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{{Short description|Geologic timescale for North American fauna}}
The '''North American land mammal ages''' ('''NALMA''') establishes a [[Geologic time scale|geologic timescale]] for [[North America]]n fauna beginning during the [[Late Cretaceous]] and continuing through to the present. These periods are referred to as ages or intervals (or stages when referring to the rock strata of that age) and were established using geographic place names where [[fossil]] materials were obtained.<ref>{{Cite journal|last=Roberto Díaz Sibaja, Eduardo Jiménez Hidalgo, Ma. Luisa García Zepeda|title=Una nueva localidad fosilífera en Oaxaca (México) y el registro más austral de Bison latifrons: Implicaciones paleobiogeográficas, paleoecológicas y paleoambientales|url=http://boletinsgm.igeolcu.unam.mx/bsgm/vols/epoca04/7001/%2812%29Diaz.pdf|journal=Boletín de la Sociedad Geológica Mexicana|volume=70|pages=201–222}}</ref>

==System==
The North American land-mammal-age system was formalized in 1941 as a series of provincial land-mammal ages.<ref>{{cite journal|last1=Wood|first1=H. E.|last2=Chaney|first2=R. W.|last3=Clark|first3=J.|last4=Colbert|first4=E. H.|last5=Jepsen|first5=G.L.|last6=Reeside|first6=J. B.|last7=Stock|first7=C.|title=Nomenclature and correlation of the North American continental Tertiary|journal=Geological Society of America Bulletin|date=1941|volume=52|issue=1|pages=1–48|doi=10.1130/gsab-52-1|bibcode=1941GSAB...52....1W}}</ref> The system was the standard for correlations in the [[Earth|terrestrial]] [[Cenozoic]] record of North America and was the source for similar time scales dealing with other continents. The system was revised into a formal [[Chronostratigraphy|chronostratigraphic]] system. This approach is nominally justified by international [[Stratigraphy|stratigraphic]] codes; it holds that first appearances of individual [[species]] in particular sections are the only valid basis for naming and defining the land-mammal ages.

The basic unit of measure is the first/last boundary statement. This shows that the [[first appearance datum|first appearance event]] of one [[taxon]] is known to predate the last appearance event of another. If two taxa are found in the same fossil [[quarry]] or at the same stratigraphic horizon, then their age-range zones overlap.<ref>{{cite book|editor-last1=Woodburne|editor-first1=Michael O.|chapter=A prospectus of the North American Mammal Ages|title=Cenozoic mammals of North America : geochronology and biostratigraphy|date=1987|publisher=University of California Press|location=Berkeley|isbn=978-0520053922|pages=285–290}}</ref>

The utility of the system led to its expansion into the Cretaceous (formalized 1986)<ref>{{cite journal|last1=Lillegraven|first1=J. A.|last2=McKenna|first2=M. C.|title=Fossil mammals from the" Mesaverde" Formation (late Cretaceous, Judithian) of the Bighorn and Wind River basins, Wyoming: with definitions of late Cretaceous North American land-mammal" ages"|journal=American Museum Novitates|date=1986|issue=2840|pages=1–68}}</ref> and the Holocene (formalized 2014).<ref name="Barnoskyetal2014">{{cite journal|last1=Barnosky|first1=A. D.|last2=Holmes|first2=M.|last3=Kircholtes|first3=R.|last4=Lindsey|first4=E.|last5=Maguire|first5=K. C.|last6=Poust|first6=A. W.|last7=Stegner|first7=M. A.|last8=Sunseri|first8=J.|last9=Swartz|first9=B.|last10=Swift|first10=J.|last11=Villavicencio|first11=N. A.|title=Prelude to the Anthropocene: Two new North American land mammal ages (NALMAs)|journal=The Anthropocene Review|volume=1|issue=3|date=2014|pages=225–242|doi=10.1177/2053019614547433|s2cid=128697655|url=https://escholarship.org/uc/item/0hs1w9js}}</ref> These additions have been used in research related to the [[Cretaceous–Paleogene extinction event]] and the ensuing recovery,<ref>{{cite book|editor-last1=Woodburne|editor-first1=Michael O.|chapter=Mammalian Biochronology of the Latest Cretaceous|title=Late Cretaceous and Cenozoic mammals of North America biostratigraphy and geochronology|date=2012|publisher=Columbia University Press|location=New York|isbn=9780231503785|pages=21–43}}</ref> and to the [[Anthropocene]] debate,<ref name=Barnoskyetal2014/> respectively. However, the ages that stretch into the Cretaceous are sometimes referred to as "[[Dinosaur paleobiogeography|North American land vertebrate ages]]" to reflect the fact that mammals, while still abundant, were not the dominant form of terrestrial life during the [[Mesozoic]].<ref name="fowler"/>

==Ages==

===Cenozoic land mammal ages===
*[[Saintaugustinean]]: Lower boundary 0.004 [[Megaannum|Ma]]. Upper boundary Present.<ref name="Barnoskyetal2014"/>
*[[Santarosean]]: Lower boundary 0.014 Ma. Upper boundary 0.004 Ma.<ref name="Barnoskyetal2014"/>
*[[Rancholabrean]]: Lower boundary 0.21 Ma. Upper boundary 0.014 Ma.<ref name="Barnoskyetal2014"/>
*[[Irvingtonian]]: Lower boundary 1.4 Ma. Upper boundary 0.21 Ma.<ref name="Barnoskyetal2014"/>
*[[Blancan]]: Lower boundary 4.7 Ma. Upper boundary 1.4 Ma.<ref name="Barnoskyetal2014"/>
*[[Hemphillian]]: Lower boundary 9.4 Ma. Upper boundary 4.7 Ma.<ref name="Barnoskyetal2014"/>
*[[Clarendonian]]: Lower boundary 12.5 Ma. Upper boundary 9.4 Ma.<ref name="Barnoskyetal2014"/>
*[[Barstovian]]: Lower boundary 16.3 Ma. Upper boundary 12.5 Ma.<ref name="Barnoskyetal2014"/>
*[[Hemingfordian]]: Lower boundary 18.5 Ma. Upper boundary 16.3 Ma.<ref name="Barnoskyetal2014"/>
*[[Arikareean]]: Lower boundary 29.5 Ma. Upper boundary 18.5 Ma.<ref name="Barnoskyetal2014"/>
*[[Whitneyan]]: Lower boundary 31.8 Ma. Upper boundary 29.5 Ma.<ref name="Barnoskyetal2014"/>
*[[Orellan]]: Lower boundary 33.9 Ma. Upper boundary 31.8 Ma.<ref name="Barnoskyetal2014"/>
*[[Chadronian]]: Lower boundary 37 Ma. Upper boundary 33.9 Ma.<ref name="Barnoskyetal2014"/>
*[[Duchesnean]]: Lower boundary 39.7 Ma. Upper boundary 37 Ma.<ref name="Barnoskyetal2014"/>
*[[Uintan]]: Lower boundary 46.2 Ma. Upper boundary 39.7 Ma.<ref name="Barnoskyetal2014"/>
*[[Bridgerian]]: Lower boundary 50.5 Ma. Upper boundary 46.2 Ma.<ref name="Barnoskyetal2014"/>
*[[Wasatchian]]: Lower boundary 54.9 Ma. Upper boundary 50.5 Ma.<ref name="Barnoskyetal2014"/>
*[[Clarkforkian]]: Lower boundary 56.2 Ma. Upper boundary 54.9 Ma.<ref name="Barnoskyetal2014"/>
*[[Tiffanian]]: Lower boundary 60.9 Ma. Upper boundary 56.2 Ma.<ref name="Barnoskyetal2014"/>
*[[Torrejonian]]: Lower boundary 63.8 Ma. Upper boundary 60.9 Ma.<ref name="Barnoskyetal2014"/>
*[[Puercan]]: Lower boundary 66 Ma. Upper boundary 63.8 Ma.<ref name="Barnoskyetal2014"/>

===Cretaceous land vertebrate ages===
*[[Lancian]]: Lower boundary 67 Ma. Upper boundary 66 Ma.<ref name="fowler">{{Cite journal|last=Fowler|first=DW|title=Revised geochronology, correlation, and dinosaur stratigraphic ranges of the Santonian-Maastrichtian (Late Cretaceous) formations of the Western Interior of North America|date=2017|journal=PLOS ONE|volume=12|issue=11|pages=e0188426|doi=10.1371/journal.pone.0188426|pmid=29166406 |pmc=5699823 |doi-access=free }}</ref>
*[[Edmontonian]]: Lower boundary 73 Ma. Upper boundary 67 Ma.<ref name="fowler"/>
*[[Kirtlandian]]: Lower boundary 75 Ma. Upper boundary 73 Ma.<ref name="fowler"/>
*[[Judithian]]: Lower boundary 79 Ma. Upper boundary 75 Ma.<ref name="fowler"/>
*[[Wahweapian]]: Lower boundary 82 Ma. Upper boundary 79 Ma.<ref>{{cite journal|last1=Ramezani|first1=J.|last2=Beveridge|first2=T.L.|last3=Rogers|first3=R.|last4=Eberth|first4=D.|last5=Roberts|first5=E.|title=Calibrating the zenith of dinosaur diversity in the Campanian of the Western Interior Basin by CA-ID-TIMS U–Pb geochronology|date=2022|journal=Sci Rep|volume=12|issue=1 |page=16026|doi=10.1038/s41598-022-19896-w|pmid=36163377 |pmc=9512893}}</ref>
*[[Aquilian]]: Lower boundary 84 Ma. Upper boundary 82 Ma.<ref name="fowler"/>

==Other continental ages==

*[[European land mammal age]]
*[[South American land mammal age]]
*[[Asian land mammal age]]

==See also==
*[[Appearance Event Ordination]]
*[[Biochronology]]

==References==
{{reflist}}

[[Category:North American land mammal ages| ]]
[[Category:Cenozoic mammals of North America| ]]
[[Category:Mesozoic mammals of North America| ]]
[[Category:Regional geologic time scales]]
[[Category:Cenozoic North America]]
[[Category:Mesozoic North America]]
[[Category:Prehistoric mammals of North America|*]]

North American land mammal age - Revision history

imported>SimLibrarian: Updated short description