[EliRivers]

Sea mines placed miles apart during the second world war sometimes end up settling right next to each other, several miles away. Sometimes tens of miles away. Sometimes next to a leftover mine from the first world war that arrived the same way.

The environment in which they exist subjects them to varying pressures and forces, making them move. When do they stop moving? When they reach a point at which those pressures and forces cease. That point is the same for all items that get swept there. Wait long enough, and if another one is part of the same system of forces that directs towards the same null point, it'll turn up. Happens with sea mines over the course of a few decades. Could it happen with skulls over tens of thousands of years? Sure could. Happens with lots of objects.