For instance, the shape and number of teeth in placental mammals and marsupials is different. Marsupials have 3 teeth in their jaw called premolars and 4 molars. Placentals have 4 or 5 premolars ...

The two groups have different modes of reproduction, yet within each group individual species that occupy similar niches have evolved similarities in overall shape, locomotion, and feeding habits.

This indicates that marsupials do not possess the fully evolved ... However, by examining living species that diverged at different points in evolutionary history, we can determine which have ...