117-07AnimalDiversNotes - Animal Diversity Lectures I...

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Animal Diversity Lectures I. Animals can be distinguished from other kingdoms by this set of characteristics. a. they are multicellular (with no cell walls but extensive extra cellular matrix of proteins aiding in cell-cell adhesion) b. most move actively at some point in their lives c. most eat other organisms, dead or alive. d. some have muscles and nervous tissue, which are found ONLY in animals. e. reproduction is either sexual, asexual or both, but there is no alternation of generations as seen in plants. f. diploid stage is usually dominant and makes haploid gametes, which are usually the only “haploid phase” A.. Evolutionary history of animals—what we know about animal origins during earth’s early history (See Chapter 24) 1. Fossil Evidence a. First animals seen by 563 mya (sponges, jelly fish, worms) but then by 520 mya, ie in the next 40 million years, representatives of every major animal group is seen. b. Doushantuo Fossils in S. China at 580-570 mya. Probably sponges, including some fossil spicules and maybe even some strange embryos fossilized during cell division. c. Ediacarian Fossils in Australia 565-544. (Similar fossils seen at different spots around globe at about the same time) soft-bodied animals without limbs or heads or mouths, but some appear radially symmetrical. Reconstructed as sessile filter feeders existing before larger carnivores were around. d. Burgess Shale in British Columbia, 525-515 mya. Famous fossil assemblage representing the early Cambrian period. Representatives of all major invertebrate groups present, including one chordate. The implications are that animals diversified and radiated at increasing rates during the previous 40 million years…the Cambrian Explosion. At this point, animals are still marine organisms…at least that is what the Burgess Shale represents, marine sediments. B. Why & how did such a rapid evolution of this group occur? 1. Ecological answers? a. Possibly climate changes or less UV radiation permitted more rapid genetic evolution; certainly as more different kinds of animals evolved, their presence opened up new opportunities (niches) for new species. Organisms do alter selection by their presence. b. Possibly the apparently explosive nature of this event is misleading and, just as a population growing exponentially increases in absolute numbers more rapidly as it gets larger (see your population growth models), number of speciation events can be larger when there are more groups to speciate.
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2. Genetic answers? HOW did animals evolve from simple into more complex forms. The development of body plans are controlled by groups of genes called homeotic genes—they code for proteins determining basic body plan. These are greatly
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117-07AnimalDiversNotes - Animal Diversity Lectures I...

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