another diagnostic feature is the neocortex of the brain, which no other vertebrate has. this is involved in the kind of flexible behavior and learning typical of mammals. reptiles and birds have much of their behavior controlled by "inherited behavior chains", which roughly translates as "instincts". almost all animals can do some learning, but mammals do far more than other vertebrates. their behavior is much more flexible than lizards, for example, and that is made possible by their neocortex.