Reptomammals were almost exclusively warm-blooded, an attribute that differentiated them from viviparous reptiles. Additionally, the presence of milk-bearing teats in females separated them from their scalier kin. These traits were more common in harsher environments, where the defensive characteristics of reptiles could be combined with the adaptable physiologies of mammals to great success. Being reptomammalian does not mean one has to be a biological anomaly defying all classification methods; however, this is sometimes the case.