1. Early Paleozoic Cambrian-Ordovician 545-440mya

2. Early Paleozoic Life
Primarily confined to shallow-water marine environments
Animals with hard body parts appear at the beginning of the Cambrian = beginning of the Phanerozoic
Cambrian summary
Ordovician summary

3. Cambrian
Two major evolutionary events at the beginning of the Cambrian:
Rapid increase in the number and types of Phyla: Brachiopoda, Mollusca, Arthropoda, Echinodermata, Vertebrata
Most Cambrian animals were herbivores that fed on algae.
Some argue that Phyla had evolved prior to the Cambrian
Reason for apparent rapid evolution:
Preserved in the rock record due to development of hard body parts
Development of hard body parts allowed new forms to evolve

4. Two major evolutionary events at the beginning of the Cambrian:
Rapid increase in the number and types of Phyla
Development of skeletons and hard body parts. Function:
Support for muscles, etc.
Protection against environment & other organisms, predators
Aid in locomotion

5. Trilobites
First group to increase and become dominant (i.e. abundant) – trilobites
Trilobite means three lobe fossil.
Approx. 50% of Cambrian fossils are trilobites.
Lived by crawling along the ocean floor, taking in sediment and digesting the organic material.

6. Trilobites
Fossil website

7. Early Paleozoic Life
Ordovician marked by evolutionary radiation of life in the seas
Two groups expanded:
Graptolites
Nautaloids
Nautiloid Cephalopod
Collected from the Maquoketa Shale (Ordovician) of Dubuque, Iowa

8. Early Paleozoic Life
By late Ordovician, burrowing animals were on the increase
Indicates a diversification in worms and other burrowers

9. NA=Laurentia
N.Europe=Baltica
Animals with hard-shells appeared in great numbers for the first time during the Cambrian.  The continents were flooded by shallow seas.  The supercontinent of Gondwana had just formed and was located near the South Pole.

10. Avalonia=exotic terrane
Movie
Gondwana shifts nearer to S. Pole by end of Ordovician; a large glacier grew there and is thought to have contributed to a global extinction event

11. What’s happening in IL?
Early Ordovician (485Ma)

12. Middle Ordovician (470Ma)

13. Late Ordovician (450Ma)

14. Early Paleozoic rocks
Cambrian– concentric pattern of deposition around margin of Laurentia
What kind of rocks do you think were deposited? Think about low vs. high energy, near vs. off shore
Fig. 13-7
Siliciclastic rocks
Carbonate plateforms
Some reef complexes (more in the Ordovician than Cambrian)

15. Late Ordovician glaciation
Tillites deposited
Two pulses of extinction, one at onset of glaciation and one at the end
Evidence from isotopes in shells
Disappearance of many fossil groups from the stratagraphic record

16. Ordovician mountain building
Taconic orogeny– eastern edge of N. America
1st event of the 3 events that built Appalachian Mountains
Fig A-C
Exotic terranes
Formed of rocks that are different than the cratonic rocks
Fossils are also different; don’t match other fossils

17. Burgess Shale
While eastern edge of N. America was active, the western edge was passive
(c) 1995 by Andrew MacRae

18. The Burgess Shaleis a site of exceptional fossil preservation, or a conservation lagerstätte.
Its fossils are preserved as dark organic films on thin layers of fine-grained shale; soft parts, such as muscle tissue or poorly calcified skeletons, are preserved in great detail