Paleozoic Life History: Invertebrates

Present-Day Marine Ecosystem

  • Ecosystem components:

    • Producers: phytoplankton, seaweed

    • Consumers: jellyfish, fish, cephalopods, etc.

    • Decomposers: bacteria

  • Studying modern ecosystems helps understand past ones.

Paleozoic Invertebrate Marine Life

  • Organism interactions influenced by physical environment.

  • Cambrian period marked by:

    • Global transgressions creating shallow habitats.

    • Changes in ocean circulation due to plate tectonics.

Cambrian Explosion

  • Early Cambrian sees appearance of most modern animal clades.

  • Fossils provide data for evolution understanding.

  • Cambrian mud banks permitting habitat for soft-bodied organisms.

  • Explosion evolution cause still debated.

Emergence of Shelly Fauna

  • Earliest hard-bodied organisms were known from Neoproterozoic.

  • First skeletonized micros fossils appeared in Early Cambrian.

Cambrian Predation

  • Anomalocaris: first macropredator (0.5m long).

  • Evolution of skeletons likely due to predator pressures.

Cambrian Marine Community

  • Major invertebrate clades evolved: trilobites, brachiopods, archaeocyathids.

  • Diverse habitats: pelagic jellyfish, nektonic arthropods, benthic sponges.

Trilobites

  • Dominant in Late Cambrian; represent >50% of fauna.

  • They first appeared in Early Cambrian and diversified rapidly.

Archaeocyathids

  • Vase-shaped, sessile organisms that built reefs.

  • Ancestors of modern sponges.

Burgess Shale

  • Discovered in 1909; crucial for early life history understanding.

  • Soft-bodied fossils preserved anaerobically, allowing for detailed studies.

Ordovician Marine Community

  • Notable for increased invertebrate diversity: Great Ordovician Biodiversification Event.

  • New habitats due to sea transgression influenced ecosystem dynamics.

Reef Builders of the Ordovician

  • Tabulate and rugose corals dominated, replacing Cambrian archaeocyathids.

Significant Paleontological Groups

  • Brachiopods: important index fossils and environmental indicators.

  • Graptolites: planktonic, suspension feeders, excellent index fossils.

  • Conodonts: feeding apparatus of unknown eel-like animals, excellent index fossils.

Mass Extinctions

  • Defined by rapid extinction rates exceeding originations, often due to environmental stresses.

  • Tropical organisms severely impacted; some clades typically survive.

End-Ordovician Mass Extinction

  • Over 100 marine invertebrate families went extinct; extensive glaciation possibly contributed.

Silurian and Devonian Communities

  • Significant rebound in diversity post-extinction; major reef building periods.

Ammonoids

  • Evolved in Early Devonian; significant marine community component and index fossils.

End-Devonian Mass Extinction

  • Marine community collapse; land plants unaffected but contributed to changes.