For reference, humans start at 6-9 pounds, and end up anywhere from 100-300 (ordinarily).
So far I have bears: born at under a pound, grow up to 500 pounds. http://www.4information.com/trivia/large-bear-birth/
A kangaroo might qualify but he is really a fetus at birth. Marsupials in general are very small at birth.
For a purely literal answer, you would be looking at a blue whale calf, since it grows into the biggest animal that is ever known to have existed on Earth. But an adult isn’t 500 times bigger than a calf, if that’s what you’re asking.
Blue whale is 170 tons on average as an adult, a calf is born at around 2.5 tons, according to wikipedia.
So percentage-wise that’s not that impressive, but in just sheer numbers of pounds added from infancy to adulthood, I don’t think you’re going to beat that.
ETA: Ninja’d!!
I don’t have any numbers, but since the OP only specifies live birth, we may want to consider some of the non mammal viviparous animals, like seahorse.
By “grows the most” do you mean adds the most weight or increases by the biggest percentage?
Not on point on either the live birth or greatest increase, but just last night I was reading about how much weight cardinals pack on in the first week or so after they hatch. I think they increase their weight by something like 6x in their first 7-9 days or so. Struck me as a pretty incredible growth rate.
I’m having a hard time finding out how much newly hatched lobsters weigh. I saw on on site what they look like when they are 8mm long, but I know they start out smaller. Some get to weigh as much as 40 pounds.
ETA: But that’s not a live birth.
I’m voting for the red kangaroo if you’re going by percentage. The neonate is about 2 grams, a full-sized male is 85kg. So it increases its mass from birth to maturity by 42,000 times.
I’m thinking frogs. Those tadpoles are damn small.
But Kangaroos are still pretty much attached to and protected by their mothers. I’m thinking boots on the ground (or at least butt) needs to be criteria here.
If you start from conception, nothing else comes close to a blue whale, which increases in weight quadrillions of times (humans (~0.07 metric tons) have around 10 trillion so if a blue whale’s (170 metric tons) cells average the same size, then it has around 25 quadrillion cells, which all come from one cell).
I was gonna nominate octopuses for the same reason…and must disqualify them also. Baby octopuses are incredibly tiny; the ones I saw were maybe two mm across.
I was also thinking of the kangaroo, but if that’s disqualified, I think the whales take the krill.
Hmm. I wonder how much a larval giant clam weighs…
In which case we also have to rule out humans and bears, whose young are also still pretty much attached to and protected by their mothers. Since the OP specifically included both humans and bears on the list, I’m thinking that no such criterion exits.
But the winner isn’t going to any vertebrate anyway.
Most sponges produce live young, and the larvae weigh less than 1/100th of a gram at the time of release despite being perfectly self sufficient. I’m not sure what a large sponge weighs. Certainly in excess of 100 kg.
So that gives us a size increase between independent juvenile and mature adult of 10, 000, 000 fold.
No way any vertebrate can come close to that.
could we also have an answer for the opposite? which animal grows the least?
The typical definition of “birth” in the biological sense – “the emergence and separation of offspring from the body of the mother” – excludes most if not all invertebrates.
Ahh, no, it doesn’t. Can you explain how it excludes *any *viviparous invertebrate? For example, in what sense is the procreation method of blowflies or sponges not “the emergence and separation of offspring from the body of the mother”?