The shortest known gestation period is the Virginian opossum, which is 12 days. The longest period belongs to the Indian elephant, which has a gestation period of 22 months.

Two marsupials share the shortest gestation period. The Virginian opossum and the yapok (an unusual, rare water opossum) have a gestation period period of 12-13 days.

Several sources cite the Eastern quoll of Australia as also having a gestation period of 12-13 days, but this is incorrect. The Eastern quoll's gestation period is 21 days.

The longest known gestation period of any animal is that of the African elephant. Its gestation period averages 660 days but can extend to 760 days.

Elephants have one of the longest gestation period among mammals. They are pregnant for a period of around 22 months. After the 22 month gestation, they giver birth to a calf that is approximately 250 pounds heavy and stands at around 2.5 feet tall

Shortest: American Opossum or Virginian Opossum - 8 days

Longest: Asiatic Elephant - 760 days

*These are mammals, the longest remains the same but the shortest would be the house fly with a gestation period of 24 hours.