Source: Pathfinder Bestiary, pg(s). 100
Brontosauruses have bulky bodies, four stout legs, and long necks topped with small heads. Their necks are counterbalanced by equally long, sinuous tails. Brontosauruses can reach seventy feet in length and over thirty tons in weight.
Brontosauruses are herbivorous, and use the reach provided by their long necks to graze from treetops. Their immense size protects them from predation, as only the largest predators can attack them. They are normally passive and docile creatures, but when angered can defend themselves with powerful sweeps of their tails and by attempting to crush targets with their feet.