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12 animals with the longest gestation period

By: Bryan Nelson on April 28, 2010, 1:22 p.m.
A mother killer whale and its calf

Photo: Jan Daly/Shutterstock

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Whales and dolphins

Whales and dolphins, also known as cetaceans, are known for their high intelligence, complex societies and peaceful personalities — it's no surprise that they also take a lot of care in developing their young. Although all species have different gestation periods, orcas have the longest period among dolphins (at about 17 months). Some sperm whales — the largest living predators — have been known to carry their young for up to 19 months.