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| Grande Coupure | |
|---|---|
| Name | Grande Coupure |
| Date | ~33.9–33.5 Ma |
| Location | Western Eurasia |
| Type | Faunal turnover |
Grande Coupure
The Grande Coupure was a major Paleogene faunal turnover event centered at the Eocene–Oligocene transition that produced abrupt extinctions and replacements among mammal assemblages in Western Eurasia and altered terrestrial ecosystems. It is recognized by a sharp turnover in fossil mammal taxa, disappearance of several endemic clades, and immigration of new groups associated with changing climates and connections to North America and Asia. Paleontologists, stratigraphers, and paleoclimatologists study the event through integrated evidence from fossil sites, isotope chronologies, and plate reconstructions involving regions such as France, Germany, and the United Kingdom.
The term was coined in early 20th‑century paleontology literature to describe a pronounced break in the late Eocene to early Oligocene fossil record of Europe, analogous to turnover intervals like the K–Pg boundary and regional events such as the Messinian Salinity Crisis. It marks the loss of endemic European taxa including several families of perissodactyls, artiodactyls, and rodents and the arrival of immigrant clades tied to dispersal routes through the Turgai Strait region and via connections with Asia and North America. Stratigraphic contexts use referents like the Priabonian and Rupelian stages to define pre‑ and post‑event intervals, with paleomagnetic and biostratigraphic correlation to global stage boundaries recognized by the International Commission on Stratigraphy.
Multiple proximate and ultimate causes have been proposed, often interacting: global cooling associated with growth of continental ice sheets on Antarctica; sea‑level fall linked to Antarctic glaciation; altered ocean circulation after tectonic shifts including closure events near the Tethys Sea and changes in gateway geometries like the North Atlantic; and dispersal via temporary land bridges across the Turgai Strait and Eurasian corridors. Extrinsic forcings such as abrupt greenhouse gas declines and shifts in atmospheric circulation tied to orbital forcing have been invoked, as well as intrinsic biotic mechanisms including competition from invading taxa, pathogen introductions, and ecological restructuring akin to turnovers seen in the Paleocene–Eocene Thermal Maximum. Paleobiogeographic modeling and comparisons with turnover events such as the Eocene–Oligocene extinction event explore how combination of climate, sea‑level, and tectonics produced selective extinctions and immigrant establishment.
Fossil records from classic localities—Quercy in France, the Geiseltal of Germany, the Baskerville and Walton faunas of the United Kingdom—show abrupt disappearance of many endemic genera of hyracodonts, anchilotheriids, and endemic rodent lineages, with concurrent first appearances of immigrant groups such as early carnivorans related to Miacis, bunodont anthracotheres, and new artiodactyl lineages. Microvertebrate assemblages, dental turnover in perissodactyl lineages, and changes in mammalian body‑size distributions are documented in faunal lists compiled by regional workers and summarized in syntheses by institutions like the Natural History Museum, London and the Muséum national d'Histoire naturelle, Paris. Taphonomic and sampling biases are assessed using comparative databases and statistical methods from paleobiology research centers and university departments.
Post‑event faunas display increased biogeographic homogenization between Eurasia and North America as immigrant clades established new radiations; examples include expansion of rodent families with modern affinities and diversification of carnivoran stem groups leading toward later Carnivora lineages. Endemic European herbivores declined, and new grazing and browsing guilds reflecting more open habitats appeared, paralleling developments in contemporaneous faunas of Asia and parts of Africa. Paleobiogeographic reconstructions employing plate‑tectonic frameworks from groups studying the Eurasian Plate and North American Plate emphasize transient dispersal corridors and barriers that controlled directionality and timing of migrations.
The interval coincides with pronounced global cooling and seasonalization leading to expansion of cooler, drier biomes across mid‑latitudes. Oxygen isotope records from marine carbonate, deep‑sea cores curated by organizations like the Integrated Ocean Drilling Program, and terrestrial paleosol studies show a shift toward heavier δ18O values consistent with ice growth on Antarctica, decreased atmospheric CO2 inferred from stomatal proxies and geochemical models, and changes in vegetation recorded in palynological records curated by botanical institutions. Vegetation shifts from closed, evergreen forests to more open, mixed deciduous and grass‑rich landscapes are evident in pollen assemblages from sites across Europe.
The main faunal turnover clusters around the boundary between the Eocene and Oligocene epochs, approximately 33.9–33.5 million years ago, and is temporally correlated with the onset of the major Oi‑1 oxygen isotope shift marking Antarctic glaciation. Correlation efforts integrate magnetostratigraphy, radiometric dates from volcanic ash beds studied by geochronology laboratories, and regional biostratigraphic markers used by researchers at institutions such as the Geological Survey of France and the German Research Centre for Geosciences. Some authors describe diachroneity at local scales, with staggered extinction and immigration pulses before and after the principal glaciation onset.
The event reshaped European mammal faunas, setting the stage for later Oligocene and Miocene radiations that produced modern lineages. It provided ecological opportunities for immigrant clades that contributed to the ancestry of groups represented in modern faunas, influenced body‑size evolution, and offers a case study for interactions among climate change, biogeography, and macroevolution. The Grande Coupure continues to inform conservation paleobiology and comparative studies connecting past turnovers—such as those recorded at the Pleistocene and Miocene boundaries—to modern biodiversity responses to climate perturbation.
Category:Paleogene events Category:Mass extinctions Category:Biogeography