The correct name is coprolite, or fossilized feces (animal waste). Our specimens come from Utah. Many rough coprolite specimens from this area are ten pounds or more, so we are talking about reasonably large animals.
It is usually not possible to determine the species of the animal producing the specimen, so emphatic claims about a specimen being genuine dinosaur dung should be viewed skeptically. Coprolite may in fact be from any species-marine creatures, amphibians, or mammals. So the specimen you have may be from a prehistoric horse, giant sloth, dinosaur, mammoth, etc. However, it is possible to take an educated guess as to what species produced the dung based on species known to have inhabited the area where the dung was found, or sometimes by an analysis of the specimen. Coprolites found in bone beds are probably from the fossilized bones of creatures found in the bed.
If the coprolite contains fossilized swamp creatures, plant matter, or animal bones, sinew, etc., one could deduce the animal to be an herbivore, carnivore, or marsh-dweller. The colors vary, depending upon the mineral content of the soil and ground water present during the fossilization process. The colors are not related to what the animal had for breakfast!
One of the most famous coprolites came from Saskatchewan, Canada, and measured seventeen inches by six inches in diameter, shaped pretty much like you’d expect. The specimen contained bone fragments and paleontologists think it may have been from a T.Rex, whose bones have been found in the area.