>>715309282
Basically the massive difference between pterosaurs and birds is that unlike birds, pterosaurs can use all 4 limbs to launch themselves

so they can use their immensely powerful flight muscles as part of the launch, which birds can't do, which is the primary limiting factor of birds in terms of what size they can become

pterosaur wings are also vastly better at soaring than birds which again helps with this: they can use up 90% of their flight energy purely on the launch and takeoff, then soar for the rest of the flight