The Mammoth Saddle is used to ride a Mammoth after you have tamed it. It can be unlocked at level 31. While riding the Mammoth you can use its melee attacks to collect wood, berries and rare mushrooms.
Survivor at rear seat can strike at the drum with rhythm (indicated at the HUD above the quickslot while at said seat), giving stamina regen and fear-immune buffs towards nearby friendly dinos.