Eggshells of flightless birds evolved on different tracks

A team of researchers led by Montana State University has recently conducted a comprehensive molecular analysis of large flightless birds such as ostriches and emus to clarify how these birds have evolved. The study shows that structural molecular analysis may complement other tools, such as genetic analysis, in accurately tracing the evolutionary history of various types of animals. The findings could also shed new light on the evolution of egg-laying dinosaurs.

In recent years, genetic analyses have allowed scientists to rewrite the evolutionary history of palaeognathae, a group of birds including emus, ostriches, and rhea that are much more adept at running than at flying. However, combining the new genetic information with other modern tools like molecular analysis could provide even more information about how and why these animals evolved their unique features.

“We wanted to know if the three types of eggshells seen in palaeognaths were inherited from a common ancestor or evolved independently,” explained study lead author Seung Choi, a postdoctoral researcher in Earth Sciences at Montana.

By using X-ray crystallography, the scientists analyzed the microstructure of eggshells from modern palaeognath birds, such as the ostrich, rhea, emu, cassowary, kiwi, elephant bird, and two types of moa, as well as the structure of fossilized eggshells from this group of birds, along with fossilized eggs of bird-like dinosaurs. Then, they compared the findings with the eggshell structure of several modern flighted birds, including the common pheasant, the European green woodpecker, the northern goshawk, and the Japanese quail.

The analyses revealed that, while the wedge-like microstructures characterizing rhea eggshells can be traced back to ancient ancestors of palaeognath birds, the prism-like microstructures of ostrich and tinamous eggs most likely evolved independently later. “The pattern of evolution in palaeognath eggshells we revealed may help ornithologists decipher the trajectory of eggshell evolution among this group of flightless birds,” Choi said.

In addition, these findings could help scientists better understand the evolution of bird-like, egg-laying dinosaurs from the Mesozoic era (252 to 66 million years ago). Finally, since the eggshells of palaeognaths are often found among the remnants of ancient human settlements, they may also provide information to archaeologists studying how ancient humans used such eggs for food and their eggshells for artistic or other practices.

“Genetic and microstructural analysis of these living fossils’ eggshells may provide new insights on the evolution of birds and dinosaurs. It may also help us better understand how early humans lived and interacted with these fascinating creatures,” concluded senior author David Varricchio, a professor of Paleobiology at Montana.

The study is published in the journal eLife.   

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By Andrei Ionescu, Earth.com Staff Writer

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