Photo: Courtesy of Dr. Thomas Stidham

Chinese researchers have revealed the oldest evidence for leaf eating in birds as the fossilized leaves were found in the stomach of an extinct early bird that once lived in Northeast China 120 million years ago, a paleontologist who participated in the project told the Global Times on Thursday.

"By applying a new technique to look for the microscopic remains of plants in the fossilized residue of the stomach of an early bird, we were able to find the oldest evidence for leaf eating in birds," Thomas Stidham, co-author of the study from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences (CAS), told the Global Times.

The discovery marks the earliest known evolution of arboreal plant-eating among birds, according to an article published on the CAS website on Tuesday.

The bird in question, named Jeholornis, was a pheasant-sized member of the second most primitive lineage of known birds. It possessed teeth and a long bony tail, similar to its predatory, feathered dinosaur relatives, according to the article.

Contrary to its predatory appearance, the microscopic analysis of the fossilized stomach residue revealed that ­Jeholornis was not a carnivore but rather a leaf-eating bird. 

The researchers discovered that the bird had consumed leaves from a group of flowering plants known as magnoliids, which includes present-day magnolia, cinnamon and avocado trees, the article revealed.

"While we knew some early birds could eat energy rich and easy to digest plant parts like fruits and seeds, we didn't know that they had evolved digestive systems that could pull nutrients out from harder to process parts like leaves. While we can tell that most of the leaves in the stomach came from magnoliid flowering plants (angiosperms), other phytoliths in the stomach show that the bird ate leaves from other extinct trees as well," Stidham said.

For a long time, scientists have believed that birds may play a crucial role in the co-evolution of flowering plants and their early diversity, which includes pollinating their flowers, eating their fruits and dispersing their seeds. However, the scarcity of fossil records makes it difficult to find conclusive evidence for such hypotheses, according to the article.

"This project helps to show that close to the origin of birds from small feathered predatory dinosaurs, some of the earliest birds had moved into the trees, became vegetarians, and began a close and globally important ecological relationship with flowering plants that has lasted for at least 120 million years," Stidham noted, adding that "we hope that other research groups will be inspired by this discovery and work together to uncover other ancient interactions between birds and plants."

This study, published in Nature Communications on July 28, was conducted by researchers from the IVPP and their collaborators, which includes people across traditional scientific disciplines like paleontology, botany, anatomy and ornithology, according to Stidham.