Squamation and ecology of thelodonts.
Squamation and ecology of thelodonts.
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DOI：
10.1371/journal.pone.0172781
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发表时间：
2017
期刊：
影响因子：
3.7
通讯作者：
Botella H
中科院分区：
文献类型：
--
作者：
Ferrón HG;Botella H
齿齿兽是古生代无颌脊椎动物的一个神秘类群，尽管我们对它们的生态和生活方式的了解仍然很少，但从分类学、生物地层学和古地理的角度对它们进行了深入研究。它们的身体覆盖着微米级的鳞片，其形态、组织学和发育过程与现存的鲨鱼极为相似。基于这些相似之处以及鲨鱼的鳞状结构和生态之间众所周知的关系，我们在这里探讨了齿齿兽的生态多样性和生活方式。为此，我们使用经典的形态计量学和判别分析来描述大量生态众所周知的现存鲨鱼物种的鳞状模式。多变量分析定义了每个生态群体的特征鳞状模式，从而建立了推断齿齿兽生活方式的比较框架。然后，我们利用这些信息来研究目前描述的 147 种齿齿兽的鳞状结构，这些齿齿兽可以从有关节和无关节的遗骸中得知。判别分析可以识别与鲨鱼类似的有鳞模式，并将它们与特定的生态群体联系起来。我们的结果表明齿齿兽具有显着的生态多样性。其中大部分可能是底栖物种，栖息在岩石环境或珊瑚礁的洞穴和裂缝中的坚硬基质中，利用其微粒鳞片提供的灵活性。与经典的解释相反，只有少数齿齿兽被放置在栖息于沙质和泥质基质的底层物种中。具有抵御外寄生虫的防御鳞片的群落物种也可能很丰富，这表明早在志留世的脊椎动物中就存在外寄生虫的社会互动和压力。物种的存在显示出低速到中速的鳞片以及可能与开放水域环境相关的生活方式，这表明齿齿兽对深水栖息地的适应。鳞片形态表明，其他一些齿齿兽是强游动的远洋物种，其中大多数在泥盆纪早期与尼克顿革命相关的时期辐射。
Thelodonts are an enigmatic group of Paleozoic jawless vertebrates that have been well studied from taxonomical, biostratigraphic and paleogeographic points of view, although our knowledge of their ecology and mode of life is still scant. Their bodies were covered by micrometric scales whose morphology, histology and the developmental process are extremely similar to those of extant sharks. Based on these similarities and on the well-recognized relationship between squamation and ecology in sharks, here we explore the ecological diversity and lifestyles of thelodonts. For this we use classic morphometrics and discriminant analysis to characterize the squamation patterns of a significant number of extant shark species whose ecology is well known. Multivariate analyses have defined a characteristic squamation pattern for each ecological group, thus establishing a comparative framework for inferring lifestyles in thelodonts. We then use this information to study the squamation of the currently described 147 species of thelodonts, known from both articulated and disarticulated remains. Discriminant analysis has allowed recognizing squamation patterns comparable to those of sharks and links them to specific ecological groups. Our results suggest a remarkable ecological diversity in thelodonts. A large number of them were probably demersal species inhabiting hard substrates, within caves and crevices in rocky environments or reefs, taking advantage of the flexibility provided by their micromeric squamations. Contrary to classical interpretations, only few thelodonts were placed among demersal species inhabiting sandy and muddy substrates. Schooling species with defensive scales against ectoparasites could be also abundant suggesting that social interactions and pressure of ectoparasites were present in vertebrates as early the Silurian. The presence of species showing scales suggestive of low to moderate speed and a lifestyle presumably associated with open water environments indicates adaptation of thelodonts to deep water habitats. Scale morphology suggests that some other thelodonts were strong-swimming pelagic species, most of them radiating during the Early Devonian in association with the Nekton Revolution.