Pteranodon
Pteranodon (; from Greek πτερόν ( pteron, "wing") and ἀνόδων (anodon, "toothless") is a genus of pterosaur that included some of the largest known flying reptiles, with wingspans over 8 meters (26 feet). They lived during the late Cretaceous geological period of North America in present-day Kansas, Alabama, Nebraska, Wyoming, and South Dakota. More fossil specimens of "Pteranodon" have been found than any other pterosaur, with about 1,200 specimens known to science, many of them well preserved with nearly complete skulls and articulated skeletons. It was an important part of the animal community in the Western Interior Seaway.
Megalodon
Due to fragmentary remains, there have been many contradictory size estimates for megalodon, as they can only be drawn from fossil teeth and vertebrae. Also because of this, the great white shark is the basis of its reconstruction and size estimation, as it is regarded as the best analogue to megalodon. Various size estimates exist for megalodon; in 1973, Hawaiian ichthyologist John E. Randall estimated that the maximum length attained by "C. megalodon" was about , while in the 1990s, marine biologists Patrick J. Schembri and Stephen Papson opined that "C. megalodon" may have approached a maximum of around in total length; Gottfried and colleagues asserted that "C. megalodon" could have reached a maximum of in total length. Nowadays, the commonly acknowledged maximum total length of "C. megalodon" is about , with the average size being , compared to the maximum recorded sizes of the great white shark at and the whale shark (the largest living fish) at . It is possible that different populations of megalodon around the globe had different body sizes and behaviors due to different ecological pressures. If it did attain a size of over , it would have been the largest known fish that has ever lived, surpassing the Jurassic fish "Leedsichthys".