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Rapid Pliocene adaptive radiation of modern kangaroos

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Science  05 Oct 2018:
Vol. 362, Issue 6410, pp. 72-75
DOI: 10.1126/science.aas8788

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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

Abstract

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.

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