They have a very small aggro radius making them easy to avoid, furthermore they hardly ever wander away from water.

In combat, wild Spinos act like glass cannons, they have the same health as Thylaceos but have high DPS plus a movement speed and attack boost in water. Sustained assault rifle fire or a tanky mount with decent attack will slaughter the poor thing.

Tamed Spinos are a different story however…

More Spinosaurus Encountering Tips