773,000-Year-Old Fossils Capture a Moment Before Human Lineages Split
Along Morocco’s Atlantic coast, hominid fossils dating to around 773,000 years ago have been discovered in a sequence of caves. The remains date from the time – and probably just before – the divergence of lineages leading to modern humans, Neanderthals and Denisovans.
Published in NatureThe study reports that fossils from the Thomas I Quarry near Casablanca are among the most precisely dated African Pleistocene hominid assemblages identified to date, based on a high-resolution magnetic recording preserved in surrounding sediments. Anatomical analysis of the mandibles and other remains places hominids near the base of later human lineages, while the site highlights the role of northwest Africa in early history. Homo evolution.
“The fossils of Hominid Cave may be the best candidates we currently have for African populations located near the root of this common ancestry, thus reinforcing the idea of a deep African origin of our species,” said Jean-Jacques Hublin, lead author of the study, in a press release.
Meetings of Pleistocene African hominids
Establishing the age of Early and Middle Pleistocene hominid fossils is difficult, in part because sediment layers are often incomplete or disrupted, and many dating techniques have wide margins of error. At Thomas Quarry I, however, the surrounding sediments have preserved an overall geological signal that provides an unusually firm anchor in time.
Mandible ThI-GH-10717 during excavation. Thomas Quarry I, Hominid Cave.
(Image credit: © JP Raynal, Casablanca Prehistory Program)
As sediments accumulate, the magnetic minerals they contain align with the Earth’s magnetic field. When this field reverses polarity – an event that occurs worldwide and almost simultaneously on geological timescales – it leaves behind a recognizable signature. Deposits at Hominid Cave record the Matuyama-Brunhes reversal, which occurred approximately 773,000 years ago.
“Seeing the Matuyama-Brunhes transition recorded with such resolution in the ThI-GH deposits allows us to anchor the presence of these hominids in an exceptionally precise chronological framework for the African Pleistocene,” said Serena Perini, co-author of the study.
By analyzing 180 magnetostratigraphic samples, the team placed the fossils directly within the transition itself.
Learn more: This 7 million-year-old fossil could reveal when ancient humans started walking upright
Fossils from an early stage of the human family tree
The hominid remains were recovered from what appears to have been a carnivore den. One femur shows clear signs of gnawing, suggesting the bodies were dragged into the cave by predators rather than intentionally buried. The assemblage includes a nearly complete adult mandible, fragments of other adult and juvenile jaws, vertebrae, and isolated teeth.
The lower jaws illustrate the variations between fossil hominids and modern humans. Tighennif 3 from Algeria (top left), ThI-GH-10717 from Thomas Quarry in Morocco (top right), and Jebel Irhoud 11 from Morocco (bottom left), compared to a mandible from a recent modern human (bottom right).
(Image credit: © Philipp Gunz, MPI for Evolutionary Anthropology)
Some features resemble hominids of the same age from Europe, including Homo ancestor from Gran Dolina in Spain, while others retain more archaic features. Together, they suggest a population that does not fit neatly into existing species categories.
Using high-resolution micro-CT scans, the researchers examined the internal structure of teeth, focusing on the enamel-dentin junction, which can preserve evolving signals even when the outer enamel is worn away.
“The analysis of this structure systematically shows the Hominid Cave hominids must be distinct from both Homo erectusand Homo ancestoridentifying them as representative of populations that could be basal to Homo sapiens and archaic Eurasian lineages,” said study co-author Matthew Skinner.
Overall, the dental evidence suggests that regional differences between human populations were already appearing by the end of the Early Pleistocene.
The role of Northwest Africa in human evolution
Findings reinforce role of Northwest Africa in early Homo evolution. During the Pleistocene, climate changes periodically opened ecological corridors across what is now the Sahara, connecting North Africa with eastern and southern regions.
“The idea that the Sahara was a permanent biogeographic barrier does not hold for this period. Paleontological evidence shows repeated connections between northwest Africa and the eastern and southern savannahs,” said Denis Geraads.
The precise dating and distinctive anatomy of the Hominid Cave fossils place this region at a pivotal point in the shared evolutionary history of modern humans, Neanderthals, and Denisovans.
Learn more: Is there an advantage to having Neanderthal DNA in the human genome?
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