Elephants weighing more than 10 tons populated an Africa with more biomass

June 9 () –

A study in fossils focused on the ecological dynamics behind the decline of African megafauna reveals elephants weighing more than 10 tons in a habitat with more biomass 4 million years ago.

The great abundance of large individuals in these fossil African communities is unparalleled in today’s ecosystems. Since then, there has been a gradual loss of large individuals from the fossil record, reflecting the long-term decline in the diversity of large mammals from the late Pliocene and Pleistocene, and results in the impoverished and “miniaturized” communities we know today.

The findings challenge previous assumptions about the causes of megafauna extinctions in Africa and provide new insights into the restructuring of ecosystems over millions of years. The research is published in the journal Science.

Faysal Bibi, from the Museum für Naturkunde in Berlin; and Juan L. Cantalapiedra, from the University of Alcalá, used measurements of thousands of fossil teeth to reconstruct the size and abundance of large African mammals (>15 kg) over the last 10 million years. Despite many uncertainties affecting preservation in the fossil record, the study revealed a very similar relationship between animal size and abundance between fossil and extant communities, indicating that fundamental ecological processes governing the structure of living communities they are also preserved in the fossil record.

Above 45 kg, the researchers found evidence of decreasing abundance with increasing size, a pattern that aligns with the ecological “metabolic scaling rule,” according to which larger species have lower population densities compared to smaller ones.

A departure from the predicted ecological pattern was that mammals between 15 and 45 kg were much less numerous than expected, both in living and fossil communities. They interpreted this as a signature of savannah habitats (where forest-dwelling monkeys and small antelopes are rare).

The big surprise came when the researchers examined how size abundance distributions changed over time. They found that earlier communities, those that lived more than 4 million years ago, had considerably higher numbers of large individuals and a higher proportion of total biomass in larger size categories than younger communities.

The sheer abundance of large individuals in these fossil African communities, with some individual elephants reaching sizes of more than 10 tons, is unparalleled in ecosystems today. Since then, there has been a gradual loss of large individuals from the fossil record, reflecting the long-term decline in the diversity of large mammals from the late Pliocene and Pleistocene, and results in the impoverished and “miniaturized” communities we know today.

The study confirms recent work defending the deep antiquity of African megafauna losses and challenging the idea that they were primarily driven by human activities. While the expansion of humans across the globe during the late Pleistocene and Holocene (the last 100,000 years) coincided with the extinction of many large animals, research supports the idea that megafaunal losses in Africa began much earlier, about 4 million years ago and long before humans learned to engage in efficient hunting. Instead, the study highlights environmental factors, such as the long-term decline in global temperatures and the expansion of tropical grasslands, as possible drivers of megafauna extinctions.

The study also found that the loss of large individuals and the restructuring of biomass distributions in African large mammal communities could be related to declines in primary productivity.

Using an established relationship between the types of mammalian tooth shapes (morphological characteristics) and the productivity of plants (net primary productivity) at present, the researchers calculated the productivity of African communities in the past.

They found a roughly two-thirds decline in productivity since the late Miocene (more than 5 million years ago), a pattern observed globally, and one that could have significantly decreased the carrying capacity of large mammal communities, led to a reduction in diversity and the accelerated extinction of large species.

The research opens new avenues to understand the dynamics of ecosystems and the complex interactions between individuals, species and their environment. By analyzing fossil abundance data and incorporating size-based approaches, scientists can gain valuable insight into the ecological dynamics underlying extinction.