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Life of the Paleozoic


Chapter 12 Life of the Paleozoic Paleozoic overview Paleozoic Fossil Record The Paleozoic was a time with abundant fossils of multicellular organisms with shells. – PowerPoint PPT presentation

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Title: Life of the Paleozoic

Chapter 12
  • Life of the Paleozoic

  • Paleozoic overview

Paleozoic Fossil Record
  • The Paleozoic was a time with abundant fossils
    of multicellular organisms with shells. As a
    result, the fossil record improves dramatically
    at the beginning of the Paleozoic Era.

Paleozoic Invertebrates
  • Representatives of most major invertebrate phyla
    were present during the Paleozoic, including
    sponges, corals, bryozoans, brachiopods,
    molluscs, arthropods, and echinoderms.
  • Almost all of the common invertebrate phyla in
    existence today had appeared by the Ordovician.

Paleozoic Vertebrates
  • Vertebrates evolved during the Paleozoic,
  • Fishes
  • Amphibians
  • Reptiles
  • Synapsids (mammal-like reptiles)
  • The first vertebrates were jawless fishes, which
    are found in rocks as old as Cambrian in China.

Paleozoic Vertebrates
  • An advanced lineage of fishes with primitive
    lungs and stout fins gave rise to the four-legged
    animals or tetrapods.
  • The transition from water-dwelling vertebrates to
    land-dwelling vertebrates depended on the
    evolution of the amniotic egg.

Paleozoic Plants
  • The first primitive land plants appeared near the
    end of the Ordovician.
  • Vascular plants expanded across the land, forming
    great forests in the Devonian.
  • The plants progressed from seedless,
    spore-bearing plants to plants with seeds but no
    flowers (gymnosperms).

Paleozoic Extinctions
  • Several mass extinctions occurred during the
    Paleozoic, including the largest extinction of
    all at the end of the Permian.
  • Other mass extinctions occurred at the end of the
    Ordovician and Devonian periods.

Paleozoic Life
  • Summary of invertebrate phyla

  • Paleozoic life includes some Precambrian forms,
    which survived into the Paleozoic, as well as
    more advanced forms
  • Unicellular eukaryotes
  • Animals
  • Invertebrates
  • Vertebrates
  • Plants

Adaptive Radiations and Extinctions
  • The Paleozoic was a time of several adaptive
    radiations and extinctions.
  • Many geologic periods began with adaptive
    radiations (times of rapid evolution).
  • Several periods ended with extinction events of
    varying severity.
  • The extinction event at the end of the Permian
    Period was the worst mass extinction in the
    history of life.

Diversity in the Paleozoic
  • Red arrows mark extinction events

Soft-bodied Animals
  • Multicellular animals evolved in the Precambrian.
    Soft-bodied Ediacaran-type organisms ranged into
    the Cambrian period.
  • Soft-bodied fossils are infrequently preserved.
  • Preservation improved with the origin of hard

  • The first animals with shells are called small
    shelly fossils.
  • Small shelly fossils are found at the base of the
    Cambrian, and in the late Neoproterozoic.
  • Most disappeared by the end of the first stage of
    the Lower Cambrian.

Small Shelly Fossils
  • Many had phosphatic shells, few mm in size.
  • Shells and skeletal remains of primitive
    molluscs, sponges, and animals of uncertain
    classification, such as Cloudina, that secreted a
    calcareous tube.

Cambrian Diversification
  • The initial Paleozoic diversification is known as
    "the Cambrian explosion. Abrupt appearance of
    many types of animals about 535 million years
    ago, followed by rapid evolution.
  • During that episode of explosive evolution, all
    major invertebrate phyla appeared in the fossil
    record (except Bryozoa).
  • Sometimes this event is referred to as
    "evolution's big bang".

Cambrian Substrate Revolution
  • Infaunal, burrowing animals evolved rapidly
    during the Cambrian, as indicated by trace
    fossils and bioturbation of sediments.
  • The dramatic change in the character of the
    seafloor sediments (from undisturbed to highly
    burrowed) has been called the "Cambrian substrate

Soft-Bodied Fossils in the Burgess Shale
  • The extraordinarily well-preserved Middle
    Cambrian Burgess Shale fauna of Canada provides a
    window into the past to view the spectacular
    diversity of the Middle Cambrian.
  • Many soft-bodied organisms are preserved in
    black shale, along with the soft parts of animals
    with shells, such as legs and gills of

Soft-Bodied Fossils in the Burgess Shale
  • The significance of the Burgess Shale is that is
    records soft-bodied organisms, and the soft parts
    of organisms with shells . The finely detailed
    preservation reveals the extraordinary diversity
    and evolutionary complexity that existed near the
    beginning of the Paleozoic.
  • Fossil sites containing abundant fossils with
    extraordinary preservation are called
    lagerstatten. Both the Burgess Shale and the
    Chengjiang fauna in China are lagerstatten.

Animals in the Burgess Shale
  • Several groups of arthropods, including
    trilobites and crustaceans
  • Sponges
  • Onycophorans
  • Crinoids
  • Molluscs
  • Corals
  • Three phyla of worms
  • Chordates (Pikaia)
  • Many others

Stratigraphic setting of the Cambrian Burgess
  • Location of the Burgess Shale fauna in British
    Columbia, Canada
  • C Onycophoran, Aysheaia, intermediate in
    evolution between segmented worms and
    arthropods.D Arthropod LeanchoilaE Arthropod

Pikaia - One of the Oldest Chordates
  • Pikaia is a fish-like lower chordate from the
    Burgess Shale.
  • Modern representatives are called lancelets, such
    as the genus Amphioxus.

  • Chordates have a notochord or dorsal stiffening
    rod associated with a nerve chord, at some stage
    in their development.
  • In vertebrates, the notochord is surrounded by
    and usually replaced by a vertebral column during
    embryonic development.
  • Vertebrates are chordates, but Pikaia pre-dates
    the evolution of vertebrae.
  • It is thought that vertebrates evolved from
    organisms similar to Pikaia.

Predators in the Cambrian Seas
  • The giant predator of the
    Cambrian seas, Anomalocaris,
    up to 60 cm long.
  • Predators would have caused
    selective pressures on prey.
    The need to avoid being eaten probably
    encouraged the evolution of hard protective
  • Predation probably also caused an increase in
    diversity of prey, as they evolved to better
    survive predation.

Other Burgess Shale Animals
  • Marrella, a "lace crab, is common in the
    Burgess Shale.
  • Hallucigenia, an onycophoran, was originally
    interpreted to walk on its spines, until claws
    were discovered on its tentacles.

The Significance of the Burgess Shale
  • The significance of the Burgess Shale is that it
    records soft-bodied organisms, and the soft parts
    of organisms with shells. The finely detailed
    preservation reveals the extraordinary diversity
    and evolutionary complexity that existed near the
    beginning of the Paleozoic.

Exceptional Preservation
  • Fossil sites containing abundant fossils with
    extraordinary preservation are called
  • Both the Burgess Shale fauna and the Chengjiang
    fauna from China are considered to be

The Chengjiang fauna
  • In 1984, the Lower Cambrian (535 my old)
    Chengjiang fossil site was discovered in Yunnan
    Province, China.
  • More than 100 species of invertebrates have been
    found, with extraordinary preservation, including
    many soft bodied forms

The Chengjiang fauna
  • Jelly fish
  • Annelid worms
  • Cnidaria
  • Porifera (sponges)
  • Brachiopods
  • Arthropods
  • Early chordates similar to Pikaia
  • The world's oldest known fish (Myllokunmingia)
  • Other species of unknown phyla

Oldest Known Fish
  • The world's oldest known fish, Myllokunmingia,
    from the Maotianshan Shale near Chengjiang, in
    the Yunnan Province of China.
  • 535 million years old.

Ordovician Diversity
  • Following a slight dip in diversity at the end of
    the Cambrian, the Ordovician was a time of
    renewed diversification.
  • Global diversity tripled.
  • The number of genera increased rapidly, and the
    number of families increased from about 160 to
  • The increase was particularly dramatic among
    trilobites, brachiopods, bivalve molluscs,
    gastropods, and corals.

Late Ordovician Extinction
  • An extinction event at the end of the Ordovician
    led to an abrupt decline in diversity.
  • This extinction event was apparently related to
    the growth of glaciers in Gondwana, coupled with
    a reduction in shallow water habitat associated
    with the lowering of sea level.

Diversity in the Paleozoic
  • Red arrows mark extinction events

Silurian Diversity
  • Diversification of marine animals occurred again
    at the beginning of the Silurian Period.
  • The period ended with only a slight drop in

Devonian Diversity
  • The Devonian saw continued diversification, but
    ended with another fairly large extinction event,
    which extended over about 20 million years.
  • Roughly 70 of marine invertebrates disappeared.
  • Because of the long duration, the extinction is
    unlikely to have been caused by a sudden,
    catastrophic event.

Carboniferous-Permian Diversity
  • In the early Carboniferous, diversity once again
  • Diversity of marine animals remained fairly
    constant throughout the Carboniferous and
  • The Late Permian is marked by a catastrophic
    extinction event which resulted in the total
    disappearance of many animal groups.

Overview of Changes in Diversity Through Time
  • Several of the periods of the Paleozoic ended
    with extinction events
  • The beginning of most of the periods of Paleozoic
    were marked by adaptive radiations
  • Maximum diversity in the Paleozoic seas
    maintained roughly constant at between 1000 and
    1500 genera
  • The largest extinction occurred at the end of the

  • Recovery of diversity in the Mesozoic was slow
    (Triassic and Jurassic)
  • Diversity increased rapidly in the Cretaceous
  • Another mass extinction occurred at the end of
    the Cretaceous
  • Diversity increased extremely rapidly, at
    unprecedented rates, at the beginning of the
  • Diversity in the Cretaceous, and Cenozoic Era was
    much greater than during the Paleozoic

Diversity in the Paleozoic
  • Red arrows mark extinction events

Unicellular Organisms in the Paleozoic Seas
  • The principal groups of Paleozoic unicellular
    animals with a significant fossils record are the
    foraminifera and the radiolaria, which belong to
    Phylum Sarcodina.
  • These organisms are unicellular eukaryotic
    organisms, and belong to Kingdom Protista.

  • Name Foraminifera means "hole bearer".
  • Chief characteristics
  • Unicellular.
  • Related to the amoeba, with pseudopods.
  • Foraminifera build tiny shells (called tests)
    which grow by adding chambers.
  • Some species (called agglutinated foraminifera)
    construct tests of tiny particles of sediement.
    This is the earliest type of foram test.
  • Other forams construct tests of calcium

  • Geologic range Cambrian to Recent.Modes of
  • Benthic or benthonic (bottom dwellers)
  • Planktic or planktonic (floaters).

Fusulinid foraminifera (fusulinids)
  • Fusulinids were abundant in the Late Paleozoic
    (primarily Pennsylvanian and Permian).
  • Their tests were similar in size and shape to a
    grain of rice.
  • Their internal structure is complex and used to
    distinguish different species.
  • Important guide fossils in the Pennsylvanian and
    Permian because they evolved rapidly, were
    abundant, and widespread geographically.

  • Chief characteristics
  • Unicellular.
  • Test or shell composed of opaline silica
  • Ornate lattice-like skeleton
  • Often spherical or radially symmetrical with
  • Geologic range Precambrian or Cambrian to
    Recent. Rare in Lower Paleozoic rocks. More
    abundant in Mesozoic and Cenozoic.
  • Mode of life Planktonic. Marine only.

Radiolaria and the Rock Record
  • Radiolarians are important constituents of chert
    at certain times in geologic history.
  • Their tests accumulate on the seafloor today to
    form radiolarian ooze, particularly in deep
    water, where any calcium carbonate shells would
    be dissolved.

Marine Invertebrates in the Paleozoic Seas
  • The fossils of shell-bearing invertebrates that
    inhabited shallow seas are common in Paleozoic
  • Archaeocyathids, sponges, corals, bryozoans,
    trilobites, molluscs, and echinoderms.
  • Many were benthic (bottom dwellers), but others,
    such as graptolites, were planktonic. Currents
    carried them over wide areas.
  • As a result, they are useful index fossils for
    global stratigraphic correlation.

Phylum Archaeocyatha
  • Name means "ancient cup"
  • Chief characteristics Conical or vase-shaped
    skeletons made of calcium carbonate.
    Double-walled structure with partitions and
  • Geologic range Cambrian only. Extinct.
  • Mode of life Attached to the sea floor.

Phylum Porifera - The Sponges
  • Name means "pore-bearing". Covered by tiny

Phylum Porifera - The Sponges
  • Chief characteristics
  • Globular, cylindrical, conical or irregular
  • Basic structure is vase-like with pores and
  • Interior may be hollow or filled with branching
  • Solitary or colonial.
  • Skeletal elements are called spicules, and they
    may be separate or joined.
  • Composition may be calcareous, siliceous or
    organic material called spongin.

Phylum Cnidaria
  • Corals, sea fans, jellyfish, and sea anemones.
  • Name Cnidaria are named for stinging cells
    called cnidoblasts or cnidocytes.
  • Many are soft-bodied but only those which form
    hard skeletal structures are readily preservable
    as fossils.

Phylum Cnidaria
  • Geologic range Late Precambrian (Proterozoic) to
    Recent for the phylum.
  • The first corals were the tabulates.
  • Mode of life Corals live attached to the sea
    floor, primarily in warm, shallow marine

Phylum Cnidaria Chief Characteristics
  • Radial symmetry
  • Mouth at the center of a ring of tentacles.

Phylum Cnidaria Chief Characteristics
  • Body form may be polyp (attached to the bottom,
    with tentacles on top) or medusa (free-swimming,

Chief Characteristics of Corals
  • May be solitary or colonial. Colonies are
    composed of many polyps living together.
  • Hard calcareous skeleton. The skeletal parts
    formed by polyps are called corallites.
  • The "cup", in which an individual coral polyp
    sits, is called the theca. Each theca is small,
    and roughly circular or hexagonal.
  • The theca is divided internally by
    vertical partitions called septae,
    arranged in a radial pattern.

Chief Characteristics of Corals
  • Types of corals are distinguished by presence or
    absence, and number of septae
  • Rugose corals (or tetracorals) have septae
    arranged in multiples of four.
  • Tabulate corals lack septae.
  • The Mesozoic and Cenozoic scleractinian corals
    (or hexacorals) have septae arranged in multiples
    of six.

Rugose Corals
  • Most rugose corals are solitary and conical
    (shaped like ice cream cones).
  • Septae are visible in the circular opening of the
  • Some rugose corals are colonial, having hexagonal
    corallites with septae (such as Hexagonaria from
    the Devonian of Michigan).

Rugose Corals
  • Geologic range Ordovician to Permian - all
  • Rugose corals were abundant in the Devonian and
    Carboniferous, but became extinct during the Late

Tabulate Corals
  • Tabulate corals are colonial and resemble
    honeycombs or wasp nests.
  • They lack septae.
  • They have horizontal plates within the theca
    called tabulae. Tabulae are one of the main
    features of the tabulate corals.

Tabulate Corals
  • Geologic range Ordovician to Permian - all
  • The principal Silurian reef formers.
  • They declined after the Silurian and their
    reef-building role was assumed by the rugose

Modern Corals
  • Modern corals are scleractinian corals.
    Scleractinian corals have septae are arranged in
    multiples of six, and are sometimes called
  • Scleractinian corals did not appear until after
    the Paleozoic
  • Geologic range Triassic to Recent.

Phylum Bryozoa
  • Name Name means "moss" (bryo) "animal" (zoa).
  • Chief characteristics
  • Colonial (many microscopic individuals living
    physically united adjacent to one another).
  • The individuals are called zooids, and they are
    housed in a hard "capsule" called a zooecium.
  • The colony is called a zoarium.

Phylum Bryozoa
  • Individual zooecia (plural of zooecium) are very
    tiny (about the size of a pin-hole, a millimeter
    or less in diameter). They are just large enough
    to be seen with the unaided eye.
  • Bryozoans may be distinguished from corals
    because of the apertures in the skeleton are much

Phylum Bryozoa
  • The bryozoan colony may resemble lace or a tiny
    net, may be delicately branching, finger-like,
    circular or dome-shaped. There are more than 4000
    living species of bryozoans, and nearly 16,000
    fossil species.

Phylum Bryozoa
  • Geologic range Ordovician to Recent.
  • Mode of life Widespread in marine environments.
    A few live in freshwater lakes and streams.

Phylum Bryozoa
  • Archimedes, from the Mississippian period, has a
    cork-screw-like central axis with a fragile
    net-like colony around the outer edge.

Phylum Brachiopoda
  • Name Name means "arm" (brachio) "foot" (pod).
  • Chief characteristics
  • Bivalved (two shells), each with bilateral
    symmetry. The plane of symmetry passes through
    the center of each shell or valve.
  • The two valves differ in size and shape in most.
    Sometimes the larger valve will have an opening
    near the hinge line through which the pedicle
    extended in life.

Phylum Brachiopoda
  • Soft parts include a lophophore consisting of
    coiled tentacles with cilia. The lophophore
    circulates water between the two valves,
    distributing oxygen and flushing out carbon
    dioxide. Water movements caused by the lophophore
    also transport food particles toward the mouth.

Phylum Brachiopoda
  • Mode of life
  • Shallow marine environments.
  • Generally attached to the sea floor.
  • Inarticulate brachiopods are known to live in
    burrows in the sediment.
  • Brachiopods are filter feeders.

Phylum Brachiopoda
  • Geologic range
  • Lower Cambrian to Recent.
  • Very abundant during the Paleozoic.
  • A few species (belonging to only three families)
    remain today.

Inarticulate Brachiopods
  • Primitive brachiopods with phosphatic or
    chitinous valves.
  • No hinge. Spoon-shaped valves held together with
    muscles and soft parts.
  • Lingula is a well known genus
  • Geologic range
  • Lower Cambrian to Recent

Articulate Brachiopods
  • Calcareous valves attached together with a hinge
    consisting of teeth and sockets.
  • Geologic range Lower Cambrian to Recent
  • Spiny brachiopods (called productids) are
    characteristic of the Carboniferous and Permian.

Phylum Mollusca
  • Clams, oysters, snails, slugs, Nautilus, squid,
    octopus, cuttlefish
  • Name Mollusca means " soft bodied".

Phylum Mollusca
  • Chief characteristics
  • Soft body enclosed within a calcium carbonate
  • A few, like slugs and the octopus, have no shell.
  • Muscular part of body of clams and snails and
    some other groups of molluscs is called the foot.

Phylum Mollusca
  • Geologic range Cambrian to Recent.
  • Mode of life Marine, freshwater, or terrestrial.
    They may swim, float or drift, burrow into mud
    or sand, bore into wood or rock, attach
    themselves to rocks, or crawl.

Types of Molluscs
  • Monoplacophorans (Neopilina)
  • Polyplacophorans or amphineurans (chitons)
  • Bivalves or pelecypods (clams, scallops)
  • Gastropods (snails and slugs)
  • Cephalopods (squid, octopus, Nautilus)
  • Scaphopods (tusk shells)

Class Monoplacophora
  • Chief characteristics
  • Single shell resembling a flattened cone or cap.
  • Soft part anatomy shows pseudo-segmented
    arrangement of gills, muscles, and other organs.
    Suggests that the primitive mollusc was a
    segmented animal. Segmentation was lost
  • Monoplacophorans are regarded as ancestral to
    bivalves, gastropods, and cephalopods.

Class Monoplacophora
  • Name Monoplacophora means "single plate-bearer".
  • Geologic range Cambrian-Recent, but only known
    as fossils from Cambrian to Devonian. Living
    monoplacophorans found in deep water off Costa
    Rica in 1952 and named Neopilina. Considered to
    be a "living fossil" .

Class Amphineura or Polyplacophora The Chitons
  • Chief characteristics Chitons have 8 overlapping
    plates covering an ovoid, flattened body.

Class Amphineura or Polyplacophora The Chitons
  • Name Polyplacophora means " many plate-bearer" .
  • Geologic range Cambrian to Recent.

Class Bivalvia or Pelecypoda
  • Clams, oysters, scallops, mussels, rudists
  • Chief characteristics
  • Skeleton consists of two calcareous valves
    connected by a hinge.
  • Bilateral symmetry plane of symmetry passes
    between the two valves.

Class Bivalvia or Pelecypoda
  • Name Bivalvia means " two" (bi) " shells"
  • Geologic range Early Cambrian to Recent
  • Mode of life Marine and freshwater. Many species
    are infaunal burrowers or borers, and others are

Class Gastropoda
  • Snails and slugs
  • Chief characteristics
  • Asymmetrical, spiral-coiled calcareous shell.
  • Name means "stomach" (gastro) "foot" (pod).
  • Geologic range Early Cambrian to Recent.
  • Mode of life Marine, freshwater or terrestrial.

Class Cephalopoda
  • Squid, octopus, Nautilus, cuttlefish
  • Name means " head" (kephale) " foot" (pod).
  • Chief characteristics
  • Symmetrical cone-shaped shell with internal
    partitions called septae
  • Shell may be straight or coiled in a spiral which
    lies in a plane.
  • Smooth or contorted sutures visible on the
    outside of some fossils mark the place where
    septae join the outer shell.

Class Cephalopoda
  • Geologic range Late Cambrian to Recent.
  • Mode of life Marine only carnivorous
    (meat-eating) swimmers.
  • Types of Paleozoic cephalopods
  • Nautiloids
  • Ammonoids
  • Coleoids

Nautiloid Cephalopods
  • The shells of nautiloid cephalopods have smoothly
    curved septa, which produce simple, straight or
    curved sutures.
  • Geologic range Cambrian to Recent.

Ammonoid Cephalopods
  • Ammonoid cephalopods have complex, wrinkled or
    crenulated septa, which produce angular or
    dendritic sutures.
  • Geologic range Devonian to Cretaceous - all

Ammonoid Cephalopods
  • There are three basic types of sutures in
    ammonoid shells
  • Goniatite or goniatitic (septae have relatively
    simple, zig-zag undulations)
  • Ceratite or ceratitic (septae have smooth "hills"
    alternating with saw-toothed "valleys")
  • Ammonite or ammonitic (septae are complexly
    branching and tree-like or dendritic)

Types of Sutures in Cephalopods
Subclass Coleoidea
  • Belemnoids (belemnites)
  • Geologic range Mississippian to Eocene - all
  • Sepioids (cuttlefish)
  • Geologic range Jurassic to Recent
  • Teuthoids (squid)
  • Geologic range Jurassic to Recent
  • Octopods (octopus)
  • Geologic range Cretaceous to Recent

Order Belemnoidea - Belemnoids
  • The belemnoids have an internal calcareous shell
    (which resembles a cigar in size, shape, and
    color) called a rostrum
  • The front part of this shell is chambered, as in
    the nautiloids and ammonoids.
  • The rostrum is made of fibrous calcite, arranged
    in concentric layers.

Class Scaphopoda
  • Tusk shells or tooth shells
  • Chief characteristics Curved tubular shells open
    at both ends.
  • Geologic range Ordovician to Recent.
  • Mode of life Marine.

Phylum Arthropoda
  • Insects, spiders, shrimp, crabs, lobsters,
    barnacles, ostracodes, trilobites, eurypterids
  • Name means "jointed" (arthro) "foot" (pod).
  • Chief characteristics
  • Segmented body with a hard exterior skeleton
    composed of chitin (organic material).
  • Paired, jointed legs.
  • Highly developed nervous system and sensory

Phylum Arthropoda
  • Geologic range Cambrian to Recent.
  • Mode of life Arthropods inhabit a wide range of
    environments. Most fossil forms are found in
    marine or freshwater sediments.

Paleozoic Arthropods and Their Geologic Ranges
  • Trilobites - Cambrian to Permian
  • Horseshoe crabs - Silurian to Recent
  • Eurypterids - Ordovician to Permian
  • Arachnids - Late Silurian to Recent
  • Ostracodes - Cambrian to Recent
  • Onychophorans - Cambrian to Recent
  • Insects - Devonian to Recent

Subphylum Trilobita - Trilobites
  • Chief characteristics
  • Body has three-lobes
  • Skeleton composed of chitin, with calcium
  • Body is divided into three segments
  • Rigid head segment - cephalon
  • Jointed, flexible middle section - thorax
  • Rigid tail piece - pygidium

Subphylum Trilobita - Trilobites
  • Name Trilobite means "three" (tri) "lobed"
  • Geologic range Cambrian to Permian
  • Mode of life Exclusively marine. Most were
    bottom dwellers living in shallow shelf

Class Eurypterida - Eurypterids
  • Extinct scorpion-like or lobster-like arthropods.
  • Predators.
  • Up to 10 ft long.
  • Geologic range Ordovician to Permian. Most are
    Silurian and Devonian.
  • Mode of life Inhabited brackish estuaries.

Class Arachnida - Arachnids
  • Scorpions, spiders, ticks, and mites
  • Scorpions are the oldest arachnids with a fossil
  • Scorpions had evolved by the Late Silurian. The
    earliest ones appear to have lived in the water,
    because their fossils have gills.
  • Scorpions, spiders, and mites are found in
    Devonian rocks.
  • Geologic range Late Silurian to Recent.

Class Ostracoda -Ostracodes
  • The ostracodes are mainly microscopic in size.
  • Tiny bivalved shell encasing a shrimp-like
  • Geologic range Cambrian to Recent.
  • Mode of life Both marine and freshwater.

Class Onychophora
  • Onychophorans share many characteristics of
    segmented annelid worms and arthropods, and are
    considered to be intermediate in evolution
    between the two groups.
  • Geologic range Cambrian to Recent

The onycophoran, Aysheaia.
Class Hexapoda - Insects
  • The insects are among the most diverse
    living group on Earth, but they are rarely
    found as fossils.
  • Body is divided into three parts, head,
    thorax, and abdomen.
  • Thorax has six legs.
  • The earliest insects were wingless.
  • Winged insects appeared by the Pennsylvanian.
  • Geologic range Middle Devonian to Recent.

Phylum Echinodermata
  • Starfish, sea urchins, sand dollars, crinoids,
    blastoids, and others
  • Name Echinodermata means "spiny" (echinos)
    "skin" (derma).

Phylum Echinodermata
  • Chief characteristics Calcite skeleton with
    five-part symmetry, superimposed on primitive
    bilateral symmetry.
  • Echinoderms have a water vascular system with
    water in a system of tubes within the body.
  • Tube feet are soft, movable parts of the water
    vascular system which project from the body and
    are used in locomotion, feeding, respiration, and
    sensory perception.

Phylum Echinodermata
  • Geologic range Cambrian to Recent.
  • Mode of life Exclusively marine. Some are
    attached to the sea floor by a stem with "roots"
    called holdfasts others are free-moving bottom
  • Similarity of embryos between echinoderms and
    chordates suggests that they may be derived from
    a common ancestral form.

Class Crinoidea - Crinoids
  • Crinoids are animals which resemble flowers.
  • They consist of a calyx with arms, atop a stem of
    calcite disks called columnals.
  • The crinoid is attached to the sea floor by
    root-like holdfasts.
  • Some living crinoids are swimmers, and not
  • Over 1000 genera are known.

  • Geologic range Middle Cambrian to Recent.
  • Especially abundant during the Mississippian.

Class Blastoidea - Blastoids
  • Blastoids are extinct animals with an armless
    bud-like calyx on a stem.
  • About 95 genera are known.
  • A common genus is Pentremites.
  • Geologic range Ordovician to Permian - all

Class Asteroidea - Starfish
  • Starfish are star-shaped echinoderms with five
  • About 430 genera are known.
  • Geologic range Ordovician to Recent.

Class Ophiuroidea Brittle Stars
  • Brittle stars have 5 arms, like starfish, but the
    arms are thin and serpent-like.
  • About 325 genera are known.
  • Geologic range Ordovician to Recent.

Class Echninodea
  • Sand dollars and sea urchins
  • Echinoids are disk-shaped, biscuit-shaped, or
  • Viewed from above, they may be circular or
    somewhat irregular in shape, but with a five-part
  • About 765 genera are known.
  • Geologic range Ordovician to Recent.

Class Holothuroidea
  • Sea cucumbers
  • Soft-bodied echinoderms resembling cucumbers.
  • They have microscopic hard parts called sclerites
    in various shapes resembling hooks, wheels and
  • About 200 genera are known.
  • Geologic range Middle Cambrian?, Middle
    Ordovician to Recent

Class Edrioasteroidea
  • Edrioasteroids
  • A group that was probably ancestral to starfish
    and sea urchins.
  • Globular, discoidal, or cylindrical tests
    (shells), many of which had concave surfaces.
  • Geologic range Early Cambrian to Middle

Class Cystoidea
  • Cystoids
  • This primitive group had a calyx attached to the
    seafloor by a stem (like crinoids and blastoids).
  • Distinctive patterns of pores on the plates of
    the calyx.
  • Geologic range Cambrian to Late Devonian. Most
    common in Ordovician and Silurian.

The Echinoderm-Backbone Connection
  • Echinoderms are closely related to chordates (the
    group that includes the vertebrates).
  • The early cell division, embryonic development,
    and larvae of echinoderms resemble those of
    chordates, and are different from those of other
  • Biochemistry of echinoderms is also similar to
    that of chordates (chemical similarities
    associated with muscle activity and chemistry of
    oxygen-carrying pigments in the blood).

Phylum Hemichordata Class Graptolithina -
  • Name Graptolite means "write" (grapto) "stone"
    (lithos), because they resemble pencil marks on

  • Chief characteristics
  • Organic (chitinous) skeletons consisting of rows
    or lines of small tubes or cups, called thecae.
  • Tubes or cups branch off a main cord or tube
    called a stem or stipe.
  • Stipes may consist of one, two, or many branches.
  • Entire colony called a rhabdosome.
  • A filament at the lower end of the rhabdosome is
    called a nema.

  • Most graptolites are found flattened and
    carbonized in black shales and mudstones.
  • Geologic range Cambrian to Mississippian. (Most
    abundant in Ordovician and Silurian.)
  • Some living organisms which may be surviving
    descendants (living fossils) have been recovered
    in 1989 in the South Pacific and later in
  • Mode of Life Planktonic (colonies attached to

Phylum Chordata
  • Vertebrates, sea squirts or tunicates, lancelets
    such as Amphioxus.
  • Name "Chord" means "string", referring to the
    nerve cord and/or notochord.
  • Geologic range Cambrian to Recent.
  • Mode of life Varied. Among the vertebrates
    alone, various members are land dwellers,
    swimmers, or fliers. Paleozoic vertebrates were
    initially in the sea, but later colonized
    freshwater and land.

Phylum Chordata
  • Chief characteristics (some are embryonic)
  • Bilateral symmetry.
  • Gill slits. These slits are a series of openings
    that connect the inside of the throat to the
    outside of the "neck".
  • Dorsal nerve cord (sometimes called a spinal
    cord). The nerve cord runs down the "back",
    connecting the brain with the muscles and other