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{{Short description|North American faunal stage}}
The '''Chadronian''' is a [[North American land mammal age|North American Land Mammal Age]] typically set from around 37,000,000 to 33,700,000 years [[Before Present|BP]], a period of {{Mya|37-33.7|million years}}.<ref name=":0">{{Cite book |last=Prothero |first=Donald R. |url=https://www.degruyter.com/document/doi/10.7312/wood13040/html |title=Late Cretaceous and Cenozoic Mammals of North America: Biostratigraphy and Geochronology |last2=Emry |first2=Robert J. |date= |publisher=Columbia University Press |year=2004 |isbn=978-0-231-13040-0 |editor-last=Woodburne |editor-first=Michael O. |pages=156–168 |chapter=5. The Chadronian, Orellan, and Whitneyan North American Land Mammal Ages |doi=10.7312/wood13040-007 |chapter-url=https://www.degruyter.com/document/doi/10.7312/wood13040-007/html}}</ref> 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.<ref name=":0" />

The beginning of the Chadronian is defined by the first appearance of ''[[Bathygenys]]'' (a [[Merycoidodontidae|merycoidodontid]], or "[[oreodont]]"). Other mammals which first appear at the start of the stage include ''[[Merycoidodon|Merycoidodon dunagani]]'' (a merycoidodontid), ''[[Brachyrhynchocyon|Brachyrhynchocyon dodgei]]'', (a [[Daphoeninae|daphoenine]] [[Amphicyonidae|amphicyonid]], or "bear dog"), and ''[[Archaeotherium]]'' (an [[Entelodontidae|entelodont]]). The early horse ''[[Mesohippus]]'' appears only slightly before the start of the Chadronian.<ref name=":0" />

== Subdivisions ==
Four subdivisions of the Chadronian were informally proposed by Prothero and Emry (1996), later formalized by the same authors in 2004.<ref name=":0" /> Type assemblages (diagnostic fossil faunas used to define the subdivision) are bolded and underlined. From youngest to oldest:
{| class="wikitable"
|- style="text-align:center; background:gainsboro;"
|'''Subdivision'''
|'''Primary index fossil'''
|'''Estimated age'''
|'''Component assemblages'''
|-
|Late Chadronian
|''[[Miniochoerus|Miniochoerus chadronensis]]''
|33.7 - 34.7 Ma
|
* '''upper Flagstaff Rim, White River Formation''' (around ash J) (Wyoming)
* Upper Chadron Formation (Nebraska)
* Peanut Peak Member, Chadron Formation (South Dakota)
* [[Florissant Formation]] (Colorado)
* Ash Springs local fauna, [[Vieja Group]] (Texas)
|-
|Middle Chadronian
|''[[Leptomeryx|Leptomeryx mammifer]]''
|34.7 - 35.7 Ma
|
* '''middle Flagstaff Rim, White River Formation''' (around ashes B-G) (Wyoming)
* Pipestone Springs and Little Pipestone Creek local faunas, [[Renova Formation]] (Montana)
* Raben Ranch local fauna, Chadron Formation (Nebraska)
* Crazy Johnson Member, Chadron Formation (South Dakota)
|-
|Late Early Chadronian
|''[[Leptomeryx|Leptomeryx yoderi]]''
|35.7 - 36.5 Ma
|
* '''lower Flagstaff Rim, White River Formation''' (around ash A) (Wyoming)
* Yoder local fauna, White River Formation (Wyoming)
* Pipestone Springs local fauna, Renova Formation (Montana)<ref name=":1">{{Cite journal |last=Hanneman |first=Debra |last2=Lofgren |first2=Don |last3=Hasiotis |first3=Stephen |last4=McIntosh |first4=William |date=2022 |title=Late Eocene (Priabonian) chronostratigraphy, depositional environment, and paleosol-trace fossil associations, Pipestone Springs, southwest Montana |url=http://dx.doi.org/10.4202/app.00901.2021 |journal=Acta Palaeontologica Polonica |volume=67 |pages=5-20 |doi=10.4202/app.00901.2021 |issn=0567-7920|doi-access=free }}</ref>
* McCarty's Mountain local fauna (Montana)
* Ahearn Member, Chadron Formation (South Dakota)
* Medicine Pole Hills local fauna (North Dakota)
* Airstrip local fauna, [[Capote Mountain Tuff]] (Texas)
|-
|Earliest Chadronian
|''[[Bathygenys]]''
|36.5 - 37 Ma
|
* '''Little Egypt local fauna, upper [[Chambers Tuff]] (Texas)'''
* Rancho Gaitan local fauna, [[Preitos Formation]] ([[Chihuahua (state)|Chihuahua]], Mexico)
* lowermost Flagstaff Rim, White River Formation? (Wyoming)
* Pipestone Springs local fauna, Renova Formation (Montana)<ref name=":1" />
* Diamond O Ranch local fauna, Renova Formation? (Montana)<ref>{{Cite journal |last=Fostowicz-Frelik |first=Łucja |last2=Tabrum |first2=Alan R. |date=2009 |title=Leporids (Mammalia, Lagomorpha) from the Diamond O Ranch Local Fauna, Latest Middle Eocene of Southwestern Montana |url=https://www.researchgate.net/publication/269036748 |journal=Annals of Carnegie Museum |language=en |volume=78 |issue=3 |pages=253–271 |doi=10.2992/007.078.0303 |issn=0097-4463}}</ref>
|}
Part of the [[Cypress Hills Formation]] (Saskatchewan, Canada) is also considered to be Chadronian in age.<ref name=":0" /> In Colorado, Chadronian mammal faunas are found in the Florissant Formation, the [[Antero Formation]],<ref>{{Cite journal |last=Sweedler |first=Rory E. |last2=Eberle |first2=Jaelyn J. |last3=Mihlbachler |first3=Matthew C. |date=2021-06-01 |title=A latest Eocene (Chadronian) brontothere (Mammalia, Perissodactyla) from the Antero Formation, South Park, Colorado |url=https://pubs.geoscienceworld.org/uwyo/rmg/article/56/1/37/599894/A-latest-Eocene-Chadronian-brontothere-Mammalia |journal=Rocky Mountain Geology |language=en |volume=56 |issue=1 |pages=37–50 |doi=10.24872/rmgjournal.56.1.37 |issn=1555-7340|url-access=subscription }}</ref> and the White River Formation in the Kings Canyon area.<ref>{{Cite journal |last=Lloyd |first=K. J. |last2=Eberle |first2=J. J. |date=2012-09-01 |title=A late Eocene (Chadronian) mammalian fauna from the White River Formation in Kings Canyon, northern Colorado |url=http://rmg.geoscienceworld.org/cgi/doi/10.2113/gsrocky.47.2.113 |journal=Rocky Mountain Geology |language=en |volume=47 |issue=2 |pages=113–132 |doi=10.2113/gsrocky.47.2.113 |issn=1555-7332|url-access=subscription }}</ref> In New Mexico, the [[Conejos Formation|Conejos]], [[Espinaso Formation|Espinaso]], [[Spears Group|Spears]], [[Sanders Canyon Formation|Sanders Canyon]], [[Bell Top Formation|Bell Top]], upper [[Rubio Peak Formation|Rubio Peak]], and upper [[Palm Park Formation|Palm Park]] formations all overlap with the Chadronian NALMA.<ref>Lucas, Spencer G. (2015). "[https://www.google.com/books/edition/Vertebrate_Paleontology_in_New_Mexico/S--oDQAAQBAJ?hl=en&gbpv=1&pg=PA149&printsec=frontcover Eocene fossil vertebrates of New Mexico]". ''New Mexico Museum of Natural History and Science Bulletin''. Vol. 68. pp. 149–157.</ref> The Iniyoo local fauna ([[Oaxaca]], Mexico) was initially reported to be Chadronian,<ref>{{Cite journal |last=Jiménez-Hidalgo |first=Eduardo |last2=Smith |first2=Krister T. |last3=Guerrero-Arenas |first3=Rosalia |last4=Alvarado-Ortega |first4=Jesus |date=2015 |title=The first Late Eocene continental faunal assemblage from tropical North America |url=https://linkinghub.elsevier.com/retrieve/pii/S0895981114001667 |journal=Journal of South American Earth Sciences |language=en |volume=57 |pages=39–48 |doi=10.1016/j.jsames.2014.12.001|url-access=subscription }}</ref> though revised dating suggests that it is [[Arikareean]] (late Oligocene) instead.<ref>{{Cite journal |last=Jiménez-Hidalgo |first=Eduardo |last2=Lander |first2=E. Bruce |last3=Israde-Alcántara |first3=Isabel |last4=Rodríguez-Caballero |first4=Nadia Wendoline |last5=Guerrero-Arenas |first5=Rosalía |date=2021 |title=Earliest Arikareean (later early Oligocene) Iniyoo local Fauna from Chilapa Formation of Santiago Yolomécatl area in northwestern Oaxaca, southern Mexico |url=https://www.researchgate.net/publication/350530655 |journal=Journal of South American Earth Sciences |language=en |volume=109 |pages=103307 |doi=10.1016/j.jsames.2021.103307}}</ref>

==References==
{{reflist}}

{{Paleogene Footer}}

[[Category:Chadronian| ]]
[[Category:Eocene life]]
[[Category:Eocene animals of North America]]

{{geochronology-stub}}

Chadronian - Revision history

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