Large Mesozoic mammals fed on young dinosaurs

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Abstract

Mesozoic mammals are commonly portrayed as shrew- or rat-sized animals that were mainly insectivorous, probably nocturnal and lived in the shadow of dinosaurs1,2,3,4,5. The largest known Mesozoic mammal represented by substantially complete remains is Repenomamus robustus, a triconodont mammal from the Lower Cretaceous of Liaoning, China6,7. An adult individual of R. robustus was the size of a Virginia opossum. Here we report a new species of the genus, represented by a skeleton with most of the skull and postcranium preserved in articulation. The new species is 50% larger than R. robustus in skull length. In addition, stomach contents associated with a skeleton of R. robustus reveal remains of a juvenile Psittacosaurus, a ceratopsian dinosaur. Our discoveries constitute the first direct evidence that some triconodont mammals were carnivorous and fed on small vertebrates, including young dinosaurs, and also show that Mesozoic mammals had a much greater range of body sizes than previously known. We suggest that Mesozoic mammals occupied diverse niches and that some large mammals probably competed with dinosaurs for food and territory.

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Figure 1: Holotype of Repenomamus giganticus (IVPP V14155).
Figure 2
Figure 3: The postcranial skeleton of R. robustus (IVPP V13605).
Figure 4: Relationship between basal mammals with attached lower jaws to show their relative sizes (adopted from ref. 7)

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Acknowledgements

We thank M.-M. Chang, Z.-H. Zhou, X.-L. Wang, X. Xu, F.-C. Zhang, Y. Wang, F. Jin and J.-Y. Zhang for help coordinating the research and fieldwork; X. Xu, X.-L. Wang, F.-C. Zhang, Z.-H. Zhou, and M. Norell for discussions on the research subject, and S.-H. Xie, S.-J. Li and A. Davidson for specimen preparation. This work was supported by funding from the Chinese Ministry of Science and Technology, the National Natural Science Foundation of China and the Chinese Academy of Sciences. Y.H. is also supported by a fellowship from the American Museum of Natural History, through the City University of New York.

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Correspondence to Yaoming Hu.

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Supplementary information

Supplementary Information Notes

This Supplementary Information text includes: (I) body mass estimation for two species of Repenomamus; (II) stomach content preparation and identification for R. robustus (IVPP V 13605); (III) Data sources for Figure 4 (sizes of the lower jaws of representative Mesozoic mammals and relatives). The file contains six figures. (DOC 1625 kb)

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Hu, Y., Meng, J., Wang, Y. et al. Large Mesozoic mammals fed on young dinosaurs. Nature 433, 149–152 (2005) doi:10.1038/nature03102

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