Ypresian (56.0–47.8 Ma)

The Ypresian is the first age of the Eocene Epoch, occurring after the Thanetian (Paleocene), and before the Lutetian
What happened during this time?
  • The Ypresian had the highest mean annual temperatures of the entire Cenozoic Era
    • Dramatic warming event probably due to the release of methane that had been trapped in sediments on the ocean floor
    • Temperatures about 30° C
    • Relatively low temperature gradients from pole to pole
    • High precipitation in a world that was essentially ice-free
  • Between 49-50 Ma, extensive mats of the water fern, Azolla, grew on top of the Arctic Ocean
    • Anoxic saltwater was over topped by freshwater zone from heavy inflow from rivers  
    • These floating plants absorbed mass quantities of carbon dioxide, and when they died sank into the anoxic zone of the ocean, preventing decomposition
    • Cores from the sediments under the Arctic ocean, show Azolla fossils that are meters thick
    • The sequestration of large amounts of carbon dioxide caused CO2 levels to drop world wide
    • This creates a cooling effect that progressed for 50 million years until the Pleistocene glaciations
  • Land connections existed between Antarctica and Australia, between North America and Europe through Greenland, and probably between North America and Asia through the Bering Strait
    • It was an important time of plate boundary rearrangement: spreading centers and transform faults changed
    • Significant effects on oceanic and atmospheric circulation and temperature
  • The oldest known nightshade (Solanaceae) is found from around 52 million years ago (Penn State 2016)
  • Earliest evidence of an orchid found as a pollinia attached to a gnat trapped in amber (
  • Polar-region fossils include warm-weather species of plants, alligators, turtles, and flying lemurs
  • Artiodactyls became smaller (dwarfism) around 55 Ma and 53 Ma due to global warming
  • Titanomyrma, a giant ant species, the size of a hummingbird, found in Wyoming (Archibald et al. 2001)
Additional Reading