Biggest animal ever to have lived? Bruhathkayosaurus may be the biggest sauropod known from remains that still exist (may be; by now you should know how much uncertainty that covers). 220 tons!!!! (Sauroposeidon in blue; Seismosaurus in orange; Argentinosaurus in purple and Diplodocus in green. Bruhathkayosaurus was larger than all of them). Blue whales weigh in at 200 tons.