Birds, macaques, bats, flies, people… Many modern animals eat fruits. For some, this is their exclusive diet, while others eat them more sporadically. In the long history of life on Earth, fruits containing seeds of flowering plants (or angiosperms) are a recent invention dating back to the Cretaceous period (-145 to -66 million years), the period when the dinosaurs disappeared. except for birds. It is the 120-million-year-old Jeholornis bird that may hold the title of the oldest fruit lover, according to a study published in the journal eLife.
Jehol Wildlife Representative
Over the past two decades, excavations in Liaoning and Heibei province in northeast China have collected a large number of fossils, including feathered dinosaurs, as well as the remains of birds and mammals. Most of these specimens are from the Lower Cretaceous (100 to 130 million years ago) and are grouped together as the “Jehol fauna”. Thus, among them is Jeholornis, a primitive bird that can reach 70 cm in length and a wingspan of about 1 m, which is not a direct relative of modern birds. It really belongs to a subclass of birds, the enantiornithes, which disappeared at the same time as other wingless dinosaurs, 66 million years ago. The first such specimen was discovered in 2002, with the remains of plants and seeds scattered around it, which seemed to have grown from its stomach, as if it had exploded. Later, other contents of the stomach, also containing seeds, could be found. Hence the first hypothesis that Jecholornis was a seed eater.
But was it really the correct conclusion? What if Jecholornis doesn’t just eat the seeds, but attacks the fruit directly containing them? To be sure, a team at the Field Museum in Chicago examined dozens of Jeholornis specimens held at the Shandong Tianyu Museum in China. She chose the one with the best preserved skull and scanned it at the Australian ANSTO (Australian Nuclear Science and Technology Organization) synchrotron in Melbourne.
Seed specimens found in the stomachs of Jeholornis specimens. Credit: paper by Hu et al, adapted from O’Connor et al 2018.
A varied diet, including fruits
Analysis has shown that the Jeholornis skull has many features that are more dinosaur-like than bird-like. However, its beak and jaws are closer to bird anatomy. Comparisons have been made to Jeholornis with seed crushers, whole seed eaters, and other fruit feeding species. It appears that this ancestral bird was definitely not a grinder, but its jaws alone do not allow us to determine its diet. Therefore, the authors looked for additional clues, in particular, by examining the digestive tract. “Birds that eat seeds have a stomach mill, a stomach,” explains Jingmai O’Connor of the Field Museum, in a statement. “They swallow rocks to help them grind their food.” Some specimens of Jeholornis have indeed been found with stomach stones, and others have been found with seeds preserved in their intestines, but no one has found Jerholornis with stomach stones and seeds at the same time. Also, the seeds found in the stomach cavities of Jeholornis are whole, not crushed.
Credit: Hu et al.
These results show that Jeholonis ate different foods at different times of the year. When fruits were available, they should have been able to feast on them. On the other hand, out of season, they could probably feed on harder plant fibers, requiring the crushing of stones to facilitate and speed up their digestion. This seasonal character is characteristic of many modern birds. “Birds can drastically change the proportions of their digestive system to match their diet at certain times of the year,” explains Jingmai O’Connor. For the authors of this study Jecholornis was the first known animal to eat fruit whole. This mode of feeding may have contributed to the dispersal of seeds and hence the growth of flowering plants. Likewise, the bird was able to develop its ability to fly in order to gain easier access to this new commodity. The interaction of plants and birds is a topic for them that we must continue to explore.