773,000-year-old Moroccan cave fossils reveal human and neandertal evolutionary split
A groundbreaking discovery in Morocco's Atlantic coast has shed new light on the timeline of African prehistory. A team of researchers has uncovered a set of ancient human fossils dating back approximately 773,000 years, with a margin of error of just 4,000 years. This remarkable precision is a rare find for fossils of this age, bringing us closer to understanding the pivotal moment in human evolution that led to the emergence of modern humans, Neandertals, and Denisovans.
The fossils, unearthed from Thomas Quarry I, provide a unique glimpse into a critical period in our evolutionary history. The site's location within raised coastal formations along the Rabat–Casablanca littoral has played a crucial role in preserving these ancient remains. Over time, the region experienced significant geological changes, including rising and falling sea levels, wind-blown dunes, and the rapid hardening of coastal sands, all of which contributed to the formation and preservation of the caves where the fossils were found.
This discovery is the culmination of over three decades of meticulous fieldwork conducted by the Moroccan-French program "Préhistoire de Casablanca." The team's dedication to long excavations, layer-by-layer mapping, and extensive geological studies across the southwest part of Casablanca has paid off, revealing an unusual cave sequence within Thomas Quarry I, known as the "Grotte à Hominidés."
Mohib emphasized the collaborative nature of the research, attributing the success to strong institutional partnerships. The study involved the Ministère de la Jeunesse, de la Culture et de la Communication Département de la Culture of the Kingdom of Morocco (through INSAP) and the Ministère de l’Europe et des Affaires Étrangères of France (through the French Archaeological Mission Casablanca), as well as support from institutions in Italy, Germany, and France, including the Università degli Studi di Milano and the Max Planck Institute for Evolutionary Anthropology.
The dating method employed in this study is magnetostratigraphy, which utilizes the Earth's magnetic field reversals recorded in sediments. The key marker is the Matuyama–Brunhes transition, the last major geomagnetic polarity reversal, which occurred around 773,000 years ago. This global and abrupt change in the magnetic field serves as a precise timestamp, allowing researchers to anchor the fossils' presence within an exceptionally accurate chronological framework for the African Pleistocene.
The team collected 180 magnetostratigraphic samples, an unusually high number for a hominin site of this age, capturing the end of the Matuyama Chron, the transition itself, and the start of the Brunhes Chron. They estimate the transition's duration to be between 8,000 and 11,000 years, providing a robust age estimate for the hominin-bearing sediments.
The fossil assemblage, which appears to come from a carnivore den, includes a hominin femur with clear signs of gnawing and consumption, a nearly complete adult mandible, a second adult half mandible, a child mandible, several vertebrae, and isolated teeth. The anatomy of these fossils reveals a mosaic of traits, with some features resembling archaic hominins and others more derived, suggesting potential population contacts between northwest Africa and southern Europe during this period.
The study's micro-CT imaging, geometric shape analysis, and comparative anatomy techniques have provided valuable insights into the fossils' ancestry and comparative anatomy. Matthew Skinner focused on the enamel-dentine junction, a hidden feature inside teeth, which can remain intact even when enamel is worn. This analysis has helped distinguish the Grotte à Hominidés hominins from Homo erectus and Homo antecessor, suggesting they may represent populations basal to Homo sapiens and archaic Eurasian lineages.
Shara Bailey highlighted the dental morphological differences between the Grotte à Hominidés hominins and later Neandertals. The teeth retain primitive features and lack traits characteristic of Neandertals, indicating that regional differences in human populations may have already been present by the end of the Early Pleistocene. This challenges the notion of the Sahara as a permanent biogeographic barrier, as evidenced by repeated connections between northwest Africa and the savannas of the East and South.
The Moroccan fossils are almost the same age as the Gran Dolina hominins and older than later Middle Pleistocene fossils tied to Neandertals and Denisovans. They are also significantly older than the earliest Homo sapiens remains at Jebel Irhoud, by approximately 500,000 years, according to the researchers. Genetic evidence places the last common ancestor of Homo sapiens, Neandertals, and Denisovans between about 765,000 and 550,000 years ago, and the Moroccan fossils align best with the older part of this range, based on their age and blend of traits.
Hublin emphasized the significance of these findings, suggesting that the fossils from the Grotte à Hominidés may be the best candidates for African populations lying near the root of this shared ancestry, reinforcing the view of a deep African origin for our species.
The practical implications of this research are far-reaching. It provides researchers with one of the most precisely dated African Pleistocene hominin assemblages, anchored to 773,000 years ago, plus or minus 4,000 years. The high-resolution magnetic record and 180 samples offer a valuable model for dating other early sites, especially where fossil ages remain uncertain. The study's findings strengthen the role of northwest Africa in early Homo evolution and support the idea of repeated connections across regions, including the Sahara. Additionally, the tooth imaging approach, including enamel-dentine junction analysis, can help identify populations even when tooth surfaces are worn.
The research findings are available online in the journal Nature, offering a comprehensive resource for further exploration and discussion.
