earth science

North American land mammal age

North American land mammal age is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand North American land mammal age rather than just read about it. In short: 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.

Key takeaways

North American land mammal age belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect North American land mammal age to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of North American land mammal age from memory before moving on to harder problems.

Reference excerpt

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

Cenozoic land mammal ages Some land mammal ages have recognized biochronological subdivisions.

Saintaugustinean: Lower boundary 0.004 Ma. Upper boundary Present. Santarosean: Lower boundary 0.014 Ma. Upper boundary 0.004 Ma. Rancholabrean: Lower boundary 0.21 Ma. Upper boundary 0.014 Ma. Irvingtonian: Lower boundary 1.4 Ma. Upper boundary 0.21 Ma. Blancan: Lower boundary 4.7 Ma. Upper boundary 1.4 Ma. Hemphillian: Lower boundary 9.4 Ma. Upper boundary 4.7 Ma. Clarendonian: Lower boundary 12.5 Ma. Upper boundary 9.4 Ma. Barstovian: Lower boundary 16.3 Ma. Upper boundary 12.5 Ma. Hemingfordian: Lower boundary 18.5 Ma. Upper boundary 16.3 Ma. Arikareean: Lower boundary 30.0 Ma. Upper boundary 18.5 Ma. Whitneyan: Lower boundary 32.0 Ma. Upper boundary 30.0 Ma. Wh2: Lower boundary 31.4 Ma. Upper boundary 30.0 Ma. Wh1: Lower boundary 32.0 Ma. Upper boundary 31.4 Ma. Orellan: Lower boundary 33.7 Ma. Upper boundary 32.0 Ma. Or4: Lower boundary 32.5 Ma. Upper boundary 32.0 Ma. Or3: Lower boundary 33.1 Ma. Upper boundary 32.5 Ma. Or2: Lower boundary 33.4 Ma. Upper boundary 33.1 Ma. Or1: Lower boundary 33.7 Ma. Upper boundary 33.4 Ma. Chadronian: Lower boundary 37.0 Ma. Upper boundary 33.7 Ma. Ch4: Lower boundary 34.7 Ma. Upper boundary 33.7 Ma. Ch3: Lower boundary 35.7 Ma. Upper boundary 34.7 Ma. Ch2: Lower boundary 36.5 Ma. Upper boundary 35.7 Ma. Ch1: Lower boundary 37.0 Ma. Upper boundary 36.5 Ma. Duchesnean: Lower boundary 40.1 Ma. Upper boundary 37.0 Ma. Uintan: Lower boundary 46.3 Ma. Upper boundary 40.1 Ma. Ui3: Lower boundary 42.8 Ma. Upper boundary 40.1 Ma. Ui2: Lower boundary 45.7 Ma. Upper boundary 42.8 Ma. Ui1: Lower boundary 46.3 Ma. Upper boundary 45.7 Ma. Bridgerian: Lower boundary 50.1 Ma. Upper boundary 46.3 Ma. Br3: Lower boundary 47.0 Ma. Upper boundary 46.3 Ma. Br2: Lower boundary 49.2 Ma. Upper boundary 47.0 Ma. Br1b: Lower boundary 50.0 Ma. Upper boundary 49.2 Ma. Br1a: Lower boundary 50.1 Ma. Upper boundary 50.0 Ma. Wasatchian: Lower boundary 55.0 Ma. Upper boundary 50.1 Ma. Wa7: Lower boundary 52.4 Ma. Upper boundary 50.1 Ma. Wa6: Lower boundary 53.0 Ma. Upper boundary 52.4 Ma. Wa5: Lower boundary 53.4 Ma. Upper boundary 53.0 Ma. Wa4: Lower boundary 54.1 Ma. Upper boundary 53.4 Ma. Wa3: Lower boundary 54.4 Ma. Upper boundary 54.1 Ma. Wa2: Lower boundary 54.7 Ma. Upper boundary 54.4 Ma. Wa1: Lower boundary 54.9 Ma. Upper boundary 54.7 Ma. Wa0: Lower boundary 55.0 Ma. Upper boundary 54.9 Ma. Clarkforkian: Lower boundary 56.2 Ma. Upper boundary 55.0 Ma. Tiffanian: Lower boundary 60.9 Ma. Upper boundary 56.2 Ma. Torrejonian: Lower boundary 63.8 Ma. Upper boundary 60.9 Ma. Puercan: Lower boundary 66 Ma. Upper boundary 63.8 Ma.

Cretaceous land vertebrate ages Lancian: Lower boundary 67 Ma. Upper boundary 66 Ma. Edmontonian: Lower boundary 73 Ma. Upper boundary 67 Ma. Kirtlandian: Lower boundary 75 Ma. Upper boundary 73 Ma. Judithian: Lower boundary 79 Ma. Upper boundary 75 Ma. Wahweapian: Lower boundary 82 Ma. Upper boundary 79 Ma. Aquilian: Lower boundary 84 Ma. Upper boundary 82 Ma.

Other continental ages European land mammal age South American land mammal age Asian land mammal age African land mammal age

See also Appearance Event Ordination Biochronology

References

Worked examples

Example 1 — a first encounter with North American land mammal age

Start with the simplest possible case. Write down what North American land mammal age claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to North American land mammal age before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about North American land mammal age ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of North American land mammal age

In research: North American land mammal age appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses North American land mammal age in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: North American land mammal age is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cenozoic North America, Cenozoic mammals of North America, Mesozoic North America, so understanding it makes those chapters shorter.
In everyday life: Look for North American land mammal age outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study North American land mammal age in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what North American land mammal age means in your own words.
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Frequently asked questions

What is North American land mammal age in simple terms?

Why does North American land mammal age matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study North American land mammal age?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on North American land mammal age.