Many animals have ivory teeth, HowStuffWorks explains, most notably elephants, hippopotamuses, walruses and narwhals. Even pigs, sperm whales and killer whales have ivory teeth, although these are not as famous as those of other animals.
Ivory teeth are fairly common to most animals, but when still part of the teeth, the substance is usually referred to as dentin. This is the bony tissue that lies just underneath the enamel. It is made of calcium phosphate and other organic materials. The quality of ivory varies depending on the animal. The highest quality ivory, which is a semi-opaque white color, is found exclusively in the tusks of African elephants.
This type of ivory is highly sought after, especially for inlays or to make jewelry, ornaments and statues, so poaching has become a huge problem. It has decimated the elephant population, reducing it by nearly half in less than a decade and putting elephants on the Endangered Species List. To try to prevent this, items made from ivory after 1947 are illegal and cannot be traded.
Some of the oldest objects made from ivory are made of mammoth ivory and date back nearly 35,000 years. Ivory was used by dozens of early civilizations as ornamentation and a symbol of riches. The ancient Greek and Roman civilizations used especially large amounts of ivory. The ivory trade only began to decrease as sources of ivory became more scarce and substitutes were developed.