Cave bear

Cave bears were a type of large, prehistoric bear that died out about ten thousand years before the 20th century.

Nimrod's Neanderthal tribe considered the cave bearholy and the tooth of one was a sign of great wisdom. Producing the tooth of a cave bear from his own pocket, the Seventh Doctor roused Nimrod from a state of unconsciousness. This also sparked Nimrod's recollection of the life he had led in his tribe. (DW: Ghost Light)