15.32 Arthropod 演变 - 高级
章节大纲
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Why would such a creature evolve?
::为什么这种生物会进化?originated well over 500 million years ago. The trilobites , shown in this from the Devonian Period (about 419 to 358 mya), were some of the earliest arthropods. The external skeleton, segmented body, and jointed appendages are clearly visible and were important evolutionary steps. Many similar trilobites were 1-3 feet long (300mm to over 700 mm). Imagine if they were still around today.
::从德文时期(约419至358米亚)以来的三叶洛比人就是最早的节肢动物。 外部骨骼、分解体和联合附着物是显而易见的,是重要的进化步骤。 许多类似的三叶洛比人长1-3英尺(300毫米至700毫米以上 ) 。 想象一下它们是否还在今天左右。Evolution of Arthropods
::亚热带动物的演变Although arthropods have a hard exoskeleton , it is not as mineralized and tough as the mollusk shell, and the of arthropods is not as complete as you might expect for an with an exoskeleton. However, there are still many useful arthropod fossils, particularly of the trilobites, as we will learn later in this section. Even with this considerable record, establishing the precise evolutionary history of the phylum has been challenging. The study of arthropod evolution is an ongoing process, and theories are modified regularly as more information is obtained through molecular comparisons between . This information will ultimately help to clarify the exact relationships between living species and their ancestors . For this lesson, we will consider one of the current hypotheses on arthropod evolution.
::虽然节肢动物有硬的外骨骼,但它没有软体外壳那么矿物化和坚硬,节肢动物也不像你预期的那样完整。然而,仍有许多有用的节肢动物化石,特别是三栖动物的化石,我们在本节稍后将了解到这一点。即使有了这个相当可观的记录,确定植物植物的精确进化史一直是具有挑战性的。对节肢动物进化的研究是一个持续的过程,随着通过分子比较获得更多的信息,理论也会定期修改。这一信息最终将有助于澄清生物物种与其祖先之间的确切关系。关于这一教训,我们将考虑目前有关节肢进化的假设之一。Fossil Record and the Trilobites
::化石记录和三龙派Arthropod fossils date back to the Cambrian period (over 500 million years ago). The most extensive group of arthropod fossils is the trilobites, a subphylum of arthropods that is entirely extinct. Trilobite fossils, like the one shown in Figure , are abundant throughout the Cambrian period (from about 540 million years ago to about 490 million years ago). Trilobites are the oldest known arthropods. Following the Cambrian period, their numbers slowly declined until about 250 million years ago when they were entirely lost from the fossil record due to extinction . This large (over 17,000 species) and well-preserved evolutionary record has contributed greatly to the study of animal and plant fossils, a field known as paleontology. Close examination of trilobite fossils has helped scientists learn about rates of within the Cambrian period and has also contributed to our understanding of the age of different sediment layers buried beneath the surface of the Earth.
::亚光石化石可以追溯到坎布里安时期(5亿多年前 ) 。最广泛的节肢化石群是三叶虫,即完全灭绝的节肢动物的子植物。像图所示,三洛比石化石在整个坎布里安时期(从大约5.4亿年前到大约4.9亿年前 ) 富足。三洛比石是最古老的已知节肢动物。在坎布里安时期之后,它们的数量慢慢下降,直到大约2.5亿年前它们由于灭绝而完全从化石记录中消失。这个庞大的(超过17 000种)和受到良好保护的进化记录极大地促进了动物和植物化石的研究,这个称为古生物学的领域。对三洛比石化石的仔细研究帮助科学家了解了坎布里安时期内的速度,也帮助我们了解地表下埋藏的不同沉积物层的年代。A fossil of a trilobite dated to the Cambrian period. The common ancestor of all arthropods likely had a basic segmented body plan like the one shown in Figure . The variations in the body plan for different arthropod subphyla will be examined in the next two lessons, likely evolved from this common ancestor.
::所有节肢动物的共同祖先可能有一个基本的分解体体计划,如图中所示。不同的节肢亚植物体计划的变化将在接下来的两个教训中加以研究,可能从这个共同的祖先演变而来。The likely ancestral arthropod body plan and evolutionary modifications. You will notice from the figure that the ancestral arthropod had an identical pair of appendages on each segment, and the segments were nearly identical, repeating units. This is true of arthropods existing today that resemble this early ancestor. During arthropod evolution, one variation on the body plan that arose involved the loss or modification of many of these appendages to carry out different functions. For example, spiders have modified appendages near the head region into sharp fangs that can be used to pierce and pulverize prey . Another variation is the fusion or grouping of several segments to form distinct body regions. The order and extent of this grouping varies greatly within the phylum. There are two small phyla with species that exist today that are very closely related to arthropods by molecular analysis. These are the Onychophora and the Tardigrada. The Comparison of Features Table shows a list comparing the major characteristics of these two phyla with Arthropoda . These three groups are thought to share a more recent common ancestor with each other than with any other phyla and may suggest some information about their common ancestor. For example, the fact that all three phyla exhibit molting suggests that their common ancestor also shed its cuticle by the process of molting.
::您将从图中注意到, 祖先的节肢动物在每一区段上都有一对相同的附着物, 而各区段则几乎完全相同, 重复单位 。 这是今天存在的节肢动物, 类似这个早期的祖先。 在节肢动物进化过程中, 身体计划出现一个变异, 导致许多这些附附着物丢失或修改以履行不同功能。 例如, 蜘蛛将头区域附近的附附着物改成尖尖尖的扇形, 可用于刺穿和刺穿猎物。 另一种变异是将几个区合并或组合成不同的体系区域。 这个组的顺序和范围在植物圈内差异很大。 今天, 有两种与节肢动物非常密切相关的物种, 它们是奥尼乔波拉和塔尔迪格拉达。 相对特征表显示了一个清单, 比较这两个植物类的主要特征与Arthropododa。 这三个组被认为与另外三个不同的体系区段的混合或组合。 这个组的组合的组合顺序和范围差异很大。 这个组的顺序和范围在植物系内部有很大不同。 今天的物种与任何共同的陈迹都表明它们的共同的陈迹过程。Comparison of Features Between Phyla Arthropoda Onychophora Tardigrada Segmented Partially segmented Segmented Rigid exoskeleton Soft outer cuticle Rigid exoskeleton Jointed appendages Unjointed appendages Unjointed appendages Molting Molting Molting Ecdysozoa and Arthropods
::Ecdysozoa 和ArthropodsEarlier evolutionary groupings of invertebrate phyla considered to be close relatives of and to be closely related to arthropods. These groupings were based on the fact that both flatworms and roundworms lack a true coelom (although you may recall from the Roundworms concept that roundworms have an incomplete, or "pseudo," coelom) and that both annelids and arthropods have segmented bodies. The increasing amount of data gathered from molecular phylogenetic studies, which compare the genetic make up of different organisms to determine how closely they are related, has called these groupings into question. It now seems likely that segmentation evolved independently in several different groups of invertebrates, a process known as convergent evolution . These studies are not yet fully resolved, but one theory that seems to be emerging is that annelids and shared a more recent common ancestor than annelids and arthropods, while arthropods and roundworms of the nematode phylum share a more recent common ancestor than either roundworms and flatworms or arthropods and annelids. If this seems confusing, that is because these studies are currently incomplete, and there are major debates going on right now between scientists about how to categorize these complex relationships. Figure compares phylogenetic trees that show both older groupings and a more current version.
::被认为是与节肢动物近亲和密切关联的无脊椎植物早期进化组群。这些组群基于以下事实:扁虫和圆虫都缺乏真正的骨架(尽管从圆虫概念中你可能记得,圆虫是一个不完整的或“假的 ” , coelom),以及蚂蚁和节肢动物都有分解体。分子血压和节肢动物研究收集的数据越来越多,这些研究比较了不同生物的基因组成,以确定它们之间的关系,因此对这些组群提出了疑问。目前,在几个不同的无脊椎动物组群中,分裂可能独立演变成一种被称为趋同进化的过程。这些研究尚未完全解决,但似乎正在出现的一个理论是,蚂蚁和同一种较新的常见的祖先,而神经植物和神经植物的圆虫类和圆虫类群比,比圆虫类和扁状虫类或节肢类的分解过程都更为常见。这些研究现在似乎正在形成一种更复杂的结构,因为这些研究正在形成一种更复杂的结构。Phylogenetic trees showing the relationships of several of the bilateral invertebrate phyla. (a) This tree illustrates our outdated understanding of the relationships between the bilateral phyla. (b) A more modern phylogenetic tree of these phyla indicates a close relationship between annelids and mollusks as well as between arthropods and nematodes. The process of ecdysis is one aspect of growth and in arthropods that may reflect their close evolutionary relationship with the phylum Nematoda . Both arthropods and roundworms undergo ecdysis. Although the cuticle of roundworms and the cuticle/exoskeleton of arthropods are structurally quite different, both must be shed periodically in order for the animal to continue growing. In this , arthropods and nematodes are called ecdysozoa to reflect the shared characteristic of molting. Future molecular studies should reveal whether the more recent groupings of these phyla are sound.
::乳腺生长过程是生长过程和节肢动物过程的一个方面,它可能反映它们与牛油果植物的密切进化关系。节肢动物和圆虫都经过了消化过程。虽然圆虫的切片和节肢动物的切片/外骨骼在结构上差别很大,但两者都必须定期脱落,以便动物继续生长。在这个过程中,节肢动物和线虫被称作摇头呆子,以反映出织物的共同特征。未来的分子研究应该揭示这些植物最近的组合是否健全。First Land Animals
::第一陆地动物The earliest animals found in the fossil record were all . Most people think that the first animals to transition from life to life on land were the . This is probably because they provide such an obvious example of the to land transition; they have the ability to both breath air and extract oxygen from water. However, it was actually the arthropods that were the first animals to adapt to life on land. This required arthropods to evolve structures that would both support their bodies outside of buoyant aquatic environments and efficiently retain water on dry land. The hard, water-impermeable exoskeleton was an important adaptation that served both of these purposes. The ability to obtain oxygen from air was also essential. The evolution of the tracheal system in helped alleviate the problem of obtaining oxygen.
::在化石记录中发现的最早的动物都是。大多数人认为,第一批动物是从生命向陆地生命过渡的第一批动物是陆地生命。这可能是因为它们提供了向陆地过渡的明显例子;它们有能力呼吸空气和从水中提取氧气;然而,实际上正是节肢动物是第一批适应陆地生命的动物。这需要节肢动物进化结构,既能支持其浮游水环境以外的身体,又能有效地将水留在旱地上。硬性、含水的外骨骼是一种重要的适应措施,为这两个目的都服务。从空气中获取氧气的能力也很重要。气管系统的发展有助于缓解获得氧气的问题。Summary
::摘要-
The study of arthropod evolution is an ongoing process, and theories are modified regularly as more information is obtained through molecular comparisons between species.
::对节肢动物进化的研究是一个持续的过程,随着通过物种之间的分子比较获得更多的信息,定期修改理论。 -
Arthropod fossils date back to the Cambrian period (over 500 million years ago).
::Arthropod化石可追溯到坎布里安时期(5亿多年前)。 -
The ancestral arthropod likely had an identical pair of appendages on each segment, and the segments were nearly identical, repeating units.
::祖先的节肢动物在每一区段上可能有一对相同的附着物,各区段几乎相同,重复使用单元。 -
During arthropod evolution, one variation on the body plan that arose involved the loss or modification of many appendages to carry out different functions.
::在节肢动物进化期间,身体计划出现一个变异,导致许多附属物丢失或修改,以履行不同职能。
Review
::回顾-
How old are arthropod fossils? Are they preserved as well as mollusks?
::节肢动物化石几岁了? 它们和软体动物一样保存吗? -
What group of extinct arthropods has an extensive fossil record? What did scientists learn from this group of arthropods?
::哪些已经灭绝的节肢动物有广泛的化石记录?科学家从这些节肢动物中学到了什么? -
What do scientists believe the ancestral arthropod looked like?
::科学家们相信祖先的节肢动物长什么样? -
What occurred during the evolution of arthropods that led to so much variation?
::在导致如此巨大差异的节肢动物进化过程中发生了什么? -
Which two small phyla of animals are very closely related to arthropods?
::哪种小动物的植物 与节肢动物关系非常密切?
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The study of arthropod evolution is an ongoing process, and theories are modified regularly as more information is obtained through molecular comparisons between species.
