But as long as suckling young are present, the embryos do not develop. When the young begin leaving the pouch, the embryos resume development and are born soon after. Some consider this type of reproduction primitive, but there is an advantage. The mother invests very little energy during the gestation period. If the mother loses an infant in the pouch due to adverse conditions, such as lack of food, she is in better physical condition to begin the reproductive process again than an animal that has invested much of its energy supporting a fetus in the womb.
Marsupials generally have more teeth than placental mammals.
Their lower jaws do not have the same number of incisors as the upper jaws and, with the exception of the fourth premolars, their teeth are not replaced. Another characteristic that sets marsupials apart from other mammals is the extra bone found in the pelvis called the marsupial bone. This bone is used to support the pouch. The marsupial brain case is small compared to placental mammals. The brain itself is missing some structures that placental mammals have.