It's very different actually - the pelican, as every other bird, uses its hind legs to push off, while the pterosaurs (and some bats) push off with their forele

It's very different actually - the pelican, as every other bird, uses its hind legs to push off, while the pterosaurs (and some bats) push off with their forelegs - and the latter ones are very powerful and can be re-used for flight, unlike the powerful hindlegs of large birds which are just dead weight when they're airborne.