Forerunners

noun

1. A runner at the front or ahead.
2. By extension, a non-competitor who leads out the competitors on to the circuit, or who runs/rides the course prior to competitor trials, usually testing or checking the way.
3. A precursor or harbinger, a warning ahead.
4. A forebear, an ancestor, a predecessor.

   "Bakelite is a forerunner of today's plastics."

5. A postage stamp used in the time before a region or area issues stamps of its own.