Evolution & Diversity Dynamics Lab, Université de Liège, 14 Allée du 6 Août, 4000, Liège, Belgium.
Department of Paleobiology, Smithsonian Institution, P.O. Box 37012, Washington, DC, 20013-7012, USA.
Sci Rep. 2020 Oct 2;10(1):16434. doi: 10.1038/s41598-020-73413-5.
Throughout their evolution, tetrapods have repeatedly colonised a series of ecological niches in marine ecosystems, producing textbook examples of convergent evolution. However, this evolutionary phenomenon has typically been assessed qualitatively and in broad-brush frameworks that imply simplistic macroevolutionary landscapes. We establish a protocol to visualize the density of trait space occupancy and thoroughly test for the existence of macroevolutionary landscapes. We apply this protocol to a new phenotypic dataset describing the morphology of short-necked plesiosaurians, a major component of the Mesozoic marine food webs (ca. 201 to 66 Mya). Plesiosaurians evolved this body plan multiple times during their 135-million-year history, making them an ideal test case for the existence of macroevolutionary landscapes. We find ample evidence for a bimodal craniodental macroevolutionary landscape separating latirostrines from longirostrine taxa, providing the first phylogenetically-explicit quantitative assessment of trophic diversity in extinct marine reptiles. This bimodal pattern was established as early as the Middle Jurassic and was maintained in evolutionary patterns of short-necked plesiosaurians until a Late Cretaceous (Turonian) collapse to a unimodal landscape comprising longirostrine forms with novel morphologies. This study highlights the potential of severe environmental perturbations to profoundly alter the macroevolutionary dynamics of animals occupying the top of food chains.
在进化过程中，四足动物反复占领海洋生态系统中的一系列生态位，产生了趋同进化的典型范例。然而，这种进化现象通常是定性的，并以广泛的框架来评估，这些框架暗示了简单的宏观进化景观。我们建立了一种可视化特征空间占据密度的方案，并彻底测试了宏观进化景观的存在。我们将该方案应用于一个新的描述短颈蛇颈龙形态的表型数据集，这是中生代海洋食物网的主要组成部分（约 2.01 亿至 0.66 亿年前）。蛇颈龙在其 1.35 亿年的历史中多次进化出这种身体结构，使它们成为研究宏观进化景观存在的理想案例。我们发现了大量证据表明，颅面具有双峰宏观进化景观，将侧扁头型与长头型分类群分开，这为已灭绝海洋爬行动物的营养多样性提供了第一个系统发育明确的定量评估。这种双峰模式早在中侏罗世就已经确立，并在短颈蛇颈龙的进化模式中一直保持到白垩纪晚期（土仑期），此时演化为以具有新颖形态的长头型为主的单峰模式。这项研究强调了严重的环境干扰有潜力深刻改变处于食物链顶端的动物的宏观进化动态。
