[ad_1]
New research challenges a long-held idea that our early tool-carrying ancestors have contributed to the disappearance of large mammals in Africa over the last millions of years. Researchers argue instead that long-term environmental changes have resulted in extinctions, mostly in the form of an expansion of grasslands probably caused by the fall of atmospheric carbon dioxide (CO2) levels.
The study was conducted by Tyler Faith, Curator of Archeology at the Natural History Museum of Utah and Adjunct Professor in the Department of Anthropology of the University of Utah. Utah. The research team also includes John Rowan from the University of Massachusetts Amherst, Andrew Du from the University of Chicago and Paul Koch from the University of California at Santa Cruz.
The study is published today in the journal Science.
"Despite decades of literature claiming that early hominins had had an impact on ancient African faunas, few attempts have been made to test this scenario or explore alternatives," said Faith. "We believe our study is a major step in understanding the magnitude of anthropogenic impacts on large mammal communities and is a compelling counter-argument to these long-held misconceptions about our ancestors."
To test the impacts of ancient hominins, researchers have compiled a record of 7 million years of herbivore extinctions in East Africa, focusing on the very large species, megaherbivores ( species over 2000 lbs). In Africa today, diversity was much greater in the past. "Lucy," three million years old (Australopithecus afarensis) shared its forest landscape with three giraffes, two rhinos, a hippopotamus and four elephant-like species in Hadar, Ethiopia.
When and why these species have disappeared has long been a mystery to archaeologists and paleontologists, despite the increasing evolution of hominins and meat-eating tool users, who are the main culprits.
"Our analyzes show a steady and long – term decline in megaherbivore diversity from 4.6 million years ago.This extinction process began more than a million years ago. 39 years before the very first evidence that human ancestors made tools or slaughtered animal carcasses the appearance of any kind of hominins capable of hunting them, such as Homo erectus, "says Faith.
Looking closer
Faith and her team have quantified the long-term changes in megaherbivores in East Africa using a dataset of more than 100 fossil assemblages spanning the last seven million years. The team also reviewed independent data on climate and environmental trends and their effects, particularly on CO2, stable carbon isotope recordings of vegetation structure and stable carbon isotopes of fossil herbivore teeth in East Africa, among others.
Their analysis reveals that over the past seven million years, significant extinctions of megaherbivores have occurred: 28 lineages have been extinguished, so that current communities do not have large animals. These results highlight the great diversity of old megaherbivore communities, many of which possess many more megaherbivore species than it currently exists in the world. set of Africa.
Further analysis showed that the decline of megaherbivores began about 4.6 million years ago and that the rate of decline in diversity has not changed since the onset of Homo erectus, a human ancestor often blamed for extinctions. On the contrary, the Faith team argues that the climate is more likely the culprit.
"The key factor in the decline of Plio-Pleistocene megaherbivores seems to be the expansion of grasslands, which is probably related to an overall decline in atmospheric CO2 Said John Rowan, a postdoctoral researcher at the University of Massachusetts Amherst, "Low CO2 levels favor tropical grasses over trees, and as a result, savannas have become less woody and more open over time. We know that many of the missing megaherbivores feed on woody vegetation, so they seem to be disappearing along with their food source. "
The loss of massive herbivores may also explain other extinctions attributed to ancient hominins. Some scientists suggest that competition with increasingly carnivorous carnosore species has resulted in the disappearance of many carnivores over the past millions of years. Faith and her team suggest an alternative.
"We know that there are also many extinctions among African carnivores and that some of them, such as saber-toothed cats, may have specialized on very large prey, perhaps juvenile elephants, "says Paul Koch. "Some of these carnivores may have disappeared with their megaherbivorous prey."
"By examining all the potential factors of megaherbivore decline, our analyzes suggest that climate and environmental changes have played a key role in past extinctions in Africa," Faith said. "It follows that, in seeking the impact of ancient hominins on ancient African ecosystems, we must focus our attention on the only species known to be able to cause them – we, Homo sapiens, over the past 300,000 years ".
Source link
