Though at first they thought otherwise, paleontologists now agreethat the animals in the Tommotian have body forms from which modern animals havedescended.
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?
To contrast predators with animals that eat plantssuch as algae
To question the effects of rapid mud slides onfossilization
To suggest that much is still unknown about animals found inthe Burgess Shale
To provide examples of fossils that cannot be assigned toa modern animal group
11. Sidneyia is an example ofa relative ofAnomalocaris and Wiwaxia
a previously unknown Burgess Shale animal
anextinct member of a currently existing category of animals
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?
It generated new ecological niches through the extinction of manyunique animals.
It was a period of rapid evolution, and evolution is oftenthought of as a slow process.
It is a period whose evolutionary sequencesare clearly marked.
It generated a very large number of ancient fossil bedscontaining soft-bodied animals.
