Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK.
Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK.
Curr Biol. 2015 Aug 17;25(16):2137-42. doi: 10.1016/j.cub.2015.06.047. Epub 2015 Jul 16.
A series of spectacular discoveries have transformed our understanding of Mesozoic mammals in recent years. These finds reveal hitherto-unsuspected ecomorphological diversity that suggests that mammals experienced a major adaptive radiation during the Middle to Late Jurassic. Patterns of mammalian macroevolution must be reinterpreted in light of these new discoveries, but only taxonomic diversity and limited aspects of morphological disparity have been quantified. We assess rates of morphological evolution and temporal patterns of disparity using large datasets of discrete characters. Rates of morphological evolution were significantly elevated prior to the Late Jurassic, with a pronounced peak occurring during the Early to Middle Jurassic. This intense burst of phenotypic innovation coincided with a stepwise increase in apparent long-term standing diversity and the attainment of maximum disparity, supporting a "short-fuse" model of early mammalian diversification. Rates then declined sharply, and remained significantly low until the end of the Mesozoic, even among therians. This supports the "long-fuse" model of diversification in Mesozoic therians. Our findings demonstrate that sustained morphological innovation in Triassic stem-group mammals culminated in a global adaptive radiation of crown-group members during the Early to Middle Jurassic.
近年来，一系列引人瞩目的发现彻底改变了我们对中生代哺乳动物的认识。这些发现揭示了中生代哺乳动物迄今尚未被察觉的生态形态多样性，表明哺乳动物在中侏罗世至晚侏罗世经历了一次重大的适应性辐射。鉴于这些新发现，必须重新解释哺乳动物宏观进化的模式，但只有分类多样性和形态差异的有限方面得到了量化。我们使用大量离散特征数据集来评估形态进化的速度和形态差异的时间模式。形态进化的速度在晚侏罗世之前显著提高，在早至中侏罗世期间出现明显的高峰。这种强烈的表型创新与明显的长期稳定多样性的逐步增加和最大差异的实现同时发生，支持早期哺乳动物多样化的“短导火索”模型。此后，速度急剧下降，直到中生代结束，甚至在兽类中，速度仍然明显较低。这支持了中生代兽类多样化的“长导火索”模型。我们的研究结果表明，三叠纪干群哺乳动物的持续形态创新最终导致早至中侏罗世期间，冠群成员的全球适应性辐射。
