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Paleozoic Life and Earth History


Animal plankton are called zooplankton and are also mostly microscopic ... and how it eats. For example, an articulate brachiopod. is a benthic, epifaunal ... – PowerPoint PPT presentation

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Title: Paleozoic Life and Earth History

Paleozoic Life and Earth History
Study of Paleozoic Life
  • The history of Paleozoic life
  • a system of interconnected biologic and geologic
  • Evolution and plate tectonics are the forces that
    drove this system
  • The opening and closing of ocean basins,
  • transgressions and regressions of epeiric seas,
  • the formation of mountain ranges,
  • and the changing positions of the continents
  • these had a profound effect on the evolution of
    the marine and terrestrial communities

The Cambrian Explosion
  • At the beginning of the Paleozoic Era,
  • animals with skeletons appeared rather abruptly
    in the fossil record
  • In fact, their appearance is described
  • as an explosive development of new types of
  • and is referred to as the "Cambrian explosion"

Sharp Contrast
  • The sudden appearance of shelled animals during
    the Early Cambrian
  • contrasts sharply with the biota living during
    the Proterozoic Eon
  • Up until the evolution of the Ediacaran fauna,
  • Earth was populated primarily by single-celled
  • The Ediacaran fauna,
  • which is found on all continents except
  • consists primarily of multicelled soft-bodied

Triggering Mechanism
  • The mechanism that triggered this event is still
  • it was likely a combination of factors
  • both biological and geological
  • For example, geologic evidence
  • indicates Earth was glaciated one or more times
    during the Proterozoic,
  • followed by global warming during the Cambrian
  • These global environmental changes may have
    stimulated evolution
  • and contributed to the Cambrian explosion

Why Skeletons
  • Along with the question of
  • why did animals appear so suddenly in the fossil
  • is the equally intriguing one of
  • why they initially acquired skeletons
  • and what selective advantage this provided
  • A variety of explanations
  • about why marine organisms evolved skeletons have
    been proposed,
  • but none is completely satisfactory or
    universally accepted

Advantages of an Exoskeleton
  • The formation of an exoskeleton
  • confers many advantages on an organism
  • It provides protection against ultraviolet
    radiation, allowing animals to move into
    shallower waters
  • (2) it helps prevent drying out in an intertidal
  • (3) it provides protection against predators
  • Recent evidence of actual fossils of predators
    and specimens of damaged prey,
  • as well as antipredatory adaptations in some
  • indicates that the impact of predation during the
    Cambrian was great

Cambrian Predation
  • Anomalocaris

Evidence of Predation
Advantages of an Exoskeleton
  • With predators playing an important role in the
    Cambrian marine ecosystem,
  • any mechanism or feature that protected an animal
    would certainly be advantageous
  • and confer an adaptive advantage to the organism
  • (4) A fourth advantage is that a supporting
  • allows animals to increase their size
  • and provides attachment sites for muscles

Mineralized Skeletons Were Successful
  • Whatever the reason,
  • the acquisition of a mineralized skeleton was a
    major evolutionary innovation
  • allowing invertebrates to successfully occupy a
    wide variety of marine habitats

Marine Invertebrate Communities
  • In order to understand the evolution of the
    marine invertebrate communities through time,
  • concentrating on the major features and changes
    that took place
  • We need to briefly examine the nature and
    structure of living marine communities
  • so that we can make a reasonable interpretation
    of the fossil record

The Present Marine Ecosystem
  • In analyzing the present-day marine ecosystem,
  • we must look at where organisms live,
  • how they get around,
  • as well as how they feed
  • Organisms that live in the water column above the
    seafloor are called pelagic
  • They can be divided into two main groups
  • the floaters, or plankton,
  • and the swimmers, or nekton

  • Plankton are mostly passive and go where currents
    carry them
  • Plant plankton
  • such as diatoms, dinoflagellates, and various
  • are called phytoplankton and are mostly
  • Animal plankton are called zooplankton and are
    also mostly microscopic
  • Examples of zooplankton include foraminifera,
    radiolarians, and jellyfish

  • The nekton are swimmers
  • and are mainly vertebrates
  • such as fish
  • the invertebrate nekton
  • include cephalopods

  • Organisms that live on or in the seafloor make up
    the benthos
  • They can be characterized
  • as epifauna (animals) or epiflora (plants),
  • for those that live on the seafloor,
  • or as infauna,
  • which are animals living in and moving through
    the sediments

Sessile and Mobile
  • The benthos can be further divided
  • into those organisms that stay in one place,
    called sessile,
  • and those that move around on or in the seafloor,
    called mobile

Marine Ecosystem
  • Where and how animals and plants live in the
    marine ecosystem

Feeding Strategies
  • The feeding strategies of organisms
  • are also important in terms of their
  • with other organisms in the marine ecosystem
  • There are basically four feeding groups
  • suspension-feeding animals remove or consume
    microscopic plants and animals as well as
    dissolved nutrients from the water
  • herbivores are plant eaters
  • carnivore-scavengers are meat eaters
  • and sediment-deposit feeders ingest sediment and
    extract the nutrients from it

Marine Ecosystem
Organism's Place
  • We can define an organism's place
  • in the marine ecosystem
  • by where it lives
  • and how it eats
  • For example, an articulate brachiopod
  • is a benthic,
  • epifaunal suspension feeder,
  • whereas a cephalopod
  • is a nektonic carnivore

Trophic Levels
  • An ecosystem includes several trophic levels,
  • which are tiers of food production and
  • within a feeding hierarchy
  • The feeding hierarchy
  • and hence energy flow in an ecosystem comprise
  • a food web of complex interrelationships among
  • the producers,
  • consumers,
  • and decomposers

Primary Producers
  • The primary producers, or autotrophs,
  • are those organisms that manufacture their own
  • Virtually all marine primary producers are
  • Feeding on the primary producers
  • are the primary consumers, which are mostly
    suspension feeders

Other Consumers
  • Secondary consumers feed on
  • the primary consumers,
  • and thus are predators, while tertiary consumers,
    which are also predators, feed on the secondary
  • Besides the producers and consumers,
  • there are also transformers and decomposers
  • These are bacteria that break down the dead
  • that have not been consumed
  • into organic compounds that are then recycled

Marine Food Web
  • Showing the relationships
  • among the
  • producers,
  • consumers,
  • and decomposers

When the System Changes
  • When we look at the marine realm today,
  • we see a complex organization of organisms
  • interrelated by trophic interactions
  • and affected by changes in the physical
  • When one part of the system changes, the whole
    structure changes,
  • sometimes almost insignificantly,
  • other times catastrophically

Changing Marine Ecosystem
  • As we examine the evolution of the Paleozoic
    marine ecosystem,
  • keep in mind how geologic and evolutionary
    changes can have a significant impact on its
    composition and structure

Changing Marine Ecosystem
  • For example, the major transgressions onto the
  • opened up vast areas of shallow seas
  • that could be inhabited
  • The movement of continents
  • affected oceanic circulation patterns
  • as well as causing environmental changes

Cambrian Skeletonized Life
  • Although almost all the major invertebrate phyla
    evolved during the Cambrian Period
  • many were represented by only a few species

Cambrian Skeletonized Life
  • the organisms that comprised the majority of
    Cambrian skeletonized life were
  • trilobites,
  • inarticulate brachiopods,
  • and archaeocyathids

Cambrian Permian
  • Trilobites
  • were by far the most conspicuous element of the
    Cambrian marine invertebrate community
  • and made up about half of the total fauna
  • Trilobites were
  • benthic
  • mobile
  • sediment-deposit feeders
  • that crawled or swam along the seafloor

  • They first appeared in the Early Cambrian,
  • rapidly diversified,
  • reached their maximum diversity in the Late
  • and then suffered mass extinctions near the end
    of the Cambrian
  • from which they never fully recovered
  • As yet no consensus exists on what caused the
    trilobite extinctions,

Trilobite Extinctions
  • but a combination of factors were likely
  • including possibly a reduction of shelf space,
  • increased competition,
  • and a rise in predators
  • It has also been suggested
  • that a cooling of the seas may have played a
  • particularly for the extinctions that took place
    at the end of the Ordovician Period

Cambrian Brachiopods
  • Cambrian brachiopods
  • were mostly primitive types called inarticulates
  • They secreted a chitinophosphate shell,
  • Inarticulate brachiopods
  • also lacked a tooth-and-socket-arrangement along
    the hinge line of their shells
  • They were
  • benthic
  • Epifaunal
  • Suspension-feeders

  • The third major group of Cambrian organisms
  • were the archaeocyathids
  • These organisms
  • were benthic sessile suspension feeders
  • that constructed reeflike structures

Ordovician Marine Community
  • A major transgression
  • that began during the Middle Ordovician
    (Tippecanoe sequence)
  • resulted in the most widespread inundation of the
  • This vast epeiric sea,
  • which experienced a uniformly warm climate during
    this time,
  • opened numerous new marine habitats
  • that were soon filled by a variety of organisms

The Tippecanoe Sequence
Striking Changes in Ordovician
  • the Ordovician was characterized by the adaptive
    radiation of many other animal phyla,
  • such as articulate brachiopods,
  • bryozoans,
  • and corals
  • with a consequent dramatic increase in the
    diversity of the total shelly fauna
  • and the start of large-scale reef building

Middle Ordovician Seafloor Fauna
  • Recreation of a Middle Ordovician seafloor fauna
    with cephalopods, crinoids, colonial corals,
    trilobites, and brachiopods

  • The Ordovician was also a time
  • of increased diversity and abundance of the
  • organic-walled phytoplankton of unknown affinity
  • which were the major phytoplankton group of the
    Paleozoic Era
  • and the primary food source of the suspension

Ordovician Reef Builders
  • During the Cambrian, archaeocyathids
  • were the main builders of reeflike structures,
  • but beginning in the Middle Ordovician
  • bryozoans, stromatoporoids,
  • and tabulate and rugose corals
  • assumed that role

Biostratigraphic Correlation
  • Three Ordovician fossil groups have proved to be
    particularly useful for biostratigraphic
  • the articulate brachiopods,
  • graptolites,
  • and conodonts
  • The articulate brachiopods,
  • present since the Cambrian,
  • began a period of major diversification in the
    shallow-water marine environment during the

  • Most graptolites were
  • planktonic animals carried about by ocean
  • Because most graptolites were planktonic
  • and most individual species existed for less than
    a million years,
  • graptolites are excellent guide fossils
  • They were especially abundant
  • during the Ordovician and Silurian periods

  • Conodonts are a group of well-known small
    toothlike fossils
  • composed of the mineral apatite
  • (calcium phosphate)
  • the same mineral that composes bone
  • Although conodonts have been known for more than
    130 years,
  • their affinity has been the subject of debate
  • until the discovery of the conodont animal in 1983

  • The conodont animal
  • preserved as a carbonized impression 40 x 2 mm
  • in the Lower Carboniferous Granton Shrimp Bed in
    Edinburgh, Scotland

Mass Extinctions
  • The end of the Ordovician was a time of mass
    extinctions in the marine realm
  • More than 100 families of marine invertebrates
    became extinct,
  • and in North America alone,
  • approximately one-half of the brachiopods and
    bryozoans died out
  • What caused such an event?
  • Many geologists think these extinctions were the
    result of the extensive glaciation
  • that occurred in Gondwana
  • at the end of the Ordovician Period

Mass Extinctions
  • Mass extinctions,
  • geologically rapid events in which an unusually
    high percentage of the fauna and/or flora becomes
  • have occurred throughout geologic time
  • for instance, at or near the end of the
  • Ordovician,
  • Devonian,
  • Permian,
  • and Cretaceous periods
  • and are the focus of much research and debate

Silurian and Devonian Marine Communities
  • The mass extinction at the end of the Ordovician
    was followed by rediversification
  • and recovery of many of the decimated groups
  • Brachiopods, bryozoans, gastropods, bivalves,
    corals, crinoids, and graptolites
  • were just some of the groups that rediversified
  • beginning during the Silurian

Silurian and Devonian Reefs
  • The Silurian and Devonian reefs
  • were dominated by
  • tabulate and colonial rugose corals and
  • While the fauna of these Silurian and Devonian
  • was somewhat different from that of earlier reefs
    and reeflike structures,
  • the general composition and structure are the
    same as in present-day reefs

  • The Silurian and Devonian periods
  • were also the time when eurypterids
  • arthropods with scorpion-like bodies and
    impressive pincers
  • were abundant, especially in brackish and
    freshwater habitats

  • Ammonoids are excellent guide fossils for the
    Devonian through Cretaceous
  • short stratigraphic ranges,
  • and widespread distribution
  • a subclass of the cephalopods,
  • evolved from nautiloids during the Early Devonian
  • and rapidly diversified

Another Mass Extinction
  • Another mass extinction occurred near the end of
    the Devonian
  • and resulted in a worldwide near-total collapse
    of the massive reef communities
  • On land, however, the seedless vascular plants
  • were seemingly unaffected,
  • although the diversity of freshwater fish
  • was greatly reduced
  • Thus, extinctions at this time
  • were most extensive in the marine realm,
  • particularly in the reef and pelagic communities

Global Cooling
  • The demise of the Middle Paleozoic reef
  • serves to highlight the geographic aspects
  • of the Late Devonian mass extinction
  • The tropical groups were most severely affected
  • in contrast, the polar communities were seemingly
    little affected
  • Apparently, an episode of global cooling was
    largely responsible for the extinctions near the
    end of the Devonian

Rapid Recovery
  • The brachiopods and ammonoids
  • quickly recovered
  • and again assumed important ecological roles,
  • while other groups, such as the lacy bryozoans
    and crinoids,
  • reached their greatest diversity during the
  • With the decline of stromatoporoids and tabulate
    and rugose corals,
  • large organic reefs virtually disappeared
  • and were replaced by small patch reefs

Mississippian Patch Reefs
  • These patch reefs were dominated by
  • crinoids, blastoids, lacy bryozoans, brachiopods,
    and calcareous algae
  • and flourished during the Late Paleozoic
  • In addition, bryozoans and crinoids contributed
    large amounts of skeletal debris
  • to the formation of the vast bedded limestones
  • that constitute the majority of Mississippian
    sedimentary rocks

The Permian Marine Invertebrate Extinction Event
  • The greatest recorded mass-extinction event
  • occurred at the end of the Permian Period
  • Before the Permian ended,
  • roughly 50 of all marine invertebrate families
  • and about 90 of all marine invertebrate species
    became extinct

Phanerozoic Diversity
  • Diversity for marine invertebrate and vertebrate
  • 3 episodes of Paleozoic mass extinction are
  • with the greatest occurring at the end of the
    Permian Period

  • Source Gibbs, On the Termination of Species,
    Scientific American Nov. 2001

  • Fusulinids, rugose and tabulate corals, several
    bryozoan and brachiopod orders,
  • as well as trilobites and blastoids
  • did not survive the end of the Permian
  • All of these groups had been very successful
    during the Paleozoic Era
  • In addition, more than 65 of all amphibians and
  • as well as nearly 33 of insects on land also
    became extinct

Mass Extinction
  • Some scenarios put forth to explain the
    extinctions include
  • (1) a meteorite impact such as occurred at the
    end of the Cretaceous Period
  • (2) a widespread marine regression resulting from
    glacial conditions,
  • (3) a reduction in shelf space due to the
    formation of Pangaea
  • (4) climatic changes,
  • (5) oceanographic changes such as anoxia,
    salinity changes, and turnover of deep-ocean

Permian Mass Extinction
  • It appears that the Permian mass extinction took
    place over an 8-million-year interval
  • which would seemingly rule out a meteorite impact
  • although, meteorite impact may have contributed
    to the Permian mass extinction
  • The second and third hypotheses can probably be
  • because most of the collisions of the continents
    had already taken place by the end of the Permian
  • and the large-scale formation of glaciers took
    place during the Pennsylvanian Period

Climatic Changes
  • Currently, many scientists think that a
    large-scale marine regression
  • coupled with climatic changes in the form of
    global warming
  • due to an increase in carbon dioxide levels
  • may have been responsible for the Permian mass
  • In this scenario, a widespread lowering of sea
    level occurred near the end of the Permian
  • thus greatly reducing the amount of shallow shelf
    space for marine organisms
  • and exposing the shelf to erosion

Impact from the Deep
  • A new model suggest intense global warming could
    trigger deaths in the sea and on land
  • Trouble begins with widespread volcanic activity
    that releases enormous volumes of carbon dioxide
    and methane
  • The gases cause rapid global warming
  • A warmer ocean absorbs less oxygen from the
  • low oxygen (anoxia) destabilizes the chemocline,
    where oxygenated water meets water permeated with
    hydrogen sulfide (H2S) generated by
    bottom-dwelling anaerobic bacteria
  • as H2S concentrations build and oxygen falls, the
    chemocline rises abruptly to the ocean surface

Impact from the Deep
  • green and purple photosynthesizing sulfur
    bacteria, which consume H2S and normally live at
    chemocline depth, now inhabit the H2S-rich
    surface waters while oxygen-breathing ocean life
  • H2S also diffuses into the air, killing animals
    and plants on land
  • and rising to the troposphere to attack the
    planets ozone layer
  • without the ozone shield, the suns ultraviolet
    (UV) radiation kills remaining life

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Burgess Shale Soft-Bodied Fossils
  • On August 30 and 31, 1909,
  • Charles D. Walcott,
  • geologist and head of the Smithsonian
  • discovered the first soft-bodied fossils
  • from the Burgess Shale (British Columbia, Canada)
  • a discovery of immense importance in deciphering
    the early history of life
  • yielded the impressions of a number of
    soft-bodied organisms
  • beautifully preserved on bedding planes
  • soft-bodied animals that lived some530 million
    years ago
  • present a much more complete picture of a Middle
    Cambrian community
  • than deposits containing only fossils of the hard
    parts of organisms

Sixty Percent Soft-Bodied
  • 60 of the total fossil assemblage of more than
    100 genera is composed of soft-bodied animals,
  • a percentage comparable to present-day marine
  • The site of deposition of the Burgess Shale
  • was located at the base of a steep submarine
  • Periodically, this unstable area
  • would slump and slide down the escarpment
  • as a turbidity current
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