An international team of researchers has identified an African hominin population that existed very early in the Homo sapiens lineage, providing new insight into the shared ancestry of Homo sapiens, Neanderthals, and Denisovans.
The discovery was made at the Thomas Quarry I site in Casablanca, Morocco, where researchers identified 773,000-year-old hominin fossils dated to Earth’s last magnetic polarity reversal. A recent paper published in Nature reported the discovery of this ancient human ancestor.
Grotte à Hominidés
The Moroccan-French collaboration “Préhistoire de Casablanca” has been conducting excavations, geoarchaeological analyses, and stratigraphic studies in the region for more than three decades. Careful work has revealed not only hominin remains, but also important information about their geological context.
“Thomas Quarry I lies within the raised coastal formations of the Rabat–Casablanca littoral, a region internationally renowned for its exceptional succession of Plio-Pleistocene palaeoshorelines, coastal dunes and cave systems,” said co-author Jean-Paul Raynal, co-director of the program. “These geological formations, resulting from repeated sea-level oscillations, aeolian phases, and rapid early cementation of coastal sands, offer ideal conditions for fossil and archaeological preservation.”
Casablanca is home to some of the most important Pleistocene paleontological and archaeological sites in Africa, illuminating the region’s evolving hominin occupation. Thomas Quarry I has already produced significant finds dating back 1.3 million years and is in close proximity to other important Pleistocene sites, such as Sidi Abderrahmane.
Together, these sites form the “Grotte à Hominidés,” a cave system formed by a marine highstand and later filled with sediment, providing a combination of high-grade preservation and stratigraphic context for the finds.
Dating the Remote Past
That stratigraphic context makes the sites unique globally, as Early and Middle Pleistocene fossils are typically difficult to accurately date. In the Grotte à Hominidés, the infill and continuous deposition create a clear magnetic signal, enhancing the reliability of dating techniques.
Roughly 773,000 years ago, the most recent of Earth’s past magnetic field reversals, the Matuyama-Bruhes transition, occurred, creating a powerful magnetic marker for modern scientists to date ancient materials against.
“Seeing the Matuyama–Brunhes transition recorded with such resolution in the ThI-GH deposits allows us to anchor the presence of these hominins within an exceptionally precise chronological framework for the African Pleistocene,” said co-author Serena Perini.
The stratigraphic sequence at Grotte à Hominidés begins during the Matuyama Chron reverse-polarity interval, continues into the transition, and then extends into the Brunhes Chron normal-polarity interval.
With an unprecedented 180 magnetostratigraphic samples, the team identified the exact stratigraphic position of the switch. The team was able to establish sediment dating to a precise enough resolution to capture even the relatively brief 8,000 to 11,000-year transition period. Faunal evidence supported the team’s conclusions, confirming what they say is the highest-resolution stratigraphic dating ever produced at a Pleistocene site.
Hellbound and Down 