Past tropical forest changes drove megafauna and hominin extinctions
New biochemical research shows significant turnovers in Southeast Asian environments and animals during the Pleistocene

Date:
October 7, 2020
Source:
Max Planck Institute for the Science of Human History
Summary:
Researchers have discovered that Southeast Asia, today renowned
for its lush rainforests, was at various points in the past
covered by sweeping grasslands. The expansion and reduction of
these grasslands had drastic effects on local megafauna, variously
supporting success and inducing extinction.



FULL STORY ==========================================================================
In a paper published today in the journal Nature, scientists from the Department of Archaeology at MPI-SHH in Germany and Griffith University's Australian Research Centre for Human Evolution have found that the loss
of these grasslands was instrumental in the extinction of many of the
region's megafauna, and probably of ancient humans too.


========================================================================== "Southeast Asia is often overlooked in global discussions of megafauna extinctions," says Associate Professor Julien Louys who led the study,
"but in fact it once had a much richer mammal community full of giants
that are now all extinct." By looking at stable isotope records in modern
and fossil mammal teeth, the researchers were able to reconstruct whether
past animals predominately ate tropical grasses or leaves, as well as the climatic conditions at the time they were alive. "These types of analyses provide us with unique and unparalleled snapshots into the diets of these species and the environments in which they roamed," says Dr. Patrick
Roberts of the MPI-SHH, the other corresponding author of this study.

The researchers compiled these isotope data for fossil sites spanning
the Pleistocene, the last 2.6 million years, as well as adding over 250
new measurements of modern Southeast Asian mammals representing species
that had never before been studied in this way.

They showed that rainforests dominated the area from present-day Myanmar
to Indonesia during the early part of the Pleistocene but began to
give way to more grassland environments. These peaked around a million
years ago, supporting rich communities of grazing megafauna such as
the elephant-like stegodon that, in turn, allowed our closest hominin
relatives to thrive. But while this drastic change in ecosystems was a
boon to some species, it also lead to the extinction of other animals,
such as the largest ape ever to roam the planet: Gigantopithecus.

However, as we know today, this change was not permanent. The tropical
canopies began to return around 100,000 years ago, alongside the classic rainforest fauna that are the ecological stars of the region today.

The loss of many ancient Southeast Asian megafauna was found to
be correlated with the loss of these savannah environments. Likewise,
ancient human species that were once found in the region, such as Homo
erectus, were unable to adapt to the re-expansion of forests.

"It is only our species, Homo sapiens, that appears to have had
the required skills to successfully exploit and thrive in rainforest environments," says Roberts. "All other hominin species were apparently
unable to adapt to these dynamic, extreme environments." Ironically,
it is now rainforest megafauna that are most at risk of extinction, with
many of the last remaining species critically endangered throughout the
region as a result of the activities of the one surviving hominin in
this tropical part of the world.

"Rather than benefitting from the expansion of rainforests over the last
few thousand years, Southeast Asian mammals are under unprecedented threat
from the actions of humans," says Louys. "By taking over vast tracts of rainforest through urban expansion, deforestation and overhunting, we're
at risk of losing some of the last megafauna still walking the Earth."

========================================================================== Story Source: Materials provided by Max_Planck_Institute_for_the_Science_of_Human_History.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Julien Louys, Patrick Roberts. Environmental drivers of megafauna
and
hominin extinction in Southeast Asia. Nature, 2020; DOI:
10.1038/s41586- 020-2810-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201007123125.htm

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