Yes, I do believe that dinosaurs and mammals did live together in harmony while living in the Garden of Eden.
Dinosaurs were probably vegetarians and not carnivorous.
It was after Adam and Eve sinned that everything began to change for the worse.
Again, that is my humble opinion, I could be wrong. The Garden of Eden was described as “paradise” so I do not believe that there was any blood shed between animals.
Sharing a vegetarian diet with dinosaurs just doesn't seem like "paradise" to me. But I guess I'd have to meet Eve before I could decide.