Cambrian
Marella
Anomalocaris
Hallucigenea
Jellyfish?
Shrimp?
Sponge?
Parts of Anomalocaris were at first thought to be three
separate animals.
Anomalocaris
Wiwaxia corrugata
Wiwaxia corrugata
Marrella splendens
Hallucigenia
GLB in the Paleozoic Era
 Central North America experienced
repeated transgressions and regressions
of shallow, tropical seas during Paleozoic
 Midwest is below equator
 Large areas of tropical coral reefs
 Seas deposited layers of materials that
became sedimentary rocks
 Limestone, shales, sandstone, gypsum
 Thornton Quarry, Sagawau Canyon limestone
Ordovician Period
 490 - 443 Million Years Ago
 Shallow, shifting seas covered most of
North America
 Biodiversity increasing rapidly
 Corals, bryozoans, crinoids, cephalopods, a
great variety of new brachiopods, trilobites
 First fish appear in fossil record
 Squid-like cephalopods were the largest
creatures in Ordovician seas.
 Cone-shaped shells sometimes reached a length
of 5 meters (about 16 ft.).
Ordovician Period
 Sea floor covered by calcium carbonate
mud produced by the breakdown of
"stony" algae and animal remains.
 Bryozoans and algae trapped the
sediment to form small mounds.
 Mounds protected animals, such as
brachiopods, corals, crinoids, starfish,
mollusks, and trilobites.
 Receptaculitids are common in the rocks
from this area.
Ordovician
Fossils
Ordovician Period
Algae with Skeletons
• Receptaculites appeared
around 488 million years ago
in the Lower Ordovician and
disappeared 250 million years
ago in the Lower Triassic.
• Their modern-day cousins,
the Dasycladaceae, are algae
that also form calcareous
skeletons.
Brachiopods
Rhynchotrema dentatum
Illinois
Onniella meeki
Illinois
Brachiopods
300 living species
of brachiopods
BrachiopodsLampshells
Crinoid
Pycnocrinus dyeri
Cincinnati, Ohio
Nautiloid Cephalopod
Plectoderas undatus
Illinois
Corals
rugose coral Grewingkia
canadensis
Cincinnati, Ohio
tabulate coral Favistella
alveolata
Illinois
Coral Reconstructions
Rugose coral
Tabulate Coral
Tentaculites - mollusc
Tentaculites incurvus
Cape Girardeau, Missouri
Tentaculites oswegoensis
 Waubonsee Creek in Oswego, IL
 Rock called Brainerd Formation
 Shale and thin dolomite
 Upper Ordovician and
Silurian
 Tentaculites oswegoensis
 Fossils found only known in
Illinois
 Animal ranged from
Oswego, IL (Kendall County)
to possibly Kankakee River
State Park in Will County.
Trilobite
Isotelus iowensis
Missouri
Graptolites
 ‘Graptolite' means 'writing in rock‘
 Hemichordate – related to echinoderms &
chordates
 Most graptolites are thought to have been
planktonic, floating or slowly sinking through the
water.
 The spiral shape of some was probably an adaptation
to slow sinking.
 Other graptolites may have been connected to gasfilled sacs, keeping them buoyant.
 Lived in water with low oxygen levels
 Fed on plankton
Graptolites
Hemichordates
Phyllograptus archaios
Spirograptus
Graptolite Reconstructions
Silurian Period
 443 - 417 Million Years Ago — Silurian Period
 Shallow, tropical sea covered Illinois (then south of
the equator)
 Reefs, corals, crinoids, and shelled invertebrates
flourished
 Delicate corals, bryozoans, and crinoids were in protected
pockets and along the sides of the reefs.
 Brachiopods, snails, clams, and trilobites were hidden
in the tangle of the complex branches of these animals
 These shelled animals were eaten by predatory, squidlike cephalopods.
 Largest animals of the time were 2-meter-long (6.5 ft.) sea
scorpions called eurypterids
Eurypterids
A group of eurypterids (sea scorpions) from
Upper Silurian rocks of the Niagara Peninsula.
Silurian Period
 Ocean reefs occurred in a band 30 degrees to
the north and south of the equator.
 Most widespread distribution of reefs in the
history of North America during Silurian
 Reefs ranged from
 less than a meter (3.3 ft.) to several kilometers in
diameter and
 less than 3 meters (about 10 ft.) to nearly 304 meters
(about 1000 ft.) high.
Silurian Period
 Rich fossil deposits in Illinois and lower
Midwest from this period
 Many fossils from ancient Silurian reefs
 e.g. Trilobites, Ammonites, Eurypterids, Corals,
Crinoids, Brachiopods, Jawless Fish, Primitive
Sharks
 Be sure to visit the online Silurian Reef exhibit from
the Milwaukee Public Museum!
 Plants and wingless insects arose
 But GLB fossils of these are rare since entire
region was under water
Silurian Period
 Silurian rocks are exposed
 Along the Kennedy Expressway at Addison
(southbound lanes)
 In the Thornton Quarry at Homewood
 In the Sag Bridge abandoned quarries (Cook County
Forest Preserves)
 Along Rock Creek in the Kankakee River State Park
 Along the Illinois River
 Near the towns of Lemont, Romeoville and Joliet.
Silurian Seat at Navy Pier
Thornton Quarry: Then and
Now
Chicago is built upon a vast
Silurian Reef.
Silurian Reef Diorama at the Field
Museum of Natural History in Chicago
 Fossil Crinoids, Brachiopods, Trilobites,
Ammonoids, Gastropods and Corals are found
in Thornton Quarry rock.
 Modern reef environments are found in warm,
shallow oceans.
 The water is usually clear of silt and wind-blown
sediments.
 Many of the reef inhabitants are filter feeders and
sediment prevents feeding.
Scene from a Silurian sea
Silurian Fossils
Bryozoan
Fenestrellina elegans
Chicago
Crinoids
Scyphocrinites sp
Eucalyptocrimus crassus
Indiana
Diorama of a Silurian Reef
Living Crinoids
Cephalopods
Nautaloid Cephalopod
Michelinoceras
Illinois
Ammonoid
Living Chambered
Nautilus
Silurian Trilobites
Calymene celebra
Milwaukee
Slab of Upper Ordovician Tyndall Limestone at the quarry
in Garson, north of Winnipeg showing a large
Receptaculites (calcareous algae) and mottles produced
by Thalassinoides burrows.
Sponges
Astylospongia praemosa
Modern Sponges
Sponge Fossils
Corals
tabulate coral Cladopora reticulata
Louisville, Kentucky
Tabulate Coral
Living Corals
Living Coral Polyps
Trilobites
Dicranurus monstrosus
Note: defensive spines
 In the late Silurian, the first-known land
plants (Cooksonia) and air-breathing
animals (millipedes, centipedes and
scorpions) appeared.
Cooksonia
Psilotum
Arthropleura
Myriopoda
Pleurojulus steuri
millipede
Pleurojulus steuri