This is a tooth from a Sperm Whale. Sperm Whales have about 23 teeth on each side of their bottom jaw – 11 more teeth than in your whole head. The teeth are not used in devouring prey of giant squid, octopus and fish, but probably for gripping their food before swallowing.
Sperm whales were hunted in the 18th and 19th centuries, for the oil produced by the spermaceti organ in their heads. It is still a mystery as to what the whale uses this oil for. The whalers used it to make soap and in oil lamps.
The teeth were used extensively as decoration and trinkets. The art of finely engraving a picture onto a tooth or tusk is called ‘scrimshaw’.