Chadronian

The Chadronian is a North American Land Mammal Age typically set from around 37,000,000 to 33,700,000 years BP, a period of 3.3 million years.^[1] The Chadronian is preceded by the Duchesnean and followed by the Orellan NALMA stages. Relative to global geological chronology (the geologic time scale), it is usually considered to fall within the later part (Priabonian stage) of the Eocene epoch, ending around the same time as the Eocene-Oligocene boundary.

The Chadronian is named after the Chadron Formation, a widespread component of the White River Group in Nebraska and South Dakota. The most well-studied examples of Chadronian strata in the White River Group/Formation are the Flagstaff Rim area of eastern Wyoming and the Toadstool Park area of northwest Nebraska.^[1]

The beginning of the Chadronian is defined by the first appearance of Bathygenys (a merycoidodontid, or "oreodont"). Other mammals which first appear at the start of the stage include Merycoidodon dunagani (a merycoidodontid), Brachyrhynchocyon dodgei, (a daphoenine amphicyonid, or "bear dog"), and Archaeotherium (an entelodont). The early horse Mesohippus appears only slightly before the start of the Chadronian.^[1]

^ ^a ^b ^c Prothero, Donald R.; Emry, Robert J. (2004). "5. The Chadronian, Orellan, and Whitneyan North American Land Mammal Ages". In Woodburne, Michael O. (ed.). Late Cretaceous and Cenozoic Mammals of North America: Biostratigraphy and Geochronology. Columbia University Press. pp. 156–168. doi:10.7312/wood13040-007. ISBN 978-0-231-13040-0.

[:0-1] Prothero, Donald R.; Emry, Robert J. (2004). "5. The Chadronian, Orellan, and Whitneyan North American Land Mammal Ages". In Woodburne, Michael O. (ed.). Late Cretaceous and Cenozoic Mammals of North America: Biostratigraphy and Geochronology. Columbia University Press. pp. 156–168. doi:10.7312/wood13040-007. ISBN 978-0-231-13040-0.

[1]