Rates of dinosaur body mass evolution indicate 170 million years of sustained ecological innovation on the avian stem lineage.
Rates of dinosaur body mass evolution indicate 170 million years of sustained ecological innovation on the avian stem lineage.
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DOI：
10.1371/journal.pbio.1001853
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发表时间：
2014-05
期刊：
影响因子：
9.8
通讯作者：
Evans DC
中科院分区：
文献类型：
--
作者：
Benson RB;Campione NE;Carrano MT;Mannion PD;Sullivan C;Upchurch P;Evans DC
早期恐龙表现出快速的进化速度，这种进化速度一直持续到鸟类的进化。关键谱系中进化性的维持可能可以解释动物物种群体之间性状多样性分布不均匀的原因。大规模的适应性辐射或许可以解释少数现存脊椎动物进化枝的巨大成功。除其他外，该假设预测，随着谱系侵入不同的生态位，主要群体的早期历史中形态进化的速度会很快。然而，很少有关于适应性辐射的研究包含深时间数据，因此现存多样性与主要灭绝辐射之间的联系尚不清楚。经过深入研究的中生代恐龙记录为此类研究提供了一个模型系统，它代表了一个在 1.7 亿年来主导陆地生态系统的生态多样化群体。此外，现存的恐龙（鸟类）有 10,000 种，是现存四足动物分支中最奇特的。我们组装了 614-622 个中生代恐龙/鸟类的复合树，以及使用肢体骨骼鲁棒性缩放关系的综合体重数据集。最大似然模型和节点高度测试揭示了早期（三叠纪）恐龙的快速进化速度和尺寸类别之间快速变化的优势。这表明早期爆发的利基填充模式，并与之前支持渐进率的研究形成鲜明对比。随后，大多数谱系的比率下降，很少利用新的生态位。然而，有羽毛的手盗龙恐龙（包括中生代鸟类）至少从中侏罗世开始持续快速进化，这表明这些类群逃避了生态位饱和的影响。这表明，持续生态创新的漫长进化史为恐龙的第二次大辐射（即鸟类）铺平了道路。因此，我们通过沿着系统发育干谱系持续快速的进化，证明了非鸟类恐龙主要灭绝的深时适应性辐射与鸟类惊人的多样化之间的联系。这就提出了一种可能性，即生物多样性的不均匀分布不仅是由于对少数现存进化枝的适应性辐射过程进行大规模外推造成的，而且也是由于生命历史上关键谱系在广阔的时间尺度上维持进化性造成的。动物表现出巨大的形态和生态多样性。这种多样性如何进化的一种可能的解释是适应性辐射的“生态位填充”模型，在该模型下，随着谱系多样化以填补不同的生态位，进化率在群体进化的早期最高。我们研究了恐龙和鸟类的体型进化模式，以测试这个模型，并探索现代多样性与主要灭绝辐射之间的联系。我们发现，从两亿多年前开始，早期恐龙的进化速度很快，恐龙的身体尺寸迅速多样化，以填补新的生态位，包括食草性。仅在导致鸟类的进化线上保持了高比率，鸟类继续产生其他恐龙中未见的新生态多样性。较小的体型可能是鸟类维持进化潜力（进化性）的关键，这打破了其他恐龙约 1 公斤的体型下限。我们的结果表明，仅某些谱系中进化性的维持解释了灭绝和现存动物群体中形态和生态多样性的不平衡分布。因此，像鸟类这样的重要生物群体可能是在数亿年的时间尺度上持续、快速的进化速度的结果。
Early dinosaurs showed rapid evolutionary rates, which were sustained on the line leading to birds. Maintenance of evolvability in key lineages might explain the uneven distribution of trait diversity among groups of animal species. Large-scale adaptive radiations might explain the runaway success of a minority of extant vertebrate clades. This hypothesis predicts, among other things, rapid rates of morphological evolution during the early history of major groups, as lineages invade disparate ecological niches. However, few studies of adaptive radiation have included deep time data, so the links between extant diversity and major extinct radiations are unclear. The intensively studied Mesozoic dinosaur record provides a model system for such investigation, representing an ecologically diverse group that dominated terrestrial ecosystems for 170 million years. Furthermore, with 10,000 species, extant dinosaurs (birds) are the most speciose living tetrapod clade. We assembled composite trees of 614–622 Mesozoic dinosaurs/birds, and a comprehensive body mass dataset using the scaling relationship of limb bone robustness. Maximum-likelihood modelling and the node height test reveal rapid evolutionary rates and a predominance of rapid shifts among size classes in early (Triassic) dinosaurs. This indicates an early burst niche-filling pattern and contrasts with previous studies that favoured gradualistic rates. Subsequently, rates declined in most lineages, which rarely exploited new ecological niches. However, feathered maniraptoran dinosaurs (including Mesozoic birds) sustained rapid evolution from at least the Middle Jurassic, suggesting that these taxa evaded the effects of niche saturation. This indicates that a long evolutionary history of continuing ecological innovation paved the way for a second great radiation of dinosaurs, in birds. We therefore demonstrate links between the predominantly extinct deep time adaptive radiation of non-avian dinosaurs and the phenomenal diversification of birds, via continuing rapid rates of evolution along the phylogenetic stem lineage. This raises the possibility that the uneven distribution of biodiversity results not just from large-scale extrapolation of the process of adaptive radiation in a few extant clades, but also from the maintenance of evolvability on vast time scales across the history of life, in key lineages. Animals display huge morphological and ecological diversity. One possible explanation of how this diversity evolved is the "niche filling" model of adaptive radiation—under which evolutionary rates are highest early in the evolution of a group, as lineages diversify to fill disparate ecological niches. We studied patterns of body size evolution in dinosaurs and birds to test this model, and to explore the links between modern day diversity and major extinct radiations. We found rapid evolutionary rates in early dinosaur evolution, beginning more than 200 million years ago, as dinosaur body sizes diversified rapidly to fill new ecological niches, including herbivory. High rates were maintained only on the evolutionary line leading to birds, which continued to produce new ecological diversity not seen in other dinosaurs. Small body size might have been key to maintaining evolutionary potential (evolvability) in birds, which broke the lower body size limit of about 1 kg seen in other dinosaurs. Our results suggest that the maintenance of evolvability in only some lineages explains the unbalanced distribution of morphological and ecological diversity seen among groups of animals, both extinct and extant. Important living groups such as birds might therefore result from sustained, rapid evolutionary rates over timescales of hundreds of millions of years.