Paleozoic Life History: Invertebrates

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Paleozoic Life History: Invertebrates

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Title: Paleozoic Life History: Invertebrates

1
Chapter 12
Paleozoic Life History Invertebrates
2
Burgess Shale

Diorama of the environment and biota
of the Phyllopod bed of the Burgess Shale,
British Columbia, Canada
algae
sponges
among others

3
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

4
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

5
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

6
Sixty Percent Soft-Bodied

In fact, 60 of the total fossil assemblage
of more than 100 genera is composed of
soft-bodied 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

7
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

8
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

9
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

10
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

11
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

12
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

13
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

14
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

15
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
soft-bodied organisms

16
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

17
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

18
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

19
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

20
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

21
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

22
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

23
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

24
Lower Cambrian Shelly Fossil

A conical sclerite of Lapworthella from
Australia
a piece of the armor covering
This specimen is several millimeters in size

25
Lower Cambrian Shelly Fossil

Archaeooides, an enigmatic spherical fossil from
the Mackenzie Mountains, Northwest Territories,
Canada
This specimen is several millimeters in size

26
Lower Cambrian Shelly Fossil

The tube of an anabaritid from the Mackenzie
Mountains, Northwest Territories, Canada
This specimen is several millimeters in size

27
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

28
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

29
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

30
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

31
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

32
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

33
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

34
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

35
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

36
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

37
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

38
Nekton

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

39
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

40
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

41
Marine Ecosystem

Where and how animals and plants live in the
marine ecosystem

Plankton Jelly fish
Nekton fish cephalopod
Sessile epiflora seaweed
Sessile epifauna bivalve
Benthos d-k
crinoid
coral
42
Marine Ecosystem
Infauna worm, bivalve
Mobile epifauna gastropod, starfish
43
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

44
Marine Ecosystem
coral
crinoid
bivalve
Suspension feeders
45
Marine Ecosystem
worm sediment-deposit feeder
Herbivores gastropod
Carnivores-scavengers starfish
46
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

47
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

48
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

49
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

50
Marine Food Web

Showing the relationships
among the
producers,
consumers,
and decomposers

51
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

52
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

53
Changing Marine Ecosystem

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

54
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

55
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

56
Cambrian Marine Community

Floating jellyfish, swimming arthropods,
benthonic sponges, and scavenging trilobites
Reconstruction

57
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

58
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,

59
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

60
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-socket-arrangement
along the hinge line of their shells

61
Articulate Brachiopods

The articulate brachiopods,
which have a tooth-and-socket arrangement,
were also present
but did not become abundant
until the Ordovician Period

62
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

63
Cambrian Reeflike Structure

Restoration of a Cambrian reeflike structure
built by archeocyathids

64
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

65
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

66
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

67
Rare Preservation Burgess Shale

Ottoia, a carnivorous worm

68
Rare Preservation Burgess Shale

Wiwaxia, a scaly armored sluglike creature whose
affinities remain controversial

69
Rare Preservation Burgess Shale

Hallucigenia, a velvet worm

70
Rare Preservation Burgess Shale

Waptia, an anthropod

71
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

72
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

73
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

74
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

75
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

76
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

77
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

78
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

79
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

80
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

81
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

82
Middle Ordovician Seafloor Fauna

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

83
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

84
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

85
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

86
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

87
Suspension Feeders Dominated Reefs

As with present-day reefs,
Ordovician reefs exhibited a high diversity of
organisms
and were dominated by suspension feeders

88
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

89
Brachiopods
90
Brachiopods

Brachiopods became a conspicuous element
of the invertebrate fauna
during the Ordovician
and in succeeding Paleozoic periods

91
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

92
Graptolites
93
Conodonts

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

94
Conodonts

Conodonts are microscopic toothlike fossils

Cahabagnathus sweeti, Copenhagen Formation
Middle Ordovician, Monitor Range, Nevada

95
Conodonts

Conodonts are microscopic toothlike fossils

Scolopodus, sp., Shingle Limestone,
Shingle Pass, Nevada

96
Conodonts

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

97
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

98
Excellent Guide Fossils

The wide distribution
and short stratigraphic range of individual
conodont species
make them excellent fossils
for biostratigraphic zonation and correlation

99
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

100
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

101
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

102
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

103
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

104
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

105
Middle Devonian Reef

Reconstruction of a Middle Devonian reef from the
Great Lakes area
with corals, cephalopods, trilobites, crinoids,
and brachiopods

106
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

107
Silurian Brackish-Marine Scene

Restoration of a Silurian brackish-marine bottom
scene
near Buffalo New York
with algae, eurypterids, gastropods, worms, and
shrimp

108
Ammonoids

Ammonoids are excellent guide fossils
for the Devonian through Cretaceous periods
with their distinctive suture patterns,
short stratigraphic ranges,
and widespread distribution

109
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

110
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

111
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

112
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

113
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

114
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

115
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

116
Mississippian Marine Life

Based on a fossil site in the Upper Mississippian
at Crawford, Indiana
Invertebrate animals shown include

blastoids
lacy bryozoans

crinoids

brachiopods

small corals

117
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

118
Permian Period

Paleogeography of North America during the
Permian Period

119
Productids

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

120
Permian Patch-Reef Community

From Glass Mountains of West Texas
including algae, productid brachiopods,
cephalopods, sponges, and corals

121
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

122
Fusulinid

Fusulinids are spindle-shaped, microscopic
benthonic foraminifera that are excellent guide
fossils for the Pennsylvanian and Permian periods
Cross section of Leptotriticites tumidus, Lower
Permian, Kansas

123
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

124
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 invertebrate species
became extinct

125
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

126
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

127
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,

128
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

129
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

130
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
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

131
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

132
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

133
End Result the Same

The end result would be the same
global warming
and disruption of the marine and terrestrial
ecosystems

134
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

135
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

136
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

137
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

138
Summary