Research suggests that giant, kraken-like octopuses may have been top predators in oceans during the Cretaceous period. These octopuses are estimated to have been quite large, with some reports indicating they may have reached sizes of up to 60 feet. The existence and size of these creatures are based on fossil evidence, including jaw fossils, although the exact timing of their dominance is unclear, with estimates ranging from 72 to 100 million years ago.