The American Bullfrog (Lithobates catesbeianus or Rana catesbeiana) often simply known as the Bullfrog in Canada and the United States, is an aquatic frog, a member of the family Ranidae, or “true frogs”, native to much of North America. This is a frog of larger, permanent water bodies, swamps, ponds, lakes, where it is usually found along the water's edge. On rainy nights, bullfrogs along with many other amphibians, go overland and may be seen in numbers on country roads. American bullfrogs live longer in warm weather. They have been widely introduced across North America (see range map). The original, naturally determined range did not include far western regions where it is found today. Bullfrogs grow on average to be about 3 and a half to 6 inches (9–15 cm) long in body length (although there are records of some as big as 8 inches), legs add another 7–10 inches (17–25 cm) to length. The adult bullfrog skeleton is representative of tetrapod vertebrates, comprising an axial skeleton (skull and vertebrae) and an appendicular skeleton (pectoral girdle and forelimbs, pelvic girdle and hindlimbs). Ranids, however, lack ribs. The pronounced pair of dorsal humps in the back of ranid frogs are the ends of the pelvic ilia, homologues of the human hips. Females have an eardrum (tympanum) the same size as their eye. Males' eardrums are larger.