Shortly after you begin, you'll see Jimmy and his crew still at sea trying to get their boat ashore. You can continue on the path afterwards, passing a crate containing a shotgun. Follow the path to the fire and use a spear to burn the bushes. The wooden structure will fall, opening up the entrance to a door.
Head out of the cave and into the field with the herd of brontosauruses. Head
across the field while avoiding being stomped on. Head in the direction the
brontosauruses are going, while maneuvering around the bushes. If you head
toward the wall where the cave is, you'll see a crate that has a shotgun in it.
Get the shotgun. Be careful of venatosauruses and the mini ones as you follow
You'll eventually see a pillar with a burning fire along the right wall. Go
around and under the waterfall to get to it. Light a spear on fire and throw
it into the pillar on the stairs across from you. Now you'll need to head back
to Carl and Hayes. Light pillars at the top of the stairs along the way. You
will have quite a few venatosauruses coming after you, and you'll need to use
your spears to fend them off. Lighting the pillars and fire keeps you from
having to constantly go back to light a spear on fire again.
Once you get back to Carl and Hayes, light the bushes behind them on fire. A
V-Rex will smash down the entrance to where you guys are. Head up the stairs
and to the end of the level.