. Time course of lung development in eight mammalian species. Monotremes (O. anatinus) and marsupials (M. domestica and M. eugenii) are born at the early saccular
phase and have a slow postnatal lung development. Altricial eutherians (M. auratus and S. murinus) start at the late saccular phase and reach the alveolar phase soon after
birth. Intermediate (T. belangeri) and precocial eutherians (C. aperea and M. proboscideus) are born at the early or advanced alveolar phase respectively.