Lesson plan
Orellan
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 . 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.
Article summary
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 . 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.
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
Bibliography
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Key claims and bibliography are generated from the same tracked claims and sources as the article page.