North American land mammal age

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North American land mammal ages (NALMA) are a simple way scientists describe when North American mammal fossils lived. The ages are named after places where fossils were found and cover time from the Late Cretaceous to today. They help scientists line up rocks and fossils from different places and times.

How it works
- NALMA was formalized in 1941 as provincial land-mammal ages and later updated to a chronostratigraphic framework. An age is defined by the first appearance of a mammal species in a rock layer; if two species appear in the same layer, their ages overlap.
- The system now includes both the Cretaceous and the Holocene (present day). In older rocks, the term “North American land vertebrate ages” is sometimes used because mammals were not always dominant on land during the Mesozoic.

Ages (oldest to youngest)

Cretaceous land vertebrate ages
- Lancian: 67–66 million years ago
- Edmontonian: 73–67 Ma
- Kirtlandian: 75–73 Ma
- Judithian: 79–75 Ma
- Wahweapian: 82–79 Ma
- Aquilian: 84–82 Ma

Cenozoic land mammal ages
- Puercan: 66–63.8 Ma
- Torrejonian: 63.8–60.9 Ma
- Tiffanian: 60.9–56.2 Ma
- Clarkforkian: 56.2–54.9 Ma
- Wasatchian: 54.9–50.5 Ma
- Bridgerian: 50.5–46.2 Ma
- Uintan: 46.2–39.7 Ma
- Duchesnean: 39.7–37 Ma
- Chadronian: 37–33.9 Ma
- Orellan: 33.9–31.8 Ma
- Whitneyan: 31.8–29.5 Ma
- Arikareean: 29.5–18.5 Ma
- Hemingfordian: 18.5–16.3 Ma
- Barstovian: 16.3–12.5 Ma
- Clarendonian: 12.5–9.4 Ma
- Hemphillian: 9.4–4.7 Ma
- Blancan: 4.7–1.4 Ma
- Irvingtonian: 1.4–0.21 Ma
- Rancholabrean: 0.21–0.014 Ma
- Santarosean: 0.014–0.004 Ma
- Saintaugustinean: 0.004 Ma to present

Other continents
- European land mammal ages, South American land mammal ages, and Asian land mammal ages.

Why it matters
- The NALMA system helps researchers study mammal evolution and large events, like the Cretaceous–Paleogene extinction, and discussions about the Anthropocene.