I may have just looked into this scene a bit more than you may have, not sure.
The different decay and bone structure found in the skulls are intriguing. Either a very large amount of time or different races account for the structure differences, but we're talking 7000+ years of time. (more on the "+" side)
I've seen similar photos of the infamous killing fields of the Pol Pot regime in Cambodia, but I would imagine that there are many locations, including monasteries that have such chambers honouring the life that was held together with these bones. Think of how special a soul must have been to have his or her bones cherished for what was thought to be eternal.
That's about it, thanks for posting the pic.
:)