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Large Mesozoic mammals fed on young dinosaurs

2005; Nature Portfolio; Volume: 433; Issue: 7022 Linguagem: Inglês

10.1038/nature03102

1476-4687

Yaoming Hu, Jin Meng, Yuan Wang, Chuankui Li,

Amphibian and Reptile Biology

We tend to think of the the mammals that lived in the shadow of the dinosaurs as scuttling around trying not to get eaten or trodden on. They were small, the size of a modern shrew or rat, feeding on insects, and active during evening hours. That picture is changing. The extinct mammal Repenomamus robustus, discovered five years ago, broke the mould: it was much bigger, the size of a Virginia opossum. And now another member of the genus Repenomamus has been found that is half as big again, the size of a badger or jackal. What's more, a specimen of R. robustus found preserved with its last meal inside its — stomach the bones of young dinosaurs. These carnivorous mammals were beginning to come out of the shadows. 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.