Is there any herbivorous pterosaur in the deep time?

Pterosaur is the first group of vertebrates with powered flight. It originated in the Late Triassic and became extinct with dinosaurs (excluding birds) at the end of the Cretaceous. Various diets of pterosaurs were proposed using different interpretations, such as content fossils and comparative anatomy. However, the understanding of the diets of many pterosaurs have still been on debate, which is mainly because of the rarity of stomach content found in pterosaurs. In this paper, the researchers found an elliptical content in the stomach position of a Sinopterus specimen. They extracted more than 300 phytoliths from the stomach content but none from the matrix of the same specimen. This demonstrates that these phytoliths, firstly appeared in pterosaurs, were eaten by this Sinopterus rather than any pollution after its death. Phytolith is a microstructure produced by all kinds of plants, and it varies among different plants and different positions of the same individual. Besides the phytoliths, many gastroliths (stones within the body cavity) were also discovered in the stomach content, which is the second pterosaur specimen with gastroliths. The combination of phytoliths and gastroliths, without any bones, scales or exoskeletons, strongly suggest that Sinopterus is herbivorous.