Space: 1999 S01 E15 The Full Circle

"The Future Is Fantastic!"

When exploring a habitable planet, members of the Alphan survey party vanish without a trace. Are they the victims of an indigenous tribe of Stone Age humanoids? The mystery deepens when a dead caveman is found to have capped teeth. Others soon notice the primitive cave chief and his mate bear an uncanny resemblance to the missing John Koenig and Helena Russell.