The Early Paleozoic Fauna:

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The Early Paleozoic Fauna earliest animal reef
formers and other benthos
186-233A Earth Life History (Fall 2001)
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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 3 - lecture cancelled -
students who gave their names should meet at my
office (Frank Dawson Adams Bldg, Room 214, at
1h20). - we leave from the FDA Building at 1h30.
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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.
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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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The finding of the Chengjiang fauna, 30 million
years younger, confirmed the diversity of the
early Cambrian fauna.
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Elrathia Middle Cambrian western Canada
Ceraurus (Neuville, Quebec)
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Several waves of extinction during Cambrian...
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Archeocyathids were simple, filter-feeding,
sponge-like animals. Their calcified skeletons
built the earliest reefs of animal origin. Corals
had not evolved yet.
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Reef framework of biogenic origin that rose over
the sea floor. Provides shelter to a diverse
community of organisms.
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Primitive corals appear in the Ordovician. Some
are solitary, horn shape (rugose corals). Their
growth bands have been used to calculate the no
of days in Paleozoic years.
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Other corals are colonial, like this tabulate
coral Favosites.
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Sponges had been around since the latest
Precambrian. Most of them leave little trace in
the fossil record. In some cases, their soft body
is supported by a flimsy skeleton of mm-size
spicules which falls apart upon death. Only
scattered spicules are found in sedimentary rocks.
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stromatoporoids sponge-related (not corals)
Shapes like stromatolites, but the framework
clearly includes mineralized pillars and layers
that used to support a filter-feeding organism.
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Brachiopods (a phylum of its own) will become the
most abundant shelly fauna of the Paleozoic
era. Most shells on todays beaches are bivalve
molluscs (clams, oysters, mussels). Until the
end of the Paleozoic, brachiopods were the most
successful group in the niche occupied today by
molluscs.
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Inarticulate brachiopods survive today with
shells very similar to those of their early
Ordovician relatives. Most use their long pedicle
to anchor themselves 10s of cm deep in the
sediment.
Lingulepsis, an inarticulate brachiopod.
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Brachiopods are different from mollusks. They
anchor their shell to a firm ground using a
muscular stem (pedicle).
This shell shows an opening for its pedicle.
Billingsella, a Cambrian orthid brachiopod