Good Shepherd - Catacombs of Saint Priscilla

The painter of the Good Shepherd in the Catacomb of Priscilla was familiar undoubtedly with Roman copies of Greek sculpture and also familiar with paintings of pastoral scenes in Roman homes. 

Notice the facial characteristics of Christ in this fresco. These characteristics are similar to figures seen in wall paintings of that time. Christ is beardless, without a halo, and not dressed in a long white robe as he is depicted in later works. 

And finally, in Christian art, halos had not come into use as a symbol at the time this was painted.