A set of ancient human fossils found on the Atlantic coast of Morocco is now on one of the tightest timelines of African prehistory. The remains are from Thomas Quarry I, and new analysis pegs them at about 773,000 years ago, less than 4,000 years old. This level of precision is rare for fossils this old, and draws you closer to a time close to the split that later led to modern humans, Neanderthals and Denisovans.
The research is led by an international team that includes Jean-Jacques Hublin from the Collège de France and the Max Planck Institute for Evolutionary Anthropology, David Lefèvre from the Université de Montpellier Paul Valéry, Giovanni Muttoni from the Università degli Studi di Milano and Abderrahim Mohib from Morocco’s Institut National des Sciences de l’Archéologie et du Patrimoine, known as INSAP. The team describes new hominin fossils that show a mix of older and more modern features and places them in a geologic record that is unusually clear.
For anyone trying to imagine the human family tree, the hardest part is often the timing. Fossils can be amazing, but their age can be unclear. Here, the timeline is the title. A high-resolution magnetic record has captured a major shift in Earth’s magnetic field, and the fossils are right there in that transition.
ThI-GH website. (CREDIT: Nature)
A long dig that finally paid off
The findings are based on more than three decades of fieldwork within the Moroccan-French “Préhistoire de Casablanca” program. You can feel the patience behind such an effort. The team did long excavations, careful layer-by-layer mapping and large geological surveys in the southwest part of the city.
That slow work revealed an unusual cave sequence inside the Thomas I Quarry, in an area known as the “Grotte à Hominidés”. The setting matters because fossils do not come from a loose or mixed layer. They came from sediments that remained in order.
Mohib framed the result as a product of collaboration, not luck. “The success of this long-term research reflects a strong institutional collaboration involving the Ministry of Youth, Culture and Communication, the Department of Culture of the Kingdom of Morocco (through INSAP) and the French Ministry of Europe and Foreign Affairs (through the French Archaeological Mission Casablanca).”
Support also came from institutions in Italy, Germany and France, including the Università degli Studi di Milano and the Max Planck Institute for Evolutionary Anthropology. This network helped transform a local cave depository into a global reference point.
A rib built to keep deep time
Thomas Quarry I is located in the uplifted coastal formations along the Rabat–Casablanca littoral. Over long periods, sea levels rose and fell, winds built dunes, and coastal sands hardened rapidly. Those changes created caves and preserved what later filled them.
Hominin specimens from ThI-GH. (CREDIT: Nature)
Jean-Paul Raynal, a co-director of the program during the dig that discovered the fossils, pointed out why the coast matters. He said the region is known for its “exceptional succession of Plio-Pleistocene palaeofloods, coastal dunes and cave systems”. He also noted that repeated sea level changes and rapid cementation created “ideal conditions for fossil and archaeological preservation”.
That larger landscape holds an unusually deep record of life and toolmaking. The wider Casablanca region documents early Acheulean stone tools and later developments, along with animal fossils that reflect changing environments.
Thomas Quarry I itself is known for very old Acheulean industries in northwest Africa, dating back to about 1.3 million years ago. The site is also near Sidi Abderrahmane, a classic reference point for Middle Pleistocene prehistory in the region.
In this larger context, Lefèvre described the “Grotte à Hominidés” as a cave system carved out of a marine high and later filled with sediments that preserved the fossils in a safe and undisturbed sequence of layers.
Dating fossils by Earth’s magnetic reversal
The dating method behind this work is magnetostratigraphy, a tool that reads changes in the Earth’s magnetic field recorded in sediments. In geologic time, the magnetic field reverses. North becomes south and the polarity reverses. These upheavals leave a sharp signal in the rock and sediment layers, and that signal is matched globally.
The key marker here is the Matuyama-Brunhes transition, the last major geomagnetic polarity reversal. It took place about 773,000 years ago. Because it is global and steep on geologic time scales, it acts as a precise time marker.
Location of Hominin Cave at the Thomas Quarry I site. (CREDIT: Nature)
At the “Grotte à Hominidés”, the rapid accumulation of sediments allowed the team to capture the transition in fine detail. Serena Perini explained why this matters. “Seeing the Matuyama-Brunhes transition recorded with such resolution in the ThI-GH deposits allows us to anchor the presence of these hominins in an exceptionally precise chronological framework for the African Pleistocene.”
The team collected 180 magnetostratigraphic samples, an unusually high number for a hominin site of this age. These samples captured the end of the Matuyama Chrono, the transition itself, and the beginning of the Brunhes Chrono. Researchers even estimate the short duration of the transition at 8,000 to 11,000 years. Hominin-bearing sediments formed during that window, which strengthens the age estimate.
The team also notes that animal evidence supports the same time frame, but treats the magnetic recording as a key anchor.
Bones from a carnivore den
The fossil assemblage appears to have come from a carnivore burrow. The researchers point to a hominin femur that shows clear signs of gnawing and consumption. The collection includes an almost complete adult mandible, a second half of an adult mandible, a child’s mandible, several vertebrae and isolated teeth.
When you imagine these discoveries, it helps to keep two ideas at once. First, these were living beings in a risky landscape. Second, their bones now sit in a rare vault locked in time.
The anatomy adds another layer of tension. The jaws and teeth show a patchwork of features, with features that appear archaic and others that appear more derivative. Some features are reminiscent of hominins from Gran Dolina la Atapuerca, which are often grouped under the label Homo antecessor. The paper suggests that ancient population contacts between northwest Africa and southern Europe may have existed earlier. By the time of the Matuyama-Brunhes transition, the groups appear clearly separated.
The stratigraphic context of the Grotte à Hominidés (ThI-GH). (CREDIT: Nature)
Clues to Ancestry and Comparative Anatomy
The team used micro-CT imaging, geometric shape analysis and comparative anatomy. Matthew Skinner focused on a hidden feature inside teeth, the enamel-dentin junction, which can remain intact even when the enamel is worn. “Using microCT imaging, we were able to study a hidden internal tooth structure, called the enamel-dentin junction, which is known to be taxonomically informative and is preserved in teeth where the enamel surface is worn away. Analysis of this structure consistently shows that Grotte à Hominidés hominins are distinct from Homomo erecessor and representative of both ancestors. populations that may be basal to Homo sapiens and archaic lineages Eurasian.”
Shara Bailey has described how the teeth differ from later Neanderthal models. “In their shapes and non-metrical features, the teeth from the Grotte à Hominidés preserve many primitive features and lack the features characteristic of Neanderthals. In this sense, they differ from Homo antecessor, which in some features are beginning to resemble Neanderthals. Dental morphological analyzes indicate that regional differences in early human populations could have already been completed by the early Pleistocene.”
The study also rejects the idea of the Sahara as a permanent wall. Denis Geraads said: “The idea that the Sahara was a permanent biogeographical barrier does not hold for this period. Paleontological evidence shows repeated connections between northwest Africa and the savannahs of the east and south.”
A candidate for the common ancestor
The fossils are about the same age as the Gran Dolina hominins and are older than the Middle Pleistocene fossils related to Neanderthals and Denisovans. They are also much older than the oldest Homo sapiens remains at Jebel Irhoud, about 500,000 years old, according to the researchers.
Genetic evidence places the last common ancestor of Homo sapiens, Neanderthals, and Denisovans between about 765,000 and 550,000 years ago. The Moroccan fossils align best with the older part of that interval, based on their age and mix of features.
Hublin summed up the stakes. “The fossils from the Grotte à Hominidés may be the best candidates we currently have for African populations that lie near the root of this common ancestry, thus strengthening the view of a deep African origin for our species.”
Practical implications of the research
This work provides researchers with one of the most precisely dated hominin assemblages from the African Pleistocene, anchored at 773,000 years ago, plus or minus 4,000 years.
The high-resolution magnetic record and 180 samples provide a model for dating other early sites, particularly where fossil ages remain uncertain.
Fossils provide new anatomical evidence for African populations near the split that later produced Homo sapiens, Neanderthals and Denisovans.
The findings reinforce the role of northwest Africa in the early evolution of Homo and support the idea of repeated connections in regions that include the Sahara.
The imaging approach of study teeth, including enamel-dentin junction analysis, can help identify populations even when tooth surfaces are worn.
The research results are available online in the journal Nature.
The original story “773,000-year-old Moroccan cave fossils reveal human-Neanderthal evolutionary divide” was published in The Brighter Side of News.
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