Are my wing-walking griffins viable?

Question

This is the third question in a series of such for my worldbuilding project that deals with plausible fantasy creatures. Previously, I have pondered cockatrices and hydras, but now we move on to another popular mythical animal, the griffin. Last two questions: Is petrifying vision plausible in an animal? and Hydras as parasitic-mating, polyandrous amphibians?

The griffin, or gryphon, is a well-known beast of fantasy that was depicted by the Egyptians, Iranians, Minoans, Greeks, Romans and Medieval people. It is said to have the body and forelegs of a lion and the head, wings and hind legs of an eagle. However, the consistent thing in all portrayals of griffins is that they have four legs and two wings.

Yes, flying quadrupeds, Bane of Worldbuilders. Such an anatomy would require the griffins to be hexapods, which isn't realistic evolutionarily. So, hexapodal griffins must be ruled out. When I realized this shortly after considering including griffins in my worldbuilding project, I thought that I'd have to simply leave them out.

But then I remembered a real-life group of giant flying animals, the Azhdarchids. The largest species in this group being the giraffe-sized Quetzalcoatlus northropi, they walked with their wings as their forelimbs.

Could a bird evolve such locomotion? My premise is that these griffins could have evolved from Accipitrids or similar birds, and grown larger and larger until they gained a wing-walking posture to sustain their massive size. Hypothetically, their movement would be very Azhdarchid-esque, and it would be about the size of a horse.

Now to the real question: would massive wing-walking birds a) evolve rather than some other method of sustaining their frame, and b) survive and hunt with such adaptations?

Answer 1

This worked out just a little long for a comment,

Simple Answer, yes!

You've already got documented evidence of a creature that moves the way you want it to, and that happened due to evolution, but they're not the only ones... Bats will fly, however if injured and unable to fly they walk along the floor in the manor described.

The Problem

The issue you may have is that creatures way back when were all larger, part of this is back then the density of the atmosphere was lower, therefore lower pressure therefore they can be bigger(oversimplification i know, not getting into that here), if Jurassic park actually existed, a T-Rex would probably be about the size of a family car, rather than a bus. so it depends on the size of the creature you want at the same time as humans, realistically your griffins/gryphon's would probably be about the size of a decent turkey

Possible work arounds

Maybe have them be smaller and be pack animals, weather good or bad is up to you and you can describe them in ways that do so, good animals would be beautiful fur covered creatures that look healthy and then hunt smaller animals intelligently, like a Wolf, whereas evil might be skinnier more leathered skin and very aggressive and act more like hyenas

Or have them be horse size, maybe talk about how they have shrunk since man first saw them, have a debate on wether man was just smaller or they have shrunk, maybe find massive bones belonging to their ancestors, after all giraffes exist and so do elephants, big animals exist all around the world, its how they act compared to smaller aimals is whats important. these animals don't fly but maybe the your gryphons walk more and only fly when needed to save the huge energy required to do so. if you think about the Rhino, Elephant and Girafe they are all slow land based animals but all can move quite quickly when they need to, but never over a great distance

Pneumatized Bones might help but you'd have to offset this against the wieght those bones would have to carry

Answer 2

I would say Absolutely, with the one caveat that they may not be quite as large as you are describing.

There are some species of bat that use their wings as a part of their non-flying locomotive strategy. eg: Vampire Bat

It depends a little on why you want them to exist, and what you want them to achieve with both their flying & non-flying locomotion. I could certainly see some evolutionary pressure moving some creatures in the direction you describe, but it would have to be fairly specific, and target the young in a fashion that creates that evolutionary development in certain directions.

I suspect that having 4 legged animals develop into flying creatures might be more likely than 2 legged birds that already have wings developing into wing walking birds.