Marine Life throughout Earth History

Proterozoic fauna
Stromatolites (cyanobacteria or blue-green algae) formed reefs.
Acritarchs are cysts of dinoflagellates or green algae.

Ediacaran-Vendian fauna (latest Proterozoic)
Radiation of soft pancake- and ribbon-shaped creatures. Some workers consider them to be primitive "jellyfish" and "worms," while others believe they are an early radiation of multicellular animals that were thin but had no internal complexity.

Tommotian (small shelly) fauna (earliest Cambrian)
Tiny cups, caps, and other hard fossils. They probably include primitive sponges and gastropods (snails).

Cambrian fauna
Trilobites (many-legged arthropods, now extinct)
Inarticulate brachiopods (the two shells come apart after death)
Primitive mollusks (look like slugs with pointed hats on)
Nautiloids (ancestors of the living chambered nautilus)
Weird echinoderms (distantly related to starfish and sea urchins)
Archaeocyathids (cone-shaped; the reef builders of the Cambrian)
Bizarre soft-bodied Burgess Shale animals such as Opabinia (five eyes and a nozzle), Wiwaxia (sclerites), Hallucigenia (spike legs and seven ?mouths), and Anomalocaris (big carnivore)

Paleozoic fauna (Ordovician to Permian)
Articulate brachiopods (the two shells stay attached after death)
Graptolites (planktonic animals found in black shales)
Conodonts (tiny teeth and plates of an illusive creature)
Ostracods (small ball-shaped crustaceans)
Rugose and tabulate corals (the primary reef builders)
Bryozoans (twig-like animals that helped make reefs)
Crinoids (stalked echinoderms like modern sea lilies)
Fusilinids (wheat-grain-shaped protists with a hard shell)
Ammonoids with simple sutures (arose from nautiloids)
Eurypterids (giant carnivorous arthropods)
Fishes (jawless, lobe-finned, ray-finned, and shark types)

Mesozoic fauna (Triassic to Cretaceous)
Ammonoids with complex sutures
Oysters and other bivalve mollusks; gastropod mollusks
Rudist bivalves (looked like corals and built reefs)
Hexacorals (primary reef builders)
Echinoids (sea urchins and sand dollars)
Planktonic foraminifera (protists with a hard shell)
Teleost fishes (advanced ray-finned fishes)
Marine reptiles: ichthyosaurs, plesiosaurs, mosasaurs, crocodiles (some giant), phytosaurs, sea turtles (some giant)

Cenozoic fauna (Tertiary and Quaternary)
Invertebrate and fish life similar to the Cretaceous
Marine mammals: whales, dolphins, porpoises, seals, manatee

Timothy H. Heaton: E-mail, Home page, Phone (605) 677-6122, FAX (605) 677-6121