Vertebrate-mediated seed dispersal is a common attribute of many living plants, and variation in the size and abundance of fleshy diaspores is influenced by regional climate and by the nature of vertebrate seed dispersers among present-day floras. However, potential drivers of large-scale variation in the abundance and size distributions of fleshy diaspores through geological time, and the importance of geographic variation, are incompletely known. This knowledge gap is important because fleshy diaspores are a key mechanism of energy transfer from photosynthesis to animals and may in part explain the diversification of major groups within birds and mammals. Various hypotheses have been proposed to explain variation in the abundance and size distribution of fleshy diaspores through time, including plant–frugivore co-evolution, angiosperm diversification, and changes in vegetational structure and climate. We present a new data set of more than 800 georeferenced fossil diaspore occurrences spanning the Triassic–Oligocene, across low to mid- to high palaeolatitudes. We use this to quantify patterns of long-term change in fleshy diaspores, examining the timing and geographical context of important shifts as a test of the potential evolutionary and climatic explanations. We find that the fleshy fruit sizes of angiosperms increased for much of the Cretaceous, during the early diversification of angiosperms from herbaceous ancestors with small fruits. Nevertheless, this did not cause a substantial net change in the fleshy diaspore size distributions across seed plants, because gymnosperms had achieved a similar size distribution by at least the Late Triassic. Furthermore, gymnosperm-dominated Mesozoic ecosystems were mostly open, and harboured low proportions of specialised frugivores until the latest Cretaceous, suggesting that changes in vegetation structure and plant–frugivore co-evolution were probably not important drivers of fleshy diaspore size distributions over long timescales. Instead, fleshy diaspore size distributions may be largely constrained by physical or life-history limits that are shared among groups and diversify as a plant group expands into different growth forms/sizes, habitats, and climate regimes. Mesozoic gymnosperm floras had a low abundance of fleshy diaspores (<50% fleshy diaspore taxa), that was surpassed by some low-latitude angiosperm floras in the Cretaceous. Eocene angiosperm floras show a mid- to high latitude peak in fleshy fruit abundance, with very high proportions of fleshy fruits that even exceed those seen at low latitudes both in the Eocene and today. Mid- to high latitude proportions of fleshy fruits declined substantially over the Eocene–Oligocene transition, resulting in a shift to more modern-like geographic distributions with the highest proportion of fleshy fruits occurring in low-latitude tropical assemblages. This shift was coincident with global cooling and the onset of Southern Hemisphere glaciation, suggesting that rapid cooling at mid- and high latitudes caused a decrease in availability of the climate conditions most favourable for fleshy fruits in angiosperms. Future research could be focused on examining the environmental niches of modern fleshy fruits, and the potential effects of climate change on fleshy fruit and frugivore diversity.

中文翻译：

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晚三叠世-渐新世肉质水硬铝石大小和丰度的变化模式

脊椎动物介导的种子传播是许多活植物的共同属性，肉质水硬铝石的大小和丰度的变化受到区域气候和当今植物区系中脊椎动物种子传播者性质的影响。然而，肉质水硬铝石的丰度和尺寸分布在地质时期发生大规模变化的潜在驱动因素以及地理变化的重要性尚不完全清楚。这种知识差距很重要，因为肉质硬水铝石是光合作用能量转移到动物的关键机制，并且可能部分解释鸟类和哺乳动物内主要群体的多样化。人们提出了各种假设来解释肉质水硬铝石的丰度和大小分布随时间的变化，包括植物与食果动物的共同进化、被子植物的多样化以及植被结构和气候的变化。我们提出了一个新的数据集，其中包含跨越三叠纪-渐新世、低古纬度、中古纬度和高古纬度的 800 多个地理参考水硬铝石化石。我们用它来量化肉质水硬铝石长期变化的模式，检查重要转变的时间和地理背景，作为对潜在进化和气候解释的测试。我们发现，在白垩纪的大部分时间里，被子植物的肉质果实尺寸有所增加，这是在被子植物从具有小果实的草本祖先的早期多样化过程中发生的。然而，这并没有导致种子植物的肉质水硬铝石尺寸分布发生实质性的净变化，因为裸子植物至少在三叠纪晚期已经达到了类似的尺寸分布。此外，以裸子植物为主的中生代生态系统大多是开放的，直到白垩纪末期为止，特化食果动物的比例较低，这表明植被结构的变化和植物与食果动物的共同进化可能不是长期尺度肉质水硬铝石尺寸分布的重要驱动因素。相反，肉质水硬铝石尺寸分布可能在很大程度上受到群体之间共享的物理或生活史限制的限制，并且随着植物群体扩展到不同的生长形式/大小、栖息地和气候状况而多样化。中生代裸子植物区系的肉质水硬铝石植物群的丰度较低（肉质水硬铝石类群<50%），白垩纪的一些低纬度被子植物区系超过了这一水平。始新世被子植物区系在中高纬度地区呈现出肉质果实丰度的高峰，肉质果实的比例非常高，甚至超过了始新世和今天低纬度地区的肉质果实。在始新世-渐新世过渡期间，中高纬度肉质水果的比例大幅下降，导致地理分布转向更现代的地理分布，其中肉质水果比例最高的肉质水果出现在低纬度热带组合中。这种转变与全球变冷和南半球冰川的开始同时发生，这表明中高纬度地区的快速变冷导致最有利于被子植物肉质果实的气候条件的减少。未来的研究可能集中于研究现代肉质水果的环境利基，以及气候变化对肉质水果和食果动物多样性的潜在影响。