New research published in eLife sheds light on the evolutionary history of large flightless birds like ostriches and emus through the molecular analysis of their eggshell structures. The study highlights the potential of structural molecular analysis as a complement to genetic analysis in tracing the evolution of animal groups. This new understanding may also have implications for the study of egg-laying dinosaurs.
Traditionally, the evolutionary tree of paleognathae birds, which include emus, ostriches, and rheas, has been based on physical characteristics. However, recent genetic analyses have provided additional insights into their evolutionary history. By combining genetic information with other modern tools, researchers aim to gain a deeper understanding of how and why these birds developed their unique characteristics.
Lead author Seung Choi, a postdoctoral researcher at Montana State University, explains that the study aimed to determine if the three distinct types of eggshells observed in paleognath birds were inherited from a common ancestor or evolved independently.
The research team employed X-ray crystallography to analyze the microstructure of eggshells from various modern paleognath birds, including ostriches, rheas, emus, cassowaries, kiwis, elephant birds, and moas. Fossilized eggshells from these birds, as well as eggs from bird-like dinosaurs, were also analyzed. To provide a comparative perspective, the eggshells of a few modern flighted birds were included in the study.
The analysis revealed that the wedge-like microstructures found in rhea eggshells can be traced back to ancient ancestors of paleognath birds. On the other hand, the prism-like microstructures of ostrich and tinamous eggs likely evolved independently at a later stage.
Choi emphasizes that understanding the evolutionary pattern of paleognath eggshells can aid ornithologists in deciphering the evolution of eggshells among this group of flightless birds.
Moreover, the insights gained from this study, along with the techniques used, may prove valuable to paleontologists studying bird-like, egg-laying dinosaurs from the Mesozoic era. Given that paleognath eggshells are frequently found in ancient human settlements, they may also provide useful information to archaeologists investigating the ways in which ancient humans utilized eggs for sustenance or artistic purposes, owing to their robust nature.
Senior author David Varricchio, a professor of paleobiology at Montana State University, highlights the potential for genetic and microstructural analysis of these living fossil’s eggshells to contribute to our understanding of bird and dinosaur evolution, as well as shed light on the interactions between early humans and these fascinating creatures.