Transcript Chapter 12 - FacultyWeb

Chapter 12
Paleozoic Life History: Invertebrates
main points this chapter1. animals with skeletons appear in Cambrian
2. ecosystem interacts with environment
3. Cambrian-evolutionary innovations
4. Ordovician- dramatic increase in diversity,
mass extinction at end Ordovician
5. Silurian& Devonian: re diversification
after end Ord mass extinction; major reef building
6. Late Devonian extinctions: marine community
again re diversified, with new organisms
7. end of Permian- greatest mass extinction in
Earth’s history occurred
Study of Paleozoic Life
• We will examine the history of Paleozoic life
– as a system of interconnected biologic and geologic
events
• 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
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 animals
– and is referred to as
– the "Cambrian explosion" by most scientists
– It is rapid, however, only in the context of geologic
time, having taken place over millions of years
Burgess Shale Soft-Bodied Fossils
• On August 30 and 31, 1909,
– Charles D. Walcott,
• geologist and head of the Smithsonian Institution,
– discovered the first soft-bodied fossils
– from the Burgess Shale,
– a discovery of immense importance in deciphering
the early history of life
• Walcott and his collecting party split open
numerous blocks of shale,
– many of which yielded the impressions
– of a number of soft-bodied organisms
– beautifully preserved on bedding planes
More Complete Picture of a
Middle Cambrian Community
• The importance of Walcott's discovery
– is that it allowed geologists a rare glimpse into a
world previously almost unknown
– that of the soft-bodied animals that lived some
530 million years ago
• The beautifully preserved fossils
–
–
–
–
from the Burgess Shale
present a much more complete picture
of a Middle Cambrian community
than deposits containing only fossils of the hard
parts of organisms
Burgess
Shale
• Diorama of the
environment
and biota
– of the
Phyllopod bed
of the Burgess
Shale,
• British
Columbia,
Canada
• algae
• sponges
• among others
Sixty Percent Soft-Bodied
• In fact, 60% of the total fossil assemblage
– of more than 100 genera is composed of softbodied animals,
– a percentage comparable to present-day marine
communities
• What conditions led to the remarkable
preservation of the Burgess Shale fauna?
• The site of deposition of the Burgess Shale
– was located at the base of a steep submarine
escarpment
Reason for the Preservation
• The animals
–
–
–
–
whose exquisitely preserved fossil remains
are found in the Burgess Shale
lived in and on mud banks
that formed along the top of this escarpment
• Periodically, this unstable area
– would slump and slide down the escarpment
– as a turbidity current
• At the base, the mud and animals carried with it
– were deposited in a deep-water anaerobic
environment devoid of life
Carbonaceous Impressions
• In such an environment,
– bacterial degradation did not destroy the buried
animals
– and they were compressed by the weight of the
overlying sediments
– and eventually preserved as carbonaceous
impressions
Rare Preservation: Burgess Shale
• Ottoia, a carnivorous worm
Rare Preservation: Burgess Shale
• Wiwaxia, a scaly
armored sluglike
creature whose
affinities remain
controversial
Rare Preservation: Burgess Shale
• Hallucigenia, a velvet worm
Rare Preservation: Burgess Shale
• Waptia, an anthropod
Basic Body Plans
• These were followed by
– an explosion of invertebrate phyla
– during the Cambrian,
– some of which are now extinct
• These Cambrian phyla
– represent the rootstock
– and basic body plans
– from which all present-day invertebrates evolved
Strangeness of the
Burgess Shale Biota
• In other words, life was much more diverse
– in terms of phyla
– during the Cambrian
– than it is today
• The reason members of the Burgess Shale biota
–
–
–
–
look so strange to us
is that no living organisms
possess their basic body plan,
and therefore many of them have been placed into
new phyla
Triggering Mechanism
• It appears likely that the Cambrian explosion
– probably had its roots firmly planted in the
Proterozoic
• However, the mechanism
– that triggered this event is still unknown and
– 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
Major Event in Earth's History
• Whatever the ultimate cause of the Cambrian
explosion,
–
–
–
–
the appearance of a skeletonized fauna
and the rapid diversification of that fauna
during the Early Cambrian
was a major event in Earth's history
Sharp Contrast
• The sudden appearance of shelled animals
– during the Early Cambrian
– contrasts sharply with the biota living
– during the preceding Proterozoic Eon
• Up until the evolution of the Ediacaran fauna,
– Earth was populated primarily
– by single-celled organisms
• The Ediacaran fauna,
• which is found on all continents except Antarctica,
– consists primarily of multicelled soft-bodied
organisms
Lower Cambrian Shelly Fossil
•
The tube of an anabaritid from the
Mackenzie Mountains, Northwest
Territories, Canada
– This specimen is several millimeters
in size
Archaeooides, an enigmatic spherical
fossil from the Mackenzie Mountains,
Northwest Territories, Canada
A conical sclerite* of
Lapworthella from Australia
•a piece of the armor
covering
Why Skeletons
• Along with the question of
– why did animals appear so suddenly in the fossil
record
– 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:
(1) It provides protection against ultraviolet radiation,
allowing animals to move into shallower waters;
(2) it helps prevent drying out in an intertidal
environment;
(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 animals,
• indicates that the impact of predation during the
Cambrian was great
Cambrian Predator
• Reconstruction of Anamalocaris
– a predator from the Early and Middle Cambrian
– It was about 45 cm long and probably fed on
trilobites
– Its gripping appendages presumably carried food to
its mouth
Wounded Trilobite
• Wounds to the body of the trilobite Olenellus
robsonensis
– The wounds have healed, demonstrating that they
occurred when the animal was alive and were not
inflicted on an empty shell
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 skeleton, whether an exo- or
endoskeleton,
– allows animals to increase their size
– and provides attachment sites for muscles
It Is Unknown Why Organisms
Evolved Mineralized Skeletons
• There currently is no clear answer about
– why marine organisms evolved mineralized
skeletons
– during the Cambrian explosion and shortly
thereafter
• They undoubtedly evolved
– because of a variety of biologic and environmental
factors
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
• Rather than focusing on
– the history of each invertebrate phylum,
– we will survey the evolution
– of the marine invertebrate communities through
time,
– concentrating on the major features and changes
that took place
• To do that, 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
• Plankton are mostly passive and go where
currents carry them
– Plant plankton
• such as diatoms, dinoflagellates, and various algae,
– are called phytoplankton and are mostly
microscopic
– Animal plankton are called zooplankton and are
also mostly microscopic
• Examples of zooplankton include foraminifera,
radiolarians, and jellyfish
Nekton
• The nekton are swimmers
– and are mainly vertebrates
• such as fish;
– the invertebrate nekton
• include cephalopods
Benthos
• 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
Plankton:
Sessile epiflora:
Nekton: fish
cephalopod
seaweed
Jelly fish
Sessile epifauna:
Benthos: d-k
bivalve
coral
crinoid
Marine Ecosystem
Infauna:
worm,
bivalve
Mobile epifauna: gastropod, starfish
Feeding Strategies
• The feeding strategies of organisms
– are also important in terms of their relationships
– 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
coral
crinoid
bivalve
Suspension feeders:
Marine Ecosystem
worm
sedimentdeposit feeder
Herbivores: gastropod
Carnivores-scavengers: starfish
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 benthonic,
– 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 consumption
– 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
food
• Virtually all marine primary producers are
phytoplankton
• 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
consumers
• Besides the producers and consumers,
– there are also transformers and decomposers
• These are bacteria that break down the dead
organisms
– 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
environment
• 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
• For example, the major transgressions onto the craton
– 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
This one slide says it all…..
Cambrian Marine Community
• The Cambrian Period was a time
– during which many new body plans evolved
– and animals moved into new niches
• As might be expected, the Cambrian
– witnessed a higher percentage of such experiments
– than any other period of geologic history
Cambrian Skeletonized Life
• Although almost all the major invertebrate
phyla
– evolved during the Cambrian Period
– many were represented by only a few species
• While trace fossils are common
– and echinoderms diverse,
• the organisms that comprised the majority of
Cambrian skeletonized life were
– trilobites,
– inarticulate brachiopods,
– and archaeocyathids
Cambrian Marine Community
• Floating jellyfish, swimming arthropods,
benthonic sponges, and scavenging trilobites
Reconstruction
Trilobites
• 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
–
–
–
–
benthonic
mobile
sediment-deposit feeders
that crawled or swam along the
seafloor
Trilobites
• They first appeared in the Early Cambrian,
–
–
–
–
–
–
rapidly diversified,
reached their maximum diversity
in the Late Cambrian,
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
involved,
– 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 role,
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,
– composed of the organic
compound chitin
– combined with calcium
phosphate
• Inarticulate brachiopods
– also lacked a tooth-and-socketarrangement
– along the hinge line of their
shells
Articulate Brachiopods
• The articulate brachiopods,
–
–
–
–
which have a tooth-and-socket arrangement,
were also present
but did not become abundant
until the Ordovician Period
Archaeocyathids
• The third major group of Cambrian organisms
– were the archaeocyathids
• These organisms
– were benthonic sessile suspension feeders
– that constructed reeflike structures
• The rest of the Cambrian fauna
–
–
–
–
consisted of representatives
of the other major phyla,
including many organisms
that were short-lived evolutionary experiments
Cambrian Reef-like Structure
• Restoration of a Cambrian reeflike structure
built by archeocyathids
Ordovician Marine Community
• A major transgression that began
– during the Middle Ordovician (Tippecanoe
sequence)
– resulted in the most widespread inundation of the
craton
• 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
Striking Changes in Ordovician
• Both sedimentation patterns and fauna
– underwent striking changes
– from the Cambrian to the Ordovician,
• Whereas the Cambrian invertebrate community
– was dominated by trilobites, inarticulate
brachiopods, and archaeocyathids,
• 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
Middle Ordovician Seafloor Fauna
• Recreation of a Middle Ordovician seafloor
fauna with cephalopods, crinoids, colonial
corals, trilobites, and brachiopods
Acritarchs
• The Ordovician was also a time
– of increased diversity and abundance
– of the acritarchs
• organic-walled phytoplankton of unknown affinity
–
–
–
–
which were the major phytoplankton group
of the Paleozoic Era
and the primary food source
of the suspension feeders
Upper Ordovician Acritarch
• Acritarch from the
Upper Ordovician
Sylvan Formation,
Oklahoma
• Acritarchs are
organic-walled
phytoplankton
– and were the
primary food source
of suspension
feeders during the
Paleozoic Era
Upper Ordovician Acritarch
• Acritarch from the
Upper Ordovician
Sylvan Formation,
Oklahoma
• Acritarchs are
organic-walled
phytoplankton
– and were the
primary food source
of suspension
feeders during the
Paleozoic Era
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
• Many of these reefs
–
–
–
–
were small patch reefs similar in size
to those of the Cambrian
but of a different composition,
whereas others were quite large
Biostratigraphic Correlation
• Three Ordovician fossil groups
– have proved to be particularly useful
– for biostratigraphic correlation
• 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 Ordovician
Brachiopods
Brachiopods became a conspicuous element
of the invertebrate fauna
during the Ordovician
and in succeeding Paleozoic periods
Graptolites
• Most graptolites were
– planktonic animals carried about by ocean currents
• 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
• Due to the fragile nature of their organic skeleton,
– graptolites are most commonly found in black shales
Conodonts
• Conodonts are microscopic toothlike
fossils composed of the mineral apatite
• (calcium phosphate)
• Cahabagnathus sweeti, Copenhagen Formation
– Middle Ordovician, Monitor Range, Nevada
Several specimens of carbonized impressions
of the conodont animal from Lower Carboniferous
rocks of Scotland reveal that it is a member of a group
of primitive jawless animals assigned to the phylum Chordata
Study of the specimens indicates that the conodont animal
was probably an elongate swimming organism
Excellent Guide Fossils
• The wide distribution
– and short stratigraphic range of individual
conodont species
– Distinctiveness make them excellent fossils
– for biostratigraphic zonation and correlation
Paleogeography of the World
• For the Late Ordovician Period
Paleogeography of the World
• For the Late Devonian Period
Eurypterids and Ammonoids
• 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,
– a subclass of the cephalopods,
– evolved from nautiloids
– during the Early Devonian and rapidly diversified
Silurian Brackish-Marine Scene
• Restoration of a
Silurian brackishmarine bottom scene
– near Buffalo New York
– with algae, eurypterids,
gastropods, worms,
and shrimp
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
Massive Reef Builders
• Recall that the Silurian and Devonian
– were times of major reef building
• While most of the Silurian radiations of
invertebrates
– represented repopulating of niches,
• organic reef builders diversified in new ways,
-building massive reefs
– larger than any produced
– during the Cambrian or Ordovician
Silurian and Devonian Reefs
• The Silurian and Devonian reefs
– were dominated by
– tabulate and colonial rugose corals and
stromatoporoids
• While the fauna of these Silurian and Devonian
reefs
–
–
–
–
was somewhat different
from that of earlier reefs and reeflike structures,
the general composition and structure
are the same as in present-day reefs
Middle Devonian Reef
• Reconstruction of a
Middle Devonian reef
from the Great Lakes
area
– with corals,
cephalopods, trilobites,
crinoids, and
brachiopods
Ammonoids
• Ammonoids are excellent guide fossils
–
–
–
–
for the Devonian through Cretaceous periods
with their distinctive suture patterns,
short stratigraphic ranges,
and widespread distribution
Ammonoid Cephalopod
• Imitoceras rotatorium (DeKoninck), an
ammonoid cephalopod
– from the Lower
Mississippian
Rockford Limestone,
near Rockford,
Indiana
– The distinctive suture
pattern, short
stratigraphic range,
and wide distribution
make ammonoids
excellent guide
fossils
Mass Extinctions
• Mass extinctions,
– those geologically rapid events
– in which an unusually high percentage
– of the fauna and/or flora becomes extinct,
• 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
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
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
communities
– 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
Actors in Extinctions
• During such a cooling,
– the disappearance of tropical conditions
– would have had a severe effect on reef
– and other warm-water organisms
• Cool-water species, on the other hand,
– could have simply migrated toward the equator
• The closing of the Iapetus Ocean
–
–
–
–
and the orogenic events of the Late Devonian
undoubtedly also played a role in these extinctions
by reducing the area of shallow shelf environments
where many marine invertebrates lived
Carboniferous and Permian
Marine Communities
• The Carboniferous invertebrate marine
community
–
–
–
–
–
responded to the Late Devonian extinctions
in much the same way as
the Silurian invertebrate marine community
responded to the Late Ordovician extinctions
that is, by renewed adaptive radiation and
rediversification
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
Carboniferous
• 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
Mississippian Marine Life
• Based on a fossil site in the Upper
Mississippian at Crawford, Indiana
• Invertebrate animals shown
include
– blastoids
– crinoids
– lacy bryozoans
– brachiopods
– small corals
Restricted Permian
Marine Faunas
• The Permian invertebrate marine faunas
–
–
–
–
–
resembled Carboniferous faunas,
but were not as widely distributed
because of the restricted size of the shallow seas
on the cratons and the reduced shelf space
along the continental margins
Permian Period
• Paleogeography of North
America during the
Permian Period
Productid Brachiopods
• The spiny and odd-shaped productids
–
–
–
–
dominated the brachiopod assemblage
and constituted an important part
of the reef complexes
that formed in the Texas region during the Permian
Permian Patch-Reef Community
• From Glass Mountains of
West Texas
– including algae, productid
brachiopods, cephalopods,
sponges, and corals
Fusulinid
• Fusulinids are spindleshaped, microscopic
benthonic foraminifera
that are excellent
guide fossils for the
Pennsylvanian and
Permian periods
– Cross section of
Leptotriticites tumidus,
Lower Permian,
Kansas
The Permian Marine Invertebrate
Extinction Event
• The greatest recorded mass-extinction event
– to affect Earth
– 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 vertebrate species
became extinct
Phanerozoic Diversity
• Diversity for marine invertebrate and vertebrate
families
– 3 episodes of
Paleozoic
mass
extinction
are visible
– with the
greatest
occurring at
the end of
the Permian
Period
Casualties
• 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 reptiles,
– as well as nearly 33% of insects on land also
became extinct
Mass Extinction
• What caused such a crisis
– for both marine and land-dwelling organisms?
• Various hypotheses have been proposed,
– but no completely satisfactory answer
– has yet been found
• 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,
Permian Mass Extinction
– (3) a reduction in shelf space due to the formation
of Pangaea,
– (4) climatic changes, and
– (5) oceanographic changes such as anoxia, salinity
changes, and turnover of deep-ocean waters
• It appears that the Permian mass extinction
– took place over an 8-million-year interval
– at the end of the Permian Period,
– which would seemingly rule out a meteorite impact
Sudden Warming
• However, recent findings indicate the
possibility
– that a meteorite impact may have contributed to the
Permian mass extinction
• The second and third hypotheses
–
–
–
–
–
can probably be eliminated
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
• In addition, current evidence indicates
– a time of sudden warming at the end of the Permian
Climatic Changes
• Currently, many scientists think that a largescale 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
extinctions
• 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
Carbon Dioxide
• Oxidation of the organic matter trapped in the
sediments ensued,
– which reduced atmospheric oxygen levels
– as well as releasing large quantities of carbon
dioxide into the atmosphere,
– resulting in increased global warming
• During this time, widespread volcanic eruptions
also took place,
– further releasing additional carbon dioxide
– into the atmosphere
– and contributing to increased climatic instability
and ecological collapse
Rise in Sea Level
• At the end of the Permian,
–
–
–
–
a rise in sea level flooded and destroyed
the nearshore terrestrial habitats,
thus causing the extinction
of many terrestrial plants and animals
• Some scientists also suggest
– that a global turnover of deep-ocean water
– would have increased the amount of carbon dioxide
– in the surface waters as well as releasing large
amounts of carbon dioxide into the atmosphere
End Result the Same
• The end result would be the same
– global warming: 245 Million years ago!!
– and disruption of the marine and terrestrial
ecosystems
Biota Dramatically Changed
• Regardless of the ultimate cause
– of the Permian mass extinctions,
– the fact is that Earth's biota
– was dramatically changed
• The resulting Triassic marine faunas
– were of low diversity,
– but the surviving species tended to be abundant
– and widely distributed around the world
• As we will see later,
– this fauna provided the rootstock
– for repopulating the world's oceans
Summary
• Multicelled organisms presumably
– had a long Precambrian history during which
they lacked hard parts
• Invertebrates with hard parts
– suddenly appeared during the Early Cambrian
– in what is called the Cambrian explosion
• Skeletons provided such advantages
–
–
–
–
as protection against predators
and support for muscles,
enabling organisms to grow large
and increase locomotor efficiency
Summary
• Hard parts probably evolved
– as a result of various geologic factors
– rather than a single cause
• Marine organisms are classified
– as plankton
• if they are floaters,
– nekton
• if they swim,
– and benthos
• if they live on or in the seafloor
Summary
• Marine organisms can be divided
– into four basic feeding groups:
– suspension feeders,
• which consume microscopic plants and animals as
well as dissolved nutrients from water;
– herbivores,
• which are plant eaters;
– and sediment-deposit feeders,
• which ingest sediment and extract nutrients from it
Summary
• The marine ecosystem consists of various
trophic levels
– of food production and consumption
• At the base are primary producers,
– upon which all other organisms are dependent
• the primary consumers
– feed on the primary producers
• higher level consumers
– can feed upon primary producers
• The decomposers are bacteria
– that break down the complex organic
compounds
– of dead organisms
– and recycle them within the ecosystem
Summary
• The Cambrian invertebrate community
– was dominated by three major groups,
• the trilobites,
• inarticulate brachiopods,
• and archaeocyathids
• Little specialization existed among the
invertebrates,
– and the most phyla were represented
– by only a few species
Summary
• The Middle Cambrian Burgess Shale
– contains one of the finest examples
– of a well-preserved soft-bodied biota in the world
• 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
– for many invertebrate phyla
Summary
• The Silurian and Devonian periods
– were times of diverse faunas
– dominated by reef-building animals,
• while the Carboniferous and Permian
periods
– saw a great decline in invertebrate diversity
• 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
Conodonts
• Conodonts are microscopic toothlike fossils
• Scolopodus, sp., Shingle Limestone,
– Shingle Pass, Nevada
Conodonts
• The conodont animal
– preserved as a carbonized impression 40 x 2 mm
– in the Lower Carboniferous Granton Shrimp Bed in
Edinburgh, Scotland
Early Invertebrate History
• In addition, new fossil sites
– and detailed stratigraphic studies
– are shedding light
– on the early history and ancestry
– of the various invertebrate phyla
How Many Phyla?
• The question that paleontologists are still
debating is
– How many phyla arose during the Cambrian?
– At the center of that debate are the Burgess Shale
fossils
• For years, most paleontologists
–
–
–
–
placed the bulk of the Burgess Shale organisms
into existing phyla,
with only a few assigned to phyla
that are now extinct
Cambrian Phyla
• Thus, the phyla of the Cambrian world
– were viewed as being essentially the same in
number
– as the phyla of the present-day world,
– but with fewer species in each phylum
• According to this view, the history of life
– has been simply a gradual increase in the diversity
of species
– within each phylum through time
• The number of basic body plans
– has therefore remained more or less constant
– since the initial radiation of multicellular organisms
Reassignment to Extant Phyla
• Discoveries of Cambrian fossils
– at localities such as Sirius Passet, Greenland, and
Yunnan, China,
– have resulted in reassignment
– of some Burgess Shale specimens back into extant
phyla
• If these reassignments to known phyla prove to
be correct,
– then no massive extinction event followed the
Cambrian explosion,
– and life has gradually increased in diversity
through time
The Cambrian Explosion
• This sudden and rapid appearance
– of new animals in the fossil record
– is rapid, however, only in the context of geologic
time,
– having taken place over millions of years
– during the Early Cambrian Period
Hox Genes
• These global environmental changes
– may have stimulated evolution
– and contributed to the Cambrian explosion
• Recent work on Hox genes, which are
• sequences of genes that control the development of
individual regions of the body,
–
–
–
–
shows that the basic body plans for all animals
was apparently established
by the end of the Cambrian explosion,
and was only slightly modified since then
Not a Recent Discovery
• Early geologists observed
– that the remains of skeletonized animals
– appeared rather abruptly in the fossil record
• Charles Darwin addressed this problem
–
–
–
–
–
in On the Origin of Species
and observed that,
without a convincing explanation,
such an event was difficult to reconcile
with his newly expounded evolutionary theory
Tremendous Biologic Change
• A time of tremendous biologic change
– began with the appearance of skeletonized animals
– near the Precambrian-Cambrian boundary
• Following this event, marine invertebrates
– began a period of adaptive radiation and evolution
– during which the Paleozoic marine invertebrate
community greatly diversified
• Indeed, the history of the Paleozoic marine
invertebrate community
– was one of diversification and extinction,
– culminating at the end of the Paleozoic Era
– in the greatest mass extinction in Earth history
Much Narrower Gap
• Now, known Proterozoic fossil assemblages
– continue right to the base of the Cambrian
• Furthermore, recent work from Namibia
– indicates that Ediacaran-like fossils
– are even present above the first occurrence
– of Cambrian index fossils
Paleozoic Invertebrate
Marine Life
• Having considered the origin, differentiation,
and evolution
–
–
–
–
of the Precambrian-Cambrian marine biota,
we now examine the changes
that occurred in the marine invertebrate community
during the Paleozoic Era
The Burgess Shale Biota
• No discussion of Cambrian life
– would be complete without mentioning
– one of the best examples
– of a preserved soft bodied fauna and flora,
• the Burgess Shale biota
• As the Sauk Sea transgressed
– from the Cordilleran shelf
– onto the western edge of the craton
• Early Cambrian sands were covered
– by Middle Cambrian black muds
– that allowed a diverse soft-bodied benthonic
community to be preserved
Rarely Preserved Organisms
• This discovery therefore
–
–
–
–
provides us with a valuable glimpse
of rarely preserved organisms
as well as the soft-part anatomy
of many extinct groups
Reinterpretation
• In recent years, the reconstruction,
classification, and interpretation
–
–
–
–
of many of the Burgess Shale fossils
have undergone a major change
that has led to new theories and explanations
of the Cambrian explosion of life
• Recall that during the Late Proterozoic
multicellular organisms evolved,
– and shortly thereafter animals
– with hard parts made their first appearance
No Clear Answer
to This Debate
• Currently, there is no clear answer to this
debate,
– and the outcome will probably be decided
– as more fossil discoveries are made
Soft-Bodied Organisms
• Microscopic calcareous tubes,
• presumably housing worm-like suspension feeding
organisms,
– have also been found at some localities
• In addition, trails and burrows,
• which represent the activities of worms
• and other sluglike animals
– are also found associated
– with Ediacaran faunas throughout the world
• The trails and burrows
– are similar to those made by present-day softbodied organisms
Time Between
• Until recently, it appeared that
– a fairly long time period existed
– between the extinction of the Ediacaran fauna
– and the evolution of the first Cambrian fossils
• That gap has been considerably narrowed
– in recent years with the discovery
– of new Proterozoic fossiliferous localities
Changing Marine Ecosystem
Suspension Feeders
Dominated Reefs
• As with present-day reefs,
– Ordovician reefs exhibited a high diversity of
organisms
– and were dominated by suspension feeders
Repopulation
• This repopulation
–
–
–
–
–
–
was probably due in part to renewed
transgressions over the craton,
and although a major drop in sea level
occurred at the end of the Silurian,
the Middle Paleozoic sea level
was generally high
Fusulinids Are Important
Guide Fossils
• Because of their
– abundance, diversity, and worldwide occurrence,
– fusulinids are important guide fossils
– for Pennsylvanian and Permian strata
• Bryozoans, sponges, and some types of
calcareous algae
– also were common elements of the Permian
invertebrate fauna
Soft-Bodied Animals and Plants
• As we discussed earlier,
– these fossils were discovered in 1909 by Charles
Walcott
– near Field, British Columbia
• They represent one of the most significant
fossil finds of the 20th century
– because they consist of impressions of soft-bodied
animals and plants
– which are rarely preserved in the fossil record
Thousands of Fossil Specimens
• Walcott returned to the site the following
summer
– and located the shale stratum
– that was the source of his fossil-bearing rocks
– in the steep slope above the trail
• He quarried the site
– and shipped back
– thousands of fossil specimens
– to the United States National Museum of Natural
History,
– where he later cataloged and studied them
Explosion of Varied Lifeforms
• This view, however, has been challenged
– by other paleontologists
– who think that the initial explosion of varied
lifeforms in the Cambrian
– was promptly followed by a short period of
experimentation
– and then extinction of many phyla
• The richness and diversity of modem lifeforms
– are the result of repeated variations of the basic
body plans
– that survived the Cambrian extinctions
Hotly Debated Topic
• Nonetheless, the cause of the sudden
appearance
– of so many different animal phyla
– during the Early Cambrian
– is still a hotly debated topic
• Newly developed molecular techniques
–
–
–
–
that allow evolutionary biologists
to compare the similarity of molecular sequences
of the same gene from different species
is being applied to the phylogeny of many
organisms
Brachiopods
The Emergence of a Shelly Fauna
• The earliest organisms with hard parts
– are Proterozoic calcareous tubes
– found associated with Ediacaran faunas
– from several locations throughout the world
• These are followed by other microscopic
skeletonized fossils
– from the Early Cambrian
– and the appearance of large skeletonized animals
– during the Cambrian explosion
Fusulinids
• The fusulinids
• spindle-shaped foraminifera
–
–
–
–
which first evolved during the Late Mississippian
and greatly diversified during the Pennsylvanian,
experienced a further diversification
during the Permian
Conodonts
• Conodonts are a group
– of well-known small tooth-like 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
Conodont Animal
• Several specimens of carbonized impressions
–
–
–
–
–
of the conodont animal
from Lower Carboniferous rocks of Scotland
reveal that it is a member of a group
of primitive jawless animals
assigned to the phylum Chordata
• Study of the specimens
– indicates that the conodont animal
– was probably an elongate swimming organism
Graptolites
Primitive Echinoderm
• Helicoplacus was a
primitive echinoderm
– that became extinct 20
million years after its first
appearance about 510
million years ago
– and was a representative of
one of several short-lived
echinoderm classes
– Such organisms illustrate
the “experimental” nature
of the Cambrian
invertebrate fauna
Lower Cambrian Shelly Fossil
• A conical sclerite* of Lapworthella from
Australia
* a piece of
the armor
covering
– This
specimen
is several
millimeters
in size
Lower Cambrian Shelly Fossil
• Archaeooides, an enigmatic spherical fossil
from the Mackenzie Mountains, Northwest
Territories, Canada
– This
specimen
is several
millimeters
in size