W3L2 An Explosion of Life.pdf

Jellyfish cnidaria comb jellies ctenophora sponges

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-- Jellyfish (cnidaria) -- Comb jellies (ctenophora) -- Sponges (porifera) Features -- Asymmetrical or Radial symmetry -- Small (usually up to a few cm) -- No hard parts -- Some fossils with no clear modern analogues 239 Precambrian The Ediacaran Fauna 240 Ediacaran jellyfish 241
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Dickinsonia : radial symmetry 3.5 cm across Fig. 18.6 242 Rangea Looks like a plant, but it’s an animal (likely related to sea anemones and corals) 0.25 cm Fig. 18.6 243 Precambrian fossil with bilateral symmetry Kimberella, a mollusc with a radula (?) 555–558 myr Fig. 18.8 244
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Precambrian fossil with bilateral symmetry Vernanimacula guizhouena (580-600 mya) Tiny! 0.1 – 0.2 mm across Includes: coelom differentiated gut mouth anus Oldest bilaterian fossil Fig. 18.8 245 580 myr old fossil eukaryote embryos Embryos from a bilaterally symmetrical animal (Arthropod? Flatworm?) Debated: some researchers argue these are single celled eukaryotes that formed inside a cyst Fig. 18.7 246 Trace fossils Tracks from a bilaterally symmetrical burrowing animal (annelid?) Fig. 18.8 247
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- Limited morphological diversity -Limited ecological diversity - Bilateral symmetry rare, but present - Mostly soft (few hard parts) Summary of the Ediacaran Fauna 248 Mode of living: -sessile filter feeders -predators that floated high in the water column Fauna dominated by: - sponges (porifera) - comb jellies (Ctenophore) - jellyfish (Cnidaria) - other soft-bodied things with no descendants that we can discern Summary of the Ediacaran Fauna 249 Geologic Time Scale We are now here Ediacaran Fauna Precambrian 250
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The Cambrian Explosion 251 The Cambrian Explosion 541 – 506 mya ~ 35 my crustaceans arthropods annelids mollusks chordates echinoderms One of the most spectacular events in the history of life. Nearly all of the remaining phyla of animals appear suddenly nematodes priapulids platyhelminthes brachiopods Etc.
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