Your bones become more resilient, allowing you withstand greater amounts of punishment.
Benefit
You gain a +6 mutation bonus to your massive damage threshold, and you number of negative hit points required to kill you increases by 4. In addition, the damage you take from a fall is reduced by one die.
Special
This mutation stacks with the Improved Damage Threshold feat. You cannot take this mutation if you have the Brittle Bones drawback.