The eyes have round pupils. The eyesight is surprisingly good, and it can probably see colors. There is a high crest along the back which recesses toward and on the tail. The large powerful clawed feet with outer toes opposed help in climbing trees. The tail can fracture but not slip off as is the case with many of the smaller lizards.
Sexes are difficult to determine in young iguanas.
Dorsal crests and the enlarged scale beneath the ears usually grow larger on the males than on the females. A 6 foot iguana can reportedly break a dog's leg with a slash of its tail. It seems to prefer to climb to the top of the canopy of the trees, probably for better vision of the surroundings. A common green iguana can spend long periods of time submerged in a stream or pond and can sleep underwater for an hour or more. This and its agile swimming ability make it a remarkable lizard.