Refitting bones to reconstruct the diversity in Middle Palaeolithic human occupations: the case of the Abric Romaní site (Capellades, Barcelona, Spain)

The composition and organisational patterns of Pleistocene human groups are a main research when it comes to the evolution of human behaviour. However, these studies are often limited by the restricted characteristics of the archaeological records and do not show enough resolution to make approaches with the necessary precision. The travertinic formations of the Abric Romaní site (Capellades, Barcelona, Spain) provide an ideal scenario to answer some questions about the European Middle Palaeolithic occupational patterns. The hearth-related accumulations from this site show many similarities with those generated by several contemporary forager groups, so each could represent the activity area of a specific social unit. This work contributes to the existing research by examining the faunal refits recovered in six stratigraphic units (H, I, J-Ja, K, L and M) that cover the chronological period between 44 and 55 ka. Faunal refits are analysed using the metric parameters of ethnographic hearth-related accumulations (the hearth itself and its corresponding drop and toss zones); significant relationships are found between many of these elements and the areas of influence of the hearths. In addition, connections between the activity areas from these refits are seen in several stratigraphic units. This phenomenon allows for greater diversity in the occupational patterns of this site to be identified than those recorded only from taphonomic studies. From this perspective, two main occupational models are proposed: (1) the simple model, in which isolated and unconnected hearth-related accumulations are identified (units H, L and—to a lesser extent—K) and (2) the complex model, primarily represented by the identification of several long-distance faunal refits connecting different activity areas (units I, J-Ja and M). Thus, this work provides deeper insights into the behavioural diversity of Middle Palaeolithic human groups, their social organisation and composition and their evolution in the region.

Metric and morphological comparison between the Arago (France) and Atapuerca-Sima de los Huesos (Spain) dental samples, and the origin of Neanderthals

The variability observed in the growing Middle Pleistocene hominin fossil record of Europe continues to trigger much debate on taxonomic issues and the biological processes that gave rise to Neanderthals. Here we present a metric and morphological comparative study of the dental samples recovered from the sites of Arago (southeast France) and Sima de los Huesos (SH) in the Sierra de Atapuerca (northern Spain). These sites are key to providing answers to these questions since they have yielded the largest hominin samples so far recovered for this time period. Despite the geographical proximity of the two sites and the contemporaneity of their hominin assemblages, we have observed remarkable metric and morphological differences between the teeth at Arago and SH. Whereas the SH teeth present an almost morphological identity with European Neanderthals, the Arago teeth exhibit a combination of plesiomorphic as well as some Neanderthal-derived features. In addition, the Arago crown dimensions are remarkably larger than those from SH, the differences being statistically significant for most variables. We hypothesize that during the Middle Pleistocene the European continent was settled at different points in time by hominin groups coming from Southwest Asia, probably from a common mother population evolving in this latter region. These first settlers can be identified by their more plesiomorphic morphology, whereas the most recent settlers are closer in appearance to Neanderthals. In addition, genetic processes such as isolation, genetic drift, directional adaptation or hybridization would have given rise to the puzzle we observe in the current fossil record.

New permanent teeth from Gran Dolina-TD6 (Sierra de Atapuerca). The bearing of Homo antecessor on the evolutionary scenario of Early and Middle Pleistocene Europe

Here we analyze the unpublished hominin dental remains recovered from the late Early Pleistocene Gran Dolina-TD6.2 level of the Sierra de Atapuerca (northern Spain), as well as provide a reassessment of the whole TD6.2 hominin dental sample. Comparative descriptions of the outer enamel surface (OES) and the enamel-dentine junction (EDJ) are provided. Overall, the data presented here support the taxonomic validity of Homo antecessor, since this species presents a unique mosaic of traits. Homo antecessor displays several primitive features for the genus Homo as well as some traits exclusively shared with Early and Middle Pleistocene Eurasian hominins. Some of these Eurasian traits were retained by the Middle Pleistocene hominins of Europe, and subsequently became the typical condition of the Neanderthal lineage. Although other skeletal parts present resemblances with Homo sapiens, TD6.2 teeth do not show any synapomorphy with modern humans. In addition, TD6.2 teeth can be well differentiated from those of Asian Homo erectus. The dental evidence is compatible with previous hypothesis about H. antecessor belonging to the basal population from which H. sapiens, Homo neanderthalensis, and Denisovans emerged. Future findings and additional research may help to elucidate the precise phylogenetic link among them.

First systematic assessment of dental growth and development in an archaic hominin (genus, Homo) from East Asia

Several human dental traits typical of modern humans appear to be associated with the prolonged period of development that is a key human attribute. Understanding when, and in which early hominins, these dental traits first appeared is thus of strong interest. Using x-ray multiresolution synchrotron phase-contrast microtomography, we quantify dental growth and development in an archaic Homo juvenile from the Xujiayao site in northern China dating to 161,000–224,000 years or 104,000–125,000 years before present. Despite the archaic morphology of Xujiayao hominins, most aspects of dental development of this juvenile fall within modern human ranges (e.g., prolonged crown formation time and delayed first molar eruption). For its estimated age-at-death (6.5 years), its state of dental development is comparable to that of equivalently aged modern children. These findings suggest that several facets of modern human dental growth and development evolved in East Asia before the appearance of fully modern human morphology. An archaic Homo juvenile from the East Asian Middle-Late Pleistocene transition has surprisingly modern dental development. An archaic Homo juvenile from the East Asian Middle-Late Pleistocene transition has surprisingly modern dental development.

Enamel and dentine dimensions of the Pleistocene hominins from Atapuerca (Burgos, Spain): A comparative study of canine teeth

Enamel and dentin patterns have awakened a considerable interest in phylogenetic studies. However, almost nothing is known about the dental tissue proportions of European Pleistocene hominins, apart from Neanderthal populations. This study aims to assess the three-dimensional dental tissue proportions of permanent canines belonging to the extensive sample of hominin teeth at Sierra de Atapuerca (Spain) through the use of microtomographic techniques. Our results show that early and middle Pleistocene populations from Atapuerca exhibit large coronal and root dentine dimensions, as well as a thinly enamelled pattern, which has been traditionally considered an autapomorphic Neanderthal trait. Therefore, these results might support an early enamel thickness decrease which is already observed 800kyr ago in Homo antecessor and maintained in later groups such as Sima de los Huesos and Neanderthal populations during the middle Pleistocene. Résumé Les patrons de proportions de l’émail et de la dentine ont éveillé un intérêt considérable dans les études phylogénétiques. Cependant, on ne connaît encore presque rien sur les proportions des tissus dentaires des hominidés du Pléistocène européen, à l’exception de celles des populations néandertaliennes. La présente étude vise à évaluer les proportions tridimensionnelles des tissus dentaires des canines permanentes issues d’un échantillon exceptionnel de dents d’homininés d’Atapuerca (Espagne) en utilisant des techniques microtomographiques. Nos résultats montrent que les populations du Pléistocène moyen et inférieur d’Atapuerca possèdent des proportions de dentine radiculaire et coronaire élevées, ainsi qu’un patron d’émail fin qui a été traditionnellement considéré comme un caractère autapomorphique des Néandertaliens. Par conséquent, ces résultats appuient l’apparition précoce d’une diminution de l’épaisseur de l’émail depuis au moins 800 ka chez Homo antecessor. Ce patron d’émail fin est également observé dans d’autres groupes plus tardifs, tels que Sima de los Huesos et les populations néandertaliennes pendant le Pléistocène moyen.