Tortoise

Tortoises were a type of reptile.

The Doctor frequently stated that "sleep is for tortoises". (PROSE: The Scales of Injustice, Deadly Reunion, AUDIO: The Mists of Time, TV: The Talons of Weng-Chiang, AUDIO: Red, PROSE: Timewyrm: Exodus, AUDIO: Other Lives, PROSE: The Last Dodo, TV: Knock Knock) Sherlock Holmes once said it to Dr. John Watson. (PROSE: All-Consuming Fire)

Earth
Giant tortoises were native to the Galápagos Islands. In 1835, they were the staple diet of the islands, much to the surprise of Evelyn Smythe. Governor Lawson had eaten tortoise so often that he could identify which island they came from just by their taste. (AUDIO: Bloodtide)

In the 26th century, Bernice Summerfield's friend Simon Kyle kept reconstituted Galapagos tortoises as pets. (PROSE: The Highest Science, Return of the Living Dad)

Tortoises were among the animals on board the Ark circa 10,000,000. (PROSE: The Ark)

Elsewhere
The planet Go-Ray was home to at least one species of tortoise or tortoise-like creature, one of which was discovered by John and Gillian. Due to the high levels of cardium on the planet, the tortoise was able to move very rapidly. (COMIC: Enter: The Go-Ray)

The Third Doctor and Jo Grant once got into a dangerous situation involving a number of giant tortoises which was caused by. After Jo was captured, the Doctor was forced to lower himself down a pit three miles deep and communicate using only his eyes to negotiate for her release. (AUDIO: The Last Fairy Tale)