Sea Otters can have purple bones due to their diet of purple sea urchins. This coloration is caused by a natural red-purple pigment found in the sea urchins called echinochrome.

When an otter consumes massive amounts of these urchins over time, its body absorbs the pigment. The echinochrome then deposits into the animal's hard tissues, permanently staining its skeleton and tooth enamel.

In biology, this phenomenon is called echinochrome staining. The intensity of the color depends entirely on how many urchins the otter eats, ranging from small streaks on the teeth to an entire skeleton turned completely purple. It is a harmless condition that works similarly to how a human's skin can temporarily turn orange after eating too many carrots.

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