Division of the Paleozoic Eratherm
of marine environments
is the Cambrian Explosion?
first shelly faunas
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
Paleozoic 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
Paleozoic 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
were formed during the Paleozoic.
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
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)
The Evolutionary Processes of Phanerozoic Biota ||The
|| Cambrian Explosion: What is the Cambrian Explosion?
of marine environments
Principles: Paleogeography || Landmasses:
Gondwanaland || Baltica
|| Siberia || Laurentia
Invertebrates: Poriferaopoda || Mollusca || Brachiopoda || Onychophora
|| Tardigrada || Arthropoda || Priapulida || Echinodremata || Annelida
|| Hemichordata || Chordata
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
System marks an important point in the history of life on earth; it is
the time when most of the major groups of animals first appear in the fossil
record. This event is sometimes called the "Cambrian Explosion",
because of the relatively short time over which this diversity of forms
appears. It was once thought that the Cambrian rocks contained the first
and oldest fossil animals, but these are now to be found in the earlier
Precambrian 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).
summary, 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 .
Ordovician is best known for the presence of its diverse marine invertebrates
(invertebrates dominate), including graptolites, trilobites, brachiopods,
and the conodonts (early vertebrates). A typical marine community consisted
of these animals, plus red and green algae, first fishes (primitive fish),
cephalopods, corals, crinoids, and gastropods. More recently, there has
been found evidence of tetrahedral spores that are similar to those of
primitive land plants, suggesting that plants invaded the land at this
sea levels at first, global cooling and glaciation , and much volcanism.
North America under shallow seas. Ends in huge extinction due
to glaciation. From the Early to Middle Ordovician, the earth experienced
a milder climate in which the weather was warm and the atmosphere contained
a lot of moisture. However, when Gondwana finally settled on the South
Pole during the Late Ordovician, massive glaciers formed causing shallow
seas to drain and sea levels to drop. This likely caused the mass extinctions
that characterize the end of the Ordovician, in which 60% of all marine
invertebrate genera and 25% of all families went extinct.
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 vascular plants (plants with water-conducting tissue as compared
with non-vascular plants like mosses) appear on land (Cooksonia is
the first known). High seas worldwide.Brachiopods , crinoids, corals.
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 impact.
Carboniferous: Wide-spread coal swamps, foraminiferans, corals, bryozoans,
brachiopods, blastoids , seed ferns, lycopsids , and other
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 ferns. 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
Permian System: "The Age of Amphibians" 280 to 248 mya.Mass
extinction, most kinds of marine animals, including trilobites.
glaciation . "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 bugs,
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 or volcanism.
: 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 Archeopteryx
fossils found there.
This fauna represents the Tommotian Age, which began about 530 million
years ago, is a subdivision of the early Cambrian. Named for rock exposures
in Siberia, the Tommotian saw the first major radiation of the animals,
or metazoans, including the first appearance of a great many mineralized
taxa such as brachiopods, trilobites, archaeocyathids, molluscs, echinoderms,
and more problematic forms. Soft-bodied members of many other phyla were
also appearing and diversifying at this time.
A few million
years before the Tommotian, in the Ediacaran (Vendian), the continents
had been joined in a single supercontinent called Rodinia (from the Russian
word for "homeland", rodina.) As the Cambrian began, Rodinia began to fragment
into smaller continents which did not always correspond to the ones we
see today. Much later, in the Permian, the continents came back together
to form a new supercontinent, called Pangaea.
of the Tomotian Fauna: A much 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 elements 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
(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.
NOTES 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.