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首页> 外文期刊>Palaeogeography, Palaeoclimatology, Palaeoecology: An International Journal for the Geo-Sciences >Early Palaeozoic palaeobiogeography and palaeoecology of stylophoran echinodenns
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Early Palaeozoic palaeobiogeography and palaeoecology of stylophoran echinodenns

机译：花粉棘皮动物的早期古生代古生物地理学和古生态

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摘要

Stylophorans (cornutes, mitrates) represent one of the most diverse classes of Cambro-Ordovician echinoderms. They were free-living, benthic, non-radiate forms, closely related to asterozoans and crinoids. Tapbonomic, sedimentological, and palaeosynecological data provide useful information on key aspects of stylophoran palaeoecology. Such a combined approach suggests that the rarity of stylophorans in proximal environments (above storm-wave base) was probably original and does not exclusively result from the possession of a loosely articulated polyplated calcitic test. Conversely, stylophorans were relatively abundant in deeper settings (below storm-wave base), where they frequently occur in low-diversity dense beds (several tens to hundreds of individuals per square metre). Such assemblages were either largely dominated by stylophorans only (Middle Cambrian-Darriwilian), or by the association of both stylophorans and ophiuroids (latest Darriwilian-Silurian). Comparison with ecological requirements of similar modern and fossil dense populations of ophiuroids suggests that stylophoran beds occurred in well-oxygenated, oligotrophic waters with low predatory pressure, and that sea temperature played a key role in the palacobiogeographic distribution of stylophorans. Seven main stylophoran biofacies are identified and described. The associated environments and tropical distribution of primitive, heavily-plated forms suggest that the initial radiation of the class probably took place in warm to temperate shallow settings (earliest Middle Cambrian-Late Cambrian). However, from this primitive stock, stylophorans radiated several times towards deeper and/or colder environments, possibly because of the lower predation pressure in such settings ("cothurnocystid" comutes in the Middle Cambrian, mitrates in the Late Cambrian, hanusiids in the Tremadocian). As a consequence, the fact that most Cambro-Ordovician comutes and mitrates were "psychrospheric" (i.e. cold-water adapted) probably explains their relatively wide palaeobiogeographic distribution. In high palaeolatitudes, Cambro-Ordovician stylophorans were abundant and diverse in shallow to deep environments, but they were generally restricted to deep settings in low palaeolatitudes. The great Caradocian transgression favoured the extension of stylophorans from circum-polar regions (e.g. western margin of Gondwana) towards external settings at lower palaeolatitudes (Avalonia, Baltica, and eastern margin of Laurentia), where one group of mitrates underwent a major radiation (anomalocystitids), and extended towards shallower (and warmer) palaeoenvironments. In contrast, all Silurian stylophoran assemblages known so far are rare, poorly diversified, and restricted to shallow, warm to temperate environments in tropical regions. This distribution partly results from (1) the probable eradication of psychrospheric forms (e.g. comutes) because of the prolonged anoxia of deep environments in the late Hirnantian-early Silurian of West Gondwana, (2) the radiation of some mitrates (anomalocystitids) in shallow tropical settings in the late Ordovician, and (3) of strong taphonomic and/or sampling biases (numerous ghost lineages). (c) 2006 Elsevier B.V. All rights reserved.
机译：针戟属（角类，有mit酸盐）代表了坎布罗-奥陶纪棘皮动物种类最丰富的类别之一。它们是自由生活的，底栖的，非辐射的形式，与星状星体和海百合紧密相关。 Tapbonomic，沉积学和古生态学数据可提供有关苯乙烯类古生态学关键方面的有用信息。这样的组合方法表明，在近端环境（风暴波波基以上）中，苯乙烯基醚的稀有性可能是原始的，并且并非仅是由于松散连接的多电镀钙测试的结果。相反，在较深的环境中（在风暴波基以下），花香属植物相对丰富，它们经常发生在低多样性的致密层中（每平方米数十至数百个人）。这样的组合要么主要由聚苯乙烯类化合物（中寒武纪-达里维利安）控制，要么由聚苯乙烯类化合物和蛇形类的结合（最新的达里维利安-西鲁里亚语）主导。与相似的现代和化石密集的蛇类类群的生态需求进行比较表明，花粉刺床发生在具有良好掠食压力的充氧，低营养的水中，海水温度在花粉刺的古生物地理分布中起着关键作用。鉴定并描述了七种主要的苯乙烯类生物相。相关的环境和原始的，大量覆盖的形态的热带分布表明，该类的初始辐射可能发生在温暖到温带的浅层环境中（最早的中寒武纪-晚寒武纪）。但是，从这种原始种群中，花香属植物向更深和/或更冷的环境辐射了数次，这可能是因为在这样的环境下捕食压力较低（“寒地囊虫”在上寒武统中上班，虫在寒武纪中的，虫，特里玛多斯人中的哈努西德人） 。结果，大多数Cambro-Ordovician上下班族和被子族都是“心理层”（即适应冷水）的事实，可能解释了它们相对较宽的古生物地理分布。在高古高原中，Cambro-Ordovician stylophorans在浅层至深层环境中丰富且多样，但通常只限于低古时代的深层环境。巨大的卡拉多西亚海侵有利于将香叶从极地地区（例如冈瓦纳西缘）向古近纬度较低的外部环境（阿瓦隆，巴尔提卡和劳伦西亚的东缘）延伸，其中一组有mit子经历了主要的辐射（异囊藻） ），并扩展到较浅（和较暖）的古环境。相反，到目前为止，所有已知的志留纪苯乙烯基团都不多见，多样性差，并且仅限于热带地区的浅，温暖到温带的环境。这种分布的部分原因是（1）西贡多瓦纳的赫南特晚期-志留纪晚期深层环境长期缺氧，从而可能根除了心理层形式（例如通勤者）;（2）在浅水区辐射了一些被子（异常囊藻）奥陶纪晚期的热带环境，以及（3）强烈的偏音和/或采样偏差（无数的鬼血统）。 （c）2006 Elsevier B.V.保留所有权利。

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