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.
Early Hominins
While this find is a boon to researchers, it represents a grisly end for the hominins involved, with the site appearing to have been a carnivore den. One of the femurs located at the site displayed clear signs of gnawing. Among the remains were a nearly complete adult mandible, a second adult half mandible, a child’s mandible, several vertebrae, and several isolated teeth.
Notably, these remains indicate extreme ancient hominin populations from northwest Africa and southern Europe may have come into contact even at this remote period. They possess archaic and derived traits, as revealed by high-resolution micro-CT imaging, geometric morphometrics, and comparative anatomical analysis. In some respects, these traits resemble those of the Homo antecessor remains discovered at Gran Dolina, a Paleolithic cave site in Spain, and are roughly contemporaneous with those remains.
Based on stratigraphic dating, the interactions predate the magnetic transition, and the populations became separated in its aftermath.
“Using microCT imaging we were able to study a hidden internal structure of the teeth, referred to as the enamel-dentine junction, which is known to be taxonomically informative and which is preserved in teeth where the enamel surface is worn away,” said co-author Matthew Skinner. “Analysis of this structure consistently shows the Grotte à Hominidés hominins to be distinct from both Homo erectus and Homo antecessor, identifying them as representative of populations that could be basal to Homo sapiens and archaic Eurasian lineages.”
Africa’s Hominins
By displaying a combination of archaic African traits mixed with those resembling Middle Pleistocene Eurasian and African morphology, the remains provide important new information about Homo sapiens, Neanderthals, and Denisovans’ last common ancestor. Genetic evidence suggests that the ancestor lived between 765,000 and 550,000 years ago, aligning with the dating of the Grotte à Hominidés site.
“In their shapes and non-metric traits, the teeth from Grotte à Hominidés retain many primitive features and lack the traits that are characteristic of Neandertals,” said co-author Shara Bailey. “In this sense, they differ from Homo antecessor, which, in some features, are beginning to resemble Neandertals. The dental morphological analyses indicate that regional differences in human populations may have been already present by the end of the Early Pleistocene.”
Northwest Africa’s role in early Homo evolution is attributable to the distinct climatic conditions of the time, when what is now the Sahara desert was a vibrant ecological corridor.
“The idea that the Sahara was a permanent biogeographic barrier does not hold for this period,” said co-author Denis Geraads. “The palaeontological evidence shows repeated connections between Northwest Africa and the savannas of the East and South.”
Lead author Jean-Jacques Hublin concluded by explaining that “the fossils from the Grotte à Hominidés may be the best candidates we currently have for African populations lying near the root of this shared ancestry, thus reinforcing the view of a deep African origin for our species.”
The paper, “Early Hominins from Morocco Basal to the Homo Sapiens Lineage,” appeared in Nature Communications on January 7, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.