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.
Like all terrestrial mammals, honey possums have four limbs.
mammals
Both birds and mammals are warm-blooded terrestrial vertebrates.
By the tracheal system.
Both. If your referring to mammals the answer is still both.
G. B. Corbet has written: 'Finding and identifying mammals' -- subject(s): Mammals, Observers' manuals 'The terrestrial mammals of Western Europe'
The spiny anteater, more correctly known as the echidna, does indeed have four legs. It is a mammal, and all terrestrial mammals have four legs.
As far as I know octopus has 8 legs ^_^ Many amphibians (frogs, salamanders, newts, etc.) live in water full time or at least part time.
Most terrestrial mammals have fur or hair and feed milk to their young.