小编整理的是
From Fish to Terrestrial Vertebrates
One of the most significant evolutionary events that occurred on Earth was the transition of water-dwelling fish to terrestrial tetrapods (four-limbed organisms with backbones). Fish probably originated in the oceans, and our first records of them are in marine rocks. However, by the Devonian Period (408 million to 362 million years ago), they had radiated into almost all available aquatic habitats, including freshwater settings. One of the groups whose fossils are especially common in rocks deposited in fresh water is the lobe-finned fish.
The freshwater Devonian lobe-finned fish rhipidistian crossopterygian is of particular interest to biologists studying tetrapod evolution. These fish lived in river channels and lakes on large deltas. The delta rocks in which these fossils are found are commonly red due to oxidized iron minerals, indicating that the deltas formed in a climate that had alternate wet and dry periods. If there were periods of drought, any adaptations allowing the fish to survive the dry conditions would have been advantageous. In these rhipidistians, several such adaptations existed. It is known that they had lungs as well as gills for breathing. Cross sections cut through some of the fossils reveal that the mud filling the interior of the carcass differed in consistency and texture depending on its location inside the fish. These differences suggest a saclike cavity below the front end of the gut that can only be interpreted as a lung. Gills were undoubtedly the main source of oxygen for these fish, but the lungs served as an auxiliary breathing device for gulping air when the water became oxygen depleted, such as during extended periods of drought. So, these fish had already evolved one of the prime requisites for living on land: the ability to use air as a source of oxygen.
A second adaptation of these fish was in the structure of the lobe fins. The fins were thick, fleshy, and quite sturdy, with a median axis of bone down the center. They could have been used as feeble locomotor devices on land, perhaps good enough to allow a fish to flop its way from one pool of water that was almost dry to an adjacent pond that had enough water and oxygen for survival. These fins eventually changed into short, stubby legs. The bones of the fins of a Devonian rhipidistian exactly match in number and position the limb bones of the earliest known tetrapods, the amphibians. It should be emphasized that the evolution of lungs and limbs was in no sense an anticipation of future life on land. These adaptations developed because they helped fish to survive in their existing aquatic environment.
What ecological pressures might have caused fishes to gradually abandon their watery habitat and become increasingly land-dwelling creatures? Changes in climate during the Devonian may have had something to do with this if freshwater areas became progressively more restricted. Another impetus may have been new sources of food. The edges of ponds and streams surely had scattered dead fish and other water-dwelling creatures. ■ A In addition, plants had emerged into terrestrial habitats in areas near streams and ponds, and crabs and other arthropods were also members of this earliest terrestrial community. ■ B Thus, by the Devonian the land habitat marginal to freshwater was probably a rich source of protein that could be exploited by an animal that could easily climb out of water. ■ C Evidence from teeth suggests that these earliest tetrapods did not utilize land plants as food; they were presumably carnivorous and had not developed the ability to feed on plants. ■ D
How did the first tetrapods make the transition to a terrestrial habitat? Like early land plants such as rhyniophytes, they made only a partial transition; they were still quite tied to water. However, many problems that faced early land plants were not applicable to the first tetrapods The ancestors of these animals already had a circulation system, and they were mobile, so that they could move to water to drink. Furthermore, they already had lungs, which rhipidistians presumably used for auxiliary breathing. The principal changes for the earliest tetrapods were in the skeletal system—changes in the bones of the fins, the vertebral column, pelvic girdle, and pectoral girdle.
Paragraph 1
One of the most significant evolutionary events that occurred on Earth was the transition of water-dwelling fish to terrestrial tetrapods (four-limbed organisms with backbones). Fish probably originated in the oceans, and our first records of them are in marine rocks. However, by the Devonian Period (408 million to 362 million years ago), they had radiated into almost all available aquatic habitats, including freshwater settings. One of the groups whose fossils are especially common in rocks deposited in fresh water is the lobe-finned fish.
1. Paragraph 1 supports which of the following statements about fish evolution?
A. Lobe-finned fish were among the earliest types of fish to appear.
B. Fish began living in freshwater habitats only after originating elsewhere.
C. Lobe-finned fish radiated into almost all available aquatic habitats.
D. During the Devonian, lobe-finned fish were more common in marine than in freshwater habitats.
Paragraph 2
The freshwater Devonian lobe-finned fish rhipidistian crossopterygian is of particular interest to biologists studying tetrapod evolution. These fish lived in river channels and lakes on large deltas. The delta rocks in which these fossils are found are commonly red due to oxidized iron minerals, indicating that the deltas formed in a climate that had alternate wet and dry periods. If there were periods of drought, any adaptations allowing the fish to survive the dry conditions would have been advantageous. In these rhipidistians, several such adaptations existed. It is known that they had lungs as well as gills for breathing. Cross sections cut through some of the fossils reveal that the mud filling the interior of the carcass differed in consistency and texture depending on its location inside the fish. These differences suggest a saclike cavity below the front end of the gut that can only be interpreted as a lung. Gills were undoubtedly the main source of oxygen for these fish, but the lungs served as an auxiliary breathing device for gulping air when the water became oxygen depleted, such as during extended periods of drought. So, these fish had already evolved one of the prime requisites for living on land: the ability to use air as a source of oxygen.
2. According to paragraph 2, what do the minerals in the delta rocks containing rhipidistian crossopterygian fossils reveal?
A. These deltas formed in dry periods but gradually became wetter.
B.These deltas contain different types of iron minerals than do the surrounding areas.
C.Most rhipidistian crossopterygian fish died when the climate became dry.
D.Rhipidistian crossopterygian fish lived in areas that experienced alternate dry and wet periods.
3. The word “advantageous” in the paragraph 2 is closest in meaning to
A. beneficial
B. necessary
C. remarkable
D. common
4. In paragraph 2, why does the author include the information that mud inside rhipidistian crossopterygian fossils differed in consistency and texture depending on where the mud was located?
A. To provide evidence that rhipidistian crossopterygian lived in river channels and lakes on large deltas.
B. To identify an effect of the oxidation of iron minerals on the evolution of rhipidistian crossopterygian.
C. To help explain why scientists have concluded that rhipidistian crossopterygian probably had lungs.
D. To explain why scientists decided to cut cross sections through some fossils of rhipidistian crossopterygian.
5. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
A. Because the lungs of these fish were able to provide only a small amount of oxygen, these fish obtained most of their oxygen through their gills during periods of drought.
B. During periods of extended drought, these fish used their lungs to increase their intake of oxygen beyond the levels absorbed by the gills in normal times.
C. Although these fish primarily used their gills to obtain oxygen, they used their lungs to obtain oxygen from the air when there was not enough in the water.
D. During periods of extended drought, the gills became an auxiliary breathing device and the lungs became the main source of oxygen for these fish.
Paragraph 3
A second adaptation of these fish was in the structure of the lobe fins. The fins were thick, fleshy, and quite sturdy, with a median axis of bone down the center. They could have been used as feeble locomotor devices on land, perhaps good enough to allow a fish to flop its way from one pool of water that was almost dry to an adjacent pond that had enough water and oxygen for survival. These fins eventually changed into short, stubby legs. The bones of the fins of a Devonian rhipidistian exactly match in number and position the limb bones of the earliest known tetrapods, the amphibians. It should be emphasized that the evolution of lungs and limbs was in no sense an anticipation of future life on land. These adaptations developed because they helped fish to survive in their existing aquatic environment.
6. According to paragraph 3, the structure of the fins of rhipidistian crossopterygian may have allowed these fish to
A.reduce the amount of oxygen needed for survival
B.develop thick, sturdy bones
C.move more efficiently in water
D.move short distances over areas that were mostly dry
7. The word “adjacent” in paragraph 3 is closest in meaning to:
A. nearby
B. available
C. temporary
D. fresh
Paragraph 4
What ecological pressures might have caused fishes to gradually abandon their watery habitat and become increasingly land-dwelling creatures? Changes in climate during the Devonian may have had something to do with this if freshwater areas became progressively more restricted. Another impetus may have been new sources of food. The edges of ponds and streams surely had scattered dead fish and other water-dwelling creatures. ■ A In addition, plants had emerged into terrestrial habitats in areas near streams and ponds, and crabs and other arthropods were also members of this earliest terrestrial community. ■ B Thus, by the Devonian the land habitat marginal to freshwater was probably a rich source of protein that could be exploited by an animal that could easily climb out of water. ■ C Evidence from teeth suggests that these earliest tetrapods did not utilize land plants as food; they were presumably carnivorous and had not developed the ability to feed on plants. ■ D
8. The word “progressively” in paragraph 4 is closest in meaning to:
A. increasingly
B. noticeably
C. occasionally
D. rapidly
9. In paragraph 4, why does the author point out that crabs and other arthropods were already living on land when the ancestors of the first tetrapods began living there?
A. To account for the presence of dead fish along the edges of ponds and streams during the Devonian.
B. To support the claim that climate change caused freshwater habitats to become more restricted during the Devonian.
C. To identify a consequence of the emergence of plants into terrestrial habitats near ponds and streams.
D. To identify a possible reason for why certain fish gradually became terrestrial organisms.
10. According to paragraph 4, teeth of the earliest tetrapods suggest that these tetrapods
A. competed with other animals for protein
B. were probably carnivores
C. could easily climb out of water
D. were able to eat plants
Paragraph 5
How did the first tetrapods make the transition to a terrestrial habitat? Like early land plants such as rhyniophytes, they made only a partial transition; they were still quite tied to water. However, many problems that faced early land plants were not applicable to the first tetrapods The ancestors of these animals already had a circulation system, and they were mobile, so that they could move to water to drink. Furthermore, they already had lungs, which rhipidistians presumably used for auxiliary breathing. The principal changes for the earliest tetrapods were in the skeletal system—changes in the bones of the fins, the vertebral column, pelvic girdle, and pectoral girdle.
11. According to paragraph 5, which of the following was true of the first tetrapods?
A. They became dependent for food on organisms already living on land.
B. They needed to develop new mechanisms for obtaining nutrients.
C. They continued to live in close association with aquatic environments.
D. They were evolutionarily far removed from their rhipidistian ancestors.
12. According to paragraph 5, what was the main way that the earliest tetrapods differed from their immediate fish ancestors?
A. The tetrapods had a different skeletal structure.
B. The tetrapods had more sources of food available
C. The tetrapods had a circulation system.
D. The tetrapods could move to new pools of water.
13. Look at the four squares [■] that indicate where the following sentence could be added to the passage.
These would have been deposited by the receding waters of droughts, during which many aquatic animals must have died.
Where would the sentence best fit? Click on a square [■] to add the sentence to the passage
14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
Drag your answer choices to the spaces where they belong. To remove an answer choice, click on it.
To review the passage, click VIEW TEXT
Freshwater lobe-finned fish may be the direct ancestors of terrestrial tetrapods.
A.Rhipidistian crossopterygian had features such as primitive lungs and thick fins that could have helped it survive dry periods.
B.During the Devonian, the number of bones increased in the fins of rhipidistians, improving such animals’ ability to swim and move over land
C.Shortly after the earliest tetrapods developed lungs, plants and other animals began to flourish on land.
D.By the Devonian period, lobe-finned fish preferred freshwater habitats to life in the ocean.
E.A drier climate and new sources of food on land may have encouraged the lobe-finned fish’s move to a terrestrial existence.
F.Early tetrapods remained closely connected to water, but several of their body structures were adapted for life on land.
参考译文
从鱼到路栖脊椎动物
地球上曾发生过的最重要的一个进化过程就是水生鱼类到陆地四足动物(有着脊骨的四足生物)的转变。鱼类可能起源于海洋，我们对于它们的最早记录都来自海洋的石头。然而，在泥盆纪(4亿8百万年前到3亿6千2百万年前之间)，它们已经散布到几乎所有的水生环境中，包括淡水环境。有一类鱼，它的化石在淡水中的岩石里特别常见，这类鱼被称作总鳍鱼。
研究四足动物进化的生物学家对于泥盆纪时期的淡水总鳍鱼非常有兴趣。这些鱼居住在大型三角洲的河道和湖泊中。这些鱼的化石被发现在三角洲的石头中，而这些石头通常都是红色的，因为其中充满氧化铁。这就显示出，这些三角洲形成时期的气候中，湿季和旱季交替出现。如果处在干旱的时期，能够让这些鱼存活下来的任何适应能力都会很有帮助。在这些总鳍鱼中，就存在着几种这样的有益的适应能力。众所周知的是，它们通过肺和腮呼吸。一些化石的横切面显示出，填满残骸内部的淤泥在厚度和构造上存在差异，而这个差异取决于淤泥在鱼体 内的位置。这些差别暗示出，在体腔的前端下面存在一个嚢状腔，这个腔只能被解释成其当做肺的功用。毫无疑问，对于这类鱼，腮是氧气的主要来源，但是当水中氧气减少，比如在长期干旱的条件下，肺也起到了一种呼吸辅助器官的作用。所以，这些鱼已经进化出了一种重要的在陆地居住的必备条件：即呼吸空气中的氧气。
这些鱼的第二种适应性能力就是肉鳍。这些鳍很厚实、肉肉的，而且很结实，中间带有骨头。它们可能已经被用来帮助鱼在陆地上缓慢移动，可能已经发达到能让这些鱼从一个几乎干涸的水池缓慢的移动到临近的池塘中，利用新水池中充足的水和氧气来生存。这些鳍最终进化成了短粗的腿。泥盆纪总鳍鱼中，鳍部骨头的数量和位置与最早期的四足动物(两栖动物)完全吻合。重要的是，肺和四肢的进化并非是因为预料到了未来在陆地上生活而产生的。这些适应性能力的进化出来的原因是，它们能够帮助总鳍鱼在当时的水生环境中幸存下来。
什么样的生态压力导致鱼逐渐放弃水生环境、转而在陆地居住呢?如果淡水地区逐渐变少，那么在泥盆纪的气候变化可能与这个进化有关。另一个原因可能是新的食物来源。池塘和小溪边必然有一些零散分散的死亡鱼类以及其他水生生物。此外，植物逐渐转移到溪边和池塘边的陆地环境，并且螃蟹和其他节肢动物也生存在于这种最早期的陆地群落中。所以，在泥盆纪时期，淡水旁边的陆地可能存在大量蛋白质，这些蛋白质可以被那些轻易地从水中爬出来的动物获取并利用。从牙齿中发现的证据指出，这些早期的四足动物不吃陆地上的植物：它们大概都是食肉动物，并且还没有进化出以植物为食的能力。
最早的四足动物是如何转变到陆地上生活的?就像很多早期植物(比如莱尼蕨类)一样，它们只产生了部分的变化：它们仍旧与水有很紧密的关系。然而，很多早期陆地植物遇到的问题不适用于这些最早的四足动物。这些动物的祖先已经具备循环系统，能够移动，所以它们能移动到水边饮水。此外，它们已经有了肺，肺可能能够帮助总鳍鱼进行辅助的呼吸。最早的四足动物的主要变化就是骨骼系统的变化，即鳍骨、脊柱、骨盆带和肩带等部位骨骼的变化。
Q1
正确答案：B
解析：B选项对应“Fish probably originated in the oceans…However, by…they had radiated into almost all available aquatic habitats, including freshwater settings”，正确。
A选项错在偷换了原文的概念，lobe-finned fish 只是说在淡水的岩石中，它的化石特别常见;C选项错误在于lobe-finned fish在所有的水生生境中都成功演化，但是文中只是提到在淡水中常见;D选项错在按照段落推断在淡水环境中更为常见，而且也没有对比。
Q2
正确答案：D
解析：根据题干，直接对应第2段第2句的“The delta rocks…indicating that the deltas formed in a climate that had alternate wet and dry periods” 所以D选项正确。
Q3
正确答案：A
解析：这句话的意思是，在干燥的气候里，任何使rhipidistian crossopterygian fish适应的变化都是advantageous的。这里的“advantageous”指“有利的”，与A选项意思相符。其余选项的意思分别是“必要的”“显著的”和“平常的”;按照正常的逻辑推理，让fish在干燥条件下生存的适应只能是有利的，同时，根据advantage的联想，对应选项，也只能选A。
Q4
正确答案：C
解析：根据题干对应原文 ，“Cross sections…differed in consistency and texture… can only be interpreted as a lung.”这句话的意思是化石的横截面表明了那些鱼残骸内部的泥土根据在鱼身体里位置的不同，在粘稠度和质地上有所差异;然后后文马上解释说这些差异暗示了在肠前端的囊状腔洞(saclike cavity)只能被解释为当肺的功能用了。和选项C表述一致。在定位句前提到了呼吸问题，其余三个选项显然是跟这段要阐述的内容没有关系。
Q5
正确答案：C
解析：高亮文本的含义是，腮是氧气大部分来源(的器官)，而肺是在例如水中氧气耗尽时时候辅助呼吸的工具，比如说特别长的干旱期。C选项转述正确。第A选项不选，lungs 和 gills的功用弄反;B选项不选，没有normal times的比较说明;D选项不选，“the gills became an auxiliary breathing device”错误，也是弄反。
Q6
正确答案：D
解析：根据题干定位到段落第二句 “They…perhaps good enough to allow a fish to flop its way …pond”，这句话的意思是…也许好到能让一条鱼扑通扑通地从一个水基本快干了的池子爬到旁边邻近的水和氧气足够多适宜生存的池塘里。对应D选项正确。
Q7
正确答案：A
解析：这句话的意思是，fins能让鱼从干了的池塘迁移到临近的水充足的池塘。这里的“adjacent”意为“邻近的”，A选项意义相符。其余选项分别是“可用的”“暂时的”“新鲜的”，不能够用来形容池塘。
Q8
正确答案：A
解析：这句话的大意是，如果考虑到淡水资源progressively 少的话，在Devonian期间的气候变化可能于此有关;这里的“progressively”意为“越来越”，与A选项同义。其余选项的意思分别是“明显地”，“偶尔地”和“迅速地”，不合语境。
Q9
正确答案：D
解析：根据题干定位“In addition… earliest terrestrial community”这句话之后解释到“habitat marginal to freshwater was probably a rich source of protein”，这句话之前说到“impetus may have been new sources of food” 提到crabs 和 arthropods 目的其实是想说在临近淡水地方有充足的蛋白质(也就是食物)供给，水池边缘的食物更丰富，这些都是某些鱼类到陆地上的原因。
Q10
正确答案：B
解析：根据题干，定位到段落最后一句话 “Evidence …were presumably carnivorous …to feed on plants” 意思是说到陆地上的鱼类一开始只是肉食动物，还没有发展进化到以植物为食。B选项正确。
Q11
正确答案：C
解析：C选项对应“they made only a partial transition, they were still quite tied to water”，正确。
Q12
正确答案：A
解析：第五段提到，tetrapods与祖先的区别存在于“skeletal system-changes in the bones of the fins, the vertebral column, pelvic girdle, and pectoral girdle”。对应A选项正确。
Q13
正确答案：填入第一个方框(A)。
解析：插入文本的意思是：这些可能是因为干旱时的潮水退去时滞留沉积下来的，而在那时，很多水栖动物一定死亡了。题目的关键在于找到“these”是什么，而根据提示“many aquatic animals must have died”，指代的应该是“dead fish and other water-dwelling creatures”，恰好填入第一个方框。其余方框的周围都没有再出现“dead aquatic animals”的同义词，不选。
Q14
正确答案：依次填入 A E F
A选项对应文章第二、三段，早期rhipidistians中肺和鳍的出现;E选项对应第四段，lobe-finned fish上陆的两个理由;F选项对应文章第五段，tetrapods的出现及特征;B选项错在原文没有精确讨论到the number of bones，只是说lobe fins。
C选项错在shortly after，而且只是一个条件之一，主语也不应该是plants and other animals;D选项错在没有比较讨论这个内容，回顾第一段内容可知。
另外有一则好消息，针对托福备考，