The Early History of Life

Stages in the development of life

  • 1) Prokaryotic cell (bacteria and cyanobacteria) (3.5 B.Y.)
  • 2) Eukaryotic cell (animal- and plant-like protists) (1.6 B.Y.)
  • 3) Multicellular eukaryotes (rare and still small) (800 M.Y.)
  • 4) Ediacara fauna (pancakes, ribbons, threads) (640 M.Y.)
  • 5) Tommotian fauna (tiny cones, caps, spirals) (544 M.Y.)
  • 6) Cambrian explosion (big adaptive radiation) (530 M.Y.)

    The well-known Cambrian fauna

  • Trilobites--90 Cambrian families, good index fossils (1 M.Y. ranges)
  • Brachiopods (mainly inarticulate forms)
  • Molluscs (primitive caps, gastropods, bivalves, cephalopods)
  • Echinoderms (many bizarre classes, but no modern forms)
  • Ostracods (small crustaceans)
  • Conodonts (cones & "teeth," whole animal found in 1980)
  • Archaeocyathids (primary reef builders of Cambrian)

    Burgess Shale Fauna (soft-bodied organisms)

  • Opabinia--five eyes, frontal nozzle, ventral mouth
  • Hallucigenia--seven pairs of legs, seven pairs of unjointed spines
  • Wiwaxia--sclerites and spines
  • Anomalocaris--large carnivore, "jellyfish" mouth, "shrimp" pinchers, "sea cucumber" body
  • Pikaia--first chordate, similar to living Amphioxus
    "In historical perspective, failures are not phyla." M. F. Glaessner
    Timothy H. Heaton: E-mail, Home page, Phone (605) 677-6122, FAX (605) 677-6121