Reading Assignment:
Chapters 9, and 10
Early
Paleozoic
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Phanerozoic Eonothem
The
Lower Paleozoic
Chronstratigraphic Divisions: Cambrian System || Ordovician System
The Cambrian System
Biological Features:
The Evolutionary Processes of Phanerozoic Biota; From Eukaryotes to Animalia
The concept of extinction || Cambrian Explosion: What is the Cambrian Explosion?
The evolution of skeletons in many animal groups The Tommotian Fauna || First Reefs: Archaeocyathids
Paleogeography || Landmasses: Gondwanaland || Baltica || Siberia || Laurentia
Paleoentological features:
Divisions of time
Lagerstätten
Biological Features:
The great radiation
Coral-strome reefs
Lower Ordovician animals: floaters and swimmers
Predatrors: Animals as a cause of stromatolite decline
Mass extinction of warm-water taxa
Geological features:
Continental glaciation
Paleoentological features:
Plants invade land?
Marine sedimets heavily burrowes
Summary of Lower Paleozoic Events
Read
Chapters nine and ten of your textbookReview
the
story of plate tectonicsFor
a more simplistic model visit this site <http://www.pbs.org/wgbh/aso/tryit/tectonics>By the end of this chapter you should be able to:
Phanerozoic Eonothem
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The 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 seas.
Many 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 States, were formed during the Paleozoic.
The Cambrian System: It derives its name from the ancient Roman name for Wales (see map below):
The
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 glaciation.
From 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).
In 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."
The Marine
Environment in the Cambrian
4.2.1.6. Permian System: "The Age of Amphibians" 280 to 248 mya.Mass extinction, most kinds of marine animals, including trilobites.
The Tommotian fauna 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.
The Burgess Shale fauna
Strata in 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.
Arthropods
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.
Reefs 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.
The Evolutionary Process of Phanerozoic Life
Major groups 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:
The opisthokonts (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.
See
Biological Principles for a review of these concepts
Schizocoels:
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.
Lophophore: 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
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The sponges or poriferans: Po·rif·e·ra (n. pl.)
[NL., fr. L. porus pore + ferre to bear.]
A grand division of the Invertebrata, including the sponges; -- called also Spongiæ, Spongida, and Spongiozoa. The principal divisions are Calcispongiæ, Keratosa or Fibrospongiæ, and Silicea.
The sponges 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.
Sponges are 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.
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Mollusca
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.
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Brachiopods 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 and Phoronida.
Although they 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.
The 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.
Brachiopods 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.
Ecology
and physiology
A. Marine,
mostly within the shelf, but some forms are abyssal.
B. Benthic
: 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.
D. Inhabit
largely the cold waters, but are present in all latitudes. Usually highly
endemic.
E. Feeding
biology
1. Feed on
fine phytoplankton (diatoms), and dissolved and colloidal material.
2. Adjustable
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.
5. Ingestion
is controlled by peristaltic movements of the esophagus and stomach.
F. Predators
: fish, men.
G. Parasites
: gregarines.
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