Alright, first, get all of your Beardies seperated. Second, can you tell us a few things,

1. What substrate are they on?
2. What type of uvb bulb are you useing? ( Is it a compact twirly bulb?)

These two things are the most likely suspects as to why. If a cagemate had attacked him id think there would be alot more damage to him. Keep him on paper towels and id personally get him checked by a vet.