Based on historian and folklorist Adrienne Mayor's theory that discoveries of well-preserved fossil Protoceratops - a small, older relative of dinosaurs like Triceratops - inspired gryphon legends. A sketch I've had sitting around for a while.

Imagine what you'd think, never having heard of dinosaurs and seeing this skeleton: http://diterlizzi.com/blog/wp-conte.....toceratops.jpg

The body is that of a large four-legged animal with clawed paws and a long tail, something like a big cat. But the head sports a (mostly) toothless hooked beak like that of a huge eagle. Obviously this is a monster with the head of an eagle and the body of a lion!

Gryphons in classical art are almost always portrayed with ears. In heraldry ears are the feature that distinguishes gryphons from eagles when only the head is show. See how Protoceratops has a bony framework supporting a head frill? If this fragile structure were broken or eroded, it would be left with paired flanges which suggest ears. Of course you know ears don't have external bones, but it's surprising how often naive drawings of skulls, especially animal skulls, have ear-shaped bony bits added by the artist.

And what about wings? I can think of a couple of explanations. One, is that the description of exactly how much of the beast was lion and how much was eagle got slightly garbled in the retelling. Another thought is that plonking wings onto animals is a fairly common way of creating mythological beasts, and artists may have felt that anything so much like a bird looked better or more correct with wings. Remember also that fossil skeletons are rarely found complete and perfectly articulated. Jumbled rib or limb bones from other partial skeletons may have made it look like the main skeleton had extra wings.