Leave the cave. You'll see Ann chased by tyrannosaurus rex. Move fast to save her.
Turn left and take the narrow wall down. You'll find yourself in the small cave and then near the river.
Move downstream until you will reach the tyrannosaurus. Pass under him without any fears, because he'll be taking care of Ann only. Turn left behind the creature and move under the rocks.
Walk ahead in the river and turn right on small 'island' between rocks. There'll be some spears so pick one and throw it in the enemy.
Now, quickly turn round and run to the stone columns, because only they can stop tyrannosaurus anger.
The wide glade is located behind the columns. Ann will run on the wall on the right. The lever is located at her way's end and only Ann can take advantage of it. Your job is to make tyrannosaurus rex busy and he's probably behind you now. Use the stone columns for protection and attack with spears lying there.
When the monster will move in Ann's way, be careful because it's very dangerous, but quite useful moment. Attack with spear to distract the creature. Then run fast to nearby column, wait until tyrannosaurus rex will approach it and try to hit him with spears all the time (he must move around the stones, not trying do destroy it). It's a hard task, but you can make it. If you'll run through the column's centre, enemy will destroy the stones with ease, but if you'll move around them, he'll fallow you and leave the 'buildings' in one piece.
You have four sections of pillars at disposal and after destroying them all, the monster will return to Ann (I have written how to take advantage of it).
Ann will inform you about opening the gate, but wait for proper moment before you'll start running.
Go through the gate (the monster will break through the obstacle and chase you again) and run quickly to the narrow slot in rocks and then up the tunnel.
You should see Ann running along the glade at the exit, so head to her quickly (take the top shelf), but if the tyrannosaurus rex will surpass you (right screenshot), you won't be able to save Ann in time.
Run to the place, where Ann will be standing. Approach her (to the brink) and you'll be safe from now on.
Proceed upwards, deep into rocks of the cave. You'll meet comrades there (without Carl) and finish current stage.