with the notable exception of Africa and Central Eurasia where hominids have been present for hundreds of thousands of years, megafaunal extinctions coincided with the global expansion of Homo Sapiens; ~30 kya in Japan, ~6 kya in the Caribbean, ~1-3 kya in the pacific islands, ~2 kya in Madagascar, ~0.7 kya in New Zealand.

Throughout the world, megafauna that persisted into the mid-Holocene and beyond tended to be found in areas where human populations never grew large – although some species, such as horses and mammoths in mainland Alaska, became extinct without significant human populations present, instead being the likely result of substantial regional climate change.

Humans as omnivorous, generalist super-predators capable of effecting and maintaining predation pressure on even the very largest animals (who had been under very little predation pressure before their arrival) had the ability to wreak havoc on megafauna, particularly vulnerable to increases in predation pressure as a result of their long lives and slow reproduction rates. Additionally, domestic animals associated with humans may have introduced diseases into endemic populations as well as competing with endemic carnivores for food. Resultant loss of keystone (to be covered in detail later) megaherbivores, leading to changing vegetation and fire regimes and loss of a food-base for megacarnivores, could then have compounded losses, setting into motion subsequent cascades of extinctions. Yet in Africa, central Asia and various other regions around the world, humans and megafauna coexisted without such drastic megafaunal extinctions as elsewhere.

Climate change has been proven to affect animals principally through the elicitation of significant, abrupt vegetation change. However, while in some areas, the timing of vegetation change coincided with various stages of extinctions, in others it did not.  Furthermore, climate shifts in the late Pleistocene are believed not to have been unusual enough to effect considerable ecological change, being neither faster nor of greater magnitude than other such shifts in the past 700 kya that didn’t result in such megafaunal devastation.

Neither human nor climate effects appear to be sufficient in themselves, but the above seems compelling evidence that a combination of human effects and climatic change (likely leaning further towards humans than climate change in the majority of cases), interacting to apply theretofore unprecedented pressure, is the likely culprit of the late Pleistocene megafaunal extinction event, characterised by short term, regional pulses.

Much of the information conveyed in this post was derived from a pair of fascinating papers, Barnosky et al. 2004 and Malhi et al. 2015, both well worth a read in their original entirety.