If people can believe that from Noah's family we have the variety of people that we can see nowadays, why would it be difficult to accept that in animal families similar differentiation has happened?
The crucial thing is, in Biblical point of view, everything was good when it was created. Then it started to become corrupted, or degenerate. All that we can see in nature supports the idea of degeneration. And nothing supports the opposite, that things would develop, become more complex, as the evolution theory suggests.
If the evolution theory would be true, we should see things become more complex, single cell organisms evolving to organisms that have legs, eyes and other complex systems. All we can see is DNA getting more errors, "whales losing their legs"... ...this means, it could easily be that in the ark there was about 460 animal families and their offspring has deteriorated to this variety that we now can see. And the speed of deteriorating seems to be increasing.