Diversity of marine animals, and extinction events over geologic time.

Paleozoic Life Forms Cambrian – explosion of phyla with hard parts. Most phyla of today except Bryozoans were present. CO2 in seawater allows hard parts? Trilobites, Archaeocyathids, mostly scavengers Burgess Shale – middle Cambrian, large diversity

Cambrian Fauna: isolated, mostly scavengers, Trilobites, Soft Bodied (burgess shale), Archaeocyathids, Arthropoda: the REAL rulers of the Earth. . .

A few localities around the world that preserve soft-bodied fossils of the Cambrian show that the "Cambrian radiation“ The Burgess Shale is found in an area of the Canadian Rocky Mountains known as the Burgess Pass, and is located in British Columbia's Yoho National Park.

Significance of Burgess Shale: Middle Cambrian, numerous phyla of soft-bodied organisms. One species, Hallucigenia, bore seven pairs of walking spines. Seven tentacles on the dorsal surface were used to grasp food. Hallucigenia Arthropod: Canadaspis

Animals in the Burgess Shale include: Several groups of arthropods, including trilobites and crustaceans Sponges Crinoids Molluscs Corals Three phyla of worms Chordates Many other species, some of which cannot be placed into known phyla

Graptolites are fossil colonial animals (phylum Hemichordata) known chiefly from the Upper Cambrian through the Lower Carboniferous. Most fossil graptolites look like nothing so much as tiny saw blades. They are thought to have been planktonic, floating or slowly sinking through the water. The shape was probably an adaptation to floating. A worldwide glaciation at the end of the Ordovician eliminated most graptolites

Ordovician / Paleozoic Fauna: Sessile organisms (attached): brachipods, crinoids, coral, bryozoans, sponges, trilobites on the wane, Nautiloid cephalopods (early), sharks and bony fish.

Ordovician marine life was dramatically different from that of the Cambrian – the most obvious difference is diversity. Ordovician seafloor is packed with animals. Cambrian=150 families, Ordovician=400 families.

Complex food chains. Ordovician Tiering Ecological tiering increased – organisms that reached half a meter or more above the seafloor.

Representative Ordovician Fossils

Most Common Ordovician fossil – Brachiopods

Ordovician Crinoids – feed several meters above the sea floor.

Ordovician – First Appearance of true coral reefs Ordovician – First Appearance of true coral reefs. Dominant reef builders: tabulates and rugose coral. Tabulate – Colonial Corals Rugose – Solitary Coral “Horn Coral”

Nautiloid cephalopods: predators of the Ordovician.

Other Common Ordovician Fauna (Paleozoic Fauna) Gastropods – first snails in Ordovician Graptolites – related to chordates, branching organisms that floated on the open ocean ** Earliest vertebrates – Jawless Fish (ostracoderms) ** First primitive land plants.

Silurian Devonian- age of fish Primitive vascular plants – tracheophytes First jawed fish – Acanthodians Devonian- age of fish Devonian Forests – tree ferns Expansion of jawed fish – bony fish First sharks – cartilaginous Lungfish – a link to amphibians Crossopterygian (drought resistant) First Amphibians – ichthyostegids, labyrinthodonts

Agnathids - Early Paleozoic Jawless fish Agnathids - Early Paleozoic Jawless fish. Oldest jawless fish is from the Cambrian Period (collective name for agnathids= ostracoderms)

Fish with cartilaginous skeletons (like sharks)- Chondrichthyes Plate-skinned fish with jaws Spiny fish with jaws Collective name for Agnathids (jawless fish) is Ostracoderms Evolution of Fish from Cambrian to Devonian

From the Late Devonian to the Middle Carboniferous, amphibians were the only vertebrates to inhabit the land. In the Late Devonian (about 375 m.y. ago), the first terrestrial vertebrate, Ichthyostega, appeared. These amphibian fossils are found in freshwater deposits.

Mass Extinctions. Two of the big five occur in the early Paleozoic.

Ordovician Extinction (443 mya) –occurred in two phases. First phase - Glaciation reduced shallow water habitat. Affected planktonic and nektonic (floating and swimming) organisms such as graptolites the most. Second phase - As warming occurred and the glaciers began to melt, organisms which were adapted to the cooler conditions began to suffer extinction. This affected several trilobite groups, corals, conodonts, and bryozoans.

Devonian Extinction (359 m.y. ago) Organisms most strongly affected (but not totally wiped out) by the Devonian extinction were: Tabulate corals Rugose corals Stromatoporoids (poriferan reef builders) Brachiopods Goniatite ammonoids Trilobites Conodonts (extinct chordates resembling eels; tooth like microfossil) Placoderm fish Complex cause that occurred over 20 m.y. Large amount of nutrients washed from land into the seas (due to land plants) may have cause algal blooms and low oxygen conditions in the seas – never experienced previously.

End of this section