The Early Paleozoic Fauna:

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The Early Paleozoic Fauna The significance of
the Burgess Shale
EPSC233 Earth Life History (Fall 2002)
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Recommended reading STANLEY Earth System
History Chapter 13, pp. 345-354.
Keywordsphyla (arthropods, brachiopods,
echinoderms, mollusks), reef formers
(archeocyathids), deposit feeders (trilobites,
mollusks), filter feeder (eocrinoids, crinoids,
brachiopods, mollusks), predators (cephalopods).
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• Wednesday October 2nd (next week)
• Next Wednesday afternoon, at 1h30, the
  Sedimentary Geology class will be taking a field
  trip to see the limestone exposures at the Laval
  Nature Centre (St Vincent de Paul Quarry).
• There will be a few extra seats in the
• vans. If you are interested in joining them,
  contact Mairi Best at mmrbest_at_eps.mcgill.ca.
• - This outing lasts the entire afternoon. If 6
  students (or more) wish to go, we will cancel the
  lecture and I will accompany you.

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In Namibia and Siberia, the Precambrian-Cambrian
boundary can be dated isotopically. Many other
localities lie below or above the boundary or
have big gaps in the rock record.
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Where igneous rocks are not available,
chemo-stratigraphy is being used as a correlation
tool. This section is from Death Valley.
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Chemostratigraphy Comparing Death Valley (AZ,
U.S.) and Mackenzie Mountains (Canada) Is this a
reliable correlation tool? Are there gaps in the
section?
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Drift of continents during the Cambrian 600, 540
and 525 million years ago.
A proto-Atlantic called Iapetus is created
along east coast of N. America.
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Most Cambrian sandstones are poor in fossils.
As sea level rose worldwide, continental
shelves were flooded. Vast areas on the
continental margins became hospitable to shelly
marine faunas. Cambrian sandstones grade upward
to shallow-water limestones. These limestones
rarely contain stromatolites, unlike Precambrian
limestones. They contain the remains of a diverse
shallow-water community of animals and algae.
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View of the Walcott Quarry, in the Burgess Shale.
Walcott, from the Smithsonian Institute started
quarrying here in 1909. He sent about 65,000
specimens to the Smithsonian.
Named UNESCO World Heritage Site in 1981. 505
Ma.
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Mud accumulated (and became shale) atthe edge of
a CaCO3 platform (algal reef).
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• Paleontologists were groping in the dark until
  complete specimens were found in the Early
  Cambrian strata from Chengjiang, China.
• - soft bodied fauna, like the Burgess Shale
• - but 30 million years older
• - evidence of predation and burrowing
• - most phyla surviving today are represented
• but complex fossils of uncertain affinities
• are also present

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Some re-assembly was required...
jaws
interpreted as jellyfish
claws
Anomalocaris
Up to 2 meters long
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The Burgess Shale fauna is not unique, other
exceptional fossiliferous deposits of Cambrian
age have been found (Emu Bay, Australia
Chengjiang, South China, Orsten, Sweden). All
confirm - the predominance and diversity of
arthropods - the existence of body plans that
seem to have disappeared - some include earliest
chordates
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The finding of the Chengjiang fauna, 30 million
years older (535 Ma), confirm the diversity of
the early Cambrian fauna.
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Burgess Shale fauna is a diverse assemblage of
soft-bodied organisms. Some display body plans
that have no counterparts to this day.
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Opabinia five eyes, a clasping limb
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Fossilized Ayshea
Hallucigenia
Reconstructed as various types of worms, whose
descendants now living in moist forests.
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LeftHyolithes an early mollusk. Became lunch
for Ottoia (right), who knew to swallow them head
first to avoid choking on them
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This worm-like creature, 4 cm-long, had a
notochord (the precursor of the vertebrate
backbone).
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We can come up with plausible links between these
strange animals and modern groups but many
Cambrian groups left no direct descendants.
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The end of the Cambrian was marked by
extinctions. The trilobites survived but many
families were wiped out. Orders within new
phyla became far more widespread. The food web
(trophic structure) became more complex.
Organisms also continued to make better use of
sediments as source of food and shelter.
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The Ordovician period saw a new wave of
diversification among the survivors from the
Cambrian.
Elrathia Middle Cambrian western Canada
Ceraurus (Neuville, Quebec) Ordovician