I'm hoping to show that not nearly -- (not even close to...) -- as many animals had to board the Ark as some think.
Picture this as an oversimplified example:
The Ark comes to rest with just the aforementioned animals (plus Noah and his family) aboard.
The unicorns disembark -- go out -- get pregnant and give birth to another unicorn, a horse, a cow, a lion and a tiger.
They get pregnant again and give birth to a hippopotamus, a platypus, an aardvark, etc.
See where I'm coming with this?
A kind is an animal with DNA specially encoded for punctuated equilibrium; and because of them, you don't need the Ark crammed full of every living creature in existence at the time, and you don't need long explanations as to how tree sloths got from the Ark to where they're found today, etc.