Palaeontologists have found birds with teeth and told us what they ate

Researchers have found seeds preserved in the fossilised remains of one of the earliest birds, Longipteryx chaoyangensis, in their stomachs, indicating that they fed on fruit. This disproves previous hypotheses that these birds preyed on fish or insects due to their strong teeth on the tips of their beaks.

Longipteryx, which lived in what is now China about 120 million years ago, were among the earliest birds, and their structure remains a mystery to scientists. Fossils of this bird were first found in 2000, at which time it was thought that their elongated skull and teeth indicated a fishing lifestyle similar to modern kingfishers. However, recent discoveries have called this theory into question.

During a visit to a museum in Shandong, China, lead study author Dr Jingmai O'Connor found two Longipteryx specimens with something unusual in the stomach area. After consulting with palaeobotanist Fabian Herrera, they concluded that these structures were nothing more than ancient seeds. The seeds belonged to the fruits of gymnosperm trees, ancestors of modern conifers and ginkgoes.

This discovery was the first evidence that Longipteryx most likely fed on fruit, not fish as previously thought. Since the climate of those times was temperate, these birds probably had a mixed diet, including fruit in season and eating insects the rest of the time.

The study of Longipteryx also raises the question of the purpose of their long beak with thick teeth. The thickness of the enamel on the teeth of this small bird is comparable to that of large predatory dinosaurs such as Allosaurus, leading scientists to wonder about another function for this amazing structure.

One hypothesis suggests that the beak and teeth may have been used in social or sexual encounters. Modern hummingbirds, for example, have similar formations on the tips of their beaks, which they use in fights over resources. Longipteryx teeth may also have been a kind of weapon to help them defend themselves or compete for territory and food.

This study helps to look at the broader question of how much the external features of fossils can accurately indicate animal behaviour. Dr O'Connor stresses the importance of studying the behaviour of ancient birds based on more complex factors than just skeletal structure.