Why did they want to do it?

[Ruby2]

Ok, some suggest that Rinkus and Sierra are actually fish eaters.  I have doubts on that for the following question actually:  What could they gain by taking over the Great Valley?  (Yes, that is their goal.  Unless it was the world, though Pterano seems to be content with just the Great Valley.)

As a fish eater, the two would not care about

1.) The green food (they'd probably spit it out)

2.) The Leaf Eaters (they don't eat that kind of meat)


Pterano wanted to make the Great Valley into a utopia but it is unknown what Rinkus and Sierra hoped to do.

All we know is that Sierra had a plan to feed Littlefoot & Co to Sharpteeth once he took over.

So either they actually are Leaf Eaters and just have funky teeeth (like perhaps the Parchys in movie 1.)  or they just enjoy bossing others around and that is their goal when they take over the Great Valley.

[DarkHououmon]

I don't recall "taking over the Great Valley" as being part of their plan. I am pretty sure their plan was more on a global scale.

As for their diet, I'm still siding with the "fish eater" argument, as it seems unlikely that they are leaf eaters. Pterano and Petrie are supposed to be fish eaters as well and yet they have flat teeth. Also we do see flyers with sharp teeth in LBT5 and they are clear meat eaters. So why would they give sharp teeth to a meat eating pterosaur, but then also give sharp teeth to another meat eating pterosaur?

The pachys could be omnivores, which would explain the sharp teeth. I should also point out that some herbivores do in fact have some sharp teeth, so it's not really that unusual.

[Malte279]

Actually Pterano is rather specific about this in the scene preceeding the (rather unexplained) abduction of Ducky (why they abducted her is in fact one of the big "why did they do that?" moments in the film, since the other adults in the Great Valley probably couldn't have cared any less about Ducky telling them that Pterano had plans for a stone in whose powers they didn't believe). Anyways, this is what Pterano says:

Yes. And I shall take my rightful place as leader of the herd and I will rule over the most beautiful, most fertile land in the world! The Great Valley!

[Dr. Rex]

I think the potential easy access to power just appealed to Rinkus and Sierra. After all, the Stone of Cold Fire was said to bring unimaginable powers. That would certainly appeal to anyone, right?