An international research team has reported the analysis of hominin fossils unearthed at Thomas Quarry I in Casablanca, Morocco. The fossils, precisely dated to approximately 773,000 ± 4,000 years ago, contribute to the understanding of the shared ancestry of Homo sapiens, Neandertals, and Denisovans, and represent the first hominin remains from Africa dating to the period between 1 million and 500,000 years ago.
Discovery Details
The hominin assemblage was discovered at the Grotte à Hominidés within Thomas Quarry I. The finds include a nearly complete adult mandible, a second adult half mandible, a child mandible, several vertebrae, and isolated teeth. A hominin femur was also recovered, displaying signs of gnawing, which researchers have interpreted as evidence of the site being used as a carnivore den. The majority of the fossils were recovered in 2008 and 2009, as part of over three decades of archaeological and geological research by the Moroccan-French Program "Préhistoire de Casablanca."
Dating Methodology
The definitive age of the fossils was established through a high-resolution magnetostratigraphic record. This technique captured the Matuyama-Brunhes geomagnetic polarity reversal, which occurred around 773,000 years ago. This reversal serves as a precise chronological marker for the Quaternary period. The continuous deposition and rapid sedimentation at the Grotte à Hominidés allowed for detailed recording of this reversal, providing a precise temporal framework for the hominin presence. Serena Perini, a geologist and paleomagnetist, noted that this technique provided the chronological certainty.
Fossil Characteristics and Analysis
High-resolution micro-CT imaging, geometric morphometrics, and comparative anatomical analysis were performed on the remains. The fossils exhibit a mosaic of archaic and derived traits. For example, they lack a defined chin, a characteristic present in Homo sapiens, but possess dental features similar to those of Homo sapiens and Neandertals.
The characteristics show similarities to Homo antecessor from Gran Dolina, Atapuerca, Spain, which date between 772,000 and 949,000 years ago. This resemblance suggests ancient population contacts between northwest Africa and southern Europe. However, analysis of the enamel-dentine junction in the teeth suggests that the Grotte à Hominidés hominins are distinct from both Homo erectus and Homo antecessor, retaining primitive features and lacking specific Neandertal traits. Jean-Jacques Hublin, a paleoanthropologist involved in the study, indicated that the fossils bear resemblances to Homo erectus while also showing traits ancestral to modern humans. The Moroccan fossils have not yet been formally classified with a scientific name.
Evolutionary Significance
These hominins are considered representative of populations that could be basal to Homo sapiens and archaic Eurasian lineages. Their combination of archaic African traits with features that approximate later Eurasian and African Middle Pleistocene morphologies provides insights into the last common ancestor of Homo sapiens, Neandertals, and Denisovans. Genetic evidence estimates this common ancestor to have lived between 765,000 and 550,000 years ago, with the paleontological evidence from the Grotte à Hominidés aligning with the older part of this timeframe.
The discovery contributes to the understanding of the ancestral species of these three groups, sometimes referred to as 'ancestor x'. Candidates for this ancestral species include Homo antecessor and Homo heidelbergensis, found in Africa and Eurasia. Ryan McRae, a paleoanthropologist, highlighted the ongoing debate regarding whether Homo erectus directly led to modern humans, Neanderthals, and Denisovans, or if a more traceable lineage exists.
Jean-Jacques Hublin suggested these finds reinforce an African origin for Homo sapiens. The findings also contribute to addressing a significant time gap in the fossil record between Homo erectus and Homo heidelbergensis.
Site Context and Broader Implications
The Rabat-Casablanca littoral, where Thomas Quarry I is located, is recognized for its succession of Plio-Pleistocene paleoshorelines, coastal dunes, and cave systems, which facilitate fossil and archaeological preservation. Thomas Quarry I is also known for containing Acheulean industries dated to approximately 1.3 million years ago.
During the period these hominins lived, the coastal landscape of Morocco was a lush wetland, supporting diverse large animals such as crocodiles, hyenas, hippos, and large cats. This discovery indicates that Northwest Africa played a role in the early evolutionary history of the genus Homo, a period when climatic fluctuations facilitated ecological connections across the Sahara region.
Morocco is also the location where some of the earliest known Homo sapiens remains, dating to approximately 330,000 to 400,000 years ago, were found at Jebel Irhoud. However, researchers caution against designating this region as the sole origin point for our species, suggesting that local geological conditions may contribute to better fossil preservation in the area.