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.
Meridiolestida Meridiolestida is a clade of non-therian mammals from South America and Africa, and potentially also Australia. It is generally classified within Dryolestida, barring one study recovering them as the sister taxa to spalacotheriid symmetrodonts. However, more recent studies have stuck to the dryolestoid interpretation. They differ from northern dryolestoids in the absence of a parastylar hook on the molariform teeth and the lack of a Meckelian groove.