bare spot on ear

Question
I have just adopted a boxer/lab mixed puppy.  He is 3 months old and I noticed a crusty area on his ear.  After I cleaned the area all the hair came off but there is no redness or any sores.  The area does not seem to be bothering him.  He is not scratching or rubbing it.  Any ideas on what the problem might be?  Thank You so much for your time.

Answer
If the pup was with other pups they play by biting each other, it could be a war wound, also many dogs get food allergies to cheese and dairy products, you may also check your dogs for ear mites or fleas, ear mites look will leave stuff in the ears that look like ear wax, fleas will leave little black specks like pepper, Hope this helped, Angela