cursor, precursor

Cursor or cursor means a movable pointer symbol on an electronic screen, such as a computer, used to mark the user's position on a screen--
Move the cursor to the red circle, and click on the left side of the mouse.
Use the mouse to move the cursor.

Precursor or precursor means something that precedes an event, and later seems to be a stage in its development--
The rise of literacy was a precursor of the modern idea of democracy.
The word processor was a precursor of the desktop computer.

 Now that you know that, you can say-
"The arrow keys were a precursor of the computer mouse."