Sudden and dramatic environmental shifts, triggered by climate change, fueled the decline of prehistoric elephants, mammoths and mastodonts -- and humans likely played only a minor role in their demise -- according to a new study.
For decades, hunter gatherers have served as the primary suspect in the case of the planet's disappeared megafauna.
After all, their descendants, modern humans, have severely degraded Earth's ecosystems and snuffed out dozens of plant and animal species.
But the latest findings -- published Thursday in the journal Nature Ecology and Evolution -- suggest the emergence of small bands of spear-wielding humans fails to explain the rise and fall of the elephants, prehistoric and otherwise.
Still, there were once many more big animals than there are today.
Thousands of years ago, a wide variety of large proboscideans -- the group of large herbivores that includes mammoths and mastodons -- roamed the planet.
Today, only three species remain, all of them endangered and relegated to the tropics of Asia and Africa.
To better understand the evolutionary history of elephants and their relatives, an international team of paleontologists conducted an exhaustive review of the adaptive characteristics evolved by 185 different proboscidean species.
The review included dental and cranial features, mastication methods, tusk size, body mass and locomotion, among other characteristics.
This analysis allowed scientists to gain a better appreciation for the wide variety of forms and ecologies that proboscideans adopted during the millions of years before the arrival of early humans. . . .
"From approximately 6 million years ago, and especially since 3 million years ago, the ecomorphological diversity of proboscideans started to decrease globally in increments, following events of climatic cooling and harshening," co-author Juha Saarinen, a postdoctoral researcher at the University of Helsinki in Finland, told UPI in an email.
According to the authors of the new study, humans fail to explain these periodic declines.
"For instance, in Africa we see the big proboscidean extinction pulse about 2.4 million years ago, when members of the evolving hominin lineage were still very much bipedal chimpanzees in terms of their functional ecology," Zhang said.
"The final proboscidean extinction surges we detected on various continents do not go hand in hand with either enhanced hunting capabilities in archaic hominins or the settlement of Homo sapiens on the different landmasses," Zhang said.
The relationships of gomphotheres to other proboscideans remain unclear, and to some extent the grouping is a wastebasket taxon to refer to proboscideans that cannot be assigned to other groups.Gomphotheres originated in Africa during the Miocene, and arrived in Eurasia after the connection of Africa and Eurasia during the Early Miocene around 19 million years ago, in what is termed the "Proboscidean Datum Event". Gomphotherium arrived in North America around 16 million years ago. Notiomastodon and Cuvieronius dispersed into South America after 2 million years ago as part of the Great American Biotic Interchange due to the formation of the Ismuthus of Panama.
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