Secrets revealed by kangaroo teeth The teeth of mammals display complex adaptations to diet and can thus provide a window into the environments of extinct species. Couzens and Prideaux used such a window to examine the expansion and diversification of kangaroos, Australia's largest herbivores (see the Perspective by Polly). True kangaroos diversified not in response to drying in the Miocene, as suggested by molecular results, but rather as grasslands expanded during the Pliocene. Furthermore, the now-extinct short-faced kangaroos were not declining because of increases in aridity at the end of the Pleistocene but instead were experiencing an increase in dietary divergence. Science, this issue p. 72; see also p. 25 Kangaroos show unexpected patterns of diversification in response to past changes in climate. Differentiating between ancient and younger, more rapidly evolved clades is important for determining paleoenvironmental drivers of diversification. Australia possesses many aridity-adapted lineages, the origins of which have been closely linked to late Miocene continental aridification. Using dental macrowear and molar crown height measurements, spanning the past 25 million years, we show that the most iconic Australian terrestrial mammals, “true” kangaroos (Macropodini), adaptively radiated in response to mid-Pliocene grassland expansion rather than Miocene aridity. In contrast, low-crowned, short-faced kangaroos radiated into predominantly browsing niches as the late Cenozoic became more arid, contradicting the view that this was an interval of global browser decline. Our results implicate warm-to-cool climatic oscillations as a trigger for adaptive radiation and refute arguments attributing Pleistocene megafaunal extinction to aridity-forced dietary change.

中文翻译：

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现代袋鼠的快速上新世适应性辐射

袋鼠牙齿揭示的秘密哺乳动物的牙齿对饮食表现出复杂的适应性，因此可以为了解灭绝物种的环境提供一个窗口。Couzens 和 Prideaux 使用这样一个窗口来检查澳大利亚最大的食草动物袋鼠的扩张和多样化（见 Polly 的观点）。正如分子结果所表明的那样，真正的袋鼠的多样化不是因为中新世的干燥而发生变化，而是随着上新世期间草原的扩张。此外，现已灭绝的短脸袋鼠并没有因为更新世末干旱程度的增加而减少，而是在经历饮食差异的增加。科学，这个问题 p。72; 另见第。25 袋鼠在应对过去的气候变化时表现出意想不到的多样化模式。区分古代和更年轻、进化更快的进化枝对于确定多样化的古环境驱动因素很重要。澳大利亚拥有许多适应干旱的谱系，其起源与晚中新世大陆干旱化密切相关。使用跨越过去 2500 万年的牙齿宏观磨损和臼齿冠高度测量，我们表明最具标志性的澳大利亚陆生哺乳动物，“真正的”袋鼠（Macropodini），适应性地辐射以响应上新世中期草原扩张而不是中新世干旱。相比之下，随着新生代晚期变得更加干旱，低冠、短脸袋鼠辐射到主要浏览的壁龛中，这与认为这是全球浏览器衰退的时期的观点相矛盾。