Repenomamus Repenomamus was the largest mammal of the Age of Dinosaurs. It was the first evidence of a Mesozoic mammal that was bigger than a mouse. In fact, Repenomamus was 3 feet long and weighed 26 to 31 pounds. This made it bigger than most of the dinosaurs of Liaoning, where it lived. In fact, there is even evidence that some dinos should have hidden from Repenomamus. In the stomach of Repenomamus were the bones of a baby Psittacosaurus. This is evidence that mammals were starting to get their revenge on dinsaurs by eating them. This would make Repenomamus the T-rex of Mesozoic mammals.