Earliest proof of plant-eating trait found in ancient birds

This prehistoric bird, as it turns out, was not a predator. The discovery of gizzard stones (gastroliths) in the stomach portions of the fossil confirmed plant-inclusive diets. 

In fact, the researchers were able to decipher what the bird had eaten just before it died. 

The prehistoric bird had eaten tree leaves from the magnoliid family of flowering plants, which includes magnolia, cinnamon, and avocado trees today. 

The paleontologists compared the three-dimensional shape of the lower jaw of this bird to some modern birds to further corroborate their idea of leaf-feeding traits in this early bird.

The lower jaw of Jeholornis is comparable to that of the hoatzin that lives in tropical forests of South America. Hoatzin largely depends on plants. 

The latest revelation shifts our understanding of the early evolution of bird diets. 

"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," LI Zhiheng from IVPP, corresponding author of the study said in a statement.

Understanding early bird diets

The symbiotic link between birds and flowering plants (angiosperms) is well known today, with birds pollinating flowers, consuming their fruits, and disseminating their seeds in the process. 

However, little is known about these ecological connections from the fossil records of ancient bird species. 

To gain a better understanding of early bird diets, the team went on to conduct a microscopic examination of plant remains within the fossilized stomach of several bird fossils. 

The goal was to look for signs of phytoliths, which are minute particles made of silica that form within plant tissues.

The authors were able to extract hundreds of phytoliths from the microscopic samples using this extensive approach.  

"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," said WU Yan from IVPP, the first author of the study. 

The findings were reported in the journal Nature Communications. 

Study abstract:

Angiosperms became the dominant plant group in early to middle Cretaceous terrestrial ecosystems, coincident with the timing of the earliest pulse of bird diversification. While living birds and angiosperms exhibit strong interactions across pollination/nectivory, seed dispersal/frugivory, and folivory, documentation of the evolutionary origins and construction of that ecological complexity remains scarce in the Mesozoic. Through the first study of preserved in situ dietary derived phytoliths in a nearly complete skeleton of the early diverging avialan clade Jeholornithidae, we provide direct dietary evidence that Jeholornisconsumed leaves likely from the magnoliid angiosperm clade, and these results lend further support for early ecological connections among the earliest birds and angiosperms. The broad diet of the early diverging avialan Jeholornis including at least fruits and leaves marks a clear transition in the early evolution of birds in the establishment of an arboreal (angiosperm) herbivore niche in the Early Cretaceous occupied largely by birds today. Morphometric reanalysis of the lower jaw of Jeholornis further supports a generalized morphology shared with other herbivorous birds, including an extant avian folivore, the hoatzin.