Resume La Mission paleoanthropologique franco-tchadienne (MPFT) est une collaboration scientifiqu... more Resume La Mission paleoanthropologique franco-tchadienne (MPFT) est une collaboration scientifique entre l'universite de Poitiers, l'universite de N'Djamena et le centre national d'appui a la recherche (CNAR) de N'Djamena. Cette mission conduit un programme international de recherches sur l'origine et les environnements des premiers Hominides et vient de decrire, au Nord Tchad, le plus ancien hominide connu. L'extraordinaire materiel fossile (un crâne sub-complet, deux fragments de mâchoire inferieure et trois dents isolees) mis au jour par la MPFT appartient a un nouvel hominide : Sahelanthropus tchadensis Brunet et al. 2002. Decouvert dans le Miocene superieur de Toros-Menalla (desert du Djourab, Nord Tchad), le nouvel hominide est associe a une faune indiquant un âge biochronologique proche de 7 Ma (base sur le degre evolutif de differentes especes de mammiferes, notamment proboscidiens, anthracotheriides et suides). Cette faune est composee d'especes de vertebres aquatiques et amphibies, ainsi que d'especes liees a la foret galerie et en ilots, la savane arboree et la prairie a graminees. Les etudes sedimentologiques sont en accord avec le caractere perilacustre de cette mosaique de paysages situee entre lac et desert. Le nouvel hominide possede un ensemble original de caracteres primitifs et derives qui permet de le considerer, non seulement comme proche du dernier ancetre commun aux chimpanzes et aux humains, mais aussi comme le plus ancien representant des hominides. Sa position geographique, 2500 km a l'ouest de la Vallee du Rift, et son âge tres ancien suggerent une vaste repartition geographique (Sahel et Afrique Orientale) des hominides anciens au moins des 6 Ma et une divergence chimpanze-humain plus ancienne (avant 7 Ma) que ne le proposaient la plupart des phylogenies moleculaires. Pour citer cet article : M. Brunet et al., C. R. Palevol 3 (2004).
Abstract This study presents a new, reliable method of dental microwear analysis, which is applie... more Abstract This study presents a new, reliable method of dental microwear analysis, which is applied to one of the largest published primate databases and to a Miocene hominoid, Ouranopithecus macedoniensis. Phase I and phase II molar facets were considered. A ...
The extant mammals have evolved highly diversified diets associated with many specialized morphol... more The extant mammals have evolved highly diversified diets associated with many specialized morphologies. Two rare diets, termitophagy and vermivory, are characterized by unusual morphological and dental adaptations that have evolved independently in several clades. Termitophagy is known to be associated with increases in tooth number, crown simplification, enamel loss, and the appearance of intermolar diastemata. We observed similar modifications at the species level in vermivorous clades, although interestingly the vermivorous mammals lack secondarily derived tools that compensate for the dentition's reduced function. We argue that the parallel dental changes in these specialists are the result of relaxed selection on occlusal functions of the dentition, which allow a parallel cascade of changes to occur independently in each clade. Comparison of the phenotypes of Rhynchomys, a vermivorous rat, and strains of mice whose ectodysplasin (EDA) pathway has been mutated revealed several shared dental features. Our results point to the likely involvement of this genetic pathway in the rapid, parallel morphological specializations in termitophagous and vermivorous species. We show that diets or feeding mechanisms in other mammals that are linked to decreased reliance on complex can lead to similar cascades of change.
INTRODUCTION Although teeth are studied for different purposes in humans and in living animals, t... more INTRODUCTION Although teeth are studied for different purposes in humans and in living animals, they are also very important in paleoanthropology, for several reasons. The first one is trivial and relates to the problem of fossilization. Paleoanthropologists must work on fossil remains, but all the parts of the body are not preserved in the same way. Some bones are more fragile and are destroyed easily. For instance, a complete skull is a very rare fossil. Other bones are more solid and they are selectively preserved. This is the case for the lower jaw, which is often preserved with the teeth. The hard tissues (enamel, dentin, and cementum) that compose the teeth favor preservation during the fossilization process. Consequently, some taxa are known only from some teeth or even one tooth. Nevertheless, it is not very prudent to describe a new taxon with an isolated tooth. Aedotontherium incognitum was considered as a new species whose type specimen was a single strange tooth from the late Miocene of India. In fact, it was a very rare fourth m3 of Sivapithecus, a close relative of Pongo, the orangutan. But when used correctly, teeth are very useful for paleoanthropologists. They are one of the results of adaptative evolu-
First lower molar development in the mouse was investigated from the cap to early bell stage usin... more First lower molar development in the mouse was investigated from the cap to early bell stage using histology, morphometry, TEM and 3D reconstructions. This period was characterized by the histogenesis of the enamel organ (EO), folding of the epithelio-mesenchymal junction and growth of the tooth. The histogenesis of the EO and appearance of the enamel knot (EK) were initiated at the early cap stage (ED14). From ED14 to ED15, the anterior and posterior extension of the EK was very prominent whilst the length of the enamel organ did not substantially change. The EK appeared as a dynamic and transitory histological structure including dying and replacement cells. At ED16, the folding of the IDE, which extended over the anterior two thirds of the molar, was the first sign of cuspidogenesis. It was accompanied by a local remodeling of the basement membrane (BM): IDE cells involved in this folding transitorily lost contact with the BM which formed a loop in the mesenchyme. During this period, the growth of the lower M1 along the antero-posterior axis was restricted to the posterior part of the molar. Histogenesis occurred in the whole EO, whilst initial cuspidogenesis was limited to the anterior part of the tooth. Distinct cell populations were thus involved in different contemporary processes leading to changes in the cell density in the mesenchyme, in the mitotic activity, in cell-shape, and cell-matrix interactions in the IDE, and remodeling of the BM where both epithelium and mesenchyme might participate.
Resume La Mission paleoanthropologique franco-tchadienne (MPFT) est une collaboration scientifiqu... more Resume La Mission paleoanthropologique franco-tchadienne (MPFT) est une collaboration scientifique entre l'universite de Poitiers, l'universite de N'Djamena et le centre national d'appui a la recherche (CNAR) de N'Djamena. Cette mission conduit un programme international de recherches sur l'origine et les environnements des premiers Hominides et vient de decrire, au Nord Tchad, le plus ancien hominide connu. L'extraordinaire materiel fossile (un crâne sub-complet, deux fragments de mâchoire inferieure et trois dents isolees) mis au jour par la MPFT appartient a un nouvel hominide : Sahelanthropus tchadensis Brunet et al. 2002. Decouvert dans le Miocene superieur de Toros-Menalla (desert du Djourab, Nord Tchad), le nouvel hominide est associe a une faune indiquant un âge biochronologique proche de 7 Ma (base sur le degre evolutif de differentes especes de mammiferes, notamment proboscidiens, anthracotheriides et suides). Cette faune est composee d'especes de vertebres aquatiques et amphibies, ainsi que d'especes liees a la foret galerie et en ilots, la savane arboree et la prairie a graminees. Les etudes sedimentologiques sont en accord avec le caractere perilacustre de cette mosaique de paysages situee entre lac et desert. Le nouvel hominide possede un ensemble original de caracteres primitifs et derives qui permet de le considerer, non seulement comme proche du dernier ancetre commun aux chimpanzes et aux humains, mais aussi comme le plus ancien representant des hominides. Sa position geographique, 2500 km a l'ouest de la Vallee du Rift, et son âge tres ancien suggerent une vaste repartition geographique (Sahel et Afrique Orientale) des hominides anciens au moins des 6 Ma et une divergence chimpanze-humain plus ancienne (avant 7 Ma) que ne le proposaient la plupart des phylogenies moleculaires. Pour citer cet article : M. Brunet et al., C. R. Palevol 3 (2004).
Abstract This study presents a new, reliable method of dental microwear analysis, which is applie... more Abstract This study presents a new, reliable method of dental microwear analysis, which is applied to one of the largest published primate databases and to a Miocene hominoid, Ouranopithecus macedoniensis. Phase I and phase II molar facets were considered. A ...
The extant mammals have evolved highly diversified diets associated with many specialized morphol... more The extant mammals have evolved highly diversified diets associated with many specialized morphologies. Two rare diets, termitophagy and vermivory, are characterized by unusual morphological and dental adaptations that have evolved independently in several clades. Termitophagy is known to be associated with increases in tooth number, crown simplification, enamel loss, and the appearance of intermolar diastemata. We observed similar modifications at the species level in vermivorous clades, although interestingly the vermivorous mammals lack secondarily derived tools that compensate for the dentition's reduced function. We argue that the parallel dental changes in these specialists are the result of relaxed selection on occlusal functions of the dentition, which allow a parallel cascade of changes to occur independently in each clade. Comparison of the phenotypes of Rhynchomys, a vermivorous rat, and strains of mice whose ectodysplasin (EDA) pathway has been mutated revealed several shared dental features. Our results point to the likely involvement of this genetic pathway in the rapid, parallel morphological specializations in termitophagous and vermivorous species. We show that diets or feeding mechanisms in other mammals that are linked to decreased reliance on complex can lead to similar cascades of change.
INTRODUCTION Although teeth are studied for different purposes in humans and in living animals, t... more INTRODUCTION Although teeth are studied for different purposes in humans and in living animals, they are also very important in paleoanthropology, for several reasons. The first one is trivial and relates to the problem of fossilization. Paleoanthropologists must work on fossil remains, but all the parts of the body are not preserved in the same way. Some bones are more fragile and are destroyed easily. For instance, a complete skull is a very rare fossil. Other bones are more solid and they are selectively preserved. This is the case for the lower jaw, which is often preserved with the teeth. The hard tissues (enamel, dentin, and cementum) that compose the teeth favor preservation during the fossilization process. Consequently, some taxa are known only from some teeth or even one tooth. Nevertheless, it is not very prudent to describe a new taxon with an isolated tooth. Aedotontherium incognitum was considered as a new species whose type specimen was a single strange tooth from the late Miocene of India. In fact, it was a very rare fourth m3 of Sivapithecus, a close relative of Pongo, the orangutan. But when used correctly, teeth are very useful for paleoanthropologists. They are one of the results of adaptative evolu-
First lower molar development in the mouse was investigated from the cap to early bell stage usin... more First lower molar development in the mouse was investigated from the cap to early bell stage using histology, morphometry, TEM and 3D reconstructions. This period was characterized by the histogenesis of the enamel organ (EO), folding of the epithelio-mesenchymal junction and growth of the tooth. The histogenesis of the EO and appearance of the enamel knot (EK) were initiated at the early cap stage (ED14). From ED14 to ED15, the anterior and posterior extension of the EK was very prominent whilst the length of the enamel organ did not substantially change. The EK appeared as a dynamic and transitory histological structure including dying and replacement cells. At ED16, the folding of the IDE, which extended over the anterior two thirds of the molar, was the first sign of cuspidogenesis. It was accompanied by a local remodeling of the basement membrane (BM): IDE cells involved in this folding transitorily lost contact with the BM which formed a loop in the mesenchyme. During this period, the growth of the lower M1 along the antero-posterior axis was restricted to the posterior part of the molar. Histogenesis occurred in the whole EO, whilst initial cuspidogenesis was limited to the anterior part of the tooth. Distinct cell populations were thus involved in different contemporary processes leading to changes in the cell density in the mesenchyme, in the mitotic activity, in cell-shape, and cell-matrix interactions in the IDE, and remodeling of the BM where both epithelium and mesenchyme might participate.
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Papers by Laurent Viriot