No. There are many aquatic mammals.
yes
Terrestrial placental mammals do have fur or hair. Marine placental mammals do not.
They are just called land mammals, or perhaps terrestrial mammals.
Like all terrestrial mammals, honey possums have four limbs.
mammals
Both birds and mammals are warm-blooded terrestrial vertebrates.
The mammals known for their unique adaptations to survive in terrestrial habitats and cannot swim are kangaroos and koalas.
By the tracheal system.
Both. If your referring to mammals the answer is still both.
Kangaroos have lungs. They are mammals and breathe air like other mammals do. Gills are found in aquatic animals like fish, not in terrestrial mammals like kangaroos.
G. B. Corbet has written: 'Finding and identifying mammals' -- subject(s): Mammals, Observers' manuals 'The terrestrial mammals of Western Europe'
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.