摘要:托福听力原材料之鲸的发源。托福听力训练原材料在备考的全过程中，常常会碰到。今日，中美网为学生们产生的托福听力原材料是讲鲸的发源的內容，下边一起来瞧瞧吧。据美国2个生物学家工作组此前*的科学研究汇报称，她们在考古学中发现的新化石更进一步证实了鲸先祖与日常生活在陆上上的食草动物相关，如牛和河马，而不是…
托福听力原材料之鲸的发源。托福听力训练原材料在备考的全过程中，常常会碰到。今日，中美网为学生们产生的托福听力原材料是讲鲸的发源的內容，下边一起来瞧瞧吧。
据美国2个生物学家工作组此前*的科学研究汇报称，她们在考古学中发现的新化石更进一步证实了鲸先祖与日常生活在陆上上的食草动物相关，如牛和河马，而不是将要绝种的食肉类动物。
老师早已了解，鲸是几千万年前由日常生活在陆上上的四肢动物演化而成的，殊不知，鲸到底是以动物王国中哪一支演化而成的一直是引起轰动的难题。
二十世纪50年代开展的免疫系统实验和近期开展的DNA实验都说明鲸的演变与食草的偶蹄喂奶动物相关，如猪、牛和河马。先前，这种实验发现的結果一直沒有获得化石考古学层面的适用，之前发现的化石则更说明鲸与食肉类动物相关。殊不知，如今二项各自开展的科研汇报的创作者称，她们各自在塔吉克斯坦不一样地域发现的化石，使她们坚信这种实验的結果是恰当的。
美国直播盒子东北地区医科院的汉斯・斯威森说，在发现了这种化石后，她们意识到，显而易见之前她们在相关鲸发源难题上的认为是不正确的。斯威森在塔吉克斯坦东北部地区地域旁遮普发现了二种五千万年之前可能是鲸先祖的四肢动物化石。以斯威森主笔，多的人合写的相关发表论文在当月21日出版发行的美国《自然》杂志期刊上。
此外一名生物学家菲利浦・金格里奇是美国密歇根大学地貌学和古生物学老师教授。他说道，她们一个考古学工作组在塔吉克斯坦南部地域俾路支海湾发现了此外二种大概4700萬年之前可能是鲸先祖的化石，在其中一架人体骨骼大部分是详细的。
金格里奇说，她们从而发现，开展DNA实验的同行业发现的結果可能是恰当的，鲸的发源与河马相关。以金格里奇主笔，多的人合写的相关毕业论文将要*在21日出版发行的一期美国《科学》杂志期刊上。但他这篇毕业论文*的时间与《自然》杂志期刊上的那篇毕业论文*的時间相差无异。
这几篇毕业论文的主题风格全是，她们发现的这类动物化石独特的耳朵形状与鲸很类似，很可能是鲸的祖先，另外这种动物化石都是有四肢和显著的足踝构造，与其他的食草偶蹄喂奶动物类似。
倘若鲸先祖与食草动物相关，那麼当代鲸的饮食结构怎样演变而成還是一个谜。一些有牙的鲸如虎鲸能够吃鱼和其他的海里喂奶动物;而此外一些鲸则有被称作鲸须的唇部构造，能够从海面中吸滤浮游动物。
金格里奇则说，他已阅到一些相关当代河马杀掉和吞掉水窝中太挨近他们的瞪羚，或许大家有点儿夸大其词了这种偶蹄动物的食草性，虽然她们以食草为主导。
Whales most likely evolved from four-legged land animals that foraged for food or hunted for fish along ocean shorelines. The ancestors of whales gradually became more dependent on the ocean for food, passing through an amphibian stage before evolving into fully aquatic animals.
Recent work with whale fossils indicates that the anklebones of whale ancestors resembled those of artiodactyls, the group of even-toed hoofed mammals that includes pigs, deer, antelopes, and hippopotamuses.
Molecular studies comparing the genetic makeup of modern whales to that of other animals indicates that the hippopotamus is the whale’s closest genetic match. Based on these studies, scientists now generally agree that whales are most closely related to artiodactyls.
The fossil record of whales spans over 50 million years to ancestors such as Pakicetus that lived around the mouths of rivers in what is now Pakistan. Pakicetus was a four-legged, land animal that measured about 2.5 m (about 8 ft) in length. The whale fossil Rodhocetus was discovered in 1993. Dating from about 46.5 million years ago, this fossil came from fully marine sediments.
Its legs were smaller than those of Pakicetus and its hind feet were turned into webbed paddles. Rodhocetus was clumsy on land, perhaps like modern sea lions. It probably swam using an up-and-down flexing of the body to power its finlike feet in the manner of otters. Unlike modern whales, it had nostrils instead of a blowhole. Rodhocetus also had a powerful tail, although scientists do not know whether this early whale had begun to evolve tail flukes.
A fossil whale known as Basilosaurus dates from 42 million years ago and represents the stage of whale evolution in which the hind legs are very small but still visible. The adult Basilosaurus reached lengths of 15 m (50 ft), but its hind limbs resembled short sticks only 0.5 m (1.6 ft) long.
Although all of the pelvic bones, leg bones, kneecaps, feet, and toe bones were present, these legs could not have been used to support such a large animal on land. Modern whales, which first appeared in the fossil record 5 million to 10 million years ago, have no visible hind limbs, although some whale species still have tiny pelvic and leg bones embedded in muscle near the spine.
总的来说：古生物学者paleontologist科学研究化石，Molecular biologist 科学研究遗传基因和DNA，分子生物学家从遗传基因剖析觉得鲸的血亲是河马hippopotamus，古生物学家之前觉得鲸的血亲是一种肉食动物。
雅思考试托福备考toefl共享托福机经
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