1. Institute of Vertebrate Paleontology & Paleoanthropology, Chinese Academy of Sciences, PO Box 643, Beijing 100044, China
2. Division of Paleontology, American Museum of Natural History, Central Park West at 79th Street, New York City, New York 10024, USA
3. Biology Program, Graduate School and City College of New York, City University of New York, New York City, New York 10016, USA

Correspondence to: Yaoming Hu^1,2,3 Correspondence and requests for materials should be addressed to Y. H. (Email: yhu@amnh.org).

Abstract

Mesozoic mammals are commonly portrayed as shrew- or rat-sized animals that were mainly insectivorous, probably nocturnal and lived in the shadow of dinosaurs^{1, 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, China^{6, 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.

1. Institute of Vertebrate Paleontology & Paleoanthropology, Chinese Academy of Sciences, PO Box 643, Beijing 100044, China
2. Division of Paleontology, American Museum of Natural History, Central Park West at 79th Street, New York City, New York 10024, USA
3. Biology Program, Graduate School and City College of New York, City University of New York, New York City, New York 10016, USA

Correspondence to: Yaoming Hu^1,2,3 Correspondence and requests for materials should be addressed to Y. H. (Email: yhu@amnh.org).

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