The scientific definition of a mammal is that it has mammary glands. The definition of a bird is feathers (not wings). You should learn a little about what you speak of before spouting your verbal diarrhea.
You really need to study some biology, this is getting silly. The scientific definition?
I'll reiterate: The animals that have hair also have mammary glands and inner-ear bones and bear live young (and share several more technical traits as well). True, the word mammal and mammary are cognate, but that's beside the point. The interesting thing is, there are two exceptions, which are only found in Australia: the platypus and the spiny anteater. They lay eggs, but share the other traits with mammals. Also, it's no longer clear that feathers are restricted to birds, as there were dinosaurs with feathers.
You should learn a little about what you speak of before spouting your verbal diarrhea.
That is also rude. Learn some manners while you're studying science.
Not quite. Milk production is part of the definition of mammal, but it also includes all the other stuff mentioned earlier (dentition -- a biggie, hair or fur, number of holes in the skull, warm-bloodedness, single lower mandible and differentiated ear bones, etc.)
Now, the first two, milk production and fur do not fossilize, but as the others are all found in mammals and they do fossilize -- and this combination is not found in any other class of animals -- any fossils exhibiting the complete collection of stuff that does fossilize and denotes mammal, can be assumed to be a mammal -- except by creationists who cannot see the forest for the trees and refuse to accept any evidence unless in the form of a living, breathing critter (and then they'd probably claim it was ginned up by geneticists in some secret laboratory to mislead good, God-fearing Christians in an effort to damn their souls to Hell).