The evolutionary causes of the latitudinal diversity gradient are debated. Hypotheses have ultimately invoked either faster rates of diversification in the tropics or more time for diversification owing to the tropical origins of higher taxa. Here, we perform the first test of the diversification rate and time hypotheses in freshwater ray‐finned fishes, a group comprising nearly a quarter of all living vertebrates.

中文翻译：

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进化时间最好地解释了淡水鱼类多样性的纬度多样性梯度

讨论了纬度多样性梯度的演化原因。假说最终归因于热带地区更快的多元化发展速度，或者由于较高的分类单元的热带起源，导致了更多的多元化发展时间。在这里，我们对淡水射线鳍鱼进行了多样化率和时间假说的首次检验，该鱼群包括所有活体脊椎动物的近四分之一。