science

Orellan

Orellan is a 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 Orellan rather than just read about it. In short: The Orellan is a North American Land Mammal Age typically set from around 33,700,000 to 32,000,000 years BP, a period of 1.7 million years. The Orellan is preceded by the Chadronian and followed by the Whitneyan NALMA stages.

Key takeaways

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

Reference excerpt

The Orellan is a North American Land Mammal Age typically set from around 33,700,000 to 32,000,000 years BP, a period of 1.7 million years. The Orellan is preceded by the Chadronian and followed by the Whitneyan NALMA stages. Relative to global geological chronology (the geologic time scale), it is usually considered to fall within the earliest part (early Rupelian stage) of the Oligocene epoch, beginning around the same time as the Eocene-Oligocene boundary. The beginning of the Orellan is defined by the first appearance of Hypertragulus calcaratus (a hypertragulid ruminant). Other mammal species which first appear at the start of the stage include Leptomeryx evansi (a leptomerycid ruminant) and Palaeolagus intermedius (an early lagomorph). Poebrotherium eximium (an early camelid) and Miohippus grandis (an early horse) last appear around the base of the Orellan, and brontotheres go extinct only shortly above the base. Orellan North America was cooler and drier than previous ages, though the middle of the continent was still a stable environment populated by the White River fauna. The Great Plains and Rocky Mountain regions were covered by temperate deciduous and conifer woodlands rather than the humid subtropical floras which characterized the Eocene.

Subdivisions The Orellan is considered to contain the following four subdivisions, from oldest to youngest:

Orellan 1: Starting at the first appearance of Hypertragulus calcaratus and ending at the first appearance of Miniochoerus affinis. Orellan 2: Starting at the first appearance of Miniochoerus affinis and ending at the first appearance of Miniochoerus gracilis. Orellan 3: Starting at the first appearance of Miniochoerus gracilis and ending at the first appearance of Merycoidodon bullatus. Orellan 4: Starting at the first appearance of Merycoidodon bullatus and ending at the first appearance of Leptauchenia major.

Fossil localities The Orellan is named after the Orella Member of the Brule Formation, a widespread subunit of the White River Group.

Colorado: White River Formation (Cedar Creek Member) Mississippi: Byram Formation Montana: Clarkston Basin, Three Forks Basin, South Townsend Basin, Jefferson Basin: Dunbar Creek Formation (= Renova Formation Dunbar Creek Member) (Easter Lily local fauna) Sage Creek Basin: Cook Ranch Formation (= Renova Formation Cook Ranch Member) (Cook Ranch, Matador Ranch local faunas) Nebraska: White River Group: Brule Formation (Orella Member B-D) North Dakota: White River Group: Brule Formation Saskatchewan: Cypress Hills Formation (Fossil Bush local fauna) South Dakota: White River Group: Brule Formation (Scenic Member) Wyoming: White River Group: Brule Formation (Orella Member) White River Formation Tepee Trail Formation (Hendry Ranch Member) (Cedar Ridge local fauna)

References

Worked examples

Example 1 — a first encounter with Orellan

Start with the simplest possible case. Write down what Orellan claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In 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 Orellan 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 Orellan 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 Orellan

In research: Orellan appears in 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 Orellan 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: Orellan is common in secondary-school and first-year university syllabi. It links to neighbouring topics Geochronology stubs, Oligocene animals of North America, Oligocene life, so understanding it makes those chapters shorter.
In everyday life: Look for Orellan 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 Orellan in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Orellan means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Orellan out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Orellan in simple terms?

Why does Orellan matter?

Because it connects several 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 Orellan?

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 Orellan.