From their enormous size we must believe they were mastodon bones, as no contemporary animals show such measurements.
Bartholinus describes a large tooth for many years exhibited as the canine of a giant which proved to be nothing but a tooth of a spermaceti whale (Cetus dentatus), quite a common fish.

Hand described an alleged giant's skeleton shown in London early in the eighteenth century, and which was composed of the bones of the fore-fin of a small whale or of a porpoise.
The celebrated Sir Hans Sloane, who treated this subject very learnedly, arrived at the conclusion that while in most instances the bones found were those of mastodons, elephants, whales, etc., in some instances accounts were given by connoisseurs who could not readily be deceived.

However, modern scientists will be loath to believe that any men ever existed who measured over 9 feet; in fact, such cases with authentic references are extremely rare Quetelet considers that the tallest man whose stature is authentically recorded was the "Scottish Giant" of Frederick the Great's regiment of giants.

This person was not quite 8 feet 3 inches tall.

Buffon, ordinarily a reliable authority, comes to a loose conclusion that there is no doubt that men have lived who were 10, 12, and even 15 feet tall; but modern statisticians cannot accept this deduction from the references offered.
From the original estimation of the height of Adam (Henrion once calculated that Adam's height was 123 feet and that of Eve 118) we gradually come to 10 feet, which seemed to be about the favorite height for giants in the Middle Ages.