The punctuation in the evolution of orbitoides in the campanian of South-West France

摘要: For the Orbitoides assemblages analyzed from a number of closely sampled sections Campanian calcarenites in south-west France there is a sudden change means several parameters internal embryonicnepionic stage. The direction accordance with nepionic acceleration principle, known to be valid for all lineages orbitoidallarger foraminifera. Below and above level morphological break we seem to dealing two longer periods without any systematic the morphology. In abrupt shift could narrowed down to lithostratigraphic distance about ten centimetres, an interval which is thought correspond time duration less than few thousand years. In none evidence found that might point to a hiatus sedimentation or notable open-marine, shallow-water environment. Since discontinuity was sections about 90 km apart (Aubeterre Meschers) must have occurred simultaneously throughout entire Aquitaine basin. If take into account that bioturbation had obliterating effect on our data, it seems safe conclude modal very large geologically instantaneous. Because no comparable morphology detected in accompanying Lepidorbitoides lineage it thought likely the fundamental population composition an autonomous happening fitting evolutional theory homeostasis and punctuation. pulsating pattern stasis parts data sets is rather weak; phyletic gradualism still acceptable theory to explain gain more advanced morphotypes loss conservative ones sequence. At end paper argued concept sympatric speciation passing through low-frequency bottlenecks suites populations is one would fit best history of orbitoidal foraminifera. This model combine random character and directional aspect evolution, are expressed various ways in better lineages.