Once you get over a certain weight, it takes more than a pound of living tissue (bone, meat, etc.) to get a pound of lift. That is why the maximum.
So the question is begged about ancient "flying" creatures. Either they didn't "fly" (glider, etc) or the environment in which they flew operated under different circumstances than ours (less gravity, heavyer "air", etc>). Each answer brings with it it's own inconsistencies.
We don't know what we don't know.
No, it's you don't know what you don't know.
Thanks goodness actual scientists do know.
But it is amusing to watch you try and tell them that they don't know, because you don't.