Another great fossil word, pretty easy to figure out: fossilized disgestive tracts.

Here's a very interesting statement about what could be learned from the gastrolith of a once-living dinosaur:

"Gastroliths tell us that dinosaurs swallowed large stones to help them grind their food."

There go Granny's chickens to the grit trough again!

I think the gastroliths were the stones that the animals swallowed.

gastrolith
Stone that was once part of the digestive system of a dinosaur or other extinct animal. Rock fragments were swallowed to assist in the grinding process in the dinosaur digestive tract, much as some birds now swallow grit and pebbles to grind food in their crop. Once the animal has decayed, smooth round stones remain – often the only clue to their past use is the fact that they are geologically different from their surrounding strata.

http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0034009.html

Thanks, Ted. I didn't make the correct connection that the gastrolith was the stone itself.