The Early Paleozoic World

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Chapter 13

• The Early Paleozoic World

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Chapter 13 - Overview

• Cambrian Life
• Paleogeography
• Tectonics - First Step in Appalachian Mtns

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Cambrian Life
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Cambrian Life
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Cambrian Explosion

• Lowermost Cambrian
• Simple skeletal fossils
• Teeth

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Tommotian Fauna
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Cambrian Explosion

• Large animals with skeletons
• Trilobites
• Arthropods with calcified segmented skeletons

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Cambrian LifeTrilobites
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Cambrian LifeTrilobites
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Cambrian Explosion

• Bottom-dwelling forms create scratch marks
• Similar to some Neoproterozoic tracks

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Cambrian Explosion

• Other abundant Early Cambrian animal groups
• Monoplacophoran mollusks
• Inarticulate brachiopods
• Echinoderms

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Cambrian Explosion

• Chengjiang fauna
• Soft- bodied creatures including
• Cnidarians
• Predatory worms
• Anomalocarids
• Huge carnivores (2 m)
• Swimmers
• Impaled prey

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Cambrian Explosion

• Modes of Life
• Deposit feeders
• Extract organic matter from sediments
• Trilobites, arthropods
• Suspension feeders
• Collect organic matter from the water
• Eocrinoids
• Attach by stalk

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Cambrian Life

• Proterozoic Holdover

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Cambrian Explosion

• Stromatolites
• Less abundant more restricted
• Weak grazing pressure in inter-tidal zone

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Cambrian Life
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Cambrian Explosion

• Reefs
• Archeocyathids
• Suspension feeders
• Probably sponges

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Cambrian LifeArcheocyathids
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Cambrian LifeArcheocyathids
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Cambrian Reef BuildersArcheocyathids
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Cambrian LifeBrachiopods
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Cambrian LiffeBrachiopods
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Cambrian LifeBryozoans
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Bryozoans
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Cambrian Explosion

• Evolutionary experimentation
• Bizarre echinoderm classes
• Few species and genera
• Tried out many body plans

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Cambrian Explosion

• Middle and Late Cambrian
• 15 M year duration
• Expansion of many groups
• Trilobites
• Echinoderns
• Conodonts
• Early fish
• Isolated bony external plates

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Cambrian Explosion

• Burgess Shale Fauna
• Western No. America
• Deep-water setting (low O2)
• Chordata
• Pikaia Notochord
• Arthropods
• Onychophorans
• Intermediate between segmented worms and
  arthropods

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Western Laurentian Margin

• Stable continental shelf
• Steep carbonate platform edge
• Accumulated thick limestone sequences

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Burgess Shale
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Western Laurentian Margin

• Burgess Shale
• Unusual fauna
• Collected by Walcott

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Burgess Shale
Genus Amiskwia sagittiformis (Unknown
affinity) Amiskwia shows us three definite body
segments a head with two prominent tentacles, an
unsegmented trunk with stubby side fins, and a
flattened tail. Fossil sizes up to 1 inch.
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Burgess Shale
Genus Anomalocaris canadensis (proto-arthropod)
This fearsome-looking beast is the largest known
Burgess Shale animal. Some related specimens
found in China reach a length of six feet!
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Burgess Shale
Genus Aysheaia peduncula (A velvet
worm) Aysheaia is thought to have been a parasite
living on sponges since it is commonly found in
association with their remains (spicules). 2
inches
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Burgess Shale
Genus Canadapsis perfecta (A crustacean)
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Burgess Shale
Genus Opabinia regalis
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Burgess Shale
Genus Pikaia gracilens (a primitive
chordate) Averaging about 1 1/2 inches in length,
Pikaia swam above the seafloor using itsbody and
an expanded tail fin.
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Burgess Shale
Hallucigenia
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Burgess Shale
An interesting, busy place indeed! Prominent at
top right the head end of Anomalocaris is shown
about to chomp on Waptia. Lower right shows
Ottoia ready to pounce on a meal of
Haplophrentis. Then, just to its left, Pikaia
swims above the substrate showing its flattened
tail. Just below center stage, Opabinia's
trunk-like snout has caught Burgessochaeta, a
bristle worm relative of Canadia (not shown.)
There, to its left, Hallucigenia and Wiwaxia
scurry along just in front of a very large
Sanctacaris. At center left, Aysheaia dines on
the sponge Vauxia while at lower left,
Microdicyton nibbles away on a companion sponge.
Above Opabinia, two Naraoia move along leaving
long tracks in the bottom sediment. The
spiny,vase-like sponge to their left is Pirania
with two attached Nisusia
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Ordovician Life

• Transgression
• Yields characteristic sedimentary pattern
• Siliciclastic sediments
• Innermost belt
• Carbonate platform
• Seaward of siliciclastics

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Ordovician Life

• Great radiation
• Graptolites
• Nautiloids
• Life in sediment
• Burrowers expanded
• Pump oxygen-bearing water into sediment
• Diversification of worms and other soft-burrowers

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Ordovician Life

• Life on the seafloor
• Diversity of benthic organisms increased
• Jawless fishes
• Grazing snails
• Articulate brachiopods
• Crinoids expanded
• Coral-strome reefs
• Rugose corals
• Tabulate corals
• Stromatoporoids

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Ordovician Life

• Sediments indicate burrowers flourished

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Ordovician Life

• Plants may have invaded land
• Inconclusive evidence
• Probably restricted to moist habitats

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Ordovician Life

• Extinctions
• Large extinction events limited diversification
• Cambrian mass extinctions
• End of Ordovician mass extinction

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Paleogeography

• Cambrian
• Cratons formed supercontinent early in Cambrian
• Progressive flooding of continents
• Regression in Middle Cambrian and again in Late
  Cambrian

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Paleogeography

• Early Ordovician
• Baltica began move from South Pole
• End of Ordovician
• Baltica moved to tropics
• Gondwanaland nearing south pole
• Glacier expanded
• Sea-level fell
• Mass extinction (2 pulses)

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Taconic Orogeny

• Ordovician mountain building
• Early Ordovician carbonate platform east coast of
  Laurentia
• Mid-Ordovician carbonate deposition stopped
  flysch sedimentation dominated

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Taconic Orogeny

• Flysch overlain by molasse
• Clastic wedge tapering towards northwest

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Taconic Orogeny

• Carbonate platform wedged into subduction zone
• Exotic terrane

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Taconic Orogeny

• Fossils of different fauna but same age

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Taconic Orogeny

• With continued collision, foreland basin migrated
  westward

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Appalachian Mountains

• Step 1 - collision with an Island Arc
• Proterozoic
• Rodinia/Grenville
• Iapetus
• Cambrian-Ordovician
• Closing Iapetus
• Wilson Cycle

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Wilson Cycle Part 1
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Wilson Cycle Part 2
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Cambrian Paleogeography
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Taconic Orogeny
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Taconic Highlands Late Ordovician
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Taconic Highlands Queenston Clastic Wedge
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Taconic Highlands Queenston Clastic Wedge
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OrdovicianPaleogeography
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Western Laurentian Margin

• Buried by turbidites
• Accumulated in oxygen-poor environment

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Western North America
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Western North America
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Sauk SequenceLate Proterozoic to Early Ordovician
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Glaciation and Mass Extinction

• Ordovician glaciation

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Glaciation and Mass Extinction

• North Africa tillites

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Glaciation and Mass Extinction

• North African glaciation

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Ordovician GlaciationSaudi Arabia
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Ordovician GlaciationSaudi Arabia
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Ordovician GlaciationSaudi Arabia
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