Prehistoric birds switched from dinosaur diets to eating leaves

In a new study published in the journal Nature Communications, scientists have unearthed the earliest evidence of avian leaf-eating behavior, dating back approximately 120 million years. 

This discovery, focusing on the extinct bird Jeholornis, fundamentally shifts our understanding of the early evolution of bird diets and their relationship with the plant kingdom.

Focus of the study

Unearthed from the northeastern region of China, the immaculately preserved Jeholornis fossil has been subjected to a revolutionary type of microscopic analysis. 

The research was conducted by experts from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences and their collaborators.

The bird is roughly the size of a modern-day pheasant. It possesses characteristics which link it closely with predatory, feathered dinosaurs, such as teeth and a long bony tail. However, an unexpected twist came to light when researchers examined the fossilized stomach contents of this juvenile, arboreal species.

What the researchers learned 

The results showed that Jeholornis was not a predator as one might assume from its dinosaur relatives. The bird had consumed tree leaves from a group of flowering plants known as magnoliids, which today include magnolia, cinnamon, and avocado trees. 

“The fossils from the Jehol Biota in China show us that very early in bird evolution they switched from predatory behaviors to using their wings to fly into trees so they could eat the fruits, seeds, and leaves of plants like so many species do today,” explained study co-author Dr. LI Zhiheng.

Today, the symbiotic relationship between birds and flowering plants, or angiosperms, is well documented, with birds pollinating flowers, consuming their fruits, and dispersing their seeds. But the fossil record had previously provided little insight into the evolutionary origins of these intricate ecological relationships.

Researchers also found gizzard stones (gastroliths) in the stomach areas of the fossil skeletons, implying that some early birds had plant-inclusive diets. Other Jeholornis fossils had fossilized fruit and seeds in their digestive systems, providing further evidence of plant consumption.

How the research was conducted 

To delve deeper into these early bird diets, the international team of scientists set out to identify microscopic fossilized plant remnants within the ancient stomach contents of the bird skeleton. This cutting-edge approach led them to search for phytoliths – tiny, resilient structures comprised of opaline silica (silicon dioxide) produced by plants.

The team meticulously processed the samples to uncover the microscopic remains of long-decayed plants. 

“After comparison with over 4,000 kinds of modern phytoliths, we can see that most of the identifiable fossil phytoliths from the stomach come from the leaves of magnoliids,” explained study first author Dr. WU Yan. This evidence further solidified the notion that Jeholornis was a leaf eater.

The team supported their conclusions with detailed statistical analysis of Jeholornis’s lower jaw, revealing similarities with extant birds known for plant-based diets, including the hoatzin, a leaf specialist native to South America’s tropical forests. These insights were provided by study co-author Dr. HU Han from Oxford University.

Implications of the study 

The study also highlights the pivotal role of flowering plants in living bird diversity. Today, many bird species rely on nectar and various plant parts to fuel their energetic flight and rapid growth, while their vibrant feather colors are often derived from their plant-based diets.

The implications of these findings are profound, as Dr. Thomas Stidham from the IVPP and a co-author of the study, said: “As we can see with this extinct, vegetarian, tree-living bird, the evolution of birds has been linked to flowering plants for over 100 million years with fruits, seeds, and even leaves serving as main courses on the bird menu starting originally when birds still had teeth and long, bony dinosaurian tails.”

This research not only uncovers a prehistoric bird’s diet but also sheds light on the long and intertwined history of bird and plant evolution, illuminating how these two branches of life have shaped each other for over a hundred million years.

Image Credit: IVPP

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