Concept:
A mural is a painting made on a wall, ceiling, cave surface or architectural surface.
Prehistoric cave paintings, Ajanta murals and temple wall paintings are all mural traditions.
Step 1: Check Assertion (A).
Prehistoric paintings were made on rock shelter walls.
Ajanta paintings were made on cave walls and ceilings.
Medieval temple paintings were made on temple walls.
Therefore, all of these can be called murals.
So, Assertion (A) is correct.
Step 2: Check Reason (R).
Prehistoric paintings were made directly on wall or rock surface.
Ajanta and temple murals were made on prepared ground or surface.
So, Reason (R) is also correct.
Step 3: Check explanation.
The Reason explains why all these painting types are called murals.
They are related to wall or architectural surface painting.
Step 4: Final conclusion.
Both Assertion and Reason are correct, and Reason explains Assertion.
Hence:
\[
\boxed{\text{(A)}}
\]