TPO5-1-3 原文the Cambrian Explosion

小马托福 TPO5 阅读解析下载三

小马托福 TPO5 阅读解析下载三。下面为大家整理了小马名师出的托福 TPO5 阅读解析的相关内容，包括了文本，解析及答案，供同学们进行下载参考。

托福 TPO5 阅读解析

TPO5-1-3 原文 The Cambrian Explosion

The geologic timescale is marked by significant geologic and biological events, including the origin of Earth about 4.6 billion years ago, the origin of life about 3.5 billion years ago, the origin of eukaryotic life-forms (living things that have cells with true nuclei) about 1.5 billion years ago, and the origin of animals about 0.6 billion years ago. The last event marks the beginning of the Cambrian period. Animals originated relatively late in the history of Earth—in only the last 10 percent of Earth’s history. During a geologically brief 100-million-year period, all modern animal groups (along with other animals that are now extinct) evolved. This rapid origin and diversification of animals is often referred to as “the Cambrian explosion.”

Scientists have asked important questions about this explosion for more than a century. Why did it occur so late in the history of Earth? The origin of multicellular forms of life seems a relatively simple step compared to the origin of life itself. Why does the fossil record not document the series of evolutionary changes during the evolution of animals? Why did animal life evolve so quickly? Paleontologists continue to search the fossil record for answers to these questions.

One interpretation regarding the absence of fossils during this important 100-million-year period is that early animals were soft bodied and simply did not fossilize. Fossilization of soft-bodied animals is less likely than fossilization of hard-bodied animals, but it does occur. Conditions that promote fossilization of soft-bodied animals include very rapid covering by sediments that create an environment that discourages decomposition. In fact, fossil beds containing soft-bodied animals have been known for many years.

全国免费咨询电话：400-0123-267 The Ediacara fossil formation, which contains the oldest known animal fossils, consists exclusively of soft-bodied forms. Although named after a site in Australia, the Ediacara formation is worldwide in distribution and dates to Precambrian times. This 700-million- year-old formation gives few clues to the origins of modern animals, however, because paleontologists believe it represents an evolutionary experiment that failed. It contains no ancestors of modern animal groups.

A slightly younger fossil formation containing animal remains is the Tommotian formation, named after a locale in Russia. It dates to the very early Cambrian period, and it also contains only soft-bodied forms. At one time, the animals present in these fossil beds were assigned to various modern animal groups, but most paleontologists now agree that all Tommotian fossils represent unique body forms that arose in the early Cambrian period and disappeared before the end of the period, leaving no descendants in modern animal groups.

A third fossil formation containing both soft-bodied and hard-bodied animals provides evidence of the result of the Cambrian explosion. This fossil formation, called the Burgess Shale, is in Yoho National Park in the Canadian Rocky Mountains of British Columbia. Shortly after the Cambrian explosion, mud slides rapidly buried thousands of marine animals under conditions that favored fossilization. These fossil beds provide evidence of about 32 modern animal groups, plus about 20 other animal body forms that are so different from any modern animals that they cannot be assigned to any one of the modern groups. These unassignable animals include a large swimming predator called Anomalocaris and a soft-bodied animal called Wiwaxia, which ate detritus or algae. The Burgess Shale formation also has fossils of many extinct representatives of modern animal groups. For example, a well-known Burgess Shale animal called Sidneyia is a representative of a previously unknown group of arthropods (a category of animals that includes insects, spiders, mites, and crabs).

Fossil formations like the Burgess Shale show that evolution cannot always be thought of as a slow progression. The Cambrian explosion involved rapid evolutionary diversification, followed by the extinction of many unique animals. Why was this evolution so rapid? No one really knows. Many zoologists believe that it was because so many ecological niches were available with virtually no competition from existing species. Will zoologists ever know the evolutionary sequences in the Cambrian explosion? Perhaps another ancient fossil bed of soft-bodied animals from 600-million-year-old seas is awaiting discovery.

全国免费咨询电话：400-0123-267 Paragraph 1: The geologic timescale is marked by significant geologic and biological events, including the origin of Earth about 4.6 billion years ago, the origin of life about 3.5 billion years ago, the origin of eukaryotic life-forms (living things that have cells with true nuclei) about 1.5 billion years ago, and the origin of animals about 0.6 billion years ago. The last event marks the beginning of the Cambrian period. Animals originated relatively late in the history of Earth—in only the last 10 percent of Earth’s history. During a geologically brief 100-million-year period, all modern animal groups (along with other animals that are now extinct) evolved. This rapid origin and diversification of animals is often referred to as “the Cambrian explosion.”

1. The word “significant” in the passage is closest in meaning to

○ numerous

○ important

○ unexplained

○ sudden

2. The word “relatively” in the passage is closest in meaning to

○ surprisingly

○ collectively

○ comparatively

○ characteristically

3. The word “diversification” in the passage is closest in meaning to

全国免费咨询电话：400-0123-267 ○ emergence of many varieties

○ steady decline in number

○ gradual increase in body size

○ sudden disappearance

Paragraph 2: Scientists have asked important questions about this explosion for more than a century. Why did it occur so late in the history of Earth? The origin of multicellular forms of life seems a relatively simple step compared to the origin of life itself. Why does the fossil record not document the series of evolutionary changes during the evolution of animals? Why did animal life evolve so quickly? Paleontologists continue to search the fossil record for answers to these questions.

4. The period discussed in the passage is referred to as an “explosion” because it

○ occurred 0.6 billion years ago, late in Earth’s history

○ was characterized by the unusually fast evolution of many new life-forms

○ was characterized by widespread animal extinction

○ was characterized by violent volcanic eruptions

5. According to Paragraph2, which of the following is NOT a question that paleontologists asked about the Cambrian explosion?

○ Why was the origin of life a simple step in Earth’s history?

○ Why did it take so long for multicellular organisms to develop?

○ Why did animal life evolve so rapidly?

全国免费咨询电话：400-0123-267 ○ Why does the fossil record lack evidence of animal evolution during that time?

6. Which of the following best describes the relationship between paragraph 2 and paragraph 3?

○ Paragraph 2 puts forward several scientific claims, one of which is rejected in paragraph 3.

○ Paragraph 2 poses several questions, and paragraph 3 offers a possible answer to one of them.

○ Paragraph 2 presents outdated traditional views, while paragraph 3 presents the current scientific conclusions.

○ Paragraph 2 introduces a generalization that is illustrated by specific examples in paragraph 3.

Paragraph 3: One interpretation regarding the absence of fossils during this important 100- million-year period is that early animals were soft-bodied and simply did not fossilize. Fossilization of soft-bodied animals is less likely than fossilization of hard-bodied animals, but it does occur. Conditions that promote fossilization of soft-bodied animals include very rapid covering by sediments that create an environment that discourages decomposition. In fact, fossil beds containing soft-bodied animals have been known for many years.

7. The word “promote” in the passage is closest in meaning to

○ complicate

○ prevent

○ encourage

全国免费咨询电话：400-0123-267 ○ affect

Paragraph 4: The Ediacara fossil formation, which contains the oldest known animal fossils, consists exclusively of soft-bodied forms. Although named after a site in Australia, the Ediacara formation is worldwide in distribution and dates to Precambrian times. This 700- million-year-old formation gives few clues to the origins of modern animals, however, because paleontologists believe it represents an evolutionary experiment that failed. It contains no ancestors of modern animal groups.

8. Which of the following is NOT mentioned in paragraph 4 as being true of the Ediacara formation?

○ It contains fossils that date back to the Precambrian period.

○ It contains only soft-bodied animal fossils.

○ It is located on a single site in Australia.

○ It does not contain any fossils of the ancestors of modern animals.

Paragraph 5: A slightly younger fossil formation containing animal remains is the Tommotian formation, named after a locale in Russia. It dates to the very early Cambrian period, and it also contains only soft-bodied forms. At one time, the animals present in these fossil beds were assigned to various modern animal groups, but most paleontologists now agree that all Tommotian fossils represent unique body forms that arose in the early Cambrian period and disappeared before the end of the period, leaving no descendants in modern animal groups.

9. 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.

全国免费咨询电话：400-0123-267 ○ The animals found in the Tommotian fossil bed were once thought to belong to a variety of modern animal groups, but now they are thought to have descended from a single group.

○ Animals in the Tommotian fossil beds were initially assigned to modern animal groups but are now thought to belong to groups that emerged and died out during the Cambrian period.

○ Though at first they thought otherwise, paleontologists now agree that the animals in the Tommotian have body forms from which modern animals have descended.

○ It is unclear whether the Tommotian fossils from the early Cambrian period represent unique body forms or whether they should be assigned to various modern animal groups.

Paragraph 6: A third fossil formation containing both soft-bodied and hard-bodied animals provides evidence of the result of the Cambrian explosion. This fossil formation, called the Burgess Shale, is in Yoho National Park in the Canadian Rocky Mountains of British Columbia. Shortly after the Cambrian explosion, mud slides rapidly buried thousands of marine animals under conditions that favored fossilization. These fossil beds provide evidence of about 32 modern animal groups, plus about 20 other animal body forms that are so different from any modern animals that they cannot be assigned to any one of the modern groups. These unassignable animals include a large swimming predator called Anomalocaris and a soft-bodied animal called Wiwaxia, which ate detritus or algae. The Burgess Shale formation also has fossils of many extinct representatives of modern animal groups. For example, a well-known Burgess Shale animal called Sidneyia is a representative of a previously unknown group of arthropods (a category of animals that includes insects, spiders, mites, and crabs).

10. Why does the author mention “Anomalocans” and “Wiwaxia”?

○ To contrast predators with animals that eat plants such as algae

○ To question the effects of rapid mud slides on fossilization

○ To suggest that much is still unknown about animals found in the Burgess Shale

○ To provide examples of fossils that cannot be assigned to a modern animal group

全国免费咨询电话：400-0123-267 11. “Sidneyia” is an example of

○ a relative of Anomalocaris and Wiwaxia

○ a previously unknown Burgess Shale animal

○ an extinct member of a currently existing category of animals

○ an animal that cannot be assigned to any modern animal group

Paragraph 7: Fossil formations like the Burgess Shale show that evolution cannot always be thought of as a slow progression. The Cambrian explosion involved rapid evolutionary diversification, followed by the extinction of many unique animals. Why was this evolution so rapid? No one really knows. Many zoologists believe that it was because so many ecological niches were available with virtually no competition from existing species. Will zoologists ever know the evolutionary sequences in the Cambrian explosion? Perhaps another ancient fossil bed of soft-bodied animals from 600-million-year-old seas is awaiting discovery.

12. What can be inferred from paragraph 7 about why the Cambrian explosion is so unusual?

○ It generated new ecological niches through the extinction of many unique animals.

○ It was a period of rapid evolution, and evolution is often thought of as a slow process.

○ It is a period whose evolutionary sequences are clearly marked.

○ It generated a very large number of ancient fossil beds containing soft-bodied animals.

Paragraph 3: One interpretation regarding the absence of fossils during this important 100- million-year period is that early animals were soft bodied and simply did not fossilize. ■Fossilization of soft-bodied animals is less likely than fossilization of hard-bodied animals, but it does occur. ■Conditions that promote fossilization of soft-bodied animals include very rapid covering by sediments that create an environment that discourages

全国免费咨询电话：400-0123-267 decomposition. ■In fact, fossil beds containing soft-bodied animals have been known for many years. ■

13. Look at the four squares [■] that indicate where the following sentence could be added to the passage.

It is relatively rare because the fossilization of soft-bodied animals requires a special environment.

Where could the sentence best fit?

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 answer choices 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.

The term “Cambrian explosion” refers to the geologically brief period during which all modern animal groups evolved.

●Little is known about the…

●While animal fossils…

●Although the reasons for the…

Answer Choices

○Little is known about the stages of evolution during the Cambrian period, in part because early animals were soft bodied and could fossilize only under particular conditions.

○While animal fossils from before the Cambrian explosion have no modern descendants, many animals that evolved during the Cambrian explosion can be assigned to modern groups.

全国免费咨询电话：400-0123-267 ○The Cambrian period is significant because it marks the emergence of eukaryotic life-forms —organisms that have cells with true nuclei.

○The Ediacara fossil formation provides the most information about the Cambrian explosion, while the earlier, Tommotian and Burgess Shale formations give clues about Precambrian evolution.

○Zoologists are awaiting the discovery of a 600-million-year-old fossil formation in order to be able to form a theory of how animal evolution progressed.

○Although the reasons for the rapid evolution of animals during the Cambrian period are not known, one proposed explanation is an abundance of niches with a lack of competitors.

参考答案：

1. ○2

2. ○3

3. ○1

4. ○2

5. ○1

6. ○2

7. ○3

8. ○3

9. ○2

10. ○4

11. ○3

12. ○2

全国免费咨询电话：400-0123-267 13. ○2

14. Little is known about the…

While animal fossils…

Although the reasons for the…

答案解析：

第一题，B，词汇题。significant 重要的，选 B important 重要的。A numerous 大量的；C unexplained 未被解释的；D sudden 突然的。

第二题，C，词汇题。relatively 相对地，选 C comparatively 相对地。A surprisingly 惊人地，令人惊讶地；B collectively 共同地，全体地， collect 动词收集，collective 形容词集体的，共同的；D characteristically 典型地，有特色地，character 性格，角色，特性，characteristic 典型的。

第三题，A，词汇题。diversification 名词多样化，来自动词 diversify 使多样化；形容词是 diverse 不同的，多样的，由此产生的名词是 diversity 多样性；选 A emergence of many varieties 许多品种的出现。B steady decline in number 数量的稳步下降；C gradual increase in body size 体型的逐渐增长；D sudden disappearance 突然消失。

第四题，B，细节题问这个时期在文章中被称为爆发是因为什么。细节题，通过 explosion 定位到本段第一句话，但是这里说的已经是 this explosion，this 指代前文已经说过的内容，所以关于为什么是爆发，只能到前文去找，看到第一段的最后一句话，正好发现了 referred to 与题干对应，这句说这种动物的迅速起源和多样化经常被称作“寒武纪爆发”，所以答案就是动物的迅速起源和多样化，本题选 B 这个时期的特点就是许多新生物形式的异常的快速进化。

第五题，A，选非题。问以下哪一个不是古生物学家提出的关于寒武纪爆发的问题。NOT 选非题，第二段一堆问号，都是关于寒武纪爆发的问题，所以本题通过选项定位。A 说为什么生命起源在地球历史上是一个简单的步骤？通过 simple step 定位到原文第三句话，这句是个陈述句，说的是多细胞生命形式的起源是一个相对简单的步骤，相比生命起源本身而言。所以文中要表达的生命起源是与简单步骤相比较的，应该比较复杂，因此 A 的问题本身就与文意冲突，而且这句话根本不是在提问，所以本题选 A。B 为什么多细

全国免费咨询电话：400-0123-267 胞有机物发展需要那么久，刚刚看的那句话在强调多细胞生物形式发展相对简单，它之前的一句问它为什么那么晚才出现，通过这两句话的结合就知道是在问为什么多细胞生物出现晚需要长时间发展，B 的 take so long to develop 与第二句的 occur so late 对应；C 为什么动物生命进化的如此快？与原文倒数第二句对应，rapidly 就是 quickly；D 为什么缺乏那段时间动物进化的化石证据？与原文倒数第三句对应， lack evidence 对应 not document。

第六题，B，段落题。问哪一项最好的描述了第二段和第三段的关系。考查段落关系，通过上一题已经知道第二段提了一堆问题，而选项中只有 B 说第二段 poses several questions,所以本题选 B，保险起见，看一下 B 后半句，说第三段对其中一个问题给出了可能的答案，所以看一下第三段第一句话，说对于化石缺失的一个解释是什么什么，而为什么化石缺失正是第二段倒数第三句提出的问题，所以 B 正确。

第七题，C，词汇题。promote 提升，促进，选 C encourage 鼓励。A complicate 使复杂化；B prevent 阻止；D affect 影响。

第八题，C，选非题。问以下关于 E 化石群的信息哪一个不对。NOT 选非题，看一眼原文发现这段都在说 E 化石群，所以这题通过选项定位。A 它包含可以追溯到前寒武纪时期的化石，通过 Precambrian 定位到原文第二句，说虽然是根据澳大利亚的一个地方命名，E 化石群是分布于全球的，而且可以追溯到前寒武纪时期，所以 A 正确不选；B 说它只包括软体动物化石，对应第一句话的最后一个小分句，only 对应 exclusively，所以 B 也对不选；C 说它位于澳大利亚一个单独的地方，与刚才看的第二句中的 worldwide in distribution 全球分布冲突，所以本题选 C。D 它不包括任何现代动物祖先的化石，与最后一句对应，也正确。

第九题，B，句子简化题。先看原句，曾经，这些化石层中的动物被认为属于多种现代动物群，但是，注意这里的 but 的转折关系，but 之后才是句子的重点，后面说大多古生物学家现在认同所有 T 化石都代表独特的生物形态，它们起源于寒武纪早期并消失于寒武纪结束之前，没有留下任何现代动物后裔。答案中只有 B 项同时表达了过去和现在认识的转折并强调了 T 化石起源并灭绝于寒武纪时期，所以答案就选 B，initially 对应 at one time，emerged and died out 对应 arose 和 disappeared。A 虽然是转折，但是后半句 T 是单一动物群的后裔，原文说的是 T 没有后裔，所以不对；C 也有转折关系，但是后半句强调的是 T 化石中的生物体有现代动物的后裔，文中说的是没有，所以也不对；D 是一个选择关系，不是转折，而且重点在说 T 化石代表哪个群体，没说存在时期，所以一定错。

全国免费咨询电话：400-0123-267 第十题，D，修辞目的题。问作者为什么要提及 A 和 W。修辞目的题，问作者意图，通过 A 和 W 定位回原文中间，说这些不能被归类的动物包括 A 和 W，其实看到这里已经可以选到正确答案 D 提供不能被分派到现代动物群组的化石的例子，因为只有它说到了是举 cannot be assigned 的例子，与 unassignable 对应。同时作者意图题说具体的信息往往是为了证明前文观点的，往前看一句，前文说这些化石层提供了关于 32 个现代动物群的证据，加上 20 个其他的与现代动物完全不同而不能被归为任何现代动物群的动物身体形式。所以 A 和 W 就是这 20 种不能被归类的动物形式的例子。

第十一题，C，细节题。问 S 是什么的一个例子。细节题，先通过 S 定位回原文最后一句话，这句就是在举例子，举例子都是用来解释说明前文的，所以直接看前一句，说 BS 化石群也包括很多已经灭绝的现在动物群的代表，所以答案就是已经灭绝的现代动物群，本题选 C 现存动物类型中灭绝的成员，currently existing category of animals 对应原文 modern animal groups。B 项不对，首先因为它说 S 是之前未知的 BS，但是原文说的是它是之前未知的节肢动物，所以本身这句话不对，而且这句话是 S 例子中的内容，不能说明 S 是用以说明什么观点的例子。

第十二题，B，推断题。问通过第 7 段怎么可以推断出为什么寒武纪大爆发是非比寻常的。inferred 推断题，通过 Cambrian explosion 定位到原文的第二句话，说寒武纪爆发包含了迅速的进化和多样化，之后伴随着大量独特动物的灭绝。通过这句话只能知道寒武纪进化快，推断不出为什么 unusual，因此要继续找其他的信息点与之相结合得到答案，而推断题通常是通过信息对比来推知新信息的，于是注意到这句话前面有一个 slow，与 rapid 成对比关系，上一句说进化通常被认为是一个缓慢的过程，所以本题选 B，因为进化通常被认为慢，而寒武纪进化很快，所以可以推知它非比寻常。

第十三题，B，句子插入题。先看句子，说它是相对罕见的因为软体动物的石化需要一个特殊的环境。句子前半句的 relatively rare 和 fossilization of soft-bodied animals，可以对应到文中第二句话的 fossilization of soft-bodied animals is less likely,所以这个句子不是插在原文第二句之前就是之后；句子的后半句说需要一个特殊环境，原文第三句的 conditions，说的就是 environment，所以这个句子就插在第二句之后第三句之前，选第二空。

第十四题，ABF，文章小结题，本文标题是寒武纪爆发，总起句说寒武纪爆发指的是一个短暂的地质时段，该阶段中所有现代动物群得到进化，所以带着进化去看选项。A 关于寒武纪时期进化阶段所知甚少，部分是因为早期动物是软体的，它们的石化需要特定的条件，第二、三段主要内容，正确；B 虽然寒武纪之前的动物化石没有现代后裔，很多在寒武纪进化的动物可以被划分到现代动物群，第 4-6 段主要内容，E 和 T 的化石层都是的化石都是寒武纪之前的化石，它们没有现代后裔，但是 BS 化石就有了，正确；C 寒武纪

全国免费咨询电话：400-0123-267 时期非常重要因为它标志了有细胞核的生物 E 生命形式的出现，不符合文章主旨，该时期因为动物迅速起源进化而重要；D E 化石为寒武纪大爆发提供了最多信息，然后早期的 T 和 BS 化石为寒武纪之前的进化提供了线索，顺序错了，E 和 T 为之前提供线索，BS 是关于寒武纪的；E 动物学家在等待一个 6 亿年老的化石层的发现，为了能够形成动物进化进程的理论，第七段最后一个小细节，而且是作者表示不太可能形成这么一个理论的语气，不是说动物学家们真的要等，所以错；F 尽管在寒武纪时期动物迅速进化的原因不明，一个被提出解释是丰富的缺乏竞争者的生存空间，第七段主要内容，正确。

参考译文：寒武纪大爆发

地质年代是由重大地质事件和生物事件标记的，包括 46 亿年前地球的形成、35 亿年前生命的起源、15 亿年前真核生物（细胞中有真核的生命体）的起源以及 6 亿年前动物的起源；最近的一个事件标志着寒武纪的开始。动物的起源相对处于地球历史的晚期——仅存在于地球历史时间的 1∕10。在短暂的 1 亿年地质学周期中，所有现代动物群（包括现在已经灭绝的生物）进化了。这次快速的动物起源和分化常常被称为“寒武纪大爆发”。

一个多世纪以来，科学家们对这次大爆发一直有疑惑。为什么它发生的得这么晚？多细胞生物的出现相对于生命的出现而言则是一次相对简单的进化。为什么化石没有记录下动物演化的一系列变化呢？为什么动物生命进化得如此迅速呢？古生物学家们仍旧在研究化石记录以期回答这些问题。

关于这重要的 1 亿年内化石的缺失，有一种解释是早期的动物都是软体动物，它们很难形成化石。软体动物的化石比硬体动物化石少见得多，但是也是存在的。促使软体动物成为化石的条件是沉积物的迅速覆盖以形成一个抑制分解的环境。事实上，含有软体动物的化石层在很多年以前就已经为人们所知了。

含有最古老的动物化石的伊迪卡拉化石群就全部由软体动物化石组成。尽管伊迪卡拉是以澳大利亚的一处地名而命名，但是伊迪卡拉沉积层的分布却遍及世界各地，并且可以追溯到前寒武纪时期。这些 7 亿年前形成的地层为现代动物的起源提供了一些新的线索。因为古生物学家们认为它代表着一次失败的进化试验，其中并没有包含任何现代动物的祖先。

以俄罗斯的一处地名而命名的 Tommotian 是一层包含动物残骸的较年轻的化石层。它形成于寒武纪的早期，并且同样只含有软体动物化石。在一段时间内，人们认为这些化石中的动物分化出了各种各样的现代动物。

全国免费咨询电话：400-0123-267 但是古生物学家们现在却认为，所有的 Tommotian 化石都仅代表在寒武纪初期出现但到寒武纪结束时就消失了的特别生物。所以它们没有在现在动物中留下后代。

第三种化石层既包含了软体动物也包含了硬体动物，它为寒武纪大爆发提供了证据。这种叫做伯吉斯页岩的化石群就在加拿大的大不列颠哥伦比亚石山上的约霍国家公园内。在寒武纪大爆发后不久，滑落的泥土迅速掩埋了成千上万的海洋动物，形成了极有利于化石形成的环境。这些化石层含有大约 32 种现代动物，还有大约 20 种与现在动物截然不同以至于不可能分类为任何一种现代动物的其他动物体。这些无法划分的动物包含一种叫做奇蝦的肉食动物和一种叫做威瓦亚虫的以岩屑和藻类为食的软体动物。伯吉斯页岩化石群也含有很多现在已经灭绝了的动物化石。例如伯吉斯页岩化石群中的一种著名动物，Sidneyia，就是一种典型的以前还不为人知的节肢动物（一种动物分类，它包括昆虫、蜘蛛、螨虫和螃蟹）。

像伯吉斯页岩化石群这样的化石层表明进化不能总是被认为是缓慢的过程。寒武纪大爆涉及到了快速的进化分化，接着就是很多独特动物的灭绝。为什么这种进化如此迅速呢？没有人真正的明白。很多动物学家认为这是很多几乎没有任何竞争性物种的环境使然。动物学家们是否知道寒武纪大爆发的动物的进化顺序呢？或许另一些含有来自于 6 亿年前的海洋动物的化石亟待发现。

来源于：小马过河

小马过河资料下载频道，欢迎您来下载！

全国免费咨询电话：400-0123-267