Note sur l'ontogenèse crânienne et les hétérochronies chez Gorilla gorilla et Pan troglodytes

Resume La comparaison par les methodes Procrustes de l'ontogenese crânienne de Pan troglodytes et de Gorilla gorilla precise la dynamique et la chronologie de leur developpement. Les arbres phenetiques confirment un gradient morphologique du nouveau-ne a l'adulte, avec un dimorphisme d'origine sexuelle plus accuse chez le gorille. La quantification des changements morphologiques par des champs vectoriels permet de visualiser et de comparer l'organisation spatiale de la croissance cranio-faciale des deux especes. On en deduit que des heterochronies du developpement (acceleration, pre-deplacement, hypermorphose par acceleration et hypermorphose par post-deplacement) sont a l'origine des varia…

A solution to the human paradox: fundamental ontogenies and heterochronies

Solving the human paradox means explaining how a genetic difference of a mere 1% can be consistent with 5 million years of anatomical transformation from great apes to present-dayHomo sapiens. The solution proposed here is that of the internal history of ontogenetic change. A concept of “fundamental ontogeny” is developed and deduced from comparison between living and fossil primates. The fossil human lineage can be summarized into five fundamental ontogenies corresponding to successive skull plans (bauplans) resulting from five major phases of craniofacial contraction: prosimians (adapiforms), monkey apes (propliopithecidae), great apes (dryopithecidae), australopithecines andHomo. The mor…

La notion d'espace morphologique,outil d'analyse de la morphodiversité des organismes

Resume L'analyse de la morphologie des organismes est une base essentielle dans la mise en evidence des changementsevolutifs. La morphologie est maintenant frequemment abordee par des procedures quantitatives, dont certaines permettent de construire de veritables cartes morphologiques ou les dissemblances et ressemblances de formes entre les organismes sont directement lisibles et quantifiees. La notion d'espace morphologique, illustree ici par differents exemples, se revele particulierement feconde pour comprendre comment la diversite morphologique d'un ensemble d'organismes (stades ontogenetiques, populations, clades) se structure, et par consequent pour interpreter en termes evolutifs ou…

Un exemple de spéciation lié à l'eustatisme: l'apparition précoce de Schackoina cabri (foraminifère planctonique mésogéen)

Investigation of planktic foraminifers from the Lower Aptian of the Vocontian Basin (SE France) reveals that Schackoina cabri makes a very discrete first appearance in the Weissi ammonite zone and not in the Deshayesi zone, i.e. before the global anoxic event OAE 1a and not after as was accepted in the literature. This discovery seems to support the recent model whereby speciation of planktic foraminifers occurred in marine lowstands and their real expansion during the ensuing sea-level rise.

L’élongation des loges chez les foraminifères planctoniques du Crétacé inférieur: une adaptation à la sous-oxygénation des eaux?

Abstract Planktic foraminifera with radially elongated chambers appeared on four occasions in the early Cretaceous of the Vocontian Basin (SE France). These appearances coincided with or followed the deposition of organic rich levels which are evidence of hypoxic to anoxic conditions at the sea-floor. In addition, oxygen deficient surface waters are inferred from the occasional presence of Hedbergellas with deformed (insufficiently calcified) walls. It is suggested that the elongation of the chambers of these foraminifera was an adaptive response to the low oxygen content of surface waters, the increased surface area of the test allowing better gas exchange with sea water and the intake of …

Cretaceous stratigraphic scales based on benthic Foraminifera in West European basins (biochronohorizons)

Quantification de révolution morphologique du crâne des Hominidés et hétérochronies

Abstract Comparisons of adult skulls of various species of great apes, fossil hominids and modern humans in the sagittal, Francfort and ortho-sagittal planes reveal a series of three separate organisation plans: ‘Great Ape’, ‘Australopithecine’ and ‘Homo’, the latter including primitive men ( Homo ergaster-erectus-neandertalensis ) and modern humans ( Homo sapiens ). Morphological changes between these plans are quantified for the first time here by vector fields. This study confirms the existence of cranio-facial contraction, which occurs as a series of leaps. The juvenile morphology of the great ape skull is broadly preserved in adult Homo sapiens, suggesting that numerous heterochronies …

Were climatic changes a driving force in hominid evolution?

International audience; A comparison of externalist and internalist approaches in hominid evolution shows that the externalist approach, with its claim that climate was responsible for the appearance of bipedalism and hominization, now seems to be ruled out by the biological, palaeogeographical, palaeontological and palaeoclimatic data on which it was based. Biological data support the embryonic origin of cranio-facial contraction, which determined the increase in cranial capacity and the shift in the position of the foramen magnum implying bipedalism. In the internalist approach, developmental biology appears as the driving force of hominid evolution, although climate exerts a significant …

Everticyclammina minuta n. sp., foraminifère nouveau del'Hauterivien-Barrémien du Bassin de Paris

Resume Un nouveau foraminifere agglutinant de l'Hauterivien-Barremiendu Bassin de Paris, Everticyclammina minuta n. sp., est decrit et figure (morphologie externe et interne). Il est caracterise par une petite taille, un profil mince a flancs subparalleles, une spire d'enroulement serree, un nombre eleve de loges par tour et des epaississements septaux bien developpes a la base du dernier tour, semi-circulaires en coupe equatoriale. Des precisions sont approtees sur sa variabilite et son evolution. Cette espece est liee a des sediments terrigenes fins (vases) du domaine infralittoral, en milieu calme, et est susceptible de supporter de legeres variations de salinite.

Analysing disparity by applying combined morphological and molecular approaches to French and Japanese carabid beetles

The expression of morphological disparity within a clade is related to its history and to the environmental parameters within which it develops. Recent developments in geometric morphometries allow quantitative estimation of morphological disparity, and facilitate comparisons with genetic data intended to provide phylogenetic information. Such comparisons were made between two sets of ground beetle species from regions that differ biogeographically and environmentally: 12 post-glacial reinvading species from NE France; and 15 Japanese species less likely to be affected by the Pleistocene glacial events. Genetic relationships were inferred from mitochondrial DNA (ND5 gene). Morphological div…

Hétérochronies du développement chez des foraminifères crétacés: Exemples et réflexions

Resume Differentes modifications de l'ontogenese (neotenie, acceleration, hypermorphose), associees a des innovations, sont illustrees chez des foraminiferes planctoniques et benthiques de l'Aptien-Albien du Bassin de Paris.