HistGeolChapt12 - Chapter 12 Paleozoic Life Invertebrates...

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Chapter 12 – Paleozoic Life - Invertebrates Trilobites are the most well-known Paleozoic fossils. http://www.ucmp.berkeley.edu/arthropoda/trilobita/ogygiopsis.gif Paleozoic fossils also include corals, crinoids, blastoids, echinoids, brachipods, gastropods, bivalves, and much more…
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Setting the stage for Paleozoic Life: Late Proterozoic transgression – global warming, rifting of Pannotia. Increasing atmospheric and oceanic O 2 contents. Flooding of craton (Sauk Sea) = creation of more, favorable shallow water habitats. Today – continental shelves = 10% of ocean area, hold 90% of species. Shallow water – within photic zone provides sunlight needed by aquatic plants (base of food webs), shallow depths promote mixing of nutrients by wind and water currents. Flooding covered landmass, lessening sources for mud. Shallow water warms more quickly – good for diversity. 2
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Near the Precambrian-Cambrian boundary (545 m.y. ago) - tremendous biologic change began with the appearance of skeletonized animals. Following this event, marine invertebrates began a period of adaptive radiation, evolution & diversification. The history of the Paleozoic marine invertebrate community was one of 1) Diversification 2) Adaptation 3) Multiple mass extinctions 4) Survival… That culminated in the greatest mass extinction in Earth history, at the end of the Paleozoic Era. 3
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The rather abrupt appearance and rapid spread of new hard-shelled organisms, at the beginning of the Paleozoic Era, is referred to as the "Cambrian explosion" by most scientists. This event took place within first 5 – 10 m.y. of the Cambrian Period. Early scientists, included Charles Darwin noticed this event in the fossil record. In “ On the Origin of the Species ”, Darwin was unable to reconcile this event with his new theory of evolution, i.e., that a single (or a few) ancestral species evolved 4
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Up until the appearance of the Ediacaran fauna, Earth was populated primarily by single-celled organisms. The Ediacaran fauna, found on all continents except Antarctica, consists primarily of multicelled soft-bodied organisms. Examples Tribrachidium heraldicum (left) and Spriggina floundersi (right) – see p. 168. 5
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the Ediacaran fauna: jellyfish and sea pens (phylum Cnidaria), segmented worms (phylum Annelida), primitive members of the phylum Arthropoda (the phylum with insects, spiders crabs, and others) At the time of the Ediacaran discovery, a signifi- cant period of time existed between the Edicaran fauna and the Cambrian Period (700 m.y. – 545 m.y.). Later discoveries elsewhere suggest survival of some Ediacaran-type fauna into the Early Cambrian Period. 6
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HistGeolChapt12 - Chapter 12 Paleozoic Life Invertebrates...

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