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Cambrian and Ordovician Periods lecture notes.doc

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Jon Houseman

Cambrian and Ordovician PeriodsSlide 1Cambrian Period540 million years agobeginnings of multicellular lifestem from 3 lineages of organisms explosion in diversity of multicellular forms many organisms are found in the shell depositslaurentia plate in which North America ultimately emerges surrounded by continental shelfshallow water lots of sunlight warmprimary productivity Slide 2 fossils contain softbodied animalsinvertebratesYoho National Park and the Burgess Shalescontains sets of animals that have never been seen again Slide 5 animals from Burgess Shales bear little resemblance to animals todaywhen multicellular life arose it was at its most diverse and complex when it first occurred the amount of complexity has been diminishing over time contrasts idea that diversity increases and Darwins idea of slow gradual change30 animal body plans appear in the Burgess Shales and some still exist today 2 new morphologiesburrowing animalsanimals that swim and chase their pray Slide 7 phylogeny starts from colonial cells choanoflagellate cells origins of animalscell that has a cell body and flagellum and a microcollar surrounding bodySlide 13choanoflagellate cells origins of animals ancestral cell to all organisms cell that has a cell body and flagellum 1 and a microvilli that forms a collarsurrounding the flagellum at the centrecell feeds as a single cell protist by pumping water movement of the flagellum brings water into the microvilli and propels it awaywater contains small photosynthetic algae primary photosynthetic organisms of the ocean and become trapped as particulate material which is then consumed byphagocytosisdevelops symmetry circularradial or bilateral Slide 9Origins of Tissueseither single cells cells working as a colony cells working together as tissue or you dont have tissue but have a group of cells that have different functionsmulticellularity if there are no tissues but have cells that do different tasksmulticellularitymulticellularitycells working together with a communication system between groups of cells different function in cells specialized functionmany cellsectoderm epidermal layer that surrounds organism endoderm epidermal layer that surrounds digestive tractmesoderm primarily muscle tissue diploblasticectoderm and endoderm found in the simplest of organismstriploblastic ectoderm endoderm and mesoderm allows for complexity the earliest divisions in phylogenySlide 11 Spongesno tissuessponges poriferamost ancestral and simple of all organisms the first animal takes choanocytes and organizes them into a sheet inside a hollow structure hollow centre with wall that has choanocytes lining the inside outside is epidermal like layerpumps water through openings in the walls and pushes it through the top for water movementas water passes by choanocytes it traps food particles and consumes it by phagocytosis outside is pinacocytes pinacoderm made of pinacocytesouter layer that allows water to move in to trap food different cell types with different functions make sponges multicellular amoebocytes travel around to feed pinacocytes in the sponges food movement sponges have skeleton of minerals minerals secreted by cells which also get food from amoebocytes cells stuck together by collagen a defining characteristic of animals uses mineralized calcium or silica for skeletoncalcium cannot be used in deep oceans due to pressuremost effective filters of ocean water process the largest amount of water and captures primary productivity Slide 12Sponge Reproduction choanocyte with flagellum morphs to sperm due to swimming structure
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