#Eocene
- Alveolina — A genus of large fossil marine foraminifera, characteristic of the Late Cretaceous and Eocene periods, having a spherical, ellipsoidal, or fusiform calcareous shell structurally divided into numerous small chambers or alveoli; a microfossil belonging to this genus. These organisms represent essential index fossils for dating sedimentary geological layers and reconstructing ancient tropical marine environments.
- Anoplotherium — A fossil ungulate mammal from the late Eocene and Oligocene epochs, characterized by the complete absence of prominent canine teeth and horns, possessing a continuous dentition and a long, robust tail. This extinct genus (Anoplotherium) serves as an essential biostratigraphic marker for reconstructing the fauna and forest environment of the European Paleogene period.
- Anthracothere — A fossil ungulate mammal belonging to the family Anthracotheriidae, structurally related to modern hippopotamuses and pigs, which lived during the Eocene and Oligocene epochs, whose skeletal remains have been frequently discovered within geological layers rich in lignite and fossil coal. This large-bodied animal possessed a specific bunodont dentition and short limbs adapted to aquatic or swampy environments, being an essential stratigraphic benchmark for dating carboniferous deposits.
- Auversian — A regional subdivision or transitional geological stage of the Middle Eocene within the Paleogene period, defined by the fossiliferous sand deposits researched in Auvers-sur-Oise, Paris Basin (France); as an adjective, it denotes the sedimentary formations or marine fauna characteristic of this epoch.