The Cambrian page from Berkeley.

Information on the Cambrian time scale and Cambrian stratigraphy from Berkeley.

Cambrian Life

Tectonic and climatic setting

Spend a few minutes to locate the various continents and their names at this time.

• North America = Laurentia
• Northern Europe = Baltica
• Gondwanaland = the southern continents.
  They are upside down for the most part. You should be able to pick out the outline of Africa (far right), Australia (upper left part of Gondwanaland), Antarctica (to the right of Australia).
  A glance at the Ordovician map will show you South America upside down on the left, nestled on Africa.

As we proceed through the Paleozoic, we will be referring to these paleogeographic reconstructions frequently to see changes as time passes.

For the Cambrian, note that the continents are separate (not all assembled into Pangea until the end of the Paleozoic), and that they are primarily located in tropical latitudes.
Also note that there are NO CONTINENTS LOCATED AT THE POLES.
This will become important later in the Paleozoic because it influences climate.

What does this mean?
Basically, if there are no continents at the poles, there was no place for glaciers to grow. Global temperatures were probably warm, because tropical waters could not flow far before running into a continent, and being deflected N or S.

Also note the distribution of rock types, such as evaporites (E). Today, the desert latitudes are at about 30 degrees N and S of the equator. Note all of the shallow sea deposits. Most are tropical, suggesting the sort of warm, shallow sea conditions needed for the formation of limestones. Indeed, the Cambrian and Ordovician are times of widespread deposition of carbonates, particularly in the Appalachian region.

Check the Cambrian Paleogeographic map (Levin, 5th edition, p. 275) to see the distribution of sedimentary environments.

CAMBRIAN FOSSIL RECORD

The Cambrian is best described as a time of evolutionary explosion. All marine invertebrate phyla appeared during this time, with the exception of the bryozoa. The dominant marine invertebrates with hardparts were the trilobites, brachiopods, and archaeocyathids. Tommotian (lowermost Cambrian)
570 - 590 my
archaeogastropods, brachiopods, sponges, archaeocyathids, hyolithids, worm-like taxa
First diverse biotas of animals with skeletons.

Between 570 - 520 my, nearly all coelomate phyla with skeletons appeared rapidly.

Origin of skeletons (shells)

Function:

1. support for muscles, etc.
   
2. protection against environment & other organisms, predators
   
3. aid in locomotion

Adaptive radiation occurred; rapid diversification of forms.

Possible reasons for the advent of skeletonization:
Increasing oxygen levels (Toewe, 1970)
Synthesis of collagen, a fibrous connective tissue in shells, cuticles, carapaces, etc. directly or indirectly requires collagen.

Oxygen priorities
Low oxygen levels: respiration & tissue synthesis
High oxygen levels: oxygen can be used for lower priority things - skeletons, shells, etc.
Oxygen reached critical threshold at this time, eliminating the need for priorities.

Evidence: modern low O2 environments have only small, soft-bodied forms.

Problems?
Muscles require collagen, suggesting that early muscles were weak, BUT early evidence for metazoans shows burrows which would require good muscles.

Stanley (1976) disagrees. Says Cambrian was a time of the initial proliferation of organisms and life in general. Says skeletonization was a major evolutionary experiment, which succeeded, leading to rapid adaptive radiation and survival of the fittest.

The earliest organisms with soft bodies may have had respiration by diffusion across body wall.
When O2 content of atm. increased, it allowed them to develop respiratory systems, circulatory systems, etc. No longer needed to use O2 diffusion. Larger body size possible.

Sudden simultaneous appearance of skeletonized taxa.
Adaptive radiation. Follows Punctuated Equilibrium model.

Cambrian fossils:

• trilobites = most conspicuous, easy to identify.
  rapid evolution. approx 90 families. good index fossils for dating (biostratigraphy)
  

  Trilobite Olenellus, Early Cambrian Denver Museum of Natural History	Trilobite Alokistocare harrisi, Middle Cambrian, Length of trilobite 1.9 inches Denver Museum of Natural History	Trilobite Acadoparadoxides briareus, Early Cambrian, Length of trilobite 18 inches Denver Museum of Natural History

• brachiopods - abundant, small, limited diversity
• molluscs - small
• echinoderms - unusual types now extinct
• archaeocyathids - primitive sponge relatives

Most Cambrian animals were herbivores that fed on algae.

A few worm-like animals and arthropods had specialized adaptations for feeding and may have been carnivores.

No large carnivores in Cambrian.

The Cambrian was a time of "evolutionary experimentation" and adaptive radiation. Many body plans were tested, but only a few succeeded during natural selection (predation, competition, etc.).

Many groups of animals appeared, but few succeeded.

The Burgess Shale

Click here to go to Dr. Gore's Burgess Shale Page

University of Calgary Burgess Shale Page
Science Web Burgess Shale Page
Yoho National Park, Canada Burgess Shale site
Wierd creatures of the Cambrian - nice 3D pictures
Paleomod Burgess Shale site
Three dimensional pictures and QuickTime movies of Burgess Shale creatures (from Japan)

In a few places in the world, there are examples of exceptional preservation of soft-bodied marine invertebrates. The Burgess Shale is the most spectacular of these. Its occurrence early in the Cambrian serves to highlight the great diversity and variety of multicellular life at this early point in its history.

Wide variety of body plans is shown in the BURGESS SHALE. Although hard parts had appeared, soft-bodied organisms were still present (as they are today).

Significance: exceptional, unique preservation of soft-bodied animals in the Cambrian.

Discovered by Charles Walcott, 1909, Canadian Rockies, British Columbia.

Good preservation indicates deposition in anoxic conditions. Many delicate details of soft part anatomy are preserved. (Legs and gills of trilobites, for ex.). Fossils found in turbidite beds in the Burgess Shale, which were swept off an adjacent, well- oxygenated, carbonate platform by turbidity currents, and killed and protected from decay in anoxic water.

More than 120 species. Includes previously unknown phyla. Arthropods, molluscs, echinoderms, coelenterates, onychophorans, priapulid worms, annelids, chordates, sponges.

References on the Burgess Shale:

• Briggs, D. E. G., 1991, Extraordinary Fossils, American Scientist, v. 79, p. 130-141.

• Briggs, D. E. G., Erwin, D. H., and Collier, F. J., 1994, The Fossils of the Burgess Shale, Smithsonian Institution Press, Washington, D.C., 238 p., QE 770 .B75

• Gould, Stephen Jay, 1989, Wonderful Life, The Burgess Shale and the Nature of History, W. W. Norton & Co., NY, 347 p., QE 770.G67

• Morris, S.C., 1989, Burgess Shale faunas and the Cambrian Explosion, Science, v. 246, p. 339-346.

• Morris, S.C., 1986, The community structure of the Middle Cambrian Phyllopod Bed (Burgess Shale), Paleontology, v. 29, part 3, p. 423-467.

• Morris, S. C. and Whittington, H. B.,1979, The Animals of the Burgess Shale, Scientific American, July, p. 122-133.

• Whittington, H. B., The Burgess Shale, 1985, Yale University Press. QE770.W6

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This page created by Pamela J. W. Gore
DeKalb College, Clarkston, GA
October 1995.
Last modified November 3, 1997