Modern elephants survived climate change in the past. More than 180 species, including mastodons, failed

(CNN) – The elephants we know and love may be the last survivors. While there are now only three species of elephants – which are endangered and can be found in Africa and Asia – they once belonged to a group called proboscideans that included 185 species that lived around the world.

In the past, researchers had blamed humans for hunting these animals to extinction thousands of years ago. However, new research suggests that climate change is likely to blame for the demise of prehistoric mammoths, mastodons, and early elephants, rather than overhunting by early humans at the end of the last Ice Age.

Waves of extreme climate change caused the Proboscideans to decline over time, ultimately causing most of them to go extinct in different parts of the world in a period between two million and about 75,000 years ago, the researchers said.

The study was published Thursday in the journal Nature Ecology & Evolution.

An international group of paleontologists created a detailed data set that analyzes the rise, evolution and fall of the 185 different species of proboscideans. This process took place over the course of 60 million years and began in North Africa. To track these elephants and their ancestors, the researchers studied world collections of fossils and focused on traits such as body size, skull shape, tusks and teeth.

“Surprisingly, for 30 million years, the first half of proboscis evolution, only two of the eight groups evolved,” said Zhang Hanwen, study co-author and honorary research associate at the Earth Sciences School of the United States. University of Bristol.

“During this time, most proboscideans were herbivores without any distinguishing characteristics, ranging in size from a pug to a wild boar. A few species became as large as a hippopotamus. However, these lineages were evolutionary dead ends. They all looked little like elephants, ”he explained.

All that changed 20 million years ago, when a migratory corridor that opened in the African-Arab tectonic plate entered the Eurasian continent. This allowed elephants and their predecessors to live in new environments, first in Eurasia and then in North America by crossing the Beringia Bridge, a strip of land that once linked Asia and North America.

Get out of Africa exposed elephants to habitats, changing climates and the need to adapt.

“The key to the game in this boom period of proboscidean evolution was ‘adapt or die,'” Zhang said. “Habitat disturbances were incessant, linked to a constantly changing global climate, and continually promoted new adaptive solutions, while proboscideans who were not keeping up were literally taken for dead.” Mastodons, once very diverse and widespread, eventually were reduced to fewer than a handful of species in the Americas, including the popular American Ice Age mastodon, “he explained.

As the Earth experienced glacial periods, elephants had to adapt: ​​the woolly mammoth, for example, had giant tusks that it could bury under the snow for food and thick fur.

When did diversity start to decline?

“We found that the ecological diversity of proboscids increased dramatically when they dispersed from Africa to Eurasia 20 million years ago and to North America 16 million years ago, when land connections were formed between these continents,” said Juha Saarinen, co-author. of the study and postdoctoral researcher in the Department of Geosciences and Geography of the University of Helsinki.

Although diversity initially increased after these events, it began to decline between 3 and 6 million years ago as the global climate cooled.

“The most ecologically versatile proboscids survived, mostly true elephants that were adapted to consuming various plant resources,” Saarinen said.

The proboscidean extinction peaks began about 2.4 million, 160,000 and 75,000 years ago in Africa, Eurasia and the Americas, respectively, according to the researchers.

“It is important to bear in mind that these ages do not demarcate the precise moment of extinctions, but rather indicate the points in time at which the proboscideans on the respective continents became subject to a greater risk of extinction,” said Juan Cantalapiedra , lead author of the study and research cecaria of the University of Alcalá in Spain.

These times do not coincide with the times when the first humans began to branch out and hunt giant herbivores, because it largely predates those advances.

“We did not anticipate this outcome,” Zhang said. “Our data refutes some recent claims about the role of archaic humans in eliminating prehistoric elephants since big game hunting became a crucial part of our ancestors’ livelihood strategy around 1.5 million years ago.” he explained.

Chris Widga, paleontologist and senior curator of the Gray Fossil Site and Museum at East Tennessee State University, believes this research points to how important it is to trace the evolutionary history of groups of animals in longer dimensions of time. Widga was not involved in the study.

“Those of us who study extinctions are often more concerned with when and where the last of a certain species disappears,” Widga said. ‘To understand whether the eventual extinction of some of these proboscidean groups was significant, we need to know something about the’ background ‘extinction rates that occur in response to global ecological and climatic changes. This research shows how proboscideans responded to large-scale climate changes and how they diversified ecologically to occupy new niches. And because proboscideans have such a huge impact on their environment, this is an important issue.

What role did hunting play?

This research also suggests that while 185 different proboscidean species have been identified with more than 2,000 fossil locations around the world, there may be more.

“As if we need more encouragement to find and describe more fossil proboscides,” Widga said.

The study authors note that overhunting by humans “may have served as a final double jeopardy” after proboscideans suffered much earlier from harsh and changeable climates.

“This is not to say that we have conclusively disproved any human involvement,” Zhang said. “In our scenario, modern humans settled on each land mass after the risk of extinction for proboscis had already escalated. An ingenious and highly adaptable social predator like our species could be the perfect black swan to deliver the coup de grace. ‘