In a twist for archaeologists, two ancient human sites in Spain recently yielded a treasure trove of bones—packed inside mounds of fossilized hyena poop.

The million-year-old droppings are part of two hyena latrines, areas where the bone-crunching carnivores piled up their waste to mark territory and keep the rest of their habitat tidy.

The fossil feces are filled with bone fragments, fungi, and bits of plant matter, including tree and grass pollen. Together with the size and texture of the samples, the contents offer clues to the environmental conditions these sites experienced hundreds of thousands of years ago.

For instance, the appearance of these preserved poop samples—or coprolites in paleontological parlance—can hint at whether a landscape was once wet or dry, says