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  • 哺乳动物 - 高级

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    One of these is not a mammal . Which one?
    ::其中一个不是哺乳动物,哪一个?

    Mammals are a class of endothermic vertebrates . They have four limbs and produce amniotic eggs . Examples of mammals include bats, whales, mice, and humans. Clearly, mammals are a very diverse group. Nonetheless, they share many traits that set them apart from other vertebrates.
    ::哺乳动物是顶端热性脊椎动物的一类,它们有四肢并产出羊蛋,哺乳动物的例子包括蝙蝠、鲸、老鼠和人类。很明显,哺乳动物是一个非常多样化的群体。尽管如此,它们与其他脊椎动物有许多不同的特征。

    Characteristics of Mammals
    ::哺乳动物的特点

    Mammals make up a class of vertebrate that contains more than 4,500 living . Examples of mammals include bats, whales, elephants, anteaters, dogs, and humans. As these examples suggest, mammals make up a diverse group of animals. Nonetheless, they share a number of characteristics that serve to set them apart from other vertebrates. 
    ::哺乳动物构成的一类脊椎动物有4,500多条生命。哺乳动物的例子包括蝙蝠、鲸、大象、蚂蚁、狗和人类。如这些例子所示,哺乳动物组成了多种多样的动物群。尽管如此,它们有一些共同的特征可以将它们与其他脊椎动物区分开来。

    Characteristics that are most often used to define the mammalian class are the presence of mammary glands and body hair. All female mammals possess mammary glands. Their function is to produce milk after the birth of an offspring. Milk is a nutritious fluid that contains disease-fighting molecules, other important chemicals, and the nutrients needed by baby mammals. The production of milk to feed the young is called lactation .
    ::哺乳动物最常用来界定哺乳动物类的特征是哺乳动物有哺乳腺和身体毛,所有雌性哺乳动物都有哺乳腺,它们的作用是在后代出生后生产牛奶。牛奶是一种营养液,含有抗疾病分子、其他重要化学物质和哺乳婴儿所需的营养物质。喂养婴儿的牛奶生产称为哺乳。

    All mammals have hair (or fur) during some or all of their life. Hair can serve several functions. The most important function usually is insulating the body to help conserve body heat (see the Mammals: (Advanced) concept). Hair can also be used for sensory perception. For example, cats use their whiskers to sense their surroundings. In addition, hair can be used to communicate threats to a potential rival or predator . Many mammals, like the cat in Figure  , can raise their fur to make themselves look larger and more threatening.
    ::所有哺乳动物一生中都有毛发(或毛皮),毛发可以发挥几种功能。最重要的功能通常是将身体隔绝,以帮助保持体温(见哺乳动物sad高级)概念)。毛也可以用于感官感知。例如,猫用胡须感知周围。此外,毛可以用来向潜在的竞争对手或掠食动物传达威胁。许多哺乳动物,如图中的猫,可以提高毛皮,使其看起来更大、更有威胁。

    lesson content
    By raising its fur, this cat looks bigger and more threatening. This might discourage a predator from attacking. This is just one of several functions of hair or fur in mammals.

    Other Traits of Mammals
    ::哺乳动物的其他遭遇

    Most mammals share several other traits. The traits in the following list are typical of, but not necessarily unique to, mammals. For example, like mammals, are warm-blooded, and some and give birth to live young.
    ::大多数哺乳动物具有其他几种特性,以下清单中的特性是哺乳动物的典型特征,但不一定是哺乳动物特有的特征。例如,与哺乳动物一样,哺乳动物是热血的,有些是活生生的。

    • Mammals are warm-blooded, meaning they can maintain a stable, relatively high body temperature. This is called endothermy.
      ::哺乳动物是热血动物, 意思是他们可以保持稳定的,相对较高的体温。这叫“循环”
    • The skin of many mammals has sweat glands .
      ::许多哺乳动物的皮肤有出血腺。
    • Mammalian lungs have millions of tiny air sacs called alveoli .
      ::哺乳动物的肺里有上百万个叫做阿尔维奥利的 微小空气囊
    • The mammalian heart is divided into four chambers, or compartments.
      ::哺乳动物的心脏被分为四间室或隔间。
    • The brains of mammals are relatively large and have a covering called the neocortex .
      ::哺乳动物的大脑相对较大 并有一个覆盖物 被称为新皮层。
    • Most mammals give birth to live young. This is called vivipary .
      ::大部分哺乳动物都是年轻生的,这叫生存动物

    Traits of Fossil Mammals
    ::化石哺乳动物的末日

    The presence of many of the mammalian traits is rarely observed in the . The traits involve soft tissues that are unlikely to be preserved in . Therefore, extinct mammals usually are identified on the basis of other traits. These generally include traits of the and teeth, which are more likely to be preserved. Fossil mammals may be identified based on the presence of one or more of the following traits:
    ::许多哺乳动物特征的存在很少见于此。这些特征涉及不可能保存的软组织。因此,灭绝的哺乳动物通常根据其他特征进行鉴定,这些特征一般包括更有可能保存的牙齿和牙齿特征。

    • Three tiny bones (called the stirrup , hammer, and anvil) in the middle ear; these bones (shown in Figure  ) give mammals exceptionally good hearing . They carry sound vibrations from the eardrum to the inner ear (see the Nervous and Endocrine Systems concepts). In other vertebrates, these bones are part of the jaw joint and are not involved in hearing.
      ::中耳的三根小骨头(称为、锤和);这些骨头(如图中所示)使哺乳动物听力极佳,从耳膜到内耳都有声震(见神经和内分泌系统概念 ) 。 在其他脊椎动物中,这些骨头是下巴合体的一部分,不参与听觉。
    • Two bony knobs (called occipital condyles ) at the base of the skull; the knobs fit into the topmost bones of the neck. In most other vertebrates, there is only one bony knob at the base of the skull. The two occipital condyles may help mammals hold up their relatively heavy, big-brained head.
      ::头骨底部的两顶骨架(所谓的骨骼骨架);颈部最顶部的骨骼中装有骨架。在大多数其他脊椎动物中,头骨底部只有一个骨架。两顶骨架可以帮助哺乳动物抬起相对较重的大脑头。
    • Teeth with different shapes and functions; mammals generally have four different types of teeth. They have sharp incisors that cut food , strong pointed canines that tear food, broad molars with several cusps (bumps on the chewing surface) that grind food, and premolars with two cusps that function similarly to canines or molars.
      ::具有不同形状和功能的牙齿;哺乳动物通常有四种不同的牙齿。 它们有尖锐的切开食物的切口、撕裂食物的尖尖犬牙、带有若干爪子(咀嚼表面的肿块)的宽角的磨牙、和与犬牙或磨牙相似的两只爪子的预摩尔牙。
    lesson content
    This drawing shows the three bones of the mammalian middle ear, using the human ear as an example. The bones are called the hammer, anvil, and stirrup. Only mammals use these bones for hearing. In reptiles, the three bones are part of the jaw joint.

    Summary
    ::摘要

    • Characteristics that are most often used to define the mammalian class are the presence of mammary glands and body hair.
      ::最经常用来界定哺乳动物种类的特征是哺乳动物腺和身体毛发的存在。
    • The most important function of hair is insulating the body to help conserve body heat.
      ::头发最重要的功能是隔绝身体 帮助保持体温
    • Three tiny bones (called the stirrup, hammer, and anvil) in the middle ear give mammals exceptionally good hearing.
      ::中耳的三根小骨头(叫做、锤和)给哺乳动物听力特别好。

    Review
    ::回顾

    1. What characteristics are most commonly used to identify mammals, especially living ones?
      ::在确定哺乳动物,特别是活哺乳动物时,最常用的特征是什么?
    2. What functions does hair (or fur) serve for mammals?
      ::毛发(或毛皮)对哺乳动物有什么作用?
    3. Why is the presence of most mammalian traits not observed in fossils?
      ::为什么化石中看不到大多数哺乳动物特征的存在?
    4. What are some defining characteristics of mammalian skeletons?
      ::哺乳动物骨骼的一些界定特征是什么?