A tortoise is a land-dwelling turtle that is part of the scientific species Testudinidae. The reptiles' shells contain 60 different bones that are made of keratin: the same substance found in human hair, skin and nails.

A tortoise shell has three main parts that include the bottom plastrom, the upper carapace and connecting cartilage that connects the top piece to the bottom piece. Tortoises also have spines, collar bones and ribs under their shells.

Many types of tortoises can live more than 100 years. One of the oldest tortoises was Harriet, a tortoise believed to have been collected by Charles Darwin on the Galapagos Island in 1835. She was housed in England before she was sent to the Australia Zoo, where she passed away in 2006.

Female tortoises can store the sperm of their mates for up to three years. They lay between two and 12 eggs in deep holes, and then abandon the underground nest. Their hatchlings incubate for 90 to 120 days and are left on their own once they hatch.

Tortoises have a vomeronasal organ, called the Jacobson's organ, along the roof of their mouths. They smell through this organ by siphoning the air around their noses and mouths into their throats.