Contextes et âge des nouveaux restes dentaires humains du Pléistocène moyen de la carrière Thomas I a Casablanca (Maroc)

Un outillage lithique acheuléen, une riche faune du Pléistocène moyenet quatre dents d’hominidés ont été extraites du remplissage de la cavité dela carrière Thomas I, célèbre depuis la découverte en 1969 d’une hémi-mandibule humaine. Depuis 1988, des fouilles sont conduites dans ce sitedans le cadre du programme franco-marocain « Casablanca ». Une riche faune mammalienne et quelques restes de reptiles et d’oiseaux sont associésà l’industrie lithique dans l’unité stratigraphique 4. La faune, introduite par les carnivores, indique un paysage peu boisé et le stade évolutif des diverstaxons suggère un âge plus récent que celui de Tighenif (Algérie). Lesmarques de découpe sont absentes, ce qui pose la question du rôle deshominidés dans l’accumulation des restes fauniques. Le travail de la pierreétait orienté vers la production d’éclats et de rares bifaces ont été introduitsdans cette partie du site. Quatre dents humaines ont été exhumées entre 1994et 2005. La datation ICP-MS par ablation laser combinant l’ESR et lesséries de l’Uranium pour modéliser l’enrichissement en Uranium a été appliquée à une prémolaire humaine : elle a fourni un âge de 501 k a. De nouvelles mesures d’âge par OSL sur les sédiments encadrant la dent datée ont respectivement donné 420 ± 34 ka au dessus et 391 ± 32 ka endessous confirmant un âge minimum centré sur une période relativement ancienne du Pléistocène moyen. Contexts and age of the new dental human fossils from Middle Pleis- tocene deposits at Thomas Quarry I (Casablanca, Morocco) – The ThomasQuarry I locality became famous in 1969 with the discovery of a humanhalf-mandible in a cave. From 1988 onwards, modern controlled excava-tions took place within the framework of the Franco-Moroccan co-operative project “Casablanca.” The stratigraphy of Thomas I Quarry is complexand represents several major episodes of coastal sedimentation that aredated to the final Lower and early Middle Pleistocene on the basis of a detailed regional lithostratigraphical and microfaciological study and formthe Oulad Hamida Morpho-stratigraphic Unit. Within this MSU, some litho-stratigraphic units fossilize a polyphase palaeo-shoreline in which caveshave developed. A continental sediment series dated to the Middle and Upper Pleistocene on lithostratigraphical and biochronological evidenceand by OSL is preserved in the Hominid Cave (GH).The top of the GH general stratigraphy shows a red complex with abun-dant microfauna (stratigraphic unit 1). Below this, a multilayer dripstone floor interbedded with loose red sands (stratigraphic units 2-3) caps thelower stratigraphic units (4 and 5). Stratigraphic unit 4 contains artefacts, fauna and hominid fossils and rests on collapsed eolianite blocks imbedded in coarse sands which form stratigraphic unit 5; this lowermost intertidalunit fossilizes a notch in the polyphase shoreline.The Acheulean lithic assemblage recovered by recent excavations inGH stratigraphic unit 4 is similar to the series collected at the time of the discovery of the first Homo fossil in 1969. It is manufactured mainlyon various quartzites available close to the site as pebbles of small tomedium size and some blocks as well as a few flint nodules collected ina secondary position from beach deposits. The flint nodules derive fromthe phosphatic plateau of the Meseta hinterland and were carried to theocean by wadis. The assemblage consists of chopper-cores (mainly uni- facial unidirectional cores with a retouched cutting edge) and cores,semi-cortical flakes obtained by direct and bipolar knapping, along withrare handaxes made from large flakes or from flat pebbles, handaxe-likecores, hammerstones and anvils. Stone knapping was mainly oriented towards flake production and a few handaxes were probably imported tothe site. A rich mammalian macrofauna supplemented by the addition of a fewreptiles and birds is associated with the lithics in GH stratigraphic unit 4.The abundance and diversity of carnivores attest to their use of the cave.The most common species is a middle-size canid, with enlarged crushing part of the dentition.The fauna indicates an open woodland environment and suggests an age younger than Tighenif in Algeria, but the remotenessof this latter site, its distance from the seashore, and the fact that it is anopen-air site may account for some of the differences.Preliminary taphonomic analysis of the megafauna indicates that thecarcasses were processed by carnivores. Cut-marks are still absent fromthis assemblage despite the association with refitted lithic artefacts, whichraises the question of any human role in the bone accumulations. Similar cases of accumulations created by humans, carnivores and porcupines havealready been described in the Mediterranean area. However, the studied assemblage comes from inside the cave, whereas any human occupationmay well have been concentrated closer to the entrance. Geological studieshave demonstrated that unit 4 containing the assemblage results fromseveral sedimentary processes having possibly mixed artefacts with bones previously accumulated by predators. Between 1994 and 2005, four teeth of Homo were recovered in strati-graphic unit 4, a right upper premolar (ThI 94 OA 23-24), another right upper premolar (ThI 95 SA 26 no 89), a first left upper incisor (ThI 95SA 26 no 90) and a left upper premolar (ThI 2005 PA 24 no 107). Theteeth are larger than those of modern humans and show moderate to heavywear Laser ablation ICP-MS dating combining tESR and U-series data for modelling U-uptake has given an US/ESR age of 501 ka for a human premolar while new OSL measurements yielded an age of 420 ± 34 ka for sediments immediately above the dated tooth and 391 ± 32 ka below. Never-theless, biostratigraphy and lithostratigraphy point to greater antiquity,towards the base of the Middle Pleistocene.
Human Evolutionary Biology