(Wikipedia/Jasper Nance) The short-lived gastrorich.
Longest and Shortest Lifespans
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JULY 30, 2008
April Holladay, HappyNews Columnist

Q: Which animal has the longest and which the shortest life span?
A: The giant tortoise lives the longest, about 177 years in captivity, and the gastrotrich (a minute aquatic animal) lives the shortest — three days.
This question brings up intriguing matters, such as: what is an animal, can we compare all animals together, when does life begin and end, what can we actually observe? Here are some answers:
Animals are living things that aren't plants. Animal cells lack cellulose walls and chlorophyll. Animals can't photosynthesize to eat; they need more complex food, like proteins. They move around when they want to and respond quickly if poked or otherwise stimulated.
Protozoans are animals, but can we include such animals in our search for extreme life spans? No, because protozoans reproduce by dividing a single parent. They are not individuals and essentially live forever, or as long as the species survives. We can't compare colonies or genetically identical organisms with distinct individuals that result from a sexual reproduction. That's comparing apples with oranges.
Certain fishes and reptiles apparently keep on growing for extended lives unless some accident befalls them. Is one of them the oldest animal? Maybe. But, such animals live in the wild. We can't observe them for the length of time it takes to determine their eventual life span. Animals move around, which makes evaluating their age difficult. We determine species life spans usually from captive animals because we can track their ages.
So, that's how I arrived at the answer--from animals in captivity. The longest-lived captive animal is the giant tortoise (177 years) and the shortest, the gastrotich (3 days).
By the way, Forest Preserve District of Cook County presents examples of extreme old age in a nature bulletin (No. 486-A, dated March 24, 1973). Here's their animal old age table, chosen from reliable records of zoos and aquariums all over the world:
Elephant - 69
Horse - 50
Hippopotamus -49
Chimpanzee - 40
Grizzly Bear -32
Bison - 30
Lion - 30
Tiger - 25
Elk - 22
Mountain Lion 20
Beaver - 19
Wolf - 16
Squirrel - 16
Chipmunk - 12
Cottontail - 10
House Mouse - 4
Turkey Buzzard 118
Swan - 102
Parrot - 80
Great Horned Owl - 68
Eagle - 55
English Sparrow - 23
Canary - 22
Humming Bird - 8
Catfish - 60
Eel - 55
Carp - 47
Mosquitofish - 2
Giant Tortoise - 152
Box Turtle - 123
Alligator - 68
Snapping Turtle 57
Cobra - 28
Cottonmouth - 21
Giant Salamander -55
Toad - 36
Bullfrog - 30
Mud Puppy - 23
Green Frog - 10
Newt - 7
Cicada - 17
Ant (queen) - 15
Finally, a Danish study of 3000 dogs indicated that the median life span of all dogs in the study was 10 years, reported Helle Friis Proschowsky, an animal scientist at Denmark's Royal Veterinary and Agricultural University and the Danish Kennel Club. Mixed breed canines generally lived for another year, dying at a median age of 11 years. Smaller breeds generally lived longer than bigger ones.
(Answered April 4, 2001)
Further Surfing:
Why do larger animals live longer than smaller ones? WonderQuest
Life Span of Ancient Man — long or short? WonderQuest
Gastrotrich, Wikipedia
Giant tortoise, Wikipedia
Life span, Encyclopedia Britannica
Q: Which mammal has longest and which the shortest life span?
A: If we just look at mammals, then primates are the longest lived group and man is the longest lived of the primates: 122 years (Jeanne Louise Calment, 1875 - 1997). Tiny shrews live the shortest: maybe 1 to 1.5 years. Interesting enough, among primates the bigger your brain, the longer you live. The faster you live, though, the shorter you live. Squirrel-like rodents live two or three times longer than mouse-like rodents because their rate of metabolism is slower.
(Answered April 4, 2001)