动物进化 -- -- 先进

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Are alligators and crocodiles prehistoric creatures?
::鳄鱼和鳄鱼是史前生物吗?

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That depends on your definition of prehistoric. It is true that these crocodilians roamed the Earth along with the dinosaurs . Crocodilians first appeared in the late Cretaceous period about 84 million years ago. They very closely resembled modern day such as crocodiles, caimans, and specifically alligators. Dinosaurs went extinct about 65 million years ago.
::这取决于你对史前的界定。 的确,这些鳄鱼和恐龙一起在地球上游荡。 鳄鱼最初出现在8400万年前的末代白鲸时期。 它们非常接近现代,比如鳄鱼、鳄鱼,特别是鳄鱼。 恐龙在大约6500万年前灭绝了。

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Major Trends in Animal Evolution
::动物演变的主要趋势

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evolution is a fascinating subject. The slow, step-wise evolutionary changes that link the earliest-known and simplest animals to the most recently evolved, highly complex animals is truly a remarkable process. Several critical steps in animal evolution take place within the large number of invertebrate phyla. These will be discussed in detail throughout the Concept Invertebrates (Advanced) chapter. In this section we will summarize those trends, and we will focus on evolutionary changes that occur between invertebrates and vertebrates within the phylum chordata .
::缓慢的、渐进的进化变化将最早已知的和最简单的动物与最近进化的高度复杂的动物联系起来,这确实是一个了不起的过程。 动物进化的几个关键步骤发生在大量无脊椎植物的体内。 这些步骤将在“无脊椎动物概念(高级)”的章节中详细讨论。 在本节中,我们将总结这些趋势,我们将侧重于在植物群中无脊椎动物和脊椎动物之间发生的进化变化。

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From a Single Cell to Multi-Celled Organisms
::从单细胞到多细胞生物体

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The first animals likely evolved from . Protists are mostly single-celled organisms , some of which grow clumped together as cellular aggregates called colonies. The evolution of may have occurred when the within a protist colony began to become specialized for different functions. The individual cells would then be dependent on other cells within the colony for survival. This would represent the first primitive multicellular animal. Strong support for this hypothesis comes from the most primitive animals: . One group of specialized cells within a sponge, called choanocytes , bears a striking resemblance to a class of protists called choanoflagellates. Choanoflagellates are single-celled organisms that have a long, thin fiber protruding from their bodies called a flagellum . The flagellum beats like a whip, and this motion allows the organism to move through the . Choanocytes also have a flagellum that is used to bring water into the sponge's body. Both choanocytes and choanoflagellates also share another distinct feature called a collar. The collar is a circle of smaller projections called microvilli that surround the flagellum. In both organisms the collar is used to trap small food molecules. Figure shows the strong similarities between choanocytes and choanoflagellates. This is further discussed in the Concept Invertebrates (Advanced) chapter.
::最初的动物可能从中演变而来。 原生动物大多是单细胞生物, 有些是作为细胞聚集体生长而成, 被称为聚居体。 其进化可能发生在原生蚁体内开始专门从事不同功能的单细胞生物。 个别细胞随后将依赖聚居区内的其他细胞生存。 这将代表第一种原始的多细胞动物。 对这一假设的有力支持来自最原始动物: 。 海绵内的一个特殊细胞组, 叫做 细胞, 与一个叫花旗球的植物类有着惊人的相似性。 花旗种是单细胞生物, 其身体中有一个长的、 薄的分纤维分泌物。 旗状细胞会像鞭子一样跳动, 使生物体能够穿过。 细胞中还有一根花旗状, 用来将水带进海绵体。 细胞和花旗也有一个不同的特征。 项圈是一个叫做微小的圆形生物圈, 叫做“ 花状” 。 。 这个小的预测圈叫做“ 花状体” , , , 挂状体在旗状体中, , , 代表着 。

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The transition from a colony to an animal likely involved the invagination of some of the cells within the aggregate in order to form a digestive cavity. This is similar to the stage of embryonic called gastrulation that we discussed in the Animals: Characteristics (Advanced) concept. In an evolutionary theory known as recapitulation, some scientists hypothesize that steps in the process of an animal’s embryonic development resemble, or “recapitulate,” the evolutionary history of the . For example, the gastrula stage of development in higher animals resembles the adult stage of primitive animals from which they evolved, such as sponges. While general similarities between embryonic development and evolutionary history do exist, modern evolutionary science rejects the theory of recapitulation. This is because these stages are not truly equivalent to the adult stages of evolutionary ancestor species. For example, there is no stage of human embryonic development that can be considered the functional equivalent of a “fish” stage, even though are evolutionary ancestors of humans.
::从蚁群向动物的转变可能涉及集合中某些细胞的渗透,以便形成消化腔。这与我们在《动物》中讨论的胚胎阶段相似:特征(高级)概念。在被称为重述的进化理论中,一些科学家假设动物胚胎发育过程中的步骤类似于,或“再生”进化史。例如,较高动物的发育轨迹阶段类似于原始动物的成熟阶段,例如海绵。虽然胚胎发育和进化史之间的确存在一般相似之处,但现代进化科学却不接受再生理论。这是因为这些阶段并不真正等同于进化祖先物种的成人阶段。例如,人类胚胎发育阶段没有可以被视为“鱼类”阶段的功能等同,即使是人类的进化祖先。

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The Cambrian Explosion: An Explanation for Multicellular Organisms
::Cambrian爆炸:多细胞生物的解释

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When did the transition from colony-forming protists to multicellular animals take place? We are not entirely sure, because of our incomplete . The first strong evidence of multicellular animals in the fossil record occurs roughly 630 million years ago, during a geological time period called the Ediacaren. Figure shows a timeline of the geological periods associated with the early fossil record.
::从聚变原生动物到多细胞动物的转变是什么时候发生的?我们并不完全确定,因为我们没有完全确定。化石记录中第一道关于多细胞动物的有力证据发生在大约6亿3千万年前,在称为Ediacaren的地质时期。图表显示了与早期化石记录相关的地质时期的时间表。

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One striking feature of the fossil record is a massive increase in the number and diversity of fossilized animals beginning in the Cambrian period. Within roughly 40 million years, from nearly all phyla of the animal first appeared. This sudden burst of animal diversity in the fossil record is known as the Cambrian explosion . There are a number of that may explain this seemingly rapid evolution. These theories are primarily based on hypothesized atmospheric conditions during and prior to the Cambrian period. For example, one theory postulates that a sudden rise in atmospheric oxygen levels facilitated the rapid evolution of animal species. However, it is not even agreed upon that this increase in the fossil record actually reflects a period of rapid evolution. Based on evolutionary time scales estimated by molecular phylogenetics , it is thought that the first animals arose several hundred million years prior to the Cambrian explosion. Yet, there is no fossil record for the existence of multicellular animals dating to that time. In this case, the fossils found in the Cambrian period may not reflect the first appearance of many of those animals. Rather, there may just be a large segment of time that is completely missing fossils of the species that lived at that time. One possible explanation for the lack of a fossils of these earlier animals is that their physical composition or the geological conditions during that time did not allow fossil preservation. This debate is currently unresolved among scientists, and it will likely require additional research to determine the most likely cause of the so-called Cambrian explosion.
::化石记录的一个惊人特征是,从坎布里安时期开始,化石化动物的数量和多样性急剧增加,从坎布里安时期开始。在大约4000万年中,从动物的几乎所有植物开始出现。化石记录中的动物多样性突然爆发被称为坎布里安爆炸。有一些可以解释这种看似迅速的演变。这些理论主要基于坎布里安时期期间和之前的虚弱大气条件。例如,一种理论假设,大气氧水平的突然上升有助于动物物种的迅速演变。然而,人们甚至不认为,在大约4000万年内,化石记录中的增加实际上反映了一个迅速演变的时期。根据对化石记录中的进化时间尺度的估计,认为第一批动物是在坎布里安爆炸之前的数亿年前出现的。然而,没有关于当时多细胞动物存在情况的化石记录。例如,在坎布里安时期发现的化石可能不会反映许多动物的首次外貌。相反,目前可能发生的大量时间是化石化武研究的早期原因。

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In addition to periods of increased diversity, the fossil record also shows periods of extinction , some on a very large scale. Extinctions occur when changing environmental conditions do not allow a species to survive. Sometimes this is a result of from a species which is better adapted to the environment. There are a great number of extinctions that occur throughout the evolution of animals. In fact, the organisms present on the earth today represent only 0.1% of all of the species that have existed through time. These extinct species, however, remain a critical part of the evolutionary history of the animal kingdom.
::除了多样性增加的时期外,化石记录还显示了灭绝的时期,有些是大规模灭绝的时期。当环境条件的改变使物种无法生存时,就会出现灭绝。有时,这是由更适合环境的物种造成的。动物进化过程中,大量灭绝现象不断发生。事实上,今天地球上的有机体只占长期存在的所有物种的0.1%。然而,这些灭绝的物种仍然是动物王国进化史的一个关键部分。

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Invertebrates to Vertebrates
::无脊椎动物到无脊椎动物

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Many major evolutionary developments occurred in the animal kingdom prior to the development of a notochord , the defining feature of the phylum chordata. These developments include the following:
::动物王国在开发一种代名词之前,就出现了许多重大的进化发展,这是植物分类的特征。

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• Bilateral symmetry .
  ::双边对称。
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• True tissue and organ systems .
  ::真正的组织和器官系统。
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• A body cavity.
  ::一个体腔。
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• Centralized .
  ::中央集权。
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• Complete digestive system with separate openings for the mouth and the anus.
  ::完全消化系统 嘴和肛门分开开口
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• A segmented body plan.
  ::一个有条块的人体计划。

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Each of these steps were essential for the evolution of higher organisms, such as mammals . They will be discussed in detail in the concepts on invertebrates.
::每一个步骤对于哺乳动物等较高生物体的进化至关重要,将在关于无脊椎动物的概念中详细讨论这些步骤。

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The phylum chordata reflects the development of the notochord. A notochord is a rod-shaped, semi-rigid support structure that forms between the dorsal nerve cord and the gut of an animal. A diagram showing the placement of the notochord within a body is shown in  Figure  .
::phylum Chordata 反映了Notochord的发展。Notochord 是一个在动物腹部和腹部之间形成的杆状半硬性支撑结构。图中显示了Notochord 在身体内的位置。

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The notochord serves as a major step in the evolution of both the internal skeleton and backbone found in vertebrates. The notochord not only provides structural support for the animal, but it also provides a place for muscle attachment. The force of muscle contractions opposing the notochord allow movement , much like how the contraction of attached to our internal skeleton causes us to move. Other features that are specific to members of the phylum chordata include a dorsal nerve cord, pharyngeal slits , an endocyst, and a post-anal tail . Pharyngeal slits and the endocyst are structural features of the pharynx that assist in feeding. In humans, none of these features persist to , but all are present at various stages during development.
::在脊椎动物体内发现的骨骼和骨骼的进化过程中,诺科索德是一个重要的步骤。诺科托尔德不仅为动物提供结构支持,而且还为肌肉的依附提供场所。反对诺科尔德的肌肉收缩力量允许运动,这与我们体内骨骼的收缩如何导致我们运动相似。其他与植物细胞细胞细胞数据成员特有的特征包括:肩神经索、pharyngeal shlits、内分泌和后尾尾尾部。法良格耳和内分泌是有助于喂食的法林克斯的结构性特征。在人类中,这些特征中没有一个持续存在,但都存在于不同的发育阶段。

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Vertebrates are one of three major subphyla of chordata. The other two subphyla consist of invertebrates. Vertebrates include over 50,000 different species. More than half of these species are fish. The defining feature of vertebrates is an internal skeleton that includes a backbone and a cranium . The classes within the subphylum vertebrata are listed in the Subphylum Vertebrata (Phylum Chordata) Table.
::Vertebrate是三大相形色体中的一种。另外两个相色体由无脊椎动物组成。Vertebrate包含5万多个不同的物种。其中一半以上是鱼类。脊椎动物的特征是内骨,包括脊柱和头核。亚脊椎动物的类别列在子脊椎动物(Phylum Chordata)表格中。

Existing Classes within the Subphylum Vertebrata (Phylum Chordata)

Class	Members	Example
Myxini	Hagfish (Jawless)
Hyperoartia	Lampreys (Jawless)
Chondrichthyes
Actinopterygii	Ray-finned fish
Sarcopterygii	Lobe-finned fish
Amphibia
Sauropsida	Reptiles
Aves
Mammalia	Mammals

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Within the vertebrates we see the evolution of increasingly complex fish, beginning with . The jawless fish evolved to form jawed, cartilaginous fish and eventually . Animals that we commonly think of as vertebrates, four-legged (or two legs and two wings) backboned animals, arose from bony fish. These tetrapod classes include the following:
::在脊椎动物中,我们看到越来越复杂的鱼类的进化,从 开始。没有下巴的鱼类进化成下巴的、卷尾的鱼类,最终形成。我们通常认为是脊椎动物的动物,四条腿(或两条腿和两根翅膀)结骨的动物,由鱼产生。这些四面形的动物包括:

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• Amphibians.
  ::两栖动物
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• Reptiles.
  ::爬行动物。
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• Birds.
  ::鸟儿
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• Mammals.
  ::哺乳动物

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Water to Land
::水对水对水

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A major evolutionary event that occurred within the vertebrates was the transition from water to land. This required a number of physiological changes to compensate for the differences between an environment and a environment. On land, animals need systems to conserve water, exchange gases internally, and move from place to place on the ground. In addition, land animals cannot rely on water currents to disperse their gametes in order to sexually reproduce. These changes began to be seen as amphibians evolved from a bony fish called a lobe-finned fish. Lobe-finned fish had what are called proto- lungs and proto-limbs. The proto-lungs enabled them to surface from the water and breath air for a short time. The proto-limbs, or lobed fins, enabled them to walk out of the water and on land for short distances. From the lobe-finned fish, amphibians evolved true lungs and true limbs for survival on land. However, most amphibians are still dependent on water to lay their eggs . Amphibian eggs are not able to survive in a non-aquatic environment because they do not have a waterproof covering. This adaptation arose with the reptiles. Reptiles have what is called an amniotic egg . In an amniotic egg, the embryo is surrounded by layers of membranes and a solid, water-impermeable shell. This allows the embryo to survive on dry land. Reptiles mark the full transition from water to land.
::脊椎动物内部发生的一个重大进化事件是从水向陆地的转变。 这需要一系列生理变化来弥补环境和环境之间的差别。 在陆地上,动物需要保护水的系统,在内部交换气体,从地方到地面的移动。 此外,陆地动物不能依靠水流散开它们的游戏来进行性繁殖。 这些变化开始被看成是两栖动物从一种叫作叶质鱼的金鱼中演变成真正的肺和真正的肢体,但大多数两栖鱼类仍然依靠水产产卵。 原生卵无法在短期内从水和呼吸空气中浮出水面。 原生动物或附着的鳍可以让它们从水中爬出水面和呼吸空气。 原生动物无法从水中爬出水面和在陆地上游走, 因为它们的卵层是坚固的, 其土壤是坚固的, 其卵层是坚固的。

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It is important to realize, however, that chordates were not the first animals to make the water to land transition. had achieved this step independently and through evolutionary changes that were quite distinct form those of vertebrates. For example, arthropods dealt with the problem of retaining water partly by using a physical feature that they had already evolved, or pre-adapted, called the exoskeleton .
::然而,重要的是要认识到,椰枣不是首先使水向陆地过渡的动物。 已经独立地实现了这一步骤,并且通过进化变化实现了这一步骤,这些变化是截然不同的脊椎动物。 比如,节肢动物通过使用它们已经进化或预先适应的物理特征,即外骨骼(exoskeleton),部分地处理了保留水的问题。

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Birds and Mammals
::鸟类和哺乳动物

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Mammals and reptiles both evolved from the same amniotic-egged ancestor. This ancestor diverged into two major groups: the synapsids (mammalian-like reptiles) and the sauropsids (reptiles). The vertebrate class mammalia evolved from the synapsids. Dinosaurs and subsequently birds (class aves) evolved from reptiles of the class sauropsid. Both birds and mammals are warm-blooded vertebrates. Warm-blooded animals have the ability to regulate internal body temperature. Birds have wings and feathers , and they lay their eggs for external development. Mammals are defined by the presence of milk-producing mammary glands in females. Additional features of mammals include hair, three middle ear , and a specialized region of the brain called the neocortex . Most mammals also exhibit vivipary . Vivipary means that, instead of laying eggs that develop outside of the mother, the embryo develops inside of the mother’s body. Human beings, the species Homo sapiens , belong to the primate order within the class mammalia. Scientists estimate that Homo sapiens arose roughly 200,000 years ago. It is important to consider that evolution is a continual process, and humans are continuing to evolve. The slow rate of evolution makes it essentially impossible to study as it is occurring, however, it is interesting to speculate on the future of human evolution. This brings up questions about the environmental pressures that will lead to the divergence of humans into new species and what this divergence will look like.
::哺乳动物和爬虫类动物都从同一个与动物有关联的进化进化过程演变成同一个与动物相联的进化过程。这一进化过程分化成两大组:突触(哺乳动物类爬虫类)和沙洛皮动物(爬虫类)。脊椎类哺乳动物从神经突变演变成。脊椎类哺乳动物和随后的鸟类(等)从类动物的爬虫类动物演变成。鸟类和哺乳动物都是温和的脊椎动物。温和血液动物有能力调节体内温度。鸟类有翅膀和羽毛,它们产卵用于外部发育。哺乳动物由产奶制品的哺乳动物群的进化过程来定义。哺乳动物的更多特征包括毛发、三个中耳和大脑的一个特殊区域(等)称为新皮质。大多数哺乳动物也表现出了生存的状态。维夫理意味着,除了在母体外产卵的进化过程之外,胚胎的进化过程也具有调节能力。鸟类的进化能力,鸟类有翅膀和羽毛类的进蛋,它们产的卵蛋蛋蛋蛋蛋蛋会产的进到外部发展。哺乳动物的进化过程,但是,人类的初和大脑的变化速度是20世纪的变的变化过程。

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Summary
::摘要

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• The first animals likely evolved from marine protists that clumped together in colonies.
  ::第一批动物可能来自海洋先质学家, 它们在聚居地中被挤成碎片。
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• The transition from a colony to an animal likely involved the formation of a digestive cavity via the invagination of some of the cells within the aggregate.
  ::从一个聚居区向动物的过渡可能涉及通过在集合体内渗透某些细胞形成消化腔。
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• The first strong evidence of multicellular animals in the fossil record occured roughly 630 million years ago during a geological time period called the Ediacaren.
  ::化石记录中的多细胞动物的首次有力证据 发生在大约6亿3千万年前 在一个地质时期,即Ediacaren(Ediacaren)
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• Major developments that occurred within the animal kingdom include bilateral symmetry, true tissue and organ systems, a body cavity, a centralized nervous system, a complete digestive system, a segmented body plan, and a notochord.
  ::动物王国内出现的主要发展包括双边对称性、真实组织和器官系统、体腔、中央神经系统、完整的消化系统、分块身体计划以及一个公分体。
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• The notochord serves as a major step in the evolution of both the internal skeleton and backbone found in vertebrates.
  ::在脊椎动物体内发现的内部骨骼和骨骼的演变过程中,诺阿科德是一个重要的步骤。
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• Vertebrates include over 50,000 different species. More than half of these species are fish.
  ::乙酸乙酸盐包括5万多种不同的物种,其中一半以上是鱼类。
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• A major evolutionary event that occurred within the vertebrates was the transition from water to land.
  ::脊椎动物内部发生的一个重大进化事件是从水向土地的过渡。

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Review
::回顾

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1. What did the first animals likely evolve from? What supports this theory?
   ::最初的动物可能来自什么?什么支持这个理论?
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2. What is the evolutionary theory known as recapitulation? Why does modern evolutionary science reject this theory?
   ::为什么现代进化科学拒绝这一理论?
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3. What are some theories that try to explain the Cambrian explosion?
   ::一些理论是什么 试图解释 Cambrian爆炸?
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4. What role does the notocord serve in animals?
   ::代号在动物中起到什么作用?
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5. As the first animals began to migrate to land, what were some challenges that their aquatic bodies faced?
   ::当第一批动物开始迁移到陆地时,它们的水生生物面临着哪些挑战?