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~ Message from a graduate student~.
Dinosaur Evolution in the Embryogenesis of Chickens


Yurika Uno
Department of Earth and Planetary Science, 2nd Year Doctoral Student
Niigata Prefecture
High School:
Niigata High School
Faculty of Science, Ochanomizu University


When I was a nursery school student, I saw the movie "Jurassic Park", which seemed to be the beginning of my interest in dinosaurs. I felt an inexpressible fascination for the huge, terrifyingly beautiful, extinct animals on the screen that I could never actually see with my own eyes. However, when I told people that I liked dinosaurs, they would say things like, "That's unusual for a girl," or "It's surprising that you like dinosaurs. For more than 20 years since then, I have continued to say that I like dinosaurs. As a result of my persistent persistence, I am now studying dinosaurs, which I had longed to do.

Many of you may have heard that the ancestors of birds can be traced back to dinosaurs. Birds emerged from the lineage of dinosaurs about 150 million years ago and still survive today. One of the major differences between dinosaurs and birds is the difference between their free-use forefeet and wings that flap in the sky. Dinosaur forefeet and bird wings are very different in appearance. However, avian wings are nothing but a modified form of dinosaur forefeet, and there are many similarities in their basic structure. On the other hand, there are some structures that make birds' forefingers wings. One such structure is the "pre-wing membrane," a membrane structure stretched over the anterior margin of the wing. In addition to feathers, the anterior wing membrane provides lift when the bird flaps its wings.

When in evolution did the formation of the anterior wing membrane open the door for flapping wings into the sky? The key to answering this question lies in the fossil record. However, in most cases, what remains in the fossil record are hard tissues such as bones, and it takes some ingenuity to study soft tissues from fossils. This is where we, as researchers, have to show our skills. In this study, I focused on "posture preserved in fossils". In present-day birds, the elbow cannot be extended beyond a certain angle because the anterior wing membrane connects the shoulder and wrist. Therefore, animals with an anterior wing membrane are expected to have elbow joints that do not exceed a certain angle even if they are preserved as fossils in sediments after death. Based on this prediction, the analysis of fossil postures suggests that anterior wing membranes were already formed at the stage of dinosaurs, before birds ( Press Release on February 27, 2023 ).

Then, how did the anterior wing membrane newly form during evolution? To answer this question, I am looking into the egg of a chicken. I observe the process of body formation from the fertilized egg through cell division and tissue differentiation at the cellular and genetic levels. The process is truly complex and mysterious, and I am always impressed by what I see. In the early stages of development, there are no wing-like structures visible in the chick embryo, but only the sprouts of the fore-foot, which are shaped like fish balls. After a few days of elongation, the elbow bends and the fingers begin to appear, and the anterior wing membrane appears on the anterior margin of the fore-foot. If we can elucidate the mechanism of the formation of the anterior wing membrane, we will be able to determine what kind of changes occurred in the forefingers of our distant ancestors, the dinosaurs.

A, Anterior wing membrane of birds. When a hole is made in the egg, an embryo lying on the yolk can be seen. The upper left of each photo shows the number of days after the fertilized egg was first warmed at 38ºC. After about the 7th day, the shape of the anterior wing membrane becomes clear.

Research is an activity to find out the truth that has not yet been seen by anyone before anyone else. If you are a stubborn person with strong intellectual curiosity, I hope you will continue to be stubborn and join this activity.



The Rigaku-bu News, January 2024

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