Exoskeleton and Endoskeleton Size Limits

An exoskeleton must thicken sharply as body weight increases, since doubling size roughly increases weight eightfold, capping most exoskeleton-bearing animals at a small size; an endoskeleton scales more efficiently since muscles attach outside it.

Insects and crustaceans stay small under their exoskeletons, while endoskeleton-bearing whales grow to enormous size.