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Conodonts, the spiky phosphatic remains (bones and teeth composed of calcium phosphate) of

tiny marine animals that probably appeared about 520 million years ago, were once among the most controversial of fossils. Both the nature of the

organism to which the remains belonged and the function of the remains were unknown. However, since the 1981 discovery of fossils preserving not

just the phosphatic elements but also other remains

of the tiny soft-bodied animals (also called conodonts) that bore them, scientists’ reconstructions of the animals’ anatomy have had important implications for hypotheses concerning the development of the vertebrate skeleton.

The vertebrate skeleton had traditionally been

regarded as a defensive development, champions of this view postulating that it was only with the much later evolution of jaws that vertebrates became predators. The first vertebrates, which were soft-

bodied, would have been easy prey for numerous invertebrate carnivores, especially if these early vertebrates were sedentary suspension feeders.

Thus, traditionalists argued, these animals developed coverings of bony scales or plates, and teeth were

secondary features, adapted from the protective bony scales. Indeed, external skeletons of this

type are common among the well-known fossils of ostracoderms, jawless vertebrates that existed from approximately 500 to 400 million years ago.

However, other paleontologists argued that many of the definitive characteristics of vertebrates, such as paired eyes and muscular and skeletal adaptations for active life, would not have evolved unless the first vertebrates were predatory. Teeth were more primitive than external armor according to this view, and the earliest vertebrates were predators.

The stiffening notochord along the back of the body, V-shaped muscle blocks along the sides,

and posterior tail fins help to identify conodonts as among the most primitive of vertebrates. The lack of any mineralized structures apart from the elements in the mouth indicates that conodonts were more

primitive than the armored jawless fishes such as the ostracoderms. It now appears that the hard parts that

first evolved in the mouth of an animal improved its efficiency as a predator, and that aggression rather

than protection was the driving force behind the origin of the vertebrate skeleton.

The second paragraph in the passage serves primarily to

A.outline the significance of the 1981 discovery of conodont remains to the debate concerning the development of the vertebrate skeleton

B.contrast the traditional view of the development of the vertebrate skeleton with a view derived from the 1981 discovery of conodont remains

C.contrast the characteristics of the ostracoderms with the characteristics of earlier soft- bodied vertebrates

D.explain the importance of the development of teeth among the earliest vertebrate predators

E.present the two sides of the debate concerning the development of the vertebrate skeleton

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This questio

n depends on understanding the second paragraph in the context of the passage as a whole. The second paragraph begins by noting the traditional view of the vertebrate skeleton—that it was a defense against predators—and then goes on to explain

that other paleontologists argued against this idea, claiming instead that vertebrates began as predators and that teeth were a more primary feature than external armor.

A.The second paragraph focuses on describing the debate rather than on the distinctive contribution of the 1981 discovery to that debate.

B.The second paragraph does not explicitly indicate whether the opposition to the

traditional view originally rested on the 1981 discovery of conodont remains. In fact, the surrounding discussion, in the first and third paragraphs, suggests that the discovery in 1981 turned out to support the opposing view, which some paleontologists already held at that time.

C.The mention of ostracoderms in the second paragraph merely serves to indicate how

the traditionalists’ arguments might have seemed plausible. The paragraph as a whole is not devoted to contrasting the ostracoderms with earlier soft-bodied vertebrates.

D.The development of teeth figures in the second paragraph, but this development is mentioned first as a feature that some believed to have been adapted from protective scales; only the final sentence of the paragraph connects teeth to early vertebrate predators.

E.Correct. According to the passage, the debate concerning the development of the vertebrate skeleton hinges on whether vertebrates began as predators, with teeth, or

whether skeletal defenses such as external armor evolved first. The primary purpose of the second paragraph is to distinguish these two sides.

The correct answer is E.