All modern birds that can fly have a special wing structure called the propagium, without which they cannot take off into the air.. The evolutionary origin of this organ remains a mystery, but new research shows that evolved from non-avian dinosaurs. The finding was made possible by statistical analysis of the limb joints preserved in fossils, and helped fill some of the knowledge gaps about the origin of bird flight.
We have long known that modern birds evolved from certain lineages of dinosaurs that lived millions of years ago. This makes researchers understand that birds have feathers, bone structure, etc. This led to the study of extinct animals to explain some of their unique features, such as However, there is something special about bird wings in particular that has piqued the interest of researchers at the Department of Earth and Planetary Sciences at the University of Tokyo.
“A bird’s wing has a structure at the front end called the propagium. a muscle that connects the shoulder to the wrist, helps flapping wings and enables the bird to fly“explains associate professor Tatsuya Hirasawa.
“It is not found in other vertebrates and has also been found to be lost or lost function in flightless birds, so we know it is necessary for flight. Therefore, to understand how flight evolved in birds, we need to know how dispersal evolved. This is what prompted us to discover some of the distant ancestors of modern birds, the theropod dinosaurs.” ”
Theropod dinosaurs, for example tyrannosaurus rex And VelociraptorIt had arms but no wings. If scientists can find evidence of an early reproduction in these dinosaurs, it would help explain how the modern bird branch of the tree of life made the transition from arms to wings.
Difficulty finding propagation in fossils
But it’s not that simple, because propagium consists of soft tissue that does not fossilize well, so direct evidence of its existence may not be found.. Therefore, the researchers had to find an indirect way to determine the presence or absence of spread in each sample.
“The solution we found to assess the presence of a span was to collect data on joint angles along the arm or wing of a dinosaur or bird,” said Yurika Uno, a graduate student in Hirasawa’s lab.
“In modern birds, the wings cannot be fully extended due to reproduction.restricts the possible range of angles between connecting sections. If we can find a similarly specific set of angles between joints in dinosaur specimens, we can be pretty sure that they also had a spread. “Through quantitative analyzes of fossilized bird and non-dinosaur postures, we found the distinct ranges of joint angles we expected.”
Building on this clue, the team discovered that the dispersal likely evolved into a group of dinosaurs known as maniraptoran theropods. including the famous Velociraptor. This was confirmed when researchers described the spread in preserved soft tissue fossils, including those of the feathered oviraptorosaurus. caudipteryx and the winged dromaeosaur germ hunter. All the specimens they found existed in this lineage before the evolution of flight.
This research means When the spread occurred is now known, leading researchers to the next question: how did it come about? Why these particular theropod species need such a structure to better adapt to their environment may be a more difficult question to answer.
The team has already begun investigating possible links between the fossil evidence and the embryonic development of modern vertebrates to see if it sheds some light on the matter. The team also believes that some theropods may have evolved dispersal, but not because of any pressure to learn to fly, as their forelimbs are built to grasp objects, not fly.
“Dinosaurs portrayed in the media are getting more and more accurate,” Hirasawa said. “At least now we can see features like feathers, but hopefully soon we can see a more up-to-date representation where theropods also have their propagium.”
Reference work: https://zoologicalletters.biomedcentral.com/articles/10.1186/s40851-023-00204-x#Fig1
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