The Cretaceous–Paleogene mass extinction approximately 66 million years ago is conventionally thought to have been a turning point in mammalian evolution1,2. Prior to that event and for the first two-thirds of their evolutionary history, mammals were mostly confined to roles as generalized, small-bodied, nocturnal insectivores3, presumably under selection pressures from dinosaurs4. Release from these pressures, by extinction of non-avian dinosaurs at the Cretaceous–Paleogene boundary, triggered ecological diversification of mammals1,2. Although recent individual fossil discoveries have shown that some mammalian lineages diversified ecologically during the Mesozoic era5, comprehensive ecological analyses of mammalian groups crossing the Cretaceous–Paleogene boundary are lacking. Such analyses are needed because diversification analyses of living taxa6,7 allow only indirect inferences of past ecosystems. Here we show that in arguably the most evolutionarily successful clade of Mesozoic mammals, the Multituberculata, an adaptive radiation began at least 20 million years before the extinction of non-avian dinosaurs and continued across the Cretaceous–Paleogene boundary. Disparity in dental complexity, which relates to the range of diets, rose sharply in step with generic richness and disparity in body size. Moreover, maximum dental complexity and body size demonstrate an adaptive shift towards increased herbivory. This dietary expansion tracked the ecological rise of angiosperms8 and suggests that the resources that were available to multituberculates were relatively unaffected by the Cretaceous–Paleogene mass extinction. Taken together, our results indicate that mammals were able to take advantage of new ecological opportunities in the Mesozoic and that at least some of these opportunities persisted through the Cretaceous–Paleogene mass extinction. Similar broad-scale ecomorphological inventories of other radiations may help to constrain the possible causes of mass extinctions9,10.
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We thank museums, institutions and individuals that made specimens available for this study (full list is available in Supplementary Information). Funding was provided by the National Science Foundation, Denver Museum, the University of Washington (G.P.W. and P.D.S.), the Australian Research Council, Monash University (A.R.E.), the Academy of Finland (A.R.E., M.F. and J.J.) and the EU SYNTHESYS program (project GB-TAF-4779) (I.J.C.).
This file contains Supplementary Text, Supplementary Figures 1-10, Supplementary Tables 1-7 and additional references.
About this article
New Phytologist (2019)