The saltwater crocodile is the largest living reptile on Earth. Males can reach six meters and weigh over 1,500 kilograms, and they range from India across Southeast Asia to northern Australia. A crocodile about 15 feet long registered a bite of over 16,000 newtons in a laboratory, roughly four times the force of an adult lion. Yet the muscles that open the jaw are so thin and weak that a few wraps of duct tape will hold the mouth shut. This episode explains that paradox and several others hidden inside one of nature’s oldest designs.

Dominant males guard the freshwater swamps and drive smaller rivals out to sea, where satellite tags revealed something unexpected. The exiles do not swim across open water. They ride surface currents, and when the tide turns against them they wait in a sheltered bay for days. Salt glands on the tongue let them stay out for weeks. Ashore they are patient ambush hunters that learn the routines of their prey, and their peg-shaped teeth explain why they need the death roll to tear a carcass apart.

• Of 20 crocodiles tagged in Australia, eight went out into the open ocean, and one covered almost 600 kilometers in 25 days.
• Nest temperature sets the sex of the young. Between 30 and 32 degrees Celsius the hatchlings are mostly male.
• A mother cracks eggs gently in her jaws and carries hatchlings to the water, yet only about 1 percent survive to adulthood.
• Hunting for skins between 1940 and 1970 killed an estimated 95 percent of northern Australia’s population before legal protection brought it back to over 100,000 adults.
• The Larrakia people of the Northern Territory treat the crocodile as a sacred totem and refuse to eat its meat.