Members of Jeholornis, a genus of early birds that lived in what is now China some 120 million years ago (Early Cretaceous epoch), are the earliest-known fruit-eating birds, according to new research led by paleontologists from the University of Oxford and Linyi University.
Jeholornis pooping out seeds from fruit, helping fruit-bearing plants take over the world. Image credit: Zhixin Han / Yifan Wang.
Birds and plants have a close relationship that has developed over millions of years.
Birds became diverse and abundant around 135 million years ago. Shortly after, plants started developing new and different kinds of fruits.
Today, fruit-eating birds help plants to reproduce by spreading seeds in their droppings.
This suggests that birds and plants have co-evolved, changing together over time. But it is not clear exactly how their relationship started.
One bird group that might hold the answers is Jeholornis, a genus of early birds that lived in China around 120 million years ago.
Paleontologists have discovered preserved seeds inside the fossilized 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.
If Jeholornis belonged to the second group, it could represent one of the early steps in plant-bird co-evolution.
“The first Jeholornis fossil that was described in 2002 has all these plant remains scattered around it, they look like they exploded out of the stomach cavity,” said Dr. Jingmai O’Connor, associate curator of fossil reptiles at the Field Museum.
“These stomach contents were superficially identified as seeds, so people argued that it was eating seeds.”
“Then 17 years later, other scientists suggested that it wasn’t just eating seeds, but whole fruits, and only the seeds preserved, since they’re harder.”
“In this study, we wanted to figure out, was it feeding on seeds alone, or was it eating fruit?”
“Clarifying between these two hypotheses is important since fruit consumption could result in co-evolutionary mutualism, whereas seed consumption does not,” said Dr. Han Hu, a researcher at Oxford University and the University of New England.
“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.”
Seeds preserved in the abdominal area of selected Jeholornis prima specimens. Image credit: Hu et al., doi: 10.7554/eLife.74751.
To solve this mystery, the study authors examined dozens of Jeholornis specimens.
The scan of one of the best-preserved specimens revealed that Jeholornis’ skull has many traits that are more like a dinosaur than a modern bird.
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.
After comparing this reconstructed skull of Jeholornis to the skulls, especially the mandibles, of modern birds, including species that grind seeds, species that crack seeds, and species that eat fruits, leaving the seeds whole, the analyses ruled out seed cracking.
“However, you’re not actually going to be able to tell different diets apart from just the mandible shape,” Dr. O’Connor said.
“But other parts of the fossils could provide additional clues. Birds that eat seeds have a gastric mill, a gizzard. They swallow stones to help them crush up their food.”
Some specimens of Jeholornis have been found with gizzard stones, and some have been found with preserved seeds in their gut, but no one’s found a Jerholornis with both gizzard stones and seeds at same time.
What’s more, the seeds found in Jeholornis stomach cavities are whole, not crushed.
These findings suggest that Jeholonis were eating different foods at different times of the year.
When fruit was available, they would have eaten whole fruits, seeds and all, and then pooped out the un-crushed seeds.
When fruit wasn’t in season, they would have eaten something different — and harder — and relied on a gizzard to crush them up.
“Birds can drastically change the proportions of their digestive system to adapt to whatever their diet is for a particular season. This is the first evidence of that plasticity in dinosaurs,” Dr. O’Connor said.
Not only were Jeholornis the first-known fruit-eaters, but they gives paleontologists a window into how birds helped fruit-producing plants evolve.
“Birds may have been recruited for seed dispersal during their earliest evolutionary stages,” Dr. Hu said.
“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.”
“Birds eating fruit and pooping out seeds far away from the parent plant can help fruit-bearing plants spread like wildfire; this pattern may have started with birds like Jeholornis.”
Jeholornis’ fruit-eating also dovetails with their traits that would have helped them fly, including a long tail that could have worked like a rudder to stabilize them in flight.
“A diet of fruit might have put evolutionary pressure on Jeholornis to be better at flying,” Dr. O’Connor said.
“You can’t just sit in one tree forever and eat its fruits, you have to be able to move around, and identify those resources by flying up and seeing where they are.”
The study was published online in the journal eLife.
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Han Hu et al. Earliest evidence for fruit consumption and potential seed dispersal by birds. eLife, published online August 16, 2022; doi: 10.7554/eLife.74751
Source link: https://www.sci.news/paleontology/fruit-eating-jeholornis-11106.html
