Types of marine environments
What is the Cambrian Explosion?
Paleontological Principles
The
first metazoans
The
first shelly faunas
Cambrianmacrofaunas
Poriferaopoda
Mollusca
Brachiopoda
Onychophora
Tardigrada
Arthropoda
Priapulida
Echinodremata
Annelida
Hemichordata
Chordata
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Pennsylvanian
Subsystem
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Mississippian
Subsystem
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This
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.
ThePaleozoic Erathem: 543 to 248 mya
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
Summary
of Lower Paleozoic Events:
1.-
Interval of time included between 543 to 438 mya
2.-
First skeletal fossils
3.-
Occurrence of the Tommotian Fauna
4.-
Development of Archaeocyathid reefs
5.-
Trilobites dominate since the upper part of the Lower Cambrian
6.-
Radiation of large animals
7.-
Mass extinction of trilobites at the end of the Cambrian
8.-
Marine sediments are weakly burrowed in the Lower Cambrian
9.-
Marine sediments are heavily burrowed in the Ordovician
10.-
First jawless fishes appeared in the middle Ordovician
11.-
Evolutionary radiation at the base of the middle Ordovician
12.-
Mass extinction of warm-water taxa
13.-
Continental glaciation at the end of the Ordovician
14.-
The landmasses (continents) in the Upper Cambrian are: Gondwanaland, Laurentia,
Baltica, and Siberia
15.-
Major plate tectonic reconfiguration in the middle part of the Upper Ordovician
16.-
Predators become very common, e.g.. nautiloids.
17.-
Earliest land plants.
The Cambrian
System:
It derives its name from the ancient Roman name for
Biological Principles: The Evolutionary Processes of Phanerozoic Biota ||The concept of extinction || Cambrian Explosion: What is the Cambrian Explosion?
Paleoecology: || Types of marine environments
Geological Principles: Paleogeography || Landmasses: Gondwanaland || Baltica || Siberia || Laurentia
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.
The Cambrian
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
Vendian strata.
The Tommotian fauna 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.
The Nature
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.
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
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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