Françoise Magniez-Jannin

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 sufficient quantities of oxygen for their metabolic needs.

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 morphological areas defined by these skull plans include more-or-less numerous species. This concept leads to renewed debate about (i) the relationship between speciation and bauplans, and (ii) the mechanisms involved in the successive steps of cranio-facial contraction and the correlated morphological changes. It is suggested that, from great apes to modern man, numerous heterochronies (hypermorphosis, hypomorphosis and post-displacements) have occurred during ontogeny, allowing the acquisition of permanent bipedalism inAustralopithecus andHomo, the increased cranial capacity of primitive forms ofHomo, and the disappearance of simian characters associated with renewed increase in cranial capacity inH. sapiens.

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.

Were climatic changes a driving force in hominid evolution

Abstract 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 influence and was involved in the following ways: (1) in the prior establishment of ecological niches that allowed the common ancestor to become differentiated into three subspecies; (2) by dividing up the area of distribution of species, resulting in the present-day subspecies of gorillas and chimpanzees; (3) by facilitating relative fluctuations of the geographical areas of distribution of the various species, particularly the spread of australopithecines across the African savanna from north (Chad, Ethiopia) to south (South Africa); (4) by determining adaptive geographical differentiations among Homo erectus and Homo sapiens (pigmentation, haemoglobin, etc.).

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 have occurred in mosaic during ontogeny (hypermorphosis, hypomorphosis, post-displacements).