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Chapter 13

Chapter 13. The Early Paleozoic World. Chapter 13 - Overview. Cambrian Life Paleogeography Tectonics - First Step in Appalachian Mtns. Cambrian Life. Cambrian Life. Cambrian Explosion. Lowermost Cambrian Simple skeletal fossils Teeth. Tommotian Fauna. Cambrian Explosion.

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Chapter 13

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  1. Chapter 13 The Early Paleozoic World

  2. Chapter 13 - Overview • Cambrian Life • Paleogeography • Tectonics - First Step in Appalachian Mtns

  3. Cambrian Life

  4. Cambrian Life

  5. Cambrian Explosion • Lowermost Cambrian • Simple skeletal fossils • Teeth

  6. Tommotian Fauna

  7. Cambrian Explosion • Large animals with skeletons • Trilobites • Arthropods with calcified segmented skeletons

  8. Cambrian LifeTrilobites

  9. Cambrian LifeTrilobites

  10. Cambrian Explosion • Bottom-dwelling forms create scratch marks • Similar to some Neoproterozoic tracks

  11. Cambrian Explosion • Other abundant Early Cambrian animal groups • Monoplacophoran mollusks • Inarticulate brachiopods • Echinoderms

  12. Cambrian Explosion • Chengjiang fauna • Soft- bodied creatures including: • Cnidarians • Predatory worms • Anomalocarids • Huge carnivores (2 m) • Swimmers • Impaled prey

  13. Cambrian Explosion • Modes of Life • Deposit feeders • Extract organic matter from sediments • Trilobites, arthropods • Suspension feeders • Collect organic matter from the water • Eocrinoids • Attach by stalk

  14. Cambrian Life • Proterozoic Holdover

  15. Cambrian Explosion • Stromatolites • Less abundant; more restricted • Weak grazing pressure in inter-tidal zone

  16. Cambrian Life

  17. Cambrian Explosion • Reefs • Archeocyathids • Suspension feeders • Probably sponges

  18. Cambrian LifeArcheocyathids

  19. Cambrian LifeArcheocyathids

  20. Cambrian Reef BuildersArcheocyathids

  21. Cambrian LifeBrachiopods

  22. Cambrian LiffeBrachiopods

  23. Cambrian LifeBryozoans

  24. Bryozoans

  25. Cambrian Explosion • Evolutionary experimentation • Bizarre echinoderm classes • Few species and genera • Tried out many body plans

  26. Cambrian Explosion • Middle and Late Cambrian • 15 M year duration • Expansion of many groups • Trilobites • Echinoderns • Conodonts • Early fish • Isolated bony external plates

  27. Cambrian Explosion • Burgess Shale Fauna • Western No. America • Deep-water setting (low O2) • Chordata • Pikaia: Notochord • Arthropods • Onychophorans • Intermediate between segmented worms and arthropods

  28. Western Laurentian Margin • Stable continental shelf • Steep carbonate platform edge • Accumulated thick limestone sequences

  29. Burgess Shale

  30. Western Laurentian Margin • Burgess Shale • Unusual fauna • Collected by Walcott

  31. Burgess Shale Genus: Amiskwia sagittiformis (Unknown affinity) Amiskwia shows us three definite body segments: a head with two prominent tentacles, an unsegmented trunk with stubby side fins, and a flattened tail. Fossil sizes up to 1 inch.

  32. Burgess Shale Genus: Anomalocaris canadensis (proto-arthropod) This fearsome-looking beast is the largest known Burgess Shale animal. Some related specimens found in China reach a length of six feet!

  33. Burgess Shale Genus: Aysheaia peduncula (A velvet worm) Aysheaia is thought to have been a parasite living on sponges since it is commonly found in association with their remains (spicules). 2 inches

  34. Burgess Shale Genus: Canadapsis perfecta (A crustacean)

  35. Burgess Shale Genus: Opabinia regalis

  36. Burgess Shale Genus: Pikaia gracilens (a primitive chordate) Averaging about 1 1/2 inches in length, Pikaia swam above the seafloor using itsbody and an expanded tail fin.

  37. Burgess Shale Hallucigenia

  38. Burgess Shale An interesting, busy place indeed! Prominent at top right the head end of Anomalocaris is shown about to chomp on Waptia. Lower right shows Ottoia ready to pounce on a meal of Haplophrentis. Then, just to its left, Pikaia swims above the substrate showing its flattened tail. Just below center stage, Opabinia's trunk-like snout has caught Burgessochaeta, a bristle worm relative of Canadia (not shown.) There, to its left, Hallucigenia and Wiwaxia scurry along just in front of a very large Sanctacaris. At center left, Aysheaia dines on the sponge Vauxia while at lower left, Microdicyton nibbles away on a companion sponge. Above Opabinia, two Naraoia move along leaving long tracks in the bottom sediment. The spiny,vase-like sponge to their left is Pirania with two attached Nisusia

  39. Ordovician Life • Transgression • Yields characteristic sedimentary pattern • Siliciclastic sediments • Innermost belt • Carbonate platform • Seaward of siliciclastics

  40. Ordovician Life • Great radiation • Graptolites • Nautiloids • Life in sediment • Burrowers expanded • Pump oxygen-bearing water into sediment • Diversification of worms and other soft-burrowers

  41. Ordovician Life • Life on the seafloor • Diversity of benthic organisms increased • Jawless fishes • Grazing snails • Articulate brachiopods • Crinoids expanded • Coral-strome reefs • Rugose corals • Tabulate corals • Stromatoporoids

  42. Ordovician Life • Sediments indicate burrowers flourished

  43. Ordovician Life • Plants may have invaded land • Inconclusive evidence • Probably restricted to moist habitats

  44. Ordovician Life • Extinctions • Large extinction events limited diversification • Cambrian mass extinctions • End of Ordovician mass extinction

  45. Paleogeography • Cambrian • Cratons formed supercontinent early in Cambrian • Progressive flooding of continents • Regression in Middle Cambrian and again in Late Cambrian

  46. Paleogeography • Early Ordovician • Baltica began move from South Pole • End of Ordovician • Baltica moved to tropics • Gondwanaland nearing south pole • Glacier expanded • Sea-level fell • Mass extinction (2 pulses)

  47. Taconic Orogeny • Ordovician mountain building • Early Ordovician carbonate platform east coast of Laurentia • Mid-Ordovician carbonate deposition stopped; flysch sedimentation dominated

  48. Taconic Orogeny • Flysch overlain by molasse • Clastic wedge tapering towards northwest

  49. Taconic Orogeny • Carbonate platform wedged into subduction zone • Exotic terrane

  50. Taconic Orogeny • Fossils of different fauna but same age

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