8. Which of the following is NOT mentioned inParagraph4 as being true of the Ediacara formation?
A It contains fossils thatdate back to the Precambrian period.
B It contains only soft-bodied animalfossils.
C It is located on a single site in Australia.
D It does notcontain any fossils of the ancestors of modern animals.
Paragraph5: Aslightly younger fossil formation containing animal remains is the Tommotianformation, named after a locale in Russia. It dates to the very early Cambrianperiod, and it also contains only soft-bodied forms. At one time, the animalspresent in these fossil beds were assigned to various modern animal groups, butmost paleontologists now agree that all Tommotian fossils represent unique bodyforms that arose in the early Cambrian period and disappeared before the end ofthe period, leaving no descendants in modern animal groups.
9. Which ofthe sentences below best expresses the essential information in the highlightedsentence in the passage? Incorrect choices change the meaning in important waysor leave out essential information.
A The animals found in the Tommotianfossil bed were once thought to belong to a variety of modern animal groups, butnow they are thought to have descended from a single group.
B Animals in theTommotian fossil beds were initially assigned to modern animal groups but arenow thought to belong to groups that emerged and died out during the Cambrianperiod.
C Though at first they thought otherwise, paleontologists now agreethat the animals in the Tommotian have body forms from which modern animals havedescended.
D It is unclear whether the Tommotian fossils from the earlyCambrian period represent unique body forms or whether they should be assignedto various modern animal groups.
Paragraph6: A third fossil formationcontaining both soft-bodied and hard-bodied animals provides evidence of theresult of the Cambrian explosion. This fossil formation, called the BurgessShale, is in Yoho National Park in the Canadian Rocky Mountains of BritishColumbia. Shortly after the Cambrian explosion, mud slides rapidly buriedthousands of marine animals under conditions that favored fossilization. Thesefossil beds provide evidence of about 32 modern animal groups, plus about 20other animal body forms that are so different from any modern animals that theycannot be assigned to any one of the modern groups. These unassignable animalsinclude a large swimming predator called Anomalocaris and a soft-bodied animalcalled Wiwaxia, which ate detritus or algae. The Burgess Shale formation alsohas fossils of many extinct representatives of modern animal groups. Forexample, a well-known Burgess Shale animal called Sidneyia is a representativeof a previously unknown group of arthropods (a category of animals that includesinsects, spiders, mites, and crabs).
10. Why does the author mentionAnomalocans and Wiwaxia?
A To contrast predators with animals that eat plantssuch as algae
B To question the effects of rapid mud slides onfossilization
C To suggest that much is still unknown about animals found inthe Burgess Shale
D To provide examples of fossils that cannot be assigned toa modern animal group
11. Sidneyia is an example ofa relative ofAnomalocaris and Wiwaxia
A a previously unknown Burgess Shale animal
B anextinct member of a currently existing category of animals
C an animal thatcannot be assigned to any modern animal group
Paragraph7: Fossilformations like the Burgess Shale show that evolution cannot always be thoughtof as a slow progression. The Cambrian explosion involved rapid evolutionarydiversification, followed by the extinction of many unique animals. Why was thisevolution so rapid? No one really knows. Many zoologists believe that it wasbecause so many ecological niches were available with virtually no competitionfrom existing species. Will zoologists ever know the evolutionary sequences inthe Cambrian explosion? Perhaps another ancient fossil bed of soft-bodiedanimals from 600-million-year-old seas is awaiting discovery.
12. Whatcan be inferred from Paragraph7 about why the Cambrian explosion is sounusual?
A It generated new ecological niches through the extinction of manyunique animals.
B It was a period of rapid evolution, and evolution is oftenthought of as a slow process.
C It is a period whose evolutionary sequencesare clearly marked.
D It generated a very large number of ancient fossil bedscontaining soft-bodied animals.
Paragraph3: One interpretation regardingthe absence of fossils during this important 100-million-year period is thatearly animals were soft bodied and simply did not fossilize. ■ Fossilization ofsoft-bodied animals is less likely than fossilization of hard-bodied animals,but it does occur. ■ Conditions that promote fossilization of soft-bodiedanimals include very rapid covering by sediments that create an environment thatdiscourages decomposition.■ In fact, fossil beds containing soft-bodied animalshave been known for many years. ■
13. Look at the four squares [■] thatindicate where the following sentence could be added to the passage.
A It isrelatively rare because the fossilization of soft-bodied animals requires aspecial environment.
B Where could the sentence bestfit?
14. Directions: An introductory sentence for a briefsummary of the passage is provided below. Complete the summary by selecting theTHREE answer choices that express the most important ideas in the passage. Someanswer choices do not belong in the summary because they express ideas that arenot presented in the passage or are minor ideas in the passage. This question isworth 2 points.
The term “Cambrian explosion” refers to thegeologically brief period during which all modern animal groupsevolved.
AnswerChoices
1. Little is known about the stages of evolution during the Cambrianperiod, in part because early animals were soft bodied and could fossilize onlyunder particular conditions.
2. While animal fossils from before the Cambrianexplosion have no modern descendants, many animals that evolved during theCambrian explosion can be assigned to modern groups.
3. The Cambrian periodis significant because it marks the emergence of eukaryotic life-forms –organisms that have cells with true nuclei
4. The Ediacara fossil formationprovides the most information about the Cambrian explosion, while the earlier,Tommotian and Burgess Shale formations give clues about Precambrianevolution.
5. Zoologists are awaiting the discovery of a 600-million-year-oldfossil formation in order to be able to form a theory of how animal evolutionprogressed.
6. Although the reasons for the rapid evolution of animals duringthe Cambrian period are not known, one proposed explanation is an abundance ofniches with a lack of competitors.
