Mexico City. Modern birds capable of flight have a wing structure called a propagation that allows them to soar through the air. The evolutionary origin of this system had remained a mystery, but new research suggests that it may have come from non-avian dinosaurs. The findings come from statistical analysis of arm connections preserved in fossils.
For the Department of Earth and Planetary Sciences of the University of Tokyo, in charge of the study published in the journal Zoological Letters, there is something special in terms of evolution. “At the top of a bird’s wing is a structure called a propagation that contains a muscle that connects to and twists the shoulder, facilitating flapping and making flight possible for the bird,” explained Tatsuya Hirasawa, an associate professor of that house of studies
“It is not found in other vertebrates, and its functions have been found to be missing or lost in flightless birds. So to understand the evolution of flight in birds we must know how the propagation did. This was what prompted us to explore some distant ancestors of modern birds, the theropod dinosaurs,” the researcher said.
This type of dinosaurs, among which are the tyrannosaurus rex and the velociraptor, they had arms instead of wings. If scientists were to find evidence of an early example of propagation in these animals, it would help explain how the modern avian branch of the tree of life moved from arms to wings. However, the tissues that make up this structure are soft, so suitable fossil remains would not be possible to find.
Instead of studying fossils, the researchers had to find an indirect way to identify the presence or lack of a propagation in the specimens. “The solution we came up with to determine the presence of such a structure was to collect data on the joint angles along the arm, or the wings, of a bird or dinosaur,” said Yurika Uno, a graduate of Hirasawa’s lab.
“In modern birds the wings cannot be fully extended due to propagation, which blocks the range of angles possible between the connected sections. If we could find just as specific a set of angles between joints in dinosaur specimens, we could be pretty sure they too had that structure, and through quantitative analyzes of fossilized bird and non-dinosaur postures, we uncovered the telltale ranges. of the joint angles that we expected”, he added.
Based on their findings, the team suggests that propagation likely evolved in a group of dinosaurs known as manirraptor theropods, including the famous velociraptor. The theory is supported by the identification of the structure in preserved soft-tissue fossils, with all samples analyzed predating the evolution of flight in that lineage.
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