Jun 7, 2017

Oldest Known Fossils for Our Species Discovered in Morocco

A composite reconstruction of the earliest known Homo sapiens fossils from Jebel Irhoud, Morocco based on micro computed tomographic scans of multiple original fossils. Dated to 300 thousand years ago, these early Homo sapiens already have a modern-looking face that falls within the variation of humans living today. However, the archaic-looking braincase indicates that brain shape, and possibly brain function, evolved within the Homo sapiens lineage.
In 1971, anthropologist Chris Stringer traveled to museums across Europe to study and measure as many Neanderthal skulls as possible for his Ph.D. One enigmatic fossil, described as an “African Neanderthal” and dated to 40,000 years ago, particularly intrigued him. Thanks to a tip shared over coffee in Paris, he found the skull stored in another anthropologist’s cupboard.

Stringer was very puzzled by what he saw.

“I knew it was no Neanderthal,” recalled Stringer, who is now a Merit Researcher at the Natural History Museum in London. “It completely lacked their puffed-out cheek bones, mid-facial prominence, and enormous nose.”

Over the years, the fossil puzzled other scientists as well. A new excavation project began in 2004 at the site where the “African Neanderthal” was found in the 1960s — Jebel Irhoud, located west of Marrakesh in Morocco. Two new papers published in Nature report the astonishing results of this lengthy project: The so-called Neanderthal and related fossils turn out to be 300,000–350,000-year-old Homo sapiens, making them the oldest known remains for our species.

The twenty-two Homo sapiens fossils discovered so far at Jebel Irhoud push back the origins of our species by over one hundred thousand years. To put this into perspective, the prior oldest securely dated Homo sapiens fossils were known from the site of Omo Kibish in Ethiopia, and were dated to 195,000 years ago.

“Even though the Jebel Irhoud fossils currently represent the oldest Homo sapiens fossil remains, we do not believe that North Africa is the ‘cradle of humankind,’” Philipp Gunz, senior author of the first of the two papers, said.

“Instead, we argue that the first Homo sapiens dispersed all over the African continent around 300,000 years ago,” added Gunz, who is a paleoanthropologist in the Department of Human Evolution at the Max Planck Institute for Evolutionary Anthropology (MPI-EVA). “These people were skilled hunters, so it is likely that they moved with their prey in the changing environments of Africa.”

View looking south of the Jebel Irhoud, Morocco site. The remaining deposits and several people excavating them are visible in the center. At the time the site was occupied by early hominins, it would have been a cave, but the covering rock and much sediment were removed by work at the site in the 1960s.
The evidence for such hunting consists of stone tools and animal remains that were found at the site with the human fossils — skulls, teeth, and long bones — that belonged to at least five individuals.

Shannon McPherron, senior author of the second paper, explained that the stone tools belong to what is known as the Middle Stone Age. Prior to this time, the predecessors of modern humans — who, with our species, comprise a group called hominins — largely relied upon big and heavy stone tools, such as hand-axes and cleavers. In the Middle Stone Age, they developed lighter and smaller tools, such as sharp pointed objects.

McPherron, an archaeologist at MPI-EVA, said many experts “think that some of the points would have served as spear points, and this would have made these Middle Stone Age peoples more effective hunters.”

Two of the new Jebel Irhoud, Morocco fossils in situ as they were discovered during excavation. In the center of the image, in a slightly more yellow brown tone, is the crushed top of a human skull (Irhoud 10) and visible just above this is a partial femur (Irhoud 13) resting against the back wall. Not visible behind the pointed rock (between the femur and the skull) is the mandible (Irhoud 11). The scale is in centimeters.
Based on the animal remains, the early humans’ prey of choice were gazelles. Fossilized zebras, wildebeest, and hartebeest were also found at the Jebel Irhoud archaeological cave site.

The ages of the finds were determined by thermoluminescence dating of the flint artifacts, which had been heated by fire. Daniel Richter of MPI-EVA, lead author of the second paper who directed the dating work, remembered how amazed he was when the results came in.

“When I first calculated the first ages, I couldn’t believe it and re-checked all parameters several times until I was sure that my thermoluminescence ages are alright,” Richter said.

Electron spin resonance dating was also employed, and was in agreement with the other results.

Middle Stone Age tool assemblages, similar to those at Jebel Irhoud, have been found throughout Africa, supporting Gunz’s statement that early Homo sapiens were nomadic hunters. Ecological barriers, such as the vast Sahara that experiences a “greening” wet period associated with plant growth every 15,000 or so years, likely played an important role in the evolution of our species. (The Sahara is currently in a dry period.)

Some of the Middle Stone Age stone tools from Jebel Irhoud, Morocco. Pointed forms such as a–i are common in the assemblage.
“This ancient population structure might explain why Homo sapiens are so diverse, despite being so closely related genetically,” Gunz said.

Jean-Jacques Hublin, who is lead author of the first paper, Gunz, and their colleagues used state-of-the-art micro computed tomographic scans and statistical shape analysis based on hundreds of 3D measurements to show that the facial shape of the Jebel Irhoud fossils is almost indistinguishable from that of modern humans living today. The methods further indicate that a partial cranium from Florisbad, South Africa, and now dated to 260,000 years ago also belonged to a Homo sapiens.

It is little wonder then that Stringer was so puzzled by the Jebel Irhoud skull that was once incorrectly labeled as being an “African Neanderthal.”

Stringer notes that the human skulls from the Moroccan site show that these early Homo sapiens had delicate cheekbones versus those of other primates and hominins. They also possessed retracted faces and jawbones like those of people today.

The excavation area is visible as a dark notch a little more than half way down the ridge line sloping to the left.
The Moroccan human fossils, however, also reveal more primitive features, such as a longer, lower braincase, strong brow-ridges, and a larger face and teeth than what individuals have now. The braincase evidence is particularly important, as many anthropologists suspect that a series of genetic changes affecting brain connectivity, organization, and development occurred in Homo sapiens, distinguishing our species from our extinct ancestors and relatives.

Intriguingly, Stringer indicated that the fossils share some features with the remains of a hominin known as “Galilee Man” from a site called “Cave of the Robbers” of about the same age in Israel. They also share features with other hominin remains unearthed at yet another Israeli site, Tabun Cave, a rock shelter located on the edge of the coastal Mount Carmel mountain range.

While the preponderance of genetic and fossil record evidence support that the evolution of Homo sapiens took place in Africa, fossils also show that the earliest known primates originated in Asia more than 40 million years ago.

Fossils for a human-ish species called “El Graeco” from the Eastern Mediterranean were recently determined to represent the oldest known hominin. The point at which humanity diverged from other primates could have then happened in this region.

An illustration of El Graeco, foreground, living in a savannah environment in the Eastern Mediterranean 7.2 million years ago.
If such an event occurred outside of Africa, then the common ancestor of Homo sapiens, Neanderthals and Denisovans might have lived outside of Africa too, but that mystery remains unsolved.

A clearer picture is emerging concerning what happened in Africa, however.

“Twenty years ago, I thought that Homo sapiens had a rapid and punctuational origin in a single location in Africa, perhaps East Africa,” Stringer said. “Now, I think it’s more like a multiregional evolution of sapiens within Africa, with different populations separated in different regions in the bad times — with some going extinct — and connecting up and exchanging genes and behaviors in the good times, climatically speaking.”

Read more at Discovery News

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