New Study Reveals the Earliest Evidence of Fruit-Eating by Birds

Carnivores eat meat, herbivores eat plants, and frugivores eat fruit. Fruit consumption is found in hundreds of animals, from toucans to fruit bats to maned wolves to humans and it is well known that current fruit-eating birds help plants to reproduce by spreading seeds in their droppings. But most fruit-bearing plants evolved relatively recently in Earth’s history, showing up for the first time in the Cretaceous: the final period of the dinosaurs. In a new paper in eLife, scientists tracked down the first fossil evidence of fruit consumption by comparing the skull shapes and stomach contents of fossil birds. The verdict: the earliest-known fruit-eating bird was an early bird called Jeholornis that lived 120 million years ago, and it may have helped contribute to the spread of the plants that dominate the world today.

“Birds are important consumers of fruit today, and play important roles in seed dispersal, but so far there has not been direct evidence of fruit consumption by early birds, outside the bird crown group,” says Dr Han Hu, a Marie Skłodowska-Curie at Department of Earth Sciences, Oxford University and the study’s first author. “This obstructs our understanding of the origins of this important plant-animal interaction.”

The crown group of birds is the group that’s alive today, Neornithes, and their direct ancestors. But other birds began evolving tens of millions of years earlier; the second-most primitive known bird was a long-tailed raven-sized creature called Jeholornis. Palaeontologists have discovered preserved seeds inside the fossilised remains of Jeholornis. The question is, how did they get there? Some birds eat seeds directly, cracking them open or grinding them up in the stomach to extract the nutrients inside. Other birds swallow seeds when they are eating fruit.

“Clarifying between these two hypotheses is important since fruit consumption could result in co-evolutionary mutualism, whereas seed consumption does not,” says Dr Hu — eating fruit and pooping out un-crushed seeds could help plants spread and evolve, but if the seeds were crushed-up and digested, that wouldn’t help the plants.

Solving this mystery required Han and co authors to examine dozens of Jeholornis specimens at China’s Shandong Tianyu Museum of Nature where they selected the one with the best-preserved skull and scanned it at the Australian Nuclear Science and Technology Organisation’s (ANSTO) Australian Synchrotron, Melbourne, Australia.

The scan revealed that Jeholornis’s skull has many traits that are more like a dinosaur than a modern bird (modern birds are the only surviving group of dinosaurs). However, the skull did have some traits in its mouth and beak, like reduced teeth, that are present in modern birds– features that could potentially hint at a “modern” diet that included fruit.

Click on the image for a video of the skull of the new Jeholornis specimen. Provided by Dr Han Hu.

The reconstructed skull was compared to the skulls, especially the mandibles, of modern bird species that either grind seeds, crack seeds or that eat fruits, leaving the seeds whole. The analyses ruled out seed cracking, however, it could not distinguish between seed grinding and fruit eating.

Hu et al. therefore compared the seed remains found inside Jeholornis fossils to seeds eaten by modern birds. The fossilised seeds were intact and showed no evidence of grinding. This suggests that Jeholornis ate whole fruits for at least part of the year.

Not only was Jeholornis the first-known fruit-eater, but it gives scientists a window into how birds helped fruit-producing plants evolve. “Birds may have been recruited for seed dispersal during their earliest evolutionary stages,” says Dr Hu. “As highly-mobile seed dispersers, early frugivorous birds might therefore indicate a potential role of bird-plant interactions during the Cretaceous Terrestrial Revolution,” in which angiosperm plants start to take over the world. This finding opens new avenues for scientists to explore how plant and birds might have evolved together. Similar analyses could unlock new information about how other species interacted with their environments.

This research will inspire the research of paleontologists, ecologists, zoologists, and botanists who are interested in bird ecology, trophic interactions, and the Cretaceous Terrestrial Revolution. It is also a flagship of applying multiple cutting-edge methods simultaneously to solve complex palaeoecological questions, which will inspire the future researchers to conduct similar analyses to reveal the extinct animals’ ecologies.

The full paper ‘Earliest evidence for fruit consumption and potential seed dispersal by birds’ is available to read in eLife: https://doi.org/10.7554/eLife.74751.

This article is adapted from releases from eLife and Field Museum.

Feature image: The Cretaceous bird Jeholornis pooping out seeds from fruit. Illustration by Zhixin Han and Yifan Wang.