【OG24-592题】It can be inferred that on the basis of the 1981 discovery of conodont remains, paleontologists could draw which of the following conclusions?_mofa留学圈mofaGRE在线题库系统_GRE在线搜题_GRE题库解析_GRE真题机经_GRE课程_GRE培训机构

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Conodonts, the spiky phosphatic remains (bones and teeth composed of calcium phosphate) of tiny marine animals that probably appeared about 520million 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 there mains 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.

he 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 moreprimitive 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.

It can be inferred that on the basis of the 1981 discovery of conodont remains, paleontologists could draw which of the following conclusions?

The earliest vertebrates were sedentary suspension feeders. Ostracoderms were not the earliest vertebrates. Defensive armor preceded jaws among vertebrates. Paired eyes and adaptations for activity are definitive characteristics of vertebrates. Conodonts were unlikely to have been predators.

正确答案： B

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文章大意逻辑
牙形石是海洋小动物的尖状磷酸盐遗迹，曾是最具争议化石之一，其所属生物性质和遗迹功能未知。1981年发现不仅保存了磷酸盐元素，还保存了软组织遗迹的化石，对脊椎动物骨骼发展假说有重要意义。传统观点认为脊椎动物骨骼是防御性发展，早期脊椎动物是久坐的悬浮进食者，发展出骨质鳞片或板覆盖物，牙齿是次要特征。但其他古生物学家认为若早期脊椎动物不是掠食性的，脊椎动物的一些明确特征（如成对眼睛、活跃生活的肌肉和骨骼适应性）就不会进化，牙齿比外部装甲更原始，最早的脊椎动物是掠食者。 文章类型及逻辑简图
文章类型为新旧观点对比。 旧观点：The vertebrate skeleton had traditionally been regarded as a defensive development. Early vertebrates were sedentary suspension feeders, developed bony scales or plates, teeth were secondary features. 新观点：However, other paleontologists argued that definitive characteristics of vertebrates would not have evolved unless the first vertebrates were predatory. Teeth were more primitive than external armor and the earliest vertebrates were predators. 问题类型及做题方法
问题类型为推断题。做题方法是根据文中“1981 discovery of conodont remains”定位相关内容进行推断。 选项分析
A选项：文中未提及最早的脊椎动物是久坐的悬浮进食者，属于无中生有，排除。 B选项：因为1981年发现的牙形石化石对脊椎动物骨骼发展假说有新的意义，动摇了传统观点中关于脊椎动物发展的一些认知，比如ostracoderms在传统观点中有相关地位，新发现可能意味着ostracoderms不是最早的脊椎动物，该项可以推断得出，当选。 C选项：文中没有对防御性装甲和颌在脊椎动物中出现先后顺序的相关推断依据，排除。 D选项：成对眼睛和适应性是脊椎动物明确特征，但不是推断出它是脊椎动物的决定性特征，排除。 E选项：文中没有提及牙形石不太可能是掠食者的相关内容，排除。

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