Speaking of dragons, I’ve been trying to nail down the physiology of some large mythological flyers for possible inclusion in my third Into the Wonder novel. I’ve come across the following rules of thumb that may prove helpful to others trying to imagine dragons, griffins, and other creatures in something like a realistic way:

• Birds have a wingspan of roughly 2 times their head-body length (falcons average around 2.5)
• Bats have a wingspan of roughly 5 times their head-body length
• Pterosaurs had a wingspan of roughly 6 times their body length (first dorsal to last sacral vertebra)

Within these parameters—and assuming the creature is not too heavy to fly at all!—a smaller ratio (like a finch) provides greater maneuverability while a larger ratio (like an albatross) provides greater endurance.

Furthermore, you can make a guess about the weight of a flying creature, or at least avoid something impossible, by taking wing loading into account. This has to do with how much weight and pressure a wing can manage. For birds, five pounds of body weight per square foot of wing surface is about the limit.

Some cool sources I found along the way:

• Solving for Dragons
• Stump the Librarian question about the wingspan of a humanoid flyer
• Posture, Locomotion, and Paleoecology of Pterosaurs