Which animal is the heaviest?

blue whale
The blue whale (Balaenoptera musculus) is the heaviest animal. It relies on the buoyancy of ocean water rather than a skeleton to support its weight. The largest specimen, caught in 1947, weighed 420,000 pounds. The average length of the blue whale is 115 feet; average weight is 287,000 pounds. The blue whale eats 8,000 pounds per day of shrimp-like krill, which are abundant in all oceans but more concentrated in the Pacific and Indian Oceans. Moving most often in pairs, blue whales feed in the polar regions and then migrate closer to the equator to breed. The blue whale was near extinction 50 years ago; in 1966 the International Whaling Commission banned the hunting of this gentle giant, which is harmless to humans. The current population of approximately 5,000 blue whales appears to be increasing.