McRaeNotes - Intro to AnimalsSponges-comb jellies .pdf -...

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BIOL 1200Dr Susan McRae1Animal evolutionChapter 27Animals evolved in tropical seas during the Precambrian period about 700 m y agoprobable common ancestor, a colonial flagellated marine protistmost animal phyla developed in a span of 60 million years during late Precambrian-early Cambrian (585-525 million years ago):‘Cambrian explosion’Cambrian began 543 m y agorich fossil assemblage includes animals with hard mineralized skeletonsBurgess shalein BC, Canada, the most famous fossil bedextremely high diversity – many species from that period now extinctdiversification of animals so rapid that its hard to determine branch points from fossilevidencerely on anatomical characters, embryology, developmental genetics & molecularsystematics of extant (living) speciesAnimals can be defined by the following features:1. multicellular, eukaryotic chemoheterotrophsingestother organisms to obtain organic nutrients(cannot synthesize organic nutrients from inorganics like plants)2. instead of cell walls, animals have structural proteins to hold cells together(most abundant:collagen) – found in extracellular matrices3. complex tissues – include muscle and nerve fibers that conduct impulses(evolved for movement)4. most reproduce sexually: diploid stage is dominant in life cycleflagellated sperm fertilizes larger nonmotile egg5.Hoxgeneshomeoticgenes expressed in developing embryo, regulatedevelopment, esp. positions of body parts in relation to one anothercontainhomeoboxsequences: specific sequences of DNA common tosome regulatory genesamong eukaryotes, only animals have homeotic genes that containhomeobox sequences =HoxgenesAnimal phylogeny & diversity(Classification)classification of animals used to be based on morphological systematicsrecently challenged by molecular sequence data – arguably more robustevidence… the currency of evolution35 phyla recognized - we will only be looking at about half of the major phyla
BIOL 1200Dr Susan McRae2Chapter 27Parazoa (colonial marine invertebrates)most primitive animals; layers of unspecialized cells, not really tissuesPhylum Porifera (‘pore bearer’ - sponges)9000 spp

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Term
Fall
Professor
mcrae
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Cnidaria, Dr Susan McRae

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