They traded in there fins for some new legs that allowed them to move around on land.
No. There are many aquatic mammals.
yes
They are just called land mammals, or perhaps terrestrial mammals.
Terrestrial placental mammals do have fur or hair. Marine placental mammals do not.
mammals
it depends of which speific mammals that you are talking about
Both birds and mammals are warm-blooded terrestrial vertebrates.
By the tracheal system.
Kangaroos are primitive mammals. There offsprings needs more protection. So they have pouch to keep there babies safe. They are only found in Australia. Incidentally the link between birds and mammals is found in Australia only in the form of echidna and platypus.
None of them...they all are examples of adaptation.
Both. If your referring to mammals the answer is still both.
it would be land