A Brief Over-view of the Etymology of Modern Goju-ryu Karate-do Kata. By Joe Swift and Mario McKenna. It is now well documented that Okinawa karate is indebted to the Southern schools of Chinese boxing for much of its technical knowledge and expertise.
Best Answer: They are all warm-blooded, and they all have hair even if you can't see it (including dolphins and whales). Mammals all share mammary glands (milk producing glands). This is the biggest feature, also mammals use 3 bones for hearing and they have hair. Should be noted that endothermy (warm-blooded) is not unique to mammals, birds also share this characteristic.
Monotremes have an unusually complex sex chromosome system which shares extensive homology to bird sex chromosomes and no homology to sex chromosomes in other mammals. This has entirely changed the way we think about the evolution of sex chromosomes in mammals as it suggests that birds and early mammals shared the sex chromosomes which evolved in the reptilian common ancestor.