Yes, all mammals have a skeleton.Yes, all mammals have a skeleton.Yes, all mammals have a skeleton.Yes, all mammals have a skeleton.Yes, all mammals have a skeleton.Yes, all mammals have a skeleton.
No, all sea animals are not mammals. Fishes are not mammals, but
dolphins are mammals.
Why are all primates mammals?
If you mean "Are all mammals primates?" then the answer is no.
Primates are a type of mammal. All primates are mammals. Not all
mammals are primates. For example, cats, dogs, bears, rodents...
these are all mammals, but not primates.