What is the medium sized marine animal that is part of the order of placental mammals?
Dugong The dugong ( , ; "Dugong dugon") is a medium-sized marine mammal. It is one of four living species of the order Sirenia, which also includes three species of manatees. It is the only living representative of the once-diverse family Dugongidae; its closest modern relative, Steller's sea cow ("Hydrodamalis gigas"), was hunted to extinction in the 18th century. The dugong is the only strictly marine herbivorous mammal.
Macropodiformes The Macropodiformes are one of the three suborders of the large marsupial order Diprotodontia. Kangaroos, wallabies and allies, bettongs, potoroos, and rat kangaroos are all members of this suborder.