Stephanie E. Pierce2014-05-06 2:31 PM

继三叠纪末灭绝后鳄鱼线祖龙的形态和生物力学差异 Morphological and biomechanical disparity of crocodile-line archosaurs following the end-Triassic extinction

论文摘要

中生代镶嵌踝类主龙表现出了不同的形态和喂养方式,这表明了相当大的生态多样性,然而宏观进化模式仍然尚未被探索。在此,我们以下颌骨作为形态功能的代表,使用了形态学和生物力学差距指标的独特组合来量化生态多样性以及中生代镶嵌踝类主龙的摄食辐射。我们复原了三大主流趋势。首先,晚三叠世镶嵌踝类主龙的多样化组合在形态和生物力学方面各不相同,这意味着高水平的生态变化; 但是随着三叠纪末期的灭绝,这种差距有所下降。其次海鳄亚目的侏罗纪辐射导致形态差异很小,只有颌骨生物力学发生了温和变化,这突出了上下颌形态的流体动力学约束。第三,新鳄类和诺托鳄亚目的白垩纪陆地辐射阶段,下颌骨形态变异极大增加。到了晚白垩世,鳄形超目进行了相当于晚三叠世镶嵌踝类主龙的各种形态的演变。与此相反,白垩纪生物力学差异并没有增加,这从形态上基本脱离了。这个神秘结果可以归因于其他可能从选择性压力下释放下颌骨的解剖区域的生物力学演变(例如头盖骨,牙列或后颅)。总体而言,我们的分析揭示了中生代镶嵌踝类主龙形态学和生物力学差距之间的复杂关系,这最终导致了特殊的进食生态和相关生活方式。


Abstract

Mesozoic crurotarsans exhibited diverse morphologies and feeding modes, representing considerable ecological diversity, yet macroevolutionary patterns remain unexplored. Here, we use a unique combination of morphological and biomechanical disparity metrics to quantify the ecological diversity and trophic radiations of Mesozoic crurotarsans, using the mandible as a morpho-functional proxy. We recover three major trends. First, the diverse assemblage of Late Triassic crurotarsans was morphologically and biomechanically disparate, implying high levels of ecological variation; but, following the end-Triassic extinction, disparity declined. Second, the Jurassic radiation of marine thalattosuchians resulted in very low morphological disparity but moderate variation in jaw biomechanics, highlighting a hydrodynamic constraint on mandibular form. Third, during the Cretaceous terrestrial radiations of neosuchians and notosuchians, mandibular morphological variation increased considerably. By the Late Cretaceous, crocodylomorphs evolved a range of morphologies equalling Late Triassic crurotarsans. By contrast, biomechanical disparity in the Cretaceous did not increase, essentially decoupling from morphology. This enigmatic result could be attributed to biomechanical evolution in other anatomical regions (e.g. cranium, dentition or postcranium), possibly releasing the mandible from selective pressures. Overall, our analyses reveal a complex relationship between morphological and biomechanical disparity in Mesozoic crurotarsans that culminated in specialized feeding ecologies and associated lifestyles.

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Stephanie E. Pierce

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