Humankind’s association with elephants and their forebears goes a long way back. But contrary to the claims that humans may have wiped them out, a new study points out that the giant jumbos may in fact, have been early victims of Climate Change.

According to new findings, it was the changes in the global environment that led to the demise of these species rather than overhunting by human beings.

In an article published in sciencedaily.com, this study on extinction of elephants’ predecessors was published recently in Nature Ecology & Evolution. What the study does is dispute the assertion that early human hunters killed the prehistoric elephants to extinction. These species included mammoths and mastodonts.

In place of this kill theory, the study suggests that the extinction of these huge beasts, when the last Ice Age ended, was characterised by successive and progressive climate-driven decline in elephant species over millions of years.

Currently, the pachyderms are limited to just three species – all endangered. Presently found in the tropics of Africa and Asia, these species are the survivors of a far more diverse and widespread group of giant herbivores.

Visitors walk past a Mastodon skeleton display at the opening of the Royal Alberta Museum, in Edmonton (Pic: Courtesy ctvnews.ca)

This group of herbivorous giants – also known as the proboscideans – includes the extinct mastodonts, stegodonts and deinotheres. England just 700,000 years ago was home to three different types of elephants. These were two giant species of mammoths and the straight-tusked elephant.

This study involving the most detailed analysis till date on the rise and fall of elephants and their predecessors was done by a group of international palaeontologists from Alcalá, Bristol, and Helsinki universities. Together they studied and examined how 185 different species of the elephants and their forerunners, adapted and spanned for 60 million years of evolution, all which started in North Africa.

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For the examination into this rich evolutionary history, the group of international palaeontologists surveyed fossil collections in different museums across the world — from Moscow's Paleontological Institute to London's Natural History Museum.

The examination of characteristics like size of the body, shape of the skull and the chewing surface of their teeth, was carried out and the team found that all proboscideans fell within one of eight sets of adaptive strategies.

Dr Zhang Hanwen, the co-author of the study and the Honorary Research Associate at the University of Bristol's School of Earth Sciences, talking about this said: "Remarkably for 30 million years, the entire first half of proboscidean evolution, only two of the eight groups evolved. Most proboscideans over this time were nondescript herbivores ranging from the size of a pug to that of a boar. A few species got as big as a hippo, yet these lineages were evolutionary dead-ends. They all bore little resemblance to elephants."

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This was to undergo change and it did when the proboscidean evolution course altered dramatically some 20 million years ago. This occurred when the Afro-Arabian plate collided into the Eurasian continent. The collision led to Arabia providing a crucial migration corridor for the diversifying mastodont-grade species to explore new habitats in Eurasia. It was not restricted to just Eurasia as they went into North America via the Bering Land Bridge.

Highlighting this crucial aspect of the study, its lead author Dr Juan Cantalapiedra, Senior Research Fellow at the University of Alcalá in Spain remarked: "The immediate impact of proboscidean dispersals beyond Africa was quantified for the very first time in our study. Those archaic North African species were slow-evolving with little diversification, yet we calculated that once out of Africa proboscideans evolved 25 times faster, giving rise to a myriad of disparate forms, whose specialisations permitted niche partition between several proboscidean species in the same habitats. One case in point being the massive, flattened lower tusks of the 'shovel-tuskers'. Such coexistence of giant herbivores was unlike anything in today's ecosystems."

Adding to this Dr Zhang observed: "The aim of the game in this boom period of proboscidean evolution was 'adapt or die'. Habitat perturbations were relentless, pertained to the ever-changing global climate, continuously promoting new adaptive solutions while proboscideans that didn't keep up were literally, left for dead. The once greatly diverse and widespread mastodonts were eventually reduced to less than a handful of species in the Americas, including the familiar Ice Age American mastodon."

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Now three million years ago the elephants and stegodonts located in Africa and eastern Asia were looking like coming out on top of the evolutionary cycle. It was then that environmental disruption took place which was connected to the coming Ice Ages. These changes really struck them hard, forcing the surviving species to adapt to the new, severe habitats. The extreme example of this is the woolly mammoth, which had thick, shaggy hair and big tusks for retrieving vegetation covered under thick snow.

The analyses done by this team showed that the final proboscidean extinction peaks started at around 2.4 million years ago for Africa, 160,000 for Eurasia and 75,000 years ago for the Americas

On this point Dr Cantalapiedra averred: "It is important to note that these ages do not demarcate the precise timing of extinctions, but rather indicate the points in time at which proboscideans on the respective continents became subject to higher extinction risk.”

Contrary to what was expected, these findings did not correlate to early human expansion and their increased ability and capability to hunt and kill megaherbivores.

Highlighting this aspect of the study, Dr Zhang said: "We didn't foresee this result. It appears as if the broad global pattern of proboscidean extinctions in recent geological history could be reproduced without accounting for impacts of early human diasporas. Conservatively, our data refutes some recent claims regarding the role of archaic humans in wiping out prehistoric elephants, ever since big game hunting became a crucial part of our ancestors' subsistence strategy around 1.5 million years ago.”

While stating that they were not disproving complete involvement of humans, Dr Zhang added: "Although this isn't to say we conclusively disproved any human involvement. In our scenario, modern humans settled on each landmass after proboscidean extinction risk had already escalated. An ingenious, highly adaptable social predator like our species could be the perfect black swan occurrence to deliver the coup de grâce."