"Leedsichthys" fossils have been difficult to interpret because the skeletons were not completely made of bone. Large parts consisted of cartilage that did not fossilize. On several occasions the enigmatic large partial remains have been mistaken for stegosaurian dinosaur bones. As the vertebrae are among the parts that have not been preserved, it is hard to determine the total body length. Estimates have varied significantly. At the beginning of the twentieth century a length of nine metres (thirty feet) was seen as plausible, but by its end "Leedsichthys" was sometimes claimed to have been over thirty metres (hundred feet) long. Recent research has lowered this to about sixteen metres (fifty feet) for the largest individuals. Skull bones have been found indicating that "Leedsichthys" had a large head with bosses on the skull roof. Fossilised bony fin rays show large elongated pectoral fins and a tall vertical tail fin. The gill arches were lined by gill rakers, equipped by a unique system of delicate bone plates, that filtered plankton from the sea water, the main food source.