The obvious answer IMO would be the red kangaroo, which starts out life the size of a bean, then at maturity weights 60+ lbs. HOWEVER, the joeys spend 9 months in the pouch, which IMO is another type of womb.
SO which animal grows the most from living outside of the mother (but can still have assistance from the mother) to maturity?
ETA I am talking percentage-wise. So even though the blue whale can gain 250,000 lbs from birth to maturity, another animal, even an insect, might grow more proportionally/exponentially than that. What creature is that?
Ocean Sunfish are often considered contenders here - from 2.5mm as fry to 3.3m+ as adults - or “60 million times their birth size” (by which I guess they mean weight)
Other contenders include big jellyfish, big crabs and tapeworms, all of which have microscopic larvae but meter+ adults.
I’d also like to nominate the anti-example: Pseudis paradoxa, a frog that’s around a quarter the size of its tadpole.
Only mammals are ‘born’, most others are hatched. Do you want to exclude them? Or how would you could those who are hatched, the moment they are passed outside of the mother, or the breaking open of the shell? And you have weird stuff like the seahorse happening where the father had a roll the development stage.
This is highly inaccurate - lots of other genera have species which practice viviparity : scorpions, cockroaches, velvet worms, sharks, frogs, snakes, and lizards, at least.
