Man! That's a whole chunck that fell out. That is right where the right lower link attaches to the axle housing. Had you been doing any heavy work with the box blade just prior to this?
That scares the heck out of me. I'm sure that is a freakish sort of thing, but if it happens after the warranty is up you'd be in for a megabuck repair. The L4400 comes with a 2 year warranty, three on the powertrain. I'm assuming the axle housing is considered part of the powertrain? It should be.