Division of the Paleozoic Eratherm
Eonothem is often referred to as the tine of "Visible Life". Organisms
with skeletons or hard shells appeared by the first time in the geological
record. The Phanerozoic Eonothem spans from 543 mya through today.
The Phanerozoic is divided into three Erathems, from older to younger:
Paleozoic, Mesozoic, and Cenozoic.
Erathem: 543 to 248 mya
Paleozoic is delimited by two of the most important events in the history
of life. At its beginning, members of Eukarya (multicelled animals)
underwent a dramatic "explosion"
in diversity, and almost all living animal
phyla appeared within a few millions of years. At the other end of
the Paleozoic, the largest mass extinction in history wiped out approximately
90% of all marine animal species. The causes of both these events are still
not fully understood and the subject of much research and controversy.
Roughly halfway in between, animals,
alike colonized the land, the insects
took to the air, and the limestone shown in this picture was deposited
near Burlington, Missouri
took up over half of the Phanerozoic, approximately 300 million
years. During the Paleozoic there were six major continental land masses;
each of these consisted of different parts of the modern continents. For
instance, at the beginning of the Paleozoic, today's western coast of North
America ran east-west along the equator, while Africa was at the South
Pole. These Paleozoic continents experienced tremendous mountain building
along their margins, and numerous incursions and retreats of shallow seas
across their interiors. Large limestone outcrops, like the one shown above,
are evidence of these periodic incursions of continental seas.
rocks are economically important. For example, much of the limestone
quarried for building and industrial purposes, as well as the coal
deposits of Western Europe and the eastern United States, were formed during
Paleozoic = Cambrian + Ordovician Systems
lower Paleozoic is an informal division of the Paleozoic Erathem which
includes the lower two systems: the Cambrian and the Ordovician. See Chronostratigraphic
of Lower Paleozoic Events:
Interval of time included between 543 to 438 mya
First skeletal fossils
Occurrence of the Tommotian Fauna
Development of Archaeocyathid reefs
Trilobites dominate since the upper part of the Lower Cambrian
Radiation of large animals
Mass extinction of trilobites at the end of the Cambrian
Marine sediments are weakly burrowed in the Lower Cambrian
Marine sediments are heavily burrowed in the Ordovician
First jawless fishes appeared in the middle Ordovician
Evolutionary radiation at the base of the middle Ordovician
Mass extinction of warm-water taxa
Continental glaciation at the end of the Ordovician
The landmasses (continents) in the Upper Cambrian are: Gondwanaland, Laurentia,
Baltica, and Siberia
Major plate tectonic reconfiguration in the middle part of the Upper Ordovician
Predators become very common, e.g.. nautiloids.
Earliest land plants.
It derives its name from the ancient Roman name for Wales (see map below):
Cambrian is characterized by: (1) the first abundant record of marine life;
(2) "The Age of Trilobites" 543 to 500 mya - (3) The Cambrian Explosion
of life occurs; (4) all existent phyla develop; (5) Many marine invertebrates
(marine animals with mineralized shells: shell-fish, echinoderms, trilobites,
brachiopods, mollusks, primitive graptolites). First vertebrates. Earliest
primitive fish; (6) mild climate; (7) the supercontinentRodinia
began to break into smaller continents (no correspondence to modern-day
land masses); (8) Mass extinction of trilobites and nautiloids
at end of Cambrian (50% of all animal families went extinct) probably due
to the Cambrian these events occurred: (1) The earliest morphological evidence
for life at 3.5 billion years, which correspond to fossils of stromatolites
(colonies of cyanobacteria ) and single, undifferentiated cells, or Prokaryotes;
(2) For 1.6 billion years these simple cells were the only kind of living
organism, until the arrival of Eukaryotes, or single cells with differentiated
nuclei and cell organelles. Although representing a large leap in complexity,
the Eukaryotes were still only single cells or cell aggregates; (3) It
took another 1.4 billion years before complex, multicellular life
made an appearance in the form of the Ediacaran faunas; (4)
the true Cambrian animals appeared about 550 million years ago followed,
that is, the metazoans or large animals with complex body plans, is termed
the Cambrian explosion; (5) In addition to the apparent phyla 'explosion'
the Cambrian also sees the advent of a modern type of community structure,
with organisms being adapted for a large range of life strategies. These
include mobile benthic, epifaunal and burrowing faunas all
interacting with each other in complex communities. Predation as a means
of acquiring food also makes an appearance at this time. What are even
more unusual are the Cambrian organisms which display seemingly bizarre
body plans and appendages, and which taxonomically are difficult to assign
to any modern phyla (see Burgess Shale type faunas).
the Cambrian fossil record indicates a distinct development from simple
organisms to organisms comparable in morphology and organization to the
present-day animals. This rapid phylogenetic development started
in the latest Proterozoic and was more-or-less finished at
the end of the Early Cambrian. The development of faunas in the Cambrian
is documented by faunal assemblages represented by (1) the Ediacara
fauna, (2) the first
complex trace fossils, (3) the earliest
shelly faunas, and (4) the onset of the typical Cambrian
macrofaunas . It is amazing that this rapid evolution took place in
an interval of less than 25 m.y., and the evolution from the first
hard-part animals to the presence of most of the present-day phyla was
restricted to an interval of probably less than 10 m.y. Multicellular
life evolved at an incredible supersonic speed, and for this reason this
part of organismal evolution is termed the "Cambrian Explosion",
or "Evolution's Big Bang."
Environment in the Cambrian
505 to 438 mya. The Ordovician represents the time of marked evolutionary
radiation of life in the seas which took place in the miidle Ordovician.
The Ordovician life includes: the first fishes, invertebrates dominate.
Primitive plants appear on land. First corals. Primitive fishes, seaweeds
and fungi. Graptolites, bryozoans, gastropods, bivalves, and echinoids.
High sea levels at first, global cooling and glaciation, and much volcanism.
North America under shallow seas. The Ordovician System ends in huge
extinction due to glaciation.
Silurian System: 438 to 408 mya. First terrestrial
plants and animals.
first jawed fishes and uniramians (like
insects, centipedes and millipedes) appeared during the Silurian (over
400 million years ago). First
plants (plants with water-conducting tissue as compared with non-vascular
plants like mosses) appear on land (Cooksonia
is the first
High seas worldwide.Brachiopods, crinoids,
Devonian System: "The Age of Fishes" 408 to 360 mya.
First amphibians, ammonites, fishes abundant.
and land plants become abundant and diverse. First tetrapods
appear toward the end of the period. First amphibians appear. First sharks,
bony fish, and ammonoids.Many coral reefs,
brachiopods, crinoids. New insects, like springtails, appeared. Mass extinction
(345 mya) wiped out 30% of all animal families)
probably due to glaciation or meteorite
Carboniferous: Wide-spread coal swamps, foraminiferans,
corals, bryozoans, brachiopods, blastoids,
seed ferns, lycopsids, and
plants. Amphibians become more common. 360 to 280 mya
Mississippian Sub-System: 360 to 325 mya:
Sharks and amphibians abundant. Large and numerous scale trees and seed
First winged insects.
Pennsylvanian Sub-System: 325 to 280 mya.
Great coal forests, conifers. First reptiles .First reptiles. Many ferns.
The first may flies and cockroaches appear.
Permian System: "The Age of Amphibians" 280 to 248 mya.Mass
extinction, most kinds of marine animals, including trilobites.
"The Age of Amphibians" - Amphibians and reptiles dominant. Gymnosperms
dominant plant life. The continents merge into a
super-continent, Pangaea. Phytoplankton and plants oxygenate the Earth's
atmosphere to close to modern levels. The first stoneflies, true
beetles, and caddisflies, The Permian ended
with largest mass extinction. Trilobites go extinct, as do 50% of all animal
families, 95% of all marine species, and many trees, perhaps caused by glaciation
are fossil localities which are highly remarkable for either their diversity
or quality of preservation; sometimes both. There are two famous Cambrian
age lagerstätten known to almost everybody with an interest
in paleontology – the Burgess Shale in Canada,
and Chengjiang in China. Other very well-known lagerstätten
include the Green River Formation of Wyoming, USA, which has produced countless
fossil fish for the commercial fossil market, the Solnhofen
Limestone of Germany, famous primarily for the
fossils found there.
this fauna represents the first evolutive occurance of the skeltetons in
many animal groups. This richer fauna appears abruptly in the middle portion
of the Lower Cambrian record. This so-called Tomotian fauna, named for
the Tommotian Stage of Early Cambrian time, was first discovered in Siberia.
It includes a host of small skeletal el¬ements that cannot be assigned
to any living phylum and that show no relation to any group of fossils
found in post-Cambrian rocks. The Tommotian fauna also contains the oldest
known mem¬bers of a few groups that survive to the present day¬sponges,
which are very simple animals monoplacophorans, which were ancestral to
all present-day groups of mollusks.
western North America have yielded a spectacular fauna of Middle Cambrian
soft-bodied animals that invites comparison with the Early Cambrian Chengjiang
fauna described earlier. The largest group of species in the North American
soft-bodied fauna comes from the Burgess Shale, in the Rocky Mountains
of British Columbia (Figure 13-10). Laterin this chapter we will examine
the environment in which the Burgess Shale formed, but for now we can simply
note that it accumu¬lated in a deep-water setting where soft-bodied
animals were buried in the absence of oxygen and bacterial decay. Among
the Burgess Shale fossils is a species that represents the Chordata, the
phylum to which verte¬brate animals belong. Pikaia, the chordate genus
of the Burgess Shale fauna, possessed a notochord-the struc¬ture that,
in some Cambrian animal group that may never be singled out, evolved into
a backbone. Recall that the lancelet possesses only a noto¬chord today.
are the most abundant of the Burgess Shale fossils, and some of them resemble
certain of the Chengjiang taxa . Also present are anomalocarids. In addition,
both the Chinese and North American fau¬nas include onychophorans.
Elongate animals with jointed legs, onychophorans are generally intermediate
in form between segmented worms and arthropods. Today members of this group
live as pred¬ators on moist forest floors, having somehow invaded the
land. Priapulid worms also occur in the Burgess Shale fauna, along with
several types of seg¬mented worms. An overall comparison of the Chinese
fauna with the younger North American fauna indicates that evolutionary
changes between Early and Middle Cambrian time were relatively minor for
soft-bodied in¬vertebrate animals.
The earliest vertebrates
Conodonts also diversified in the course of the Cambrian Period. Their
teeth, which are abundant in the fossil record, reveal nothing of their
body form, but the recent discovery of fossils of their soft bodies has
shown them to have been small swimming animals; the teeth themselves indicate
that conodonts were the earliest known vertebrate animals. Similar small
teeth in very early Cambrian faunas may represent conodont ancestors.
The oldest organic reefs with skeletal frameworks are low mounds that formed
in Lower Cambrian time, beginning in the Tommotian. The main builders of
these reefs were archaeocyathids, which apparently were suspension feeders
that pumped water through holes in their vase-shaped and bowl-shaped skeletons.
Archaeocyathids were probably sponges, the simplest of which resemble them
in general body plan. Although archaeocyathids were the primary frame builders
of Lower Cambrian reefs, organisms of unknown taxonomic relationships actually
contributed a larger volume of calcium carbonate to these reefs by encrusting
archaeocyathid skeletons and binding them together. At the end of Lower
Cambrian time, nearly all archaeocyathids became extinct. From then until
mid-Ordovician time, all that remained were small, inconspicuous reeflike
structures formed by the en¬crusting organisms that had previously
lived with the archaeocyathids.
Process of Phanerozoic Life
of animals are already present in the Phanerozoic, at the beginning
of the Cambrian System, thier phylogenetic development is shown in the
following diagrams as shown below:
(Greek: ??????- (opisth?-) = "rear, posterior" + ?????? (kontos) = "pole"
i.e. flagellum) are a broad group of eukaryotes, including both the animal
and fungus kingdoms, together with the phylum Choanozoa of the protist
kingdom. Both genetic and ultrastructural studies strongly support that
opisthokonts form a monophyletic group. One common characteristic is that
flagellate cells, such as most animal sperm and chytrid spores, propel
themselves with a single posterior flagellum. This gives the groups its
name. In contrast, flagellate cells in other eukaryote groups propel themselves
with one or more anterior flagella.
Biological Principles for a review of these concepts
A group of animal phyla, including Bryozoa, Brachiopoda, Phoronida, Sipunculoidea,
Echiuroidea, Priapuloidea, Mollusca, Annelida, and Arthropoda, all characterized
by the appearance of the coelom as a space in the embryonic mesoderm.
A horseshoe-shaped ciliated organ located near the mouth of brachiopods,
bryozoans, and phoronids that is used to gather food.
to Unit Plan
ON THE CLASSIFICATION OF ORGANISMS
or poriferans: Po·rif·e·ra (n. pl.)
L. porus pore + ferre to bear.]
division of the Invertebrata, including the sponges; -- called also Spongiæ,
Spongida, and Spongiozoa. The principal divisions are Calcispongiæ,
Keratosa or Fibrospongiæ, and Silicea.
or poriferans (from Latin porus "pore" and ferre "to bear") are animals
of the phylum Porifera. They are primitive, sessile, mostly marine, water
dwelling filter feeders that pump water through their bodies to filter
out particles of food matter. Sponges represent the simplest of animals.
With no true tissues (parazoa), they lack muscles, nerves, and internal
organs. Their similarity to colonial choanoflagellates shows the probable
evolutionary jump from unicellular to multicellular organisms. There are
over 5,000 modern species of sponges known, and they can be found attached
to surfaces anywhere from the intertidal zone to as deep as 8,500 m (29,000
feet) or further. Though the fossil record of sponges dates back to the
Neoproterozoic Era, new species are still commonly discovered.
a diverse group of sometimes common types, with about 5000 species known
across the world. Sponges are primarily marine, but around 150 species
live in fresh water. Sponges have cellular-level organization, meaning
that that their cells are specialized so that different cells perform different
functions, but similar cells are not organized into tissues and bodies
are a sort of loose aggregation of different kinds of cells. This is the
simplest kind of cellular organization found among parazoans.
One of the
divisions of phyla of the animal kingdom containing snails, slugs, octopuses,
squids, clams, mussels, and oysters; characterized by a shell-secreting
organ, the mantle, and a radula, a food-rasping organ located in the forward
area of the mouth.
are marine animals that, upon first glance, look like clams. They are actually
quite different from clams in their anatomy, and they are not closely related
to the molluscs. They are lophophorates, and so are related to the Bryozoa
seem rare in today's seas, they are actually fairly common. However, they
often make their homes in very cold water, either in polar regions or at
great depths in the ocean, and thus are not often encountered. There are
about 300 living species of brachiopods.
are a large group of solitary and exclusively marine organisms with a very
good geologic history throughout most of the Phanerozoic and are among
the most successful benthic macroinvertebrates of the Paleozoic. They are
typified by two mineralized valves which enclose most of the animal. Like
the bryozoans, brachiopods are filter feeders which collect food particles
on a ciliated organ called the lophophore. An excellent example of a brachiopod
lophophore can be seen in the Recent terebratulid. Brachiopods differ
in many ways from bryozoans (in both soft and hard-part morphology), and
are thus considered by most workers as a separate but closely related phylum.
However, one of the most distinguishing features of brachiopods is the
presence of a pedicle, a fleshy stalk-like structure that aids the animal
in burrowing and maintaining stability. The pedicle can be seen in the
Recent Lingula. Currently, brachiopods are divided into two or three
major groups. We depart from your text in considering two major groups:
Class Inarticulata (including lingulids), and Class Articulata based on
the presence or absence of hinge teeth and sockets.
superficially resemble bivalve mollusks in that the animal secretes a bivalved
(two-part) shell of calcium carbonate or a combination of calcium phosphate
and chitinous organic substance. However, Bivalve mollusks generally
have shells that are equal in size and shape (although mirror images of
each other), whereas the two shells of brachiopods are of unequal size
(the technical term is inequalvalved). The valve (shell) that has
the attachment for the pedicle is the pedicle valve which is usually the
lower and larger valve. This valve includes the pedicle opening.
mostly within the shelf, but some forms are abyssal.
: sessile or burrowing. Substrates: rock, shells, algal stems, soft sediment.
C. Not colonial
but tend to aggregate intraspecifically and interspecifically, which seems
to depend on the larval settlement.
largely the cold waters, but are present in all latitudes. Usually highly
1. Feed on
fine phytoplankton (diatoms), and dissolved and colloidal material.
ciliary current created by the lophophore ciliation. Distinct inhalant
and exhalant apertures. Particles are trapped on the filaments and converge
in the groove down to the mouth. There is mucus, but it seems not
to play a major role here.
3. In burrowing
species, the mantle setae prevent fouling by the sediment. Mucus
is secreted by the gland zone of the mantle lobes.
4. Some species
can reverse the water current when particles accumulate within the lophophore.
is controlled by peristaltic movements of the esophagus and stomach.
: fish, men.