Haplorrhini
From Halopedia, the Halo wiki
Haplorrhini is an achievement in Halo: The Master Chief Collection. It is obtained by finding the third, "lonely" Caveman near the end of the level Sierra 117. The achievement is worth 5 Gamerscore.
The third Caveman can be found in the area where you rescue Sergeant Johnson.
Immediately after the cutscene where the brute chieftan throws Johnson into a cell, a phantom is seen departing the area. The caveman is seated among some foliage in a small alcove where the faces of the cliff meet, just above and behind the phantom as it is taking off.
It is possible to reach the lonely caveman in co-operative play by exploiting a glitch. However, zooming in on the Caveman with a scoped weapon (repeatedly if necessary) from the bridge below the phantom is sufficient to unlock the achievement.
Trivia[edit]
Haplorrhini (or Haplorhini) is the suborder of primates which includes apes and, conversely, modern humans.