Weeping Angels

With the appearance of marble statues, the Weeping Angels are an ancient race of humanoids who are known primarily for their main defense mechanism: to go into quantum lock and turn to stone if observed.

Biology

Little is known of the actual Biological make-up of such a creature primarily because it is theoretically impossible to examine them: examination means we could see them and to see them would start their ability and turn to stone. However, they are also quite fast when not observed, with the apperance of them being statues helping them survive.