By Will Dunham
WASHINGTON, Jan 7 (Reuters) – Fossilized bones and teeth dating to 773,000 years ago unearthed in a Moroccan cave are providing a deeper understanding of the emergence of Homo sapiens in Africa, representing the remains of archaic humans who may have been close ancestors of our species.
Researchers said the fossils – lower jawbones of two adults and a toddler as well as teeth, a thigh bone and some vertebrae – were unearthed in a cave called Grotte à Hominidés at a site in the city of Casablanca. The cave appears to have been a den for predators, with the thigh bone bearing bite marks suggesting the person may have been hunted or scavenged by a hyena.
The researchers said the most appropriate interpretation is that these fossils represent an evolved form of the archaic human species Homo erectus, which first appeared about 1.9 million years ago in Africa and later spread to Eurasia.
The bones and teeth display a mix of primitive and more modern human characteristics. They fill a gap in the African fossil record of species in the human evolutionary lineage – called hominins – from about one million to 600,000 years ago.
According to the researchers, the fossils may represent an African population that existed shortly before the evolutionary split of the lineages that led to Homo sapiens in Africa and two closely related hominins – the Neanderthals and Denisovans – that inhabited Eurasia.
“I would be cautious about labeling them as ‘the last common ancestor,’ but they are plausibly close to the populations from which later African – Homo sapiens – and Eurasian – Neanderthal and Denisovan – lineages ultimately emerged,” said paleoanthropologist Jean-Jacques Hublin of Collège de France in Paris and the Max Planck Institute for Evolutionary Anthropology in Germany, lead author of the study published on Wednesday in the journal Nature.
“The fossils show a mosaic of primitive and derived traits, consistent with evolutionary differentiation already underway during this period, while reinforcing a deep African ancestry for the Homo sapiens lineage,” Hublin added.
The oldest-known fossils of Homo sapiens, dating to about 315,000 years ago, also were found in Morocco, at an archaeological site called Jebel Irhoud.
Knowing the age of the Grotte à Hominidés fossils, based on the magnetic signature of cave sediments surrounding the fossils, helped the researchers assess how this population fit into the human family tree.
“Establishing the age was essential to the interpretation of this material,” Hublin added.
The fossils were buried by fine sediments over time and the cave entrance was sealed by a dune, enabling exceptional preservation of the remains. Hundreds of stone artifacts and thousands of animal bones also were discovered in the cave.
The Grotte à Hominidés human fossils are roughly the same age as fossils from a site called Gran Dolina near Atapuerca in Spain that represent an archaic human species called Homo antecessor. In fact, these fossils share some traits.
“The similarities between Gran Dolina and Grotte à Hominidés are intriguing and may reflect intermittent connections across the Strait of Gibraltar, a hypothesis that deserves further investigation,” Hublin said.
Hominins from this time possessed body proportions similar to ours but with smaller brains.
The jawbone, or mandible, of the Grotte à Hominidés child, who was about 1-1/2 years old, was complete, while the mandible of one of the adults was nearly complete and the other was partial. One of the adult jawbones was built more robustly than the other, suggesting one was from a man and the other from a woman. The largest of the fossils was the adult thigh bone, or femur.
These people were capable of hunting prey but roamed a dangerous landscape and sometimes found themselves as the hunted, with large carnivores including big cats and hyenas on the prowl.
“Only the femur displays clear evidence of carnivore modification – gnawing and tooth marks – indicating consumption by a large carnivore. However, the cave appears primarily to have been a carnivore den that hominins used only occasionally. The absence of tooth marks on the mandibles does not imply that other parts of the bodies were not consumed by hyenas or other carnivores,” Hublin said.
(Reporting by Will Dunham, Editing by Rosalba O’Brien)
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