Repenomamus is the largest mammal known from the Cretaceous period of China, and it is the mammal for which there is the best evidence that it fed on dinosaurs. It is not possible to determine if Repenomamus actively hunted live dinosaurs or scavenged dead dinosaurs.
Repenomamus was probably not a fast runner. The humerus and femur left their joints at a somewhat splayed angle, and the legs were relatively short compared to the body. The feet were plantigrade. Repenomamus's behavior and overall body shape may have resembled those of modern day Tasmanian devils.
Repenomamus was carnivorous. A specimen of R. robustus has been discovered with the fragmentary skeleton of a juvenile Psittacosaurus preserved in its stomach. This the strongest evidence that Mesozoic mammals fed on dinosaurs, and this created interest in the popular press. There were, however, earlier indications that Mesozoic mammals fed on dinosaurs (see Archaeornithoides).