We can be certain that Job was a contemporary of Abraham. This means that when Job describes God overturning mountains, he's recounting something that happened recently, about 200 or so years before him.
Abraham and Job
Dinosaur Classification
Whether or not a Biblical word translated as a kind of serpent refers to something which may have been a dinosaur is context dependent. Sometimes a snake is just a snake. Sometimes a serpent is a Sauropod.