early paleozoic cambrian-ordovician 545-440mya. early paleozoic life primarily confined to...
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Early Paleozoic Cambrian-Ordovician
545-440mya
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
Cambrian• Two major evolutionary events at the
beginning of the Cambrian:1. 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
• Two major evolutionary events at the beginning of the Cambrian:
1. Rapid increase in the number and types of Phyla
2. Development of skeletons and hard body parts. Function:• Support for muscles, etc.• Protection against environment & other
organisms, predators• Aid in locomotion
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.
• Trilobites
• Fossil website
Early Paleozoic Life• Ordovician marked by evolutionary radiation
of life in the seas• Two groups expanded:
– Graptolites http://www.graptolite.net/Graptolites/index.html
– Nautaloids
Nautiloid CephalopodCollected from the Maquoketa Shale (Ordovician) of Dubuque, Iowa
http://web.eps.utk.edu/courses/HistoricalGeo/graptolites.html
Early Paleozoic Life• By late Ordovician, burrowing animals
were on the increase
• Indicates a diversification in worms and other burrowers
• 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.
NA=Laurentia
N.Europe=Baltica
• 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
Avalonia=exotic terrane
What’s happening in IL?
•Early Ordovician (485Ma)
•Middle Ordovician (470Ma)
•Late Ordovician (450Ma)
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)
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
Ordovician mountain building• Taconic orogeny– eastern edge of N. America
– 1st event of the 3 events that built Appalachian Mountains
– Fig. 13-20 A-C
• Exotic terranes– Formed of rocks that are different than the cratonic
rocks – Fossils are also different; don’t match other fossils
Burgess Shale• While eastern edge of N. America was
active, the western edge was passive
(c) 1995 by Andrew MacRae
• 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