North American land mammal age

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The North American land mammal ages (NALMA) establishes a geologic timescale for North American 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.[1]


The North American land-mammal-age system was formalized in 1941 as a series of provincial land-mammal ages.[2] The system was the standard for correlations in the 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 chronostratigraphic system. This approach is nominally justified by international 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 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.[3]

The utility of the system led to its expansion into the Cretaceous (formalized 1986)[4] and the Holocene (formalized 2014).[5] These additions have been used in research related to the Cretaceous–Paleogene extinction event and the ensuing recovery,[6] and to the Anthropocene debate,[5] respectively. However, the ages that stretch into the Cretaceous are sometimes referred to as "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.[7]


Cenozoic land mammal ages[edit]

Cretaceous land vertebrate ages[edit]

Other continental ages[edit]

See also[edit]


  1. ^ Roberto Díaz Sibaja, Eduardo Jiménez Hidalgo, Ma. Luisa García Zepeda. "Una nueva localidad fosilífera en Oaxaca (México) y el registro más austral de Bison latifrons: Implicaciones paleobiogeográficas, paleoecológicas y paleoambientales" (PDF). Boletín de la Sociedad Geológica Mexicana. 70: 201–222.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  2. ^ Wood, H. E.; Chaney, R. W.; Clark, J.; Colbert, E. H.; Jepsen, G.L.; Reeside, J. B.; Stock, C. (1941). "Nomenclature and correlation of the North American continental Tertiary". Geological Society of America Bulletin. 52 (1): 1–48. Bibcode:1941GSAB...52....1W. doi:10.1130/gsab-52-1.
  3. ^ Woodburne, Michael O., ed. (1987). "A prospectus of the North American Mammal Ages". Cenozoic mammals of North America : geochronology and biostratigraphy. Berkeley: University of California Press. pp. 285–290. ISBN 978-0520053922.
  4. ^ Lillegraven, J. A.; McKenna, M. C. (1986). "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"". American Museum Novitates (2840): 1–68.
  5. ^ a b c d Barnosky, A. D.; Holmes, M.; Kircholtes, R.; Lindsey, E.; Maguire, K. C.; Poust, A. W.; Stegner, M. A.; Sunseri, J.; Swartz, B.; Swift, J.; Villavicencio, N. A. (2014). "Prelude to the Anthropocene: Two new North American land mammal ages (NALMAs)". The Anthropocene Review. 1 (3): 225–242. doi:10.1177/2053019614547433. S2CID 128697655.
  6. ^ Woodburne, Michael O., ed. (2012). "Mammalian Biochronology of the Latest Cretaceous". Late Cretaceous and Cenozoic mammals of North America biostratigraphy and geochronology. New York: Columbia University Press. pp. 21–43. ISBN 9780231503785.
  7. ^ a b c d e f Fowler, DW (2017). "Revised geochronology, correlation, and dinosaur stratigraphic ranges of the Santonian-Maastrichtian (Late Cretaceous) formations of the Western Interior of North America". PLOS ONE. 12 (11): e0188426. doi:10.1371/journal.pone.0188426. PMC 5699823. PMID 29166406.
  8. ^ "Rancholabrean age/stage".
  9. ^ Alroy, J. (2000). "New methods for quantifying macroevolutionary patterns and processes". Paleobiology. 26 (4): 707–733. doi:10.1666/0094-8373(2000)026<0707:NMFQMP>2.0.CO;2. S2CID 26470169.
  10. ^ "Irvingtonian age/stage".
  11. ^ "Blancan age/stage".
  12. ^ "Hemphillian age/stage".
  13. ^ "Clarendonian age/stage".
  14. ^ "Barstovian age/stage".
  15. ^ "Hemingfordian age/stage".
  16. ^ "Harrisonian age/stage".
  17. ^ "Monroecreekian age/stage".
  18. ^ "Geringian age/stage".
  19. ^ "Whitneyan age/stage".
  20. ^ "Orellan age/stage".
  21. ^ "Chadronian age/stage".
  22. ^ "Duchesnean age/stage".
  23. ^ "Uintan age/stage".
  24. ^ "Bridgerian age/stage".
  25. ^ "Wasatchian age/stage".
  26. ^ "Clarkforkian age/stage".
  27. ^ "Tiffanian age/stage".
  28. ^ "Torrejonian age/stage".
  29. ^ "Puercan age/stage".
  30. ^ Ramezani, J.; Beveridge, T.L.; Rogers, R.; Eberth, D.; Roberts, E. (2022). "Calibrating the zenith of dinosaur diversity in the Campanian of the Western Interior Basin by CA-ID-TIMS U–Pb geochronology". Sci Rep. 12 (1): 16026. doi:10.1038/s41598-022-19896-w. PMC 9512893. PMID 36163377.