Cambrian Stage 3 is the still unnamed third stage of theCambrian. It succeedsCambrian Stage 2 and precedesCambrian Stage 4, although neither its base nor top have been formally defined. The plan is for its lower boundary to correspond approximately to the first appearance oftrilobites, about 521 million years ago,^[2] though the globally asynchronous appearance of trilobites warrants the use of a separate, globally synchronous marker to define the base.^[3] The upper boundary and beginning ofCambrian Stage 4 is informally defined as the first appearance of thetrilobite generaOlenellus orRedlichia around 514.5 million years ago.^[4]

TheInternational Commission on Stratigraphy has not officially named the 3rd stage of the Cambrian. The stage approximately corresponds to the "Atdabanian", which is used by geologists working inSiberia.^[5]

The oldesttrilobite known isLemdadella which appears at the beginning of theFallotaspis zone.^[6] TheCambrian radiation of animal phyla ends here, after the diversification and origination ofarthropods,molluscs,lophophorates,chordates (includingvertebrates) among others.^[7]

• Zhang (2017). "Challenges in defining the base of Cambrian Series 2 and Stage 3".Earth-Science Reviews.172:124–139.Bibcode:2017ESRv..172..124Z.doi:10.1016/j.earscirev.2017.07.017.

• "GSSP Table - Paleozoic Era". Geologic Timescale Foundation.Archived from the original on 2023-10-08. Retrieved2024-06-13.
• "GSSPs - The Cambrian System 2019". International Commission on Stratigraphy.Archived from the original on 2023-07-21.

• Cambrian geochronology
• Geological ages
• Cambrian Series 2

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