I noticed you said, "one of your new beardies" which leads me to believe that you have a few,...and that maybe they are living together? I don't know how a severe cut could occur otherwise....
Well if this is the case, separate them immediately! Despite seeing dozens of them crammed together in pet stores, this is not a good idea to do once you purchase them.
In the store, they are forced to live in close quarters to one another, and a hierarchy cannot be established because there is not enough room to establish dominance,(usually by young males). Either way, once you bring a few home, and put a couple into your tank, there is much more room per lizard than there was in the store. At this point, they will do what comes naturally to them and establish a territory/bully inferrior tankmates.
I had this happen when I made the novice mistake of putting my first two babies in the same tank. The current, 3 year old male that I have attacked his tankmate, repeatidly biting the others forearms until they (the arms) died up to the elbows and eventually broke off! The other guy (or girl) lived, (I KNOW!) for another 6 or so months before it finally died. (Probably due to an infection). Sadly there was not much to do at that point.
SO in summation, separate them if that is the case.