And the order of rodents includes everything from mice and rats to beavers, porcupines, prairie dogs, squirrels and capybaras.A rodent doesn't evolve into a rodent. It may change characteristics but it is still a rodent. And rodents multiply quite quickly.
Exactly how long are you saying that it took for this original pair of "rodent kind" animals to evolve into what we have today, with more than 2,000 species? How long do you think it took the porcupine to develop quills (or perhaps for all the other species to lose their quills, I suppose), for the beaver to develop its webbed feet and distinctive tail, or for all the other specialized development to occur that we see in rodents?