Unravelling the functional biomechanics of dental features and tooth wear

Most of the morphological features recognized in hominin teeth, particularly the topography of the occlusal surface, are generally interpreted as an evolutionary functional adaptation for mechanical food processing. In this respect, we can also expect that the general architecture of a tooth reflects a response to withstand the high stresses produced during masticatory loadings. Here we use an engineering approach, finite element analysis (FEA), with an advanced loading concept derived from individual occlusal wear information to evaluate whether some dental traits usually found in hominin and extant great ape molars, such as the trigonid crest, the entoconid-hypoconulid crest and the protostylid have important biomechanical implications. For this purpose, FEA was applied to 3D digital models of three Gorilla gorilla lower second molars (M2) differing in wear stages. Our results show that in unworn and slightly worn M2s tensile stresses concentrate in the grooves of the occlusal surface. In such condition, the trigonid and the entoconid-hypoconulid crests act to reinforce the crown locally against stresses produced along the mesiodistal groove. Similarly, the protostylid is shaped like a buttress to suffer the high tensile stresses concentrated in the deep buccal groove. These dental traits are less functional in the worn M2, because tensile stresses decrease physiologically in the crown with progressing wear due to the enlargement of antagonistic contact areas and changes in loading direction from oblique to nearly parallel direction to the dental axis. This suggests that the wear process might have a crucial influence in the evolution and structural adaptation of molars enabling to endure bite stresses and reduce tooth failure throughout the lifetime of an individual

The effectiveness of using carbonate isotope measurements of body tissues to infer diet in human evolution: Evidence from wild western chimpanzees (Pan troglodytes verus)*

Changes in diet throughout hominin evolution have been linked with important evolutionary changes. Stable carbon isotope analysis of inorganic apatite carbonate is the main isotopic method used to reconstruct fossil hominin diets; to test its effectiveness as a paleodietary indicator we present bone and enamel carbonate carbon isotope data from a well-studied population of modern wild western chimpanzees (Pan troglodytes verus) of known sex and age from Taï, Cote d'Ivoire.We found a significant effect of age class on bone carbonate values, with adult chimpanzees being more 13C- and 18O-depleted compared to juveniles. Further, to investigate habitat effects, we compared our data to existing apatite data on eastern chimpanzees (P. troglodytes schweinfurthii) and found that the Taï chimpanzees are significantly more depleted in enamel d13Cap and d18Oap compared to their eastern counterparts. Our data are the first to present a range of tissue-specific isotope data from the same group of wild western chimpanzees and, as such, add new data to the growing number of modern non-human primate comparative isotope datasets providing valuable information for the interpretation of diet throughout hominin evolution. By comparing our data to published isotope data on fossil hominins we found that our modern chimpanzee bone and enamel data support hypotheses that the trend towards increased consumption of C4 foods after 4 Ma (millions of years ago) is unique to hominins

Paléoanthropologie

Enseignement Cours et séminaires – Traits de contraintes énergétiques au cours de l’évolution humaine Introduction Les contraintes énergétiques représentent un enjeu majeur pour l’adaptation des organismes qui doivent extraire de l’énergie de leur environnement en quantité suffisante, sous la forme de nourriture pour les animaux. Cette énergie doit ensuite être allouée aux différentes fonctions vitales. Le coût de ces fonctions varie selon les organes impliqués et d’une espèce à l’autre. L’ac..

Pleistocene hominins as a resource for carnivores. A c. 500,000-year-old human femur bearing tooth-marks in North Africa (Thomas Quarry I, Morocco)

In many Middle Pleistocene sites, the co-occurrence of hominins with carnivores, who both contributed to faunal accumulations, suggests competition for resources as well as for living spaces. Despite this, there is very little evidence of direct interaction between them to-date. Recently, a human femoral diaphysis has been recognized in South-West of Casablanca (Morocco), in the locality called Thomas Quarry I. This site is famous for its Middle Pleistocene fossil hominins considered representatives of Homo rhodesiensis. The bone was discovered in Unit 4 of the Grotte à Hominidés (GH), dated to c. 500 ky and was associated with Acheulean artefacts and a rich mammalian fauna. Anatomically, it fits well within the group of known early Middle Pleistocene Homo, but its chief point of interest is that the diaphyseal ends display numerous tooth marks showing that it had been consumed shortly after death by a large carnivore, probably a hyena. This bone represents the first evidence of consumption of human remains by carnivores in the cave. Whether predated or scavenged, this chewed femur indicates that humans were a resource for carnivores, underlining their close relationships during the Middle Pleistocene in Atlantic Morocco

Endocranial Volume and Brain Growth in Immature Neandertals

Microstructural studies have suggested that an extended period of growth was absent in representatives of Homo erectus, and that Neandertals reached adulthood significantly more rapidly than modern humans. In addition to general rate of growth, a prolonged postnatal period of brain development allows humans to develop complex cognitive and social skills. Conditions in brain growth similar to those observed in extant humans were not established in the first representatives of Homo erectus. To assess the degree of secondary altriciality reached by Neandertals, we examined the most complete skulls available for immature Neandertal specimens. The endocranial volumes were evaluated by using equations based on external cranial measurements. The proportional endocranial volumes (PEV) of these fossils were compared to the PEV of known age modern children from Western Europe and to a developmental series of Pan troglodytes. We present an estimation of the cranial capacity of Krapina 1. Although Neandertal children are close to the modern variation, the position of the youngest specimens in the upper range of variation led us to propose that Neandertals may have displayed a slightly more primitive pattern with respect to the speed of brain growth

L'Homme châtelperronien de la Grotte du Renne et l'inventaire des vestiges humains des grottes d'Arcy-sur-Cure

International audienc

Premolar root and canal variation in South African Plio-Pleistocene specimens attributed to Australopithecus africanus and Paranthropus robustus

South African hominin fossils attributed to Australopithecus africanus derive from the cave sites of Makapansgat, Sterkfontein, and Taung, from deposits dated between about 2 and 3 million years ago (Ma), while Paranthropus robustus is known from Drimolen, Kromdraai, and Swartkrans, from deposits dated between about 1 and 2 Ma. Although variation in the premolar root complex has informed taxonomic and phylogenetic hypotheses for these fossil hominin species, traditionally there has been a focus on external root form, number, and position. In this study, we use microtomography to undertake the first comprehensive study of maxillary and mandibular premolar root and canal variation in Australopithecus africanus and Paranthropus robustus (n = 166 teeth) within and between the species. We also test for correlations between premolar size and root morphology as predicted under the ‘size/number continuum’ (SNC) model, which correlates increasing root number with tooth size. Our results demonstrate previously undocumented variation in these two fossil hominin species and highlight taxonomic differences in the presence and frequency of particular root types, qualitative root traits, and tooth size (measured as cervix cross-sectional area). Patterns of tooth size and canal/root number are broadly consistent with the SNC model, however statistically significant support is limited. The implications for hominin taxonomy in light of the increased variation in root morphology documented in this study are discussed

Virtual reconstruction of the Le Moustier 2 newborn skull.

Here we present a virtual skull reconstruction of the Le Moustier 2 neonate based on high-resolution computed tomographic data of the delicate original fragments. In the first step, the digital fragments were assembled based on anatomical criteria. If parts were missing on one side, or were better preserved on one side than the other, we used the software Avizo to reflect them across a midsagittal symmetry plane. Missing parts of the braincase were estimated based on complete reference crania using geometric morphometrics, so as to estimate endocranial volume (EV).When we compare our reconstruction of Le Moustier 2 to modern human neonates, we find that many morphological characteristics that separate Neandertal adults from modern human adults are already established at the time of birth. Neandertal features can already be detected in the shape of the orbit, the projection of the midface, the relative size and shape of the nose, the nasal bones, and the shape of the mandibular notch. The shape differences between Le Moustier 2 and modern human neonates in the cranial base are extremely subtle. Around the time of birth modern humans and Neandertals have very similar endocranial shapes and volumes. Our EV estimates for Le Moustier 2 range between 408–428 cc.Our reconstruction of Le Moustier 2 shows that most facial differences between modern humans and Neandertals develop prenatally as they are already established at the time of birth. Most shape differences in the braincase between modern humans and Neandertals, however, develop after birth. Our reconstruction of Le Moustier 2 therefore supports the notion that modern humans and Neandertals reach similar adult endocranial capacity through different postnatal ontogenetic pathways

Recent origin of low trabecular bone density in modern humans

Humans are unique, compared with our closest living relatives (chimpanzees) and early fossil hominins, in having an enlarged body size and lower limb joint surfaces in combination with a relatively gracile skeleton (i.e., lower bone mass for our body size). Some analyses have observed that in at least a few anatomical regions modern humans today appear to have relatively low trabecular density, but little is known about how that density varies throughout the human skeleton and across species or how and when the present trabecular patterns emerged over the course of human evolution. Here, we test the hypotheses that (i) recent modern humans have low trabecular density throughout the upper and lower limbs compared with other primate taxa and (ii) the reduction in trabecular density first occurred in early Homo erectus, consistent with the shift toward a modern human locomotor anatomy, or more recently in concert with diaphyseal gracilization in Holocene humans. We used peripheral quantitative CT and microtomography to measure trabecular bone of limb epiphyses (long bone articular ends) in modern humans and chimpanzees and in fossil hominins attributed to Australopithecus africanus, Paranthropus robustus/early Homo from Swartkrans, Homo neanderthalensis, and early Homo sapiens. Results show that only recent modern humans have low trabecular density throughout the limb joints. Extinct hominins, including pre-Holocene Homo sapiens, retain the high levels seen in nonhuman primates. Thus, the low trabecular density of the recent modern human skeleton evolved late in our evolutionary history, potentially resulting from increased sedentism and reliance on technological and cultural innovations