North American land mammal age

A North American land mammal age is a biostratigraphic interval recognized by characteristic fossil mammal assemblages, especially for subdividing and correlating Cenozoic strata.

Biostratigraphy: A branch of stratigraphy that uses fossils to establish the relative ages and correlations of rock layers. Land mammal ages are biostratigraphic units defined through fossil occurrence and succession.
Index fossil: A fossil taxon useful for dating or correlating strata because it is distinctive and has a limited geological range. Some characteristic mammals help identify particular intervals across separate localities.
Wasatchian: An early Eocene North American land mammal age characterized by distinctive mammalian faunas. It illustrates how a named interval is tied to a characteristic assemblage.
Geologic time scale: A chronological framework that divides Earth history into nested intervals based on rocks, fossils, and dating. It provides the global framework against which regional mammal ages are correlated.
Biochronology: The study of time relationships among organisms and fossil assemblages. It distinguishes a fossil-defined interval of time from the rock bodies that record it.
First appearance datum: The lowest stratigraphic occurrence of a taxon in a particular sequence. A taxon's first appearance can mark a candidate boundary in a mammal succession.
Clarendonian: A North American land mammal age of the Miocene, named for fossil deposits near Clarendon, Texas. Its regional name and fossil record show how these ages are established.
North American land mammal stage: A formal regional stratigraphic unit defined by fossil content in North American sedimentary rocks. Stage names concern rock units, while age usage concerns the corresponding interval of time.
Land mammal age: A regional biostratigraphic interval characterized by a distinctive assemblage of terrestrial mammal fossils. The North American sequence is one regional application of this broader convention.
Last appearance datum: The highest stratigraphic occurrence of a taxon in a particular sequence. Extinctions and disappearing taxa can help delimit faunal intervals.

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