Complex sentence: Most placental mammals participate in placentophagy, including herbivores; exceptions include Pinnipedia, Cetacea, the camel and (in most cases) the human.
Split into simpler sentences: Most placental mammals participate in placentophagy, including herbivorous ones. Pinnipedia and Cetacea are exceptions to mammalian placentophagy, as are the camel and (in most cases) the human.