The sedimentary rock formed from coral shells and skeletons piled up on the ocean floor is called limestone.

Here's why:

* Coral Reefs: Coral reefs are built by tiny animals called coral polyps. These polyps secrete a hard calcium carbonate skeleton.

* Accumulation: Over time, the skeletons of dead coral polyps accumulate on the ocean floor, forming thick layers.

* Lithification: These layers are compacted and cemented together by minerals dissolved in seawater, transforming them into solid rock.

Limestone is a common sedimentary rock and can be found in many parts of the world.