A CSS dropdown menu example using tetrapod groups as navigation items. The "Mammals" item provides an example of a multi-level dropdown. See the HTML Dog Dropdowns tecnhique article for more information.
Tetrapods are a major group of animals containing those that evolved from fish and developed four limbs. They comprise the major sub-groups of amphibians, reptiles, mammals, and birds. "Tetrapod" literally means four-footed.