https://phys.org/news/2018-05-fossilized-feces-reveal-early-cretaceous.html

The researchers selected 433 coprolites from a collection of almost 2,000 and then analyzed their shape, contents, and chemical composition. The specimens varied widely in shape and size, suggesting they belonged to a diverse range of aquatic vertebrates. These animals were likely carnivores that fed mainly on fish, such as ray-finned fishes and crocodiles, because their faeces were filled with bits of fish scales and small fish bones. This hypothesis was supported by chemical analyses, which revealed large amounts of bone residues in the coprolites.

These findings uncover some of the feeding behaviors of Early Cretaceous aquatic vertebrates and support previous fossil evidence suggesting that Las Hoyas was a rich and diverse wetland ecosystem.