What are the Major Groups of Mammal?
There are three major living groups of mammal: placental mammals, monotremes, and marsupials. A fourth group, the multituberculates, is now extinct. Of the three living groups, the placental mammals is by far the largest, and probably the most well known; after all, you are a placental mammal, and if you own mammalian pets, the chances are very high that they are placental mammals as well. These groups of mammals are what are known as infraclasses taxonomically, meaning that they are ranked below class and subclass, but above order. No matter what infraclass a mammal is in, it shares a number of traits with other mammals. All mammals have a neocortex, a region of the brain which is unique to the mammals, and they also have three middle ear bones and a single jaw bone. Mammals also possess sweat glands, and they are capable of producing milk through the use of specialized glands. Mammals also possess hair, and specially designed skulls which connect with their neck vertebrae while prote
