The term 'Serengeti Heavyweight' refers to two of the largest animals found in the Serengeti National Park in Tanzania, Africa: the rhino (5 letters) and the ELEPHANT (8 letters). The rhino is a large, herbivorous mammal with thick skin and one or two horns on its snout. The ELEPHANT is the largest land mammal, with a long trunk and large ears. Both animals are considered keystone species in the Serengeti, as they play an important role in maintaining the balance of the ecosystem.