Answer:
The answer is that the fossil that was found deeper in the rocks than others was an ancestor of the surrounding, shallower skeletons.
Step-by-step explanation:
It is clear the skeletons are related because of the similar structures. The reason it is different from the other skeletons is because it is older than them, and they have evolved. You can tell it is older than them because it is deeper in the rock, because the landmass has changed between it's lifetime, and it' descendants.