Norwoodia
''Norwoodia'' is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived from 501 to 490 million years ago during the Dresbachian faunal stage of the late Cambrian Period The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million .... References Ptychoparioidea Ptychopariida genera Cambrian trilobites Cambrian trilobites of North America Paleozoic life of Yukon {{Ptychopariida-stub Cambrian genus extinctions ...
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Dresbachian
The Dresbachian is a Maentwrogian regional stage of North America, lasting from 501 to 497 million years ago. It is part of the Upper Cambrian and is defined by four trilobite zones. It overlaps with the ICS-stages Guzhangian, Paibian and the lowest Jiangshanian. The Dresbachian overlies the Middle Cambrian Albertan series, and is the lowest stage of the Upper Cambrian Croixian series, followed by the Franconian stage. The Dresbachian extinction event, about 502 million years ago, was followed by the Cambrian–Ordovician extinction event about million years ago. Naming The term is derived from the town of Dresbach which is located in southeastern Minnesota on the Mississippi River. Definition The Dresbachian is defined by four trilobite zones: ''Cedaria''-, ''Crepicephalus''-, '' Aphelaspis''- and '' Dunderbergia'' trilobite zones. Events The Dresbachian extinction event during the Late Cambrian was the second of two severe extinctions during the first period of the Paleoz ...
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