Chapter 12
Paleozoic
Life History
Introduction
 Animals with skeletons appeared abruptly at the
beginning of the Paleozoic Era and experienced a
short period of rapid evolutionary diversification.
Geo-inSight 1., p. 572
Introduction
During the Paleozoic Era, the invertebrates
experienced several times of diversification.
These were followed
by extinction,
culminating in the
greatest recorded
mass extinction in
Earth’s history at the
end of the Permian
Period.
p. 561
What Was The Cambrian Explosion?
Multicelled organisms presumably had a long
Precambrian history, but they lacked hard parts.
Multicelled Organisms
evolved to invertebrates
with hard parts during
the Early Cambrian in
what is called the
“Cambrian explosion”.
Fig. 21.1a, p. 563
The Emergence of A Shelly Fauna
 Hard parts probably evolved as a result of
various geologic and biologic factors rather
than from a single cause.
 Sea creatures began to grow shells or
exoskeletons provided such advantages as:
 Protection from the sun Why ?
 Moisture Retention Why?
 Muscular Support for muscles, enabling
organisms to grow large and
 Protection from Predators
Fig. 21.1b, p. 563
Paleozoic Invertebrate Marine Life
The Present Marine Ecosystem
Marine organisms are classified as
 Plankton – the floaters
 Nekton – the swimmers
 Benthos - if they live on
or in the seafloor.
Fig. 21.2, p. 565
Paleozoic Invertebrate Marine Life
 The Present Marine Ecosystem
 Marine organisms are divided
into four basic feeding groups:
 Suspension feeders - consume
microscopic plants and animals
as well as dissolved nutrients
from water
 Herbivores - the plant eaters
 Carnivores – the scavengers,
which are meat eaters
 Sediment-deposit feeders - ingest
sediment and extract nutrients
from it.
Fig. 21.2, p. 565
Paleozoic Invertebrate Marine Life
Cambrian Marine Community
 The Cambrian invertebrate community was
dominated by three major groups:
 Trilobites, Brachiopods, and Archaeocyathids.
 Little specialization
existed among the
invertebrates, and
most phyla were
represented by only
a few species.
Fig. 21.4, p. 566
Invertebrates and
Guide Fossils or Index Fossils
Paleozoic Invertebrate Marine Life
The Burgess Shale Biota
 The Middle Cambrian Burgess Shale contains one of
the finest examples of a well-preserved soft-bodied
biota in the world.
Fig. 21.6b-d, p. 567
Paleozoic Invertebrate Marine Life
Ordovician Marine Community
 The Ordovician marine
invertebrate community
marked the beginning of
the dominance by the
shelly fauna and the start
of large-scale reef building.
 The end of the Ordovician
Period was a time of major
extinctions of many
invertebrate phyla.
Fig. 21.7, p. 568
Paleozoic Invertebrate Marine Life
Silurian and Devonian Marine Communities
 The Silurian and Devonian Periods were times of
diverse faunas dominated by reef-building animals.
Fig. 21.8, p. 569
Fig. 21.9, p. 569
Paleozoic Invertebrate Marine Life
Carboniferous and Permian Marine
Communities
 The Carboniferous and
Permian Periods saw a
great decline in
invertebrate diversity.
Fig. 21.12, p. 571
Paleozoic Invertebrate Marine Life
The Permian Marine Invertebrate
Mass Extinction
 A major extinction
occurred at the end of the
Paleozoic Era, affecting
the invertebrates as well
as the vertebrates. Its
cause is still being
debated.
Fig. 21.13, p. 571
Vertebrate Evolution
 Chordates are characterized by a notochord, dorsal
hollow nerve cord, and gill slits.
 The earliest chordates were soft-bodied organisms
that were rarely fossilized. Vertebrates are a
subphylum of the chordates.
 They had spinal cords but no Jaws “Ostracoderms”
Fish
 Fish are the earliest known vertebrates, with their
first fossil occurrence in Upper Cambrian rocks.
They diversified rapidly during the Paleozoic Era.
Cenozoic
Mesozoic
Neogene
Paleogene
Cretaceous
Jurassic
Triassic
Paleozoic
Permian
Carboniferous
Ostracoderms
Devonian
Silurian
Ordovician
Cambrian
Cartilaginous fish
Placoderms
Lobe-finned fish
Acanthodians
Ray-finned
fish
Fish
 They have had a long and varied history, including
jawless and jawed armored forms (ostracoderms and
placoderms), cartilaginous forms, and bony forms.
Fig. 21.18, p. 576
Fish
 Crossopterygians, a group of lobefinned fish, gave rise to the
amphibians.
 The link between crossopterygians
and the earliest amphibians is
convincing and includes a close
similarity of bone and tooth
structures.
 The transition from fish to
amphibians occurred during the
Devonian.
Fig. 21.23, p. 579
Amphibian
Vertebrates Invade The Land
 Amphibians first appear in the fossil record
during the Devonian, having made the transition
from water to land.
 They became extremely
abundant during the
Pennsylvanian Period
when coal forming
swamps were
widespread.
 During the Carboniferous,
the labyrinthodont
amphibians were the
dominant terrestrial
vertebrate animals.
Fig. 21.22, p. 578
Evolution of The Reptiles
The Land Is Conquered
 The evolution of the amniote egg allowed
reptiles to colonize all parts of the land
beginning in the Late Mississippian.
 The earliest fossil record
of reptiles is from the Late
Mississippian.
Fig. 21.27, p. 582
Evolution of The Reptile
The Land Is Conquered
 Pelycosaurs or sail-back reptiles were the dominant
reptile group during the Early Permian.
 The therapsids or mammal-like reptiles dominated the
landscape for the rest of the Permian Period.
Fig. 21.29, p. 583
Fig. 21.30, p. 583
Plant Evolution
 In making the transition from water to land, plants had
to overcome the same basic problems as animals -namely, desiccation, reproduction, and gravity.
Table 21.3, p. 584
Plant Evolution
 The earliest fossil record of land plants is from
Middle to Upper Ordovician rocks.
 These plants were probably small and
bryophyte-like in their overall organization.
 The evidence comes from spores released by
plants, not actual plant fossils.
Plant Evolution
 The oldest known vascular land plants first appear
in the Middle Silurian. The evolution of vascular
tissue was an important event in plant evolution.
 It allowed food and
water to be transported
throughout the plant
and provided the plant
with additional support.
Fig. 21.35, p. 589
Plant Evolution
 The ancestor of terrestrial vascular plants was
probably some type of green algae
 This is based on such similarities as:
Pigmentation
Metabolic enzymes
Reproductive cycles
Plant Evolution
Silurian and Devonian Floras
 The earliest seedless vascular plants
were small, leafless stalks with
spore-producing structures on their
tips.
 From this simple beginning, plants
evolved many of the major structural
features characteristic of today’s
plants.
Fig. 21.31, p. 585
Plant Evolution
Silurian and Devonian Floras
 By the end of the Devonian Period, forests with
tree-sized plants up to 10 m tall had evolved.
 The Late Devonian also witnessed the evolution of
flowerless seed plants (gymnosperms) whose
reproductive style freed them from having to stay
near water.
Fig. 21.32, p. 585
Plant Evolution
 Late Carboniferous and Permian Floras
 The Carboniferous
Period was a time of
vast coal swamps,
conditions ideal for the
seedless vascular
plants.
 Seedless vascular
plants, such as ferns,
were very abundant
during the
Pennsylvanian Period.
Fig. 21.34, p. 588
Plant Evolution
 Late Carboniferous and Permian Floras
 With the onset of more arid conditions during the
Permian, the gymnosperms became the dominant
element of the world’s forest.
End of
Chapter 12