Thursday, June 8, 2017

Oldest Homo Sapiens Skull

Jebel Irhoud is an archaeological site located near Sidi Moktar, about 100 km (60 mi) west of Marrakesh, Morocco. It is noted for the hominid fossils that have been found there since the site's discovery in 1960. Originally thought to be Neanderthal, the specimens have since been assigned to Homo sapiens and have been dated to over 300,000 years ago. This makes them the oldest known fossil remains of Homo sapiens and there is some speculation that humans were present throughout Africa far earlier than previously thought, but the fossil record to date is too sparse to prove this idea.

Finds at the Site

The site is the remnants of a solutional cave filled with 8 metres (26 ft) of deposits from the Pleistocene era, located on the eastern side of a karstic outcrop of limestone at an altitude of 562 metres (1,844 ft). It was discovered in 1960 when the area was being mined for the mineral baryte. A miner discovered a skull in the wall of the cave, extracted it and gave it to an engineer, who kept it as a souvenir for a time. It was eventually handed over to the University of Rabat, who organised a joint French-Moroccan expedition to the site in 1961, headed by the French researcher Émile Ennouchi. Ennouchi's team identified the remains of around 30 species of mammals, some of which are associated with the Middle Pleistocene, but the stratigraphic provenance is unknown. Another excavation was carried out by Jacques Tixier and Roger de Bayle des Hermens in 1967 and 1969 in which 22 layers were identified in the cave. The lower 13 layers were found to contain signs of human habitation including a Mousterian-period industry of Levallois facies. These included blades, arrowheads, knives, scrapers, drills and other tools made of flint.

The site is particularly noted for the hominid fossils found there. Ennouchi discovered a skull which he termed Irhoud 1 and is now on display in the Rabat Archaeological Museum. He discovered part of another skull, designated Irhoud 2, the following year and subsequently uncovered the lower mandible of a child, designated Irhoud 3. Tixier's excavation found 1,267 recorded objects including skulls, a humerus designated Irhoud 4 and a hip bone recorded as Irhoud 5. Further excavations were carried out by American researchers in the 1990s and by a team led by Jean-Jacques Hublin from 2004. Animal remains found at the site have enabled the ancient ecology of the area to be reconstructed. It was quite different to the present and probably represented a dry, open and perhaps steppe-like environment roamed by equids, bovids, gazelles, rhinoceros and various predators.

Other Findings

When comparing the fossils with those of modern humans the main difference is the elongated shape of the fossil braincase. According to the researchers this indicates that brain shape, and possibly brain functions, evolved within the Homo sapiens lineage and relatively recently. Evolutionary changes in brain shape are likely to be associated with genetic changes of the brain's organization, interconnection and development and may reflect adaptive changes in the way the brain functions. Such changes may have caused the human brain to become rounder and two regions in the back of the brain to become enlarged over thousands of years of evolution.

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