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Chapter 18: The Cambrian Explosion and Beyond
Chapter Study Questions
Chapter Study Questions
This activity contains 12 questions.
Match the evolutionary process described in this chapter listed below to the description that is the best match for it.
Using the pull-down menus, match each item in the left column to the corresponding item in the right column.
punctuated equilibrium
stasis
gradualism
mass extinction
habitat tracking, or dynamic stasis, or zigzag evolution
adaptive radiation
1.1 rapid diversification of a lineage
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D
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F
1.2 evolutionary change that fluctuates back and forth as habitats change
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F
1.3 global disappearance of a very high percentage of species in a very short time
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F
1.4 the occurrence of long spans of time without detectable evolutionary change
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F
1.5 brief bursts of evolutionary change separated by long times with little change
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B
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F
1.6 steady evolutionary change over a long period of time
A
B
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D
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F
Match the fossil type described in this chapter listed below to the description that is the best match for it.
Using the pull-down menus, match each item in the left column to the corresponding item in the right column.
mold
unaltered remains
compression or impression fossils
trace fossil
permineralized fossil
cast
2.1 a three-dimensional model formed when sediment invades an empty space
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B
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F
2.2 a three-dimensional fossil formed when minerals replace cellular materials
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B
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F
2.3 an original body part that has lasted an unusually long time
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B
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2.4 a two-dimensional outline of an organism
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F
2.5 an empty space left when organic remains decay after being buried
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2.6 a burrow, track, or other sign of an animal's activity
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F
Which of the following statements about the Cambrian explosion is true?
started 565 million years ago.
is the time when the first multicellular animals appear in the fossil record.
was too sudden to be explainable by natural selection.
includes the first known fossil representatives of most animal phyla.
agrees with molecular-based estimates of when most animal phyla first evolved.
lasted 2 million years.
Which of the following statements regarding Edicaran organisms is false?
Edicaran organisms include diploblasts like sponges, jellyfish, and comb jellies.
Edicaran organisms occur in the Burgess Shale .
Edicaran organisms include some small bilateral animals.
Edicaran organisms were usually just a few centimeters across.
Edicaran organisms occurred just before the Cambrian explosion.
Decide which of the following statements are correct.
Punctuated equilibrium is difficult to distinguish from gradualism in cases when ancestor and descendant species overlap.
Stasis may mask underlying zig-zag evolution.
Fossil cheilostome bryozoans show a pattern of punctuated equilibrium.
Gradualism sometimes occurs with periods of stasis.
"Living fossils" demonstrate that stasis is correlated with low genetic variation.
Mode of evolution differs in different taxa.
Older lineages have a risk of extinction compared to younger lineages.
Higher.
Similar.
Lower.
How and why do adaptive radiations occur? Give examples to illustrate your answer.
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How common is punctuated equilibrium, and is it the only significant mode of evolution, as Gould and Eldredge hypothesized? How do we know?
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Look again at Figure 18.25, Jablonski's data on survivorship curves for fossil bivalves and gastropods. Why is it significant that the three lines have different slopes? What factors affected extinction risk in this study?
To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
Briefly list the major groups of taxa that survived the K-T extinction, and those that did not. How did body size affect risk of extinction? What other traits were associated with survival of the mass extinction? What animals on Earth today have some of the traits that are associated with probability of surviving a mass extinction?
To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
What is the evidence that humans caused extinctions in the past? How did human-caused extinctions in the past differ from those that are thought to be occurring today?
To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
Describe three methods commonly used to assess current extinction rate. What are some problems with each method? How does the current extinction rate compare to background extinction rate?
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