CAMBRIAN- "AGE OF TRILOBITES"

A INDEX FOSSILS

• Trilobites
1. most scavangers (ventral mouth)
2. some free swimming

B. OTHER INVERTEBRATES

• Archeocyathids
1. floursihed in the early Cambrian
• Brachiopods
1. inarticulate and thin shelled articulte types present
• Mollusks
1. not abundant, most simple gastropods fist in Late Cambrain) and a few pelecypods
2. cephalopods (first LateCambrian) were simple types with small, traight or slightly coiled shells
• Echinodermata
1. Holothurioidea (sea cucumbers)
2. Asteroidea (starfish)

C. REEF FORMERS

• no true reefs of colonial corals

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ORDOVICIAN- "AGE OF GRAPTOLITES"

A. INDEX FOSSILS

• Graptolites
1. pelagic and benthic
2. colonial related to modern hemicordates
3. along with the pelagic trilobites among the only fossils found in deep water shales
• Conodonts very abundant

B. OTHER INVERTEBRATES

• Foraminifera- first appearance
• Crustaceans- ostracod first appearance
• Echinoderms
1. cystoids
2. blastoids
3. crinoids
4. echinoids
• Cnidaria-Tabulate and Rugose Corals
1. honeycomb
2. chain
3. solitary
• Cephalopods
1. flourished, 10 orders
2. straight selled forms up to 15 to 30', largest animals yet to live
3. chief large, fast predators

C. REEF FORMERS

• Stromatoporoids
1. became a major reef forming group in the upper Middle Ordovician
2. sponges, multilayed structure with small mounds on each each layer and star shaped canals centered on mounds
3. interior usually recrystallized
4. major reef formers to end of Devonian
• colonial rugose and tabulate corals begin contributing in Middle Ordovician

D. VERTEBRATES (members of the Phylum Chordata)

• arose from Hemichordates (partial notochords) which include modern acorn worms and extinct graptolites
• oldest from Cambrian Burgess Shale (Pikaia)
• first with true bone (Subphylum Vertebrata)
1. first vertebrates
2. Ostracoderms (fish)
3. jawless
4. filter feeders
5. Late Cambrian

E. LAND PLANTS

• first evidence in Middle Ordovician (cuticle and spores). Probably bryophytes (amphibious plants).

F. EXTINCTION

• third largest extinction of geologic record during last 2 m.y. of Ordovocian
• 12% of families and 80% of genera
• Gonwana glaciation, cooling, lower sea level (200-300 feet)

F. Land Animals

• first in latest Ordovician (trace fossils of root feeders)