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Tortoises were a type of reptile.
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)
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 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)
The Third Doctor and Jo Grant once got into a dangerous situation involving a number of giant tortoises which was caused by the Master. 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)