The recorded history of the domestic dog demonstrates an explosion of variations in a relatively short time frame, driven by both natural and artificial selection criteria. Selective breeding can result in quite rapid and drastic changes to the form of an organism. Almost as if this rapid adaptation was a deliberately designed feature of life. There's no need for a hypothetical Noah to have carried more than one pair of dogs / wolves and still account for all of the variations we see today. Similarly, other kinds of animals, living in different ecosystems, with different selection pressure could exhibit the same rapid variations without requiring aeons of time elapsing.
On the other hand, in a stable environment, natural selection pressure can also serve to keep the form of organisms constant. eg Predators eating the weak, females choosing the mates that match their ideal image of the species. If you assume there was a period of massive disruption, where each organism must adapt to the new ecosystem they find themselves in, change can be very rapid.