NOVA

- [Narrator] Alaska is the last place on Earth one might expect to find large reptiles, but the discovery of fossils has revealed dinosaurs could live farther north than what was once thought possible.

Now, this team hopes to answer some fundamental questions.

- What kind of animals lived here?

How did they survive the arctic winters?

- Where did they get their food?

- [Narrator] During these winter months, food for the plant eaters would've withered or died.

Karen Chin is one of the world's leading experts in dinosaur dung.

She's been investigating hadrosaur diet by studying the fossilized remains of their feces, known as coprolites.

(upbeat music) (machine hums) - [Narrator] At 100 times magnification, even the individual fossilized cells of the dinosaur's last meal are visible.

Investigating coprolites from non-polar dinosaurs living in southern Utah and Montana, Karen finds something intriguing.

- We can see chunks of intact wood, and that's where you see all of the cells are almost glued together.

They're glued together with lignin.

But then you can also see all of these loose cells all over the place in no particular order scattered all around.

And that indicates rotting wood.

To break down lignin, it requires oxygen.

So that can't happen in an animal's gut.

It has to happen outside where there's access to oxygen.

So we know that the wood was degraded, decomposed before it was ingested by the dinosaur.

I was quite surprised.

Why were they eating so much wood?

- [Narrator] The incredible new evidence suggests the southern hadrosaurs could diversify their diets, feeding on rotting wood to survive.

- Where are you gonna get protein if you're a herbivore?

You can go to a rotting log where there's lots of creepy crawlers, like beetles and millipedes, and pill bugs.

(bugs scatter across wood) - [Narrator] It raises the tantalizing possibility that this could have been a winter food source for Alaskan dinosaurs as well.