Lions and tigers are both FELINES. There is nothing extraordinary about this and it does not prove evolution from lower orders to higher, or from one completely different species to another. I don't think even creationists would argue that mutation does not exist. It is possible that these two animals had an ancestor - who was also a FELINE, and that a mutation occurred, possibly as a result of climate. Who knows. NO ONE DOES.
This is one of the central problems with evolutionists. When you try to demonstrate your theory, you keep doing so with examples that are only variations within a species. Lions and tigers are members of the feline family. Same as little house cats. Big deal.
You and a lion are both mammals. If two felines can have a common ancestor, why can't two mammals? Explain the distinction.
But since we know that changes occur that result in offspring not able to mate with the parent species it is technically a new species.
Like with the theory of continental drift, no eyewitness has seen one continent break up into two even though we can measure the drift of land masses. But Africa is always Africa and South America is always South America. Likewise we don't see frogs evolving into giraffe.