The Time Traveller

First things first, you need one of your characters to smell like a dinosaur. Once that's done, head to the prehistoric era. You'll find a real dino there. As you get close, it'll notice your character and start chasing you. Your goal is to lead it left into a short cavern and trap it there.

Now, switch to another character. Bring this character all the way down to the same general area as the trapped dino, but this time, head left on the level above. Here you'll meet Thog. Grab one of Thog's stone wheels and push it to the right, so it drops down onto the trapped dino's head, killing it.

With the dino dealt with, use one of your characters in the prehistoric period to head all the way to the right of Thog. You'll find a Cave Painting there. After grabbing it, head up and right towards a stone and some dripping liquid. You need to push this boulder to the right.

Here's the tricky part: while still gripping the boulder you just pushed, immediately switch to another character who is in the past. Now, travel forward to the present time. If you pushed the boulder correctly in the past, a well should now be built in the present.

Just like you did with the boulder, use your present-day character to hold onto the Well crank. While holding it, switch to your character in the future.

Take your final character to the future and head to the location of the well in the past. You'll find the Bucket on display there. Grab it.

Now, head back to where the dino was and collect some Oil from its remains. Use this oil to start the Combustion Engine via the Engine Oil Intake. This will power up the Elevator Button. Press it!

Finally, push the wheel all the way to the time machine. Bring it back to Thog in the past. You'll need to crush him with another wheel, just like you did with the dino earlier.

With Thog's lineage dealt with, head back to the future and grab the Smurg that was on display. Now, back in the present, use the key to exit left and complete this section.