North American land mammal age

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.

System

The North American land-mammal-age system was formalized in 1941 as a series of provincial land-mammal ages. 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.

The utility of the system led to its expansion into the Cretaceous (formalized 1986) and the Holocene (formalized 2014). These additions have been used in research related to the Cretaceous–Paleogene extinction event and the ensuing recovery, and to the Anthropocene debate, 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.

Ages

Some land mammal ages have recognized biochronological subdivisions.

The lower boundary of each age or subdivision is the upper boundary of the next lower age or subdivision.

AgeSubdivisionLower boundary Global epoch / stage Polarity chron(s) Major events
Cenozoic land mammal ages
Saintaugustinean0.0004 Ma

(1540 CE)

 Holocene –

Anthropocene

 C1n The Columbian exchange: European colonization introduces domesticated horses, pigs, cattle, and many other non-native organisms into North America
Santarosean 0.014 Ma. Holocene Humans become well-established in North America, bringing domesticated dogs. End of the last ice age. The Late Pleistocene extinctions wipe out many species of megafauna, particularly xenarthrans (glyptodonts, pampatheres, ground sloths), proboscideans (mammoths, mastodons, gomphotheres), carnivorans (short-faced bears, saber-toothed cats, dire wolves), and native horses and camels
Late Pleistocene
Rancholabrean0.210 Ma. The ice age continues. Bison expand south of Alaska alongside other northerly specialists such as caribou, muskoxen, moose, and woolly mammoths.
Middle Pleistocene
Irvingtonian1.4 Ma. C1r.2r – C1n The ice age continues. Mammoths expand south of Alaska.
Early Pleistocene
Blancan4.7 Ma. C3n – C1r.2r The cooling climate reaches a tipping point, leading to the start of the Quaternary glaciation (ice age). Modern grasslands, deserts, and tundra are well-established. The Isthmus of Panama fully forms, intensifying the Great American Biotic Interchange. Many North American mammals spread into South America, while terror birds, glyptodonts, and pampatheres spread north. The last North American ailurids (red pandas) and rhinos lived during this age. The last and largest borophagine dogs go extinct. Modern horses (Equus) are abundant. Hyenas make a brief foray into the continent via Asia.
Late Pliocene
Early Pliocene
Hemphillian9.4 Ma. C4An – C3n The last of the Miocene hallmarks (oreodonts, mylagaulids, dromomerycids) die out. Rabbits and short-faced bears diversify. Deer and bovids (sheep and cow relatives) enter the continent from Asia, alongside saber-toothed cats and skunks. Ground sloths enter from South America during an early phase of the Great American Biotic Interchange.
Late Miocene
Clarendonian12.5 Ma. C5Ar – C4An Bear dogs diminish, while "false saber-toothed cats" make a brief comeback in the form of barbourofelids.
Middle Miocene
Barstovian16.3 Ma. C5Cn – C5Ar After the Middle Miocene Climatic Optimum, the global climate cools dramatically, and scrubland spreads through the southwest. Proboscideans (elephant relatives, like mastodons and gomphotheres) arrive in North America alongside hemicyonine bears.
Hemingfordian 18.5 Ma. C5Er – C5Cn Savanna and other grassy habitats dominate the landscape. Grazing horse species become more common than browsing species. Miocene variants of oreodonts, camels, and rhinos are well-established, though White River hallmarks are practically extinct. More carnivorans spread into North America, including procyonids (racoon relatives), ailurids (red panda relatives), amphicyonine bear dogs, and true cats, which end the "cat gap". Near the end of this age, the Middle Miocene Climatic Optimum leads to a brief resurgence of warm forests.
Early Miocene
Arikareean 30.0 Ma. C11n – C5Er Temperate forests dominate, but grasses begin to take over the ground cover. The White River fauna is gradually replaced with typical Miocene groups. Extinct mylagaulids ("horned gophers") supplement a growing set of still-living rodent families. Artiodactyl diversity increases with early pronghorns, peccaries, dromomerycids, and synthetoceratines. Chalicotheres briefly enter the continent. Canine and borophagine dogs diversify alongside the earliest mustelids. Native primates, hyaenodonts, and nimravids ("false saber-toothed cats") go extinct, beginning the "cat gap".
Late Oligocene
Early Oligocene
WhitneyanWh231.4 Ma. C12r – C11n The White River fauna persists, though Eocene rodent families die out as modern rodents cement their roles.
Wh132.0 Ma. C12r
OrellanOr432.5 Ma. C12r Despite cooling and drying at the Eocene-Oligocene boundary, few North American mammals go extinct at this time. Artiodactyls are abundant. Rhinos are less common than before, but true tapirs appear and horses spread into open habitats. Dogs (particularly hesperocyonines) diversify.
Or333.1 Ma. C13n – C12r
Or233.4 Ma. C13n
Or133.7 Ma. C13r – C13n
ChadronianCh434.7 Ma. Late Eocene C15n – C13r The White River fauna is in full swing. Modern rodents families (early beavers, squirrels, gophers, cricetids, etc.) replace older, more tropical families. Early relatives of bears, peccaries, and rabbits. The last and largest brontotheres live during this age.
Ch335.7 Ma. C16n – C15n
Ch236.5 Ma. C16r – C16n
Ch137.0 Ma. C17n – C16r
Duchesnean41.4 Ma. Middle Eocene C19n – C17n Mammals start to more closely resemble the succeeding White River fauna. Early oreodonts, canids (dogs), daphoenine amphicyonids ("bear dogs"), and entelodonts ("hell pigs") evolve or immigrate into North America, while primates decline and Paleocene holdouts such as mesonychians die out.
UintanUi342.8 Ma. C20n – C19n Tropical rainforests begin to break apart into seasonal woodlands. Artiodactyls diversify, with new families related to hippos, camels, and ruminants. Perissodactyls, particularly early rhinos and brontotheres, are still going strong. Older herbivores like taeniodonts and uintatheres die out. The earliest nimravids ("false saber-toothed cats") appear near the end of the Uintan, replacing the last of the oxyaenids.
Ui245.7 Ma. C20r – C20n
Ui146.3 Ma. C21n – C20r
BridgerianBr347.0 Ma. C21r – C21n The Early Eocene Climatic Optimum leads to a "Bridgerian crash", with a temporary reduction of mammal diversity. Even so, perissodactyls, true primates, rodents, and hyaenodonts continue to diversify.
Br249.2 Ma. Early Eocene C22n – C21r
Br1b50.0 Ma. C22r – C22n
Br1a50.1 Ma. C23r – C22r
WasatchianWa752.4 Ma. C24n.1r – C23r The Paleocene-Eocene thermal maximum marks the arrival of more modern mammal groups and the decline of many Paleocene forms. Omomyids (tarsier relatives) and strepsirrhines (lemur relatives) fill in for declining "plesiadapiforms". Rodents diversify, including early relatives of squirrels and beavers. Early perissodactyls (relatives of horses, rhinos, tapirs, brontotheres) appear and begin to diversify. Artiodactyls also appear, though are less common at this time. Hyaenodonts enter the continent.
Wa653.0 Ma. C24n.3n – C24n.1r
Wa553.4 Ma. C24r – C24n.3n
Wa454.1 Ma. C24r
Wa354.4 Ma. C24r
Wa254.7 Ma. C24r
Wa154.9 Ma. C24r
Wa056.0 Ma. C24r
Clarkforkian57.5 Ma. Late Paleocene C25n – C24r Rodents, tillodonts, and coryphodontids immigrate from Asia. Oxyaenids and nyctitheriids diversify alongside a continued turnover of "plesiadapiform" and "condylarth" groups.
Tiffanian 62.3 Ma. C26r – C25n "Condylarths" and "plesiadapiforms" experience diversity turnover, with new families supplanting older forms. Pantodonts diversify. Earliest oxyaenids. Near the end of the Tiffanian, uintatheres and arctostylopids immigrate from Asia.
Middle Paleocene
Torrejonian65.1 Ma. Early Paleocene C28r – C27n Continued diversification, particularly among "plesiadapiforms" and other primate relatives, alongside new types of "condylarths" such as phenacodontids. Mesonychians become some of the earliest large mammalian carnivores on the continent. Palaeanodonts (pangolin relatives), nyctitheriids (shrew relatives), and viverravids (carnivoran relatives) appear. Some new groups (apatemyids, pantolestids, pantodonts) have no close living relatives.
Puercan66 Ma. C29r – C28r Multituberculates, metatherians, and cimolestans survive into the Cenozoic as Cretaceous holdovers. Many new Paleocene mammals appear: taeniodonts, "condylarths" (early hoofed omnivores), and possible primate relatives such as Purgatorius.
Cretaceous land vertebrate ages
Lancian67 Ma.
"Edmontonian"73 Ma.
Kirtlandian75 Ma.
Judithian79 Ma.
Wahweapian82 Ma.
Aquilian84 Ma.

Other continental ages

See also

References

  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 978-0-520-05392-2.
  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. 1 2 3 4 5 6 7 8 9 10 11 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 978-0-231-50378-5.
  7. 1 2 3 4 5 6 7 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. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Hodnett, John-Paul M.; Welsh, Edward T.; Santucci, Vincent L.; Tweet, Justin S. (2022). "A Middle Eocene brontothere (Mammalia; Perissodactyla; Brontotheriidae) from Yellowstone National Park, Wyoming". FOSSIL RECORD 8. New Mexico Museum of Natural History and Science. p. 211.
  9. 1 2 Kelly, T.S.; Murphey, P.C.; Walsh, S.L. (2012). "New records of small mammals from the middle Eocene Duchesne River Formation, Utah, and their implications for the Uintan–Duchesnean North American Land Mammal Age transition." Paludicola 8: 208–251.
  10. 1 2 Anemone, Robert L.; Jones, Matthew F.; Van Regenmorter, John; Beard, K. Christopher (2024-05-03). "A latest Paleocene mammal fauna from the Great Divide Basin in southern Wyoming and a revised biozonation of the Clarkforkian land mammal age". Journal of Vertebrate Paleontology. 44 (3). doi:10.1080/02724634.2024.2424139. ISSN 0272-4634.
  11. ↑ Speijer, R.P.; Pälike, H.; Hollis, C.J.; Hooker, J.J.; Ogg, J.G. (2020), "The Paleogene Period", Geologic Time Scale 2020, Elsevier, pp. 1087–1140, doi:10.1016/B978-0-12-824360-2.00028-0, ISBN 978-0-12-824360-2, retrieved 2026-08-30{{citation}}: CS1 maint: work parameter with ISBN (link)
  12. ↑ Sprain, C. J.; Renne, P. R.; Wilson, G. P.; Clemens, W. A. (2015-03-01). "High-resolution chronostratigraphy of the terrestrial Cretaceous-Paleogene transition and recovery interval in the Hell Creek region, Montana". Geological Society of America Bulletin. 127 (3–4): 393–409. doi:10.1130/B31076.1. ISSN 0016-7606.
  13. ↑ 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.