Based on the paragraph below, what bone was used to estimate the height of William the Conquerer?

No authentic portrait of William has been found; the contemporary depictions of him on the Bayeux Tapestry and on his seals and coins are conventional representations designed to assert his authority. There are some written descriptions of a burly and robust appearance, with a guttural voice. He enjoyed excellent health until old age, although he became quite fat in later life. He was strong enough to draw bows that others were unable to pull and had great stamina. Geoffrey Martel described him as without equal as a fighter and as a horseman. Examination of William's femur, the only bone to survive when the rest of his remains were destroyed, showed he was approximately 5 feet 10 inches (1.78 m) in height.

His femur.