【词汇】托福同义词串串烧(115)- From Fish to Terrestrial Vertebrates

TPO-44-1 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 saddlelike 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.


题目

【题目】1. The word “advantageous” in the passage is closest in meaning to

○beneficial

○necessary

○remarkable

○common

【题目】2. The word “adjacent” in the passage is closest in meaning to

○Nearby

○Available

○Temporary

○Fresh

【题目】3. The word “progressively” in the passage is closest in meaning to

○increasingly

○noticeably

○occasionally

○rapidly


单词解释和答案

1、advantageous

[ad·van·ta·geous || ‚ædvən’teɪdʒəs]

adj.  有利的; 有益的; 有助的

【反义词】:  disadvantageous

【原句】: If there were periods of drought, any adaptations allowing the fish to survive the dry conditions would have been advantageous.

【题目】1. The word “advantageous” in the passage is closest in meaning to

○beneficial★

○necessary

○remarkable

○common


2、adjacent

[ad·ja·cent || ə’dʒeɪsənt]

adj.  毗连的, 邻近的, 接近的

n.  近邻

【同义词】:  adjoining / near / neighboring / next to / touching

【原句】: 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.

【题目】2. The word “adjacent” in the passage is closest in meaning to

○Nearby★

○Available

○Temporary

○Fresh


3、progressively

[pro’gres·sive·ly || prə’gresɪvlɪ]

adv.  前进地; 日益增加地

【原句】: Changes in climate during the Devonian may have had something to do with this if freshwater areas became progressively more restricted.

【题目】3. The word “progressively” in the passage is closest in meaning to

○increasingly★

○noticeably

○occasionally

○rapidly


参考译文

从鱼到陆地脊椎动物

在地球上发生的最重要的进化事件之一就是:水栖鱼类过渡到陆地四足动物(有脊骨的四肢生物)。鱼可能起源于海洋,并且我们的第一条关于它们的记录是在海洋岩石中的。然而,到泥盆纪为止(4亿800万至3亿6200万年前),它们已经辐射到几乎所有可及的水生生物栖息地,包括淡水环境。在淡水沉积的岩石中特别常见的化石群中的一个种群就是叶鳍鱼。

研究四足动物进化的生物学家对淡水泥盆系肉鐘鱼rhipidistiancrossopterygian特别感兴趣的。这些鱼生活在大型三角洲上的河道和湖泊。化石常在这些三角洲的岩石中发现,而这些岩石由于氧化铁矿物,通常都是红色的,表明三角洲形成于干湿交替时期。如果有干旱的时期,任何使鱼能够在干燥条件下生存的适应能力都将是有利的。在这些rhipidistians中,这样的适应性是存在的。大家都知道他们有肺也有鳃可以用来呼吸。通过一些化石的横截面显示,由于在鱼体内的位置不同,填满尸体内部的泥在稠度和纹理上都有所不同。这些差异表明,肠道前端下方的囊状腔只能被理解为是一个肺。鳃无疑是这些鱼获得氧气的主要来源,但当水中的氧气耗尽的时候,比如在长期干旱的时候,肺可以充当一个辅助呼吸装置。所以,这些鱼已经进化出在陆地生活的首要条件之一,那就是用空气作为氧源的能力。

这些鱼的第二个适应是在叶鳍的结构中。这些鳍厚实肉多,相当结实,中间有一个中心轴。在陆地上,他们可以被用来作为虚弱的运动装置,也许足够好,让鱼从一个几乎干涸的池塘,笨拙地一到一个相邻的池塘,这个池塘有足够的水和氧气让它们生存。这些翼片最终变短,变成粗短的腿。泥盆纪rhipidistian鳍骨骼和已知最早的四足动物(两栖动物)的肢骨在数量和位置完全匹配。应该强调的是,肺和四肢的进化不可能是对未来陆地生活的语气。这些适应性的发展是因为它们帮助鱼在他们现有的水环境中存活。

是什么生态压力可能导致鱼类逐渐放弃他们的水栖息地,并逐渐成为陆生动物的?如果淡水地区逐渐变得更加受限,那么泥盆纪的气候变化可能和这个有关。另一个推动力可能是新的食物来源。池塘和溪流的边缘,肯定有零星的死去的鱼和其他的水栖生物。此外,植物出现在溪流和池塘附近区域的陆生生境,蟹和其他节肢动物也是这个最早的陆地社区的成员。因此,到泥盆纪,淡水边缘的土地生态环境可能是一个丰富的蛋白质来源,可以被轻松爬出水的动物利用。从牙齿上获得的证据表明这些早期四足动物的未利用土地植物作为食物;他们都是肉食动物,没有开发以植物为食的能力。

如何使第一个四足动物的陆地生境过渡?像早期的陆生植物如莱尼蕨类,他们只有只进行了部分的孤独,它们仍然很依赖水。然而,早期陆地植物面对的许多问题并不适用于第一批四足动物。这些动物的祖先已经有了一个循环系统,他们是可移动的,所以他们可以移动到水边暍暍。此外,他们已经有了肺,这大概是扇鳍鱼类用于辅助呼吸的。最早的四足动物的主要变化是在骨骼系统——鐘的骨骼、脊柱、骨盆、和肩带的变化。

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