Pterosaurs represent the earliest group of vertebrates with powered flight capability, originating in the Late Triassic and becoming extinct alongside non-avian dinosaurs by the end of the Cretaceous. For decades, paleontologists have proposed various dietary hypotheses for these volant reptiles—insectivory, piscivory, filter-feeding, or even herbivory. To resolve this question, researchers have employed multiple approaches including skeletal morphology, functional analysis, and dietary residues. However, consensus on feeding habits has only been reached for one or two pterosaur taxa. Dietary residues—particularly stomach contents—serve as the most crucial direct evidence to settle these debates. Yet only six pterosaur specimens with preserved stomach contents have been reported to date: one Eudimorphodon from the Triassic and five Jurassic Rhamphorhynchus specimens, with most stomach contents dominated by fish remains. This scarcity of evidence underlies the ongoing controversies surrounding pterosaur diets.
A recent study published in Science Bulletin has now provided the first direct evidence for herbivory in pterosaurs. The research team discovered a 7.7-cm-long stomach content within a Sinopterus specimen. CT scanning of the slab fossil revealed this mass positioned between the ribs and gastralia, confirming its in situ preservation. The scan further detected numerous small gastroliths within the stomach content, while over 300 phytoliths extracted from a small piece of stomach content. Phytoliths are microscopic silica structures formed during plant growth, exhibiting distinct morphologies across plant species and even within different parts of the same plant. This discovery marks both the first phytolith extraction from any pterosaur and the second documented pterosaur specimen containing gastroliths.
To confirm that Sinopterus was truly a plant-eater, researchers carefully eliminated other possible explanations. First, they ruled out contamination by showing that the surrounding rock contained none of the phytoliths found in the stomach. Next, they considered whether the plant material might have come from eating other plant-consuming animals. But Sinopterus had a fast, bird-like metabolism – if it had eaten vertebrates or insects, some traces like bones, scales, or hard insect shells would have remained in its stomach, yet none were present. The idea that it ate soft-bodied creatures like caterpillars also didn't hold up: why would it need so many stomach stones if it wasn't grinding tough food? These stones are typically used by animals to break down hard materials like insect shells or plants, making them unnecessary for digesting soft prey. Finally, earlier studies of Tapejara – a close relative – showed it had strong jaws suited for plant-eating, further supporting this conclusion.
Therefore, the phytoliths represent direct dietary intake, while the gastroliths functioned as grinding tools for plant material processing.
Science Bulletin