Chapter 17: The Cambrian Explosion and Beyond

1.	Explain why the following are relatively common in the fossil record: marine-dwelling forms burrowing species recent organisms pollen grains [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
2.	Explain why the following are relatively rare in the fossil record: desert-dwelling forms species that were capable of flight organisms that lived over 3 billion years ago flowers [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
3.	Define the Phanerozoic and Proterozoic eras. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
4.	What important events occurred during the following time intervals? the boundary between the Silurian and Devonian periods the Cambrian period the boundary between the Permian and Triassic periods the Cretaceous period [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
5.	In what sense is the Cambrian period "explosive?" In what sense is the term "explosion" misleading? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
6.	Compare and contrast the Ediacaran and Burgess Shale faunas. What phyla are found in each? How did the species that were present differ in terms of their morphology and ecology? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
7.	What is an adaptive radiation? State two hypotheses to explain why adaptive radiations occur. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
8.	Compare and contrast mass extinctions and background extinctions. How do their size and geographic and taxonomic extent differ? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
9.	Suppose that a species first appears in the fossil record 350 Ma. Why is it logical to argue that this species actually existed before this date? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
10.	What data support the hypothesis that the origin of bilaterians, the deuterostome-protostome split, and the lophotrochozoan-ecdysozoan split all occurred long before the Cambrian explosion? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
11.	If data confirm that a mass extinction event occurred at the end of the Proterozoic era, what would be the consequences for our understanding of why the Cambrian explosion occurred? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
12.	Why would a rise in the availability of oxygen help explain why the Cambrian explosion occurred? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
13.	Give an example of an adaptive radiation. Provide evidence to support the claim that the radiation originated with one or a few species, that it was rapid, and the descendant groups occupy a wide array ecological niches. Suggest a hypothesis to explain why the radiation occurred. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
14.	List the evidence in favor of the impact hypothesis for the K-T extinction. Which piece of evidence do you find most persuasive, and why? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
15.	Why would a meteor strike lead to global cooling, or what researchers call an "impact winter?" [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
16.	Do you accept the hypothesis that a mass extinction event is currently underway? Why or why not? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
17.	Terrestrial fossils from a particular time (say, 230 Ma) are patchily distributed around the world. Instead of being evenly distributed over the continents in a continuous thin layer, they often occur in narrow strips or pockets a few miles wide. Why is this? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
18.	Most fossils of Mesozoic birds are from marine diving birds. Relatively few terrestrial species are known. Does this mean that most Mesozoic birds were, in fact, marine diving birds? Explain your reasoning. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
19.	The rise of angiosperm plants is widely thought to be due to competitive superiority over gymnosperms. However, it is not clear just what gave angiosperms the edge. Some of the hypotheses are that (1) angiosperms may have a better method of pollination, (2) angiosperms have a better method of water transport, and (3) angiosperms have more efficient leaves and can grow faster. Briefly outline experiments that would test these theories. (Remember that both angiosperms and gymnosperms are still alive today, including primitive angiosperms such as Amborella, and thus are available for experiments.) [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
20.	Suppose that during the Pleistocene, a new species of lion arose gradually in western North America and then rapidly migrated to eastern North America. Now suppose you are a paleontologist whose only good fossil lions are from eastern North America. Would it appear to you that the new lion evolved gradually or suddenly? What further information would you need to correctly evaluate whether Pleistocene lions evolved primarily via punctuated equilibrium versus gradualism? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
21.	One of the (many) mysteries of the K-T extinction is the different fate of ammonites and nautiloids. These were molluscs with buoyant, chambered shells that lived in open-water habitats. Ammonites went extinct during the K-T extinction, but some nautiloids survived. The two groups had different reproductive strategies. Ammonites are thought to have produced many free-swimming young each year that fed near the ocean surface and grew rapidly. In contrast, a female nautilus produces just a few large eggs each year, each of which rests quietly in the depths for up to a year before hatching into a small, slow-growing nautilus. Based on these different reproductive strategies, suggest a possible hypothesis for why the nautiloids, but not the ammonites, might have been able to survive an asteroid impact. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
22.	In 1996, Gregory Retallack announced that he had found shocked quartz crystals dating from the same time as the end-Permian extinction. What is the implication of this finding? Other geologists point out that no one has found any evidence of elevated iridium from these strata (despite much searching). What is the significance of the lack of iridium? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
23.	Suppose you are talking to a friend about extinctions, and you mention that humans are known to have caused thousands of extinctions in the last few millenia. Your friend responds "So? Extinction is natural. Species have always gone extinct. So it's really not something we need to worry about." Is your friend correct that extinction is natural? Is the current rate of extinction typical? Is your friend correct that if extinctions are natural, then they are not a problem for the dominant life forms on Earth? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.