2023-05-25 16:26:26 来源：中国教育在线

托福阅读真题Official 44 Passage 1（七）

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.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.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.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.

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.

Question 13 of 14

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.

正确答案：A

题目详解

题型分类：插入句子题

题干分析：考察句子和句子之间的衔接关系。插入句中的关键词these，指代前面的某内容，且为复数；也说明插入句子和前面句子有衔接关系。线索词drought；died，指出内容上的关联，说明前面提到了与干旱和死亡有关的内容。插入句译为：干旱时期，水量减少，水逐渐退去，水生生物会死掉。这些可以因干旱时期退去的水量而积存起来。

选项分析：

A选项此空前面提到气候变化导致水域有限，死鱼出现等内容，可以判断插入句中these指的就是这些scattered dead fish and other water-dwelling creatures。气候变化导致水域有限对应插入句中的drought，dead fish对应插入句中died。因此从逻辑和内容上都构成衔接。

B选项此空前面提到了植物的出现和其他生物的出现，与死亡的词不构成衔接。

C选项此空前面的句子用thus开头，说明做总结，不再提及干旱时期的具体描述。

D选项此空前面提到了牙齿出现证明的内容，为新的信息和内容，与插入句子不构成逻辑和内容上的关联。

Question 14 of 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.

Freshwater lobe-finned fish may be the direct ancestors of terrestrial tetrapods.

Answer Choices:

A.

Rhipidistian crossopterygian had features such as primitive lungs and thick fins that could have helped it survive dry periods.

B.

By the Devonian period,lobe-finned fish preferred freshwater habitats to life in the ocean.

C.

During the Devonian,the number of bones increased in the fins of rhipidistians,improving such animals’ability to swim and move over land.

D.

A drier climate and new sources of food on land may have encouraged the lobe-finned fish’s move to a terrestrial existence.

E.

Shortly after the earliest tetrapods developed lungs,plants and other animals began to flourish on land.

F.

Early tetrapods remained closely connected to water,but several of their body structures were adapted for life on land.

正确答案：ADF

题目详解

题型分类：文章总结题

题干分析：选择概括性的正确选项。

选项分析：

A选项是综合了第二段和第三段的重要信息，为两段的概括性总结。Rhipidistian crossopterygian had features such as primitive lungs and thick fins that could have helped it survive dry periods对应第二段的第四、五、六句If there were periods of drought,any adaptations allowing the fish to survive the dry conditions would have been advantageous...It is known that they had lungs as well as gills for breathing。和第三段的前三句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...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。

D选项对应第四段的重要信息。A drier climate对应第四段的第二句Changes in climate...if freshwater areas became progressively more restricted，new sources of food对应第四段的第三句Another impetus may have been new sources of food第四段后面就是对此展开的具体例子说明。

F选项对应第五段的重要信息。Early tetrapods remained closely connected to water对应第五段的第二句...they were still quite tied to water，but several of their body structures were adapted for life on land对应第五段的最后一句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。

B选项中使用preferred这个词在文中没有表达过与此相关的意思。无中生有。

C选项说到鳍的骨骼数量增加，提升了游泳和陆上移动能力，而文中最后一句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并没有说骨骼数量的增加。无中生有。

E选项说在四足动物出现肺不久，植物和其他动物在陆地上发展起来。而原文中developed lungs的内容出现在第二段，用来说明鱼进化的一个适应性改变。plants and other animals began to flourish on land出现在第四段，用来说明鱼进化成陆生生物的原因。两者之间在文中并无关联，也不存在先后顺序。

译文

>> 雅思 托福 免费测试、量身规划、让英语学习不再困难