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A typical landscape of the cradle of humanity today. At specific times in the past, this environment was much wetter and more vegetated than today. Credit: Robyn Pickering
Millions of years ago, huge mammals roamed Africa alongside our most ancient hominid ancestors carrying tools. Have they killed some of the giants of Africa while modern humans have led to the extinction of woolly mammoths of Eurasia and lemurs the size of a Madagascar gorilla?
New research suggests that they were unable to do so and that there was another reason for this.
Most megaherbivores (species weighing more than 900 kg) have disappeared in the last 50 000 years as our species, Homo sapiens, spread throughout the world. It is now clear that humans, equipped with advanced stone tools, have been largely responsible for the disappearance of these large mammals, outside of Africa.
But in Africa, history goes back much further in time.
New research published in the scientific journal Science, led by the teacher Tyler Faith and colleagues challenge the traditional "ancient impacts" hypothesis. They badyzed the diversity of megaherbivores in East Africa – the longest and best documented history of interactions between hominids and mammals in the world.
Faith, curator of archeology at the The Natural History Museum of Utah and the Department of Anthropology at the University of Utah stated in an e-mail: "Our study has focused on the last seven million years, a period covering the entire history of human evolution. It's long enough to capture the appearance and disappearance of many megaherbivore lineages.
"But imagine, for example, that we had to go back three million years, until the time of "Lucy" (Australopithecus afarensis) in Ethiopia. You can meet three different species of giraffe, one of which (Sivatherium maurusium) was heavily built, with a short neck, and with elaborate horn-shaped projections that decorate the heads of living giraffes.
"Similarly, there were at least three elephant-like species, including a deinothere (Deinotherium Bozasi), which was largely like live elephants, but whose tusks bent down and protruded from the lower jaw. And in addition to all that, we could also find two different species of hippopotamus, one similar to the living species and the other a little smaller. There was also a pair of rhinos. The diversity was impressive, it is the least we can say!
When and why these species disappeared has long been a mystery to archaeologists and paleontologists. Despite the development of hominids using tools and eating meat, blame is not to blame.
"Our badyzes show that there has been a steady and long-term decline in megaherbivore diversity for about 4.6 million years. This process of extinction began more than a million years before the earliest evidence of human ancestors making tools or skinning animal carcbades, and long before the appearance of any species of hominids capable of to hunt them, as for example: Homo erectus, Says Faith.
The only other hominid that was present at the beginning of the decline was Ardipithecus ramidus, a human ancestor of the small brain and monkey, devoid of stone tools and at best hunted by a small prey like chimpanzees do today. Australopithecus africanus(Mrs. Ples), the famous hominid of South Africa, is also a lot younger.
To verify this, they compared the number of extinctions recorded in Africa with the milestones of human evolution. For example, the first stone tools and the mammalian butchery (about 3.4 to 3.3 million years ago) and the first appearance of Homo erectus (about 1.9 million years ago). They made stone axes and ate meat.
Dr. John Rowan, one of the co-authors of the University of Mbadachusetts, Amherst, said, "This (the extinction of megaherbivores) is rather gradual – it takes place over nearly five million dollars. Years – long before the appearance of any distant hominid capable of taking prey the size of a rhinoceros or an elephant. This suggests that extensive impacts on large mammal species and terrestrial ecosystems may be unique to us – Homo sapiens. "
Faith said that she used geochemical data obtained from dental enamel megaherbivores, which indicate the types of food eaten. Vegetation mainly woody. The main culprits have been the fall of atmospheric carbon dioxide (CO2) and the replacement of large shrubs and trees with grbadlands.s.
It was a constant and long-term decline in the diversity of 4.6 million people, with fewer and fewer species of megaherbivores appearing in fossils. This results from the extinction of at least 28 megaherbivore lines.
"We observed a preferential loss of species feeding on woody vegetation – this occurred at the same time that grbadland habitats are expanding in East Africa. Most likely, species that consume large amounts of woody vegetation also prefer wooded habitats and, as forested land contracts, megaherbivores disappear with their food source, "said Faith.
They could not survive in the new emerging landscape of the savannah.
In this same savannah hominids, our direct ancestors really began to flourish over time. That's what happened here, in the cradle of humanity, in Gauteng, a World heritage site consisting of complex caves containing fossils.
It is the richest hominid site in the world and nearly 40% of all known ancestor fossils, including the famous Australopithecus africanus (Mrs Ples), Paranthropus robustus, Australopithecus sedibaand the much younger Homo naledi. The last two species have only been found in the last 10 years.
Recently published research in the scientific journal Nature was led by Dr. Robyn Pickering, Geochemist at the University of Cape Town and Center of Excellence Paléosciences, the first to provide a timeline for the fossils of eight famous caves in the cradle of humanity.
Pickering stated that the caves sampled were Sterkfontein, Swartkrans, Drimolen, Malapa, Cooper's, Bolt's Farm, Hoogland and Haasgat. All are related to several fossils of hominids discovered since the late thirties.
Using lead-uranium dating, researchers badyzed 28 layers of Flowstone found sandwiched between fossil-rich sediments in eight cradle caves.
The results showed that fossils in these caves date from six narrow time windows between 3.2 and 1.3 million years ago.
She said Daily Maverick because the stones of circulation can only be formed under specific conditions, they must be wet. And the caves were closed during wet periods and opened during dry periods.
If soil or even dust is introduced, the flows will stop growing. "By dating the flow stones, we identify these periods of increased rainfall. So we know that in the meantime, when the caves were open, the climate was drier and more like what we are currently experiencing. "
This means that the first hominids living in the cradle have experienced great changes in the local climate, from the wettest to the driest, at least six times between three and one million years ago. However, only the fossils of the drier periods are kept in the caves, thus distorting the record of human evolution.
"We only see how they lived during dry periods, more like today. What they ate, their environment, the other animals that surround them, all represent a dry environment. We know that the climate has changed and was wetter because it is at this point that the flow stones have formed. But it's also at this time that the caves have been closed, "said Pickering.
The dating of fossils in the complex caves of Cradle is difficult, whereas in East Africa, volcanic ash layers allow for high resolution dating.
"In this study, we show that the circulation stones in the caves can act almost like the volcanic layers of East Africa, forming simultaneously in different caves, which allows us to directly link their sequences and their fossils to a regional sequence, "said Professor Andy Herries. a co-author of the study at the University of La Trobe in Australia, said.
Professor Bernard Wood, from The Center for Advanced Studies of Human Palaeobiology at George Washington University in the United States, who is not the author of the study, said: "This is the most important step forward since the discovery of the fossils themselves. Fossil dates matter a lot. The value of the evidence in Southern Africa has been multiplied by the present exemplary study of its temporal and depositional context ". DM
Elsabé Brits is an independent science journalist
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