Based on fossil record, the dinosaur known as Spinosaurus and the prehistoric clade of marine mammals known as pliosaurs are the most apt top contenders for the title of "largest carnivore known to man." The Spinosaurus is the largest known carnivorous dinosaur, with fossil records indicating that this dinosaur could reach lengths of 50 feet and weigh more than 20 tons, but evidence of potential pliosaur size is inconclusive due to incomplete fossilized specimens. A partially fictionalized 1999 documentary from the BBC posited that there may have been pliosaurs that weighed more than 150 tons and were more than 82 feet long, but there is no fossil evidence to support this idea.
Though there is no evidence to show that there were ever pliosaurs that were so incredibly huge, there is some evidence to support the idea that these carnivorous marine reptiles could grow large enough to potentially give the Spinosaurus a run for its money. Of the fossil fragments that do exist, scientists have been able to make an educated guess that there may have been pliosaurs that were larger than the Spinosaurus. This educated guess is based on fossil evidence from what is supposed to be an adolescent pliosaur that likely measured about 49 feet in length, meaning the animal had the potential to grow even larger.