1323442048_CHAPTER_18_SPR

1323442048_CHAPTER_18_SPR - EVOLUTION/LECTURE1 Evolution...

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EVOLUTION/LECTURE1 file:///E|/CH18-CAMBRIAN-SPRING-2008/CHAPTER%2018_SPR_2008.HTML[12/8/2011 2:57:50 PM] Evolution ( PCB 4674 ). Chapter 18. The Cambrian explosion and beyond Main topics of lecture: I: The Cambrian explosion: 1.- The Cambrian fossils and multicellular animals 2.- The Ediacaran and Burgess shale faunas 3.- Was the Cambrian explosion really explosive? 4.- What caused the Cambrian explosion? II: Macroevolutionary patterns - Geological time scale: 5.- Adaptive radiations 6.- Stasis III: Extinction: 7.- Mass extinctions and background extinctions 8.- Cretaceous - Tertiary: High-impact extinction I: The Cambrian explosion: 1.- The Cambrian fossils and multicellular animals 1.1.- Once the fundamental life processes of DNA replication, protein synthesis, respiration, and cell division had evolved, a spectacular diversification of life ensued. Breakthroughs like the evolution of photosynthesis and the nuclear membrane occurred. These events spanned some 3.2 billion years ago and during this interval all organisms, with the exception of some red, brown, and green algae, were unicellular. 1.2.- The first multicellular animals do not appear in the fossil record until about 565 million years ago. But then, over a span of just 40 million years, virtually every major phylum of animals appeared. This period is called the Cambrian explosion . Geologically speaking this span of time represents the blink of an eye/ Although it represents a mere 0.8% of the Earth's history, it ranks as one of the great events in the history of life. The goal of this chapter is to introduce these and other turning points that have taken place over the last 543 million years. This interval in Earth history is called the Phanerozoic eon . 1.3.- A fossil is any trace left by an organism that lived in the past. There are
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EVOLUTION/LECTURE1 file:///E|/CH18-CAMBRIAN-SPRING-2008/CHAPTER%2018_SPR_2008.HTML[12/8/2011 2:57:50 PM] three main types of bias in the fossil record: Geographic, taxonomic, and temporal. There is a propensity for fossils to come from lowland and marine habitats. To appreciate the taxonomic bias more fully, consider this: Marine organisms dominate the fossil record, but make up only 10% of extant species. A full two-thirds of animal phyla living today lack any sort of mineralized hard parts, such as bone or shell, that are amenable to fossilization. Critical parts of plants, including reproductive structures such as flowers, are seldom preserved. The temporal bias results because the Earth's crust is constantly being recycled. When tectonic plates subduct or mountains erode, their fossils go with them. As a result old rocks are rarer than new rocks, and our ability to sample ancient life forms is relatively poor. 1.4.- It is important to realize, however, that these types of sampling issues are by no
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This note was uploaded on 01/11/2012 for the course PBC 4674 taught by Professor Ortega during the Spring '12 term at FIU.

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1323442048_CHAPTER_18_SPR - EVOLUTION/LECTURE1 Evolution...

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