New discovery confirms the long-debated hypothesis that the ancient winged reptiles ate plants

About 120 million years ago, an aerial reptile known as a pterosaur fell from the sky over northeastern China and died in a shallow pond. A fine layer of sediment washed over it, preserving not only its skeleton, but, to the delight of modern paleontologists, its stomach. The resulting fossil, as reported in Science Bulletin last week, is the first pterosaur ever found with a belly full of plants.

“This is a once-in-a-hundred-years discovery,” says David Martill, a paleontologist at the University of Portsmouth who was not involved in the research. He adds that the new evidence is a “smoking gun” for pterosaur herbivory, showing definitively that the fierce-looking winged creatures were not always carnivorous.

Pterosaurs are thought to have gobbled up animal food, from reptiles to fish and insects. The five known examples of stomach contents in the pterosaur fossil record support that picture: All come from a genus called Rhamphorhynchus and confirm it ate fish. Still, a few researchers argued based on anatomical characteristics such as the size and shape of the animals’ beaks that some species might have eaten plants. For instance, toothless pterosaurs known as tapejarids had parrotlike beaks, seemingly suited to grinding up fruits, nuts, and seeds. But such indirect evidence wasn’t enough to sway most researchers. 

The new study focuses on Sinopterus atavismus, a species of tapejarid with a wingspan of 2 to 4 meters in adulthood. This specimen—a juvenile measuring 1.5 meters across—was first described in 2019 by a team led by Xinjun Zhang and Shunxing Jiang, two of the new study’s lead authors and paleontologists at Shenyang Normal University and the Chinese Academy of Sciences, respectively. The species hails from the Jehol Biota in northeastern China, which is famous for exceptionally well-preserved fossils. Between 133 million and 120 million years ago, the area was dotted with calm lakes and wetlands that nearby volcanoes periodically blanketed with ashfall. Carcasses swept into these waters were sometimes buried by sinking volcanic ash, which encased the remains in an anoxic tomb. As a result, fossils found in the region occasionally preserve not just bones, but color, soft tissue, or stomach contents.

This specimen of S. atavismus had a clearly discernable stomach with potential food inside. So another team led by Jiang and Zhang probed it more closely with a series of high-resolution x-rays from different angles. The team found that the stomach contained two types of minerals never before seen in pterosaur fossils—and both strongly pointed toward herbivory.

At the top of the pterosaur’s stomach, the imaging revealed numerous large quartz crystals. Quartz is often found within gastroliths, a type of mineralized stomach stone that many modern animals such as birds and lizards store in their gizzards or stomachs to help crush hard foods such as plants. 

Lower in the stomach, Jiang and Zhang’s team discovered hundreds of phytoliths, small mineral deposits that build up between growing plant cells. Phytoliths have been spotted in dinosaurs just twice before, in species known to be vegetarian: in the dung of a plant-eating dinosaur and on the teeth of a plant-eating dinosaur.

To other researchers, their presence in the pterosaur's belly is telling. “Direct evidence is fundamental to settling this kind of debate,” says R. Pêgas at the University of São Paulo, who was not involved in the study. “This closes the debate and confirms that pterosaurs had more dietary diversity than previously thought.” Martill says the evidence made him a convert. “I, for one, thought that the fine beak tip of tapejarids was most likely used for picking small water fleas from shallow water or for eating insects.”

Now, researchers need to factor herbivory into their picture of the winged reptiles. Pinning phytoliths to specific plants can be difficult, but those found within the pterosaur appear to come mostly from woody plants, with a few from flowering plants or conifers. “I think that our study opens a new window with several possibilities to better understand extinct animals, including their feeding behavior,” says study co-author Alexander Kellner, a paleontologist at the Federal University of Rio de Janeiro.

Pterosaur researchers already have plenty to chew on. “This is a fascinating discovery and one that could so easily have been overlooked,” Martill says. “We now have to re-evaluate the ecology of quite a wide range of pterosaurs.”