Cambrian bivalved arthropod reveals origin of arthrodization
Cambrian bivalved arthropod reveals origin of arthrodization
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DOI：
10.1098/rspb.2012.1958
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发表时间：
2012-12-07
影响因子：
4.7
通讯作者：
Caron, Jean-Bernard
中科院分区：
文献类型：
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作者：
Legg, David A.;Sutton, Mark D.;Caron, Jean-Bernard
现存节肢动物多种多样且无处不在，构成了大多数现代生态系统的主要组成部分。早古生代 Konservat Lagerstatten 的证据表明，自寒武纪以来一直是这种情况。尽管如此，节肢动物起源的细节仍然不清楚，尽管大多数假设认为最早的节肢动物是底栖捕食者或食腐动物，例如伏仙鱼或巨龟（“大附肢”节肢动物）。在这里，我们描述了一种来自伯吉斯页岩地层郁金香床地区（寒武纪，第 3 系列，第 5 阶段）的新节肢动物，它拥有一个带有丝状附属物的弱硬化胸部，包裹在双壳甲壳中，以及一个强硬化、细长的腹部和尾节。分支分析表明该分类群是双壳甲壳的并系群系底栖动物中最基础的成员。该等级发生在节肢动物（具有节肢动物躯干四肢的泛节肢动物）的基部，表明关节化（外骨骼的硬化和关节）的进化是为了促进游泳。捕食性和完全底栖习性在真节肢动物干系中进化得较晚，并在鲎科动物（海蜘蛛）和真螯动物（鲎和蜘蛛纲动物）中保留了类似形态。
Extant arthropods are diverse and ubiquitous, forming a major constituent of most modern ecosystems. Evidence from early Palaeozoic Konservat Lagerstatten indicates that this has been the case since the Cambrian. Despite this, the details of arthropod origins remain obscure, although most hypotheses regard the first arthropods as benthic predators or scavengers such as the fuxianhuiids or megacheirans ('great-appendage' arthropods). Here, we describe a new arthropod from the Tulip Beds locality of the Burgess Shale Formation (Cambrian, series 3, stage 5) that possesses a weakly sclerotized thorax with filamentous appendages, encased in a bivalved carapace, and a strongly sclerotized, elongate abdomen and telson. A cladistic analysis resolved this taxon as the basal-most member of a paraphyletic grade of nekto-benthic forms with bivalved carapaces. This grade occurs at the base of Arthropoda (panarthropods with arthropodized trunk limbs) and suggests that arthrodization (sclerotization and jointing of the exoskeleton) evolved to facilitate swimming. Predatory and fully benthic habits evolved later in the euarthropod stem-lineage and are plesiomorphically retained in pycnogonids (sea spiders) and euchelicerates (horseshoe crabs and arachnids).