Oh, okay. I thought you wanted something like a flying elephant or whale.
had a rather enormous wing span according to fossils,
Some did, some didn't. The biggest got up to 25-30 feet, but there's an extinct bird with a wingspan almost as wide, the Argentavis magnificens:
yet evolution doesn’t, over ga-jillions of years, account for other equally larger animals flyng such as pterodactyls did, why is that?
Dunno. Why should it?