Brazilian researcher Joâo Botelho has successfully achieved an experimental reversal to produce a dinosaur-like trait in birds. The scientist inhibited a maturation gene in a chicken, causing it to develop with leg bones that resemble those of its prehistoric ancestors.
This experimental achievement is reminiscent of paleontologist Jack Horner’s TED talk, “Building a Dinosaur From a Chicken,” but the scientists contend that their goal is to understand the genetics of the transition between theropod dinosaurs and modern birds.
Every chicken possesses a long, spine-like bone in the drumstick, known as the fibula, which is one of the two long bones of the lower leg. The bone in dinosaurs, however, is tube-shaped and reaches all the way down to the ankle.
As dinosaurs evolved into birds, the fibula lost its lower end, and no longer connected to the ankle. It eventually became shorter than the other bone in the lower leg, the tibia.
Scientists have known for some time now that bird embryos first developed tubular, dinosaur-like fibula, which eventually would become shorter than the tibia. That is when it acquires its adult, splinter-like shape.
While working at the lab of Alexander Vargas at the University of Chile, Botelho noticed this change, inspiring him to study the mechanisms that underlie this transformation. He found that molecular mechanisms of maturation were active early at the lower end, ceasing cell division and growth. Inhibiting a maturation gene (Indian Hedgehog) resulted in the tubular fibula and the tibia developing in an identical way to a dinosaur’s.
This is different from normal bone development, in which the shaft matures and ceases growth long before the ends do.
Botelho and the rest of his team believe that the early growth at the lower end of the fibula occurs because of the influence of a nearby bone in the ankle, the calcaneus. The calcaneus in bird embryos presses against the lower end of the fibula, a process different than any other animal.
Botelho believes that at this stage, the lower end of the fibula receives signals more similar to those at the bone shaft. During normal development, the calcaneum will then become detached from the fibula. However, its distal end has already become committed to shaft-like development, maturing early.
In the chickens with experimentally dinosaur-like lower legs, the calcaneum was attached to the fibula. Botelho confirmed the calcaneum strongly expresses a gene that allows growth at both ends of the bones.
“The experiments are focused on single traits to test specific hypotheses,” says Vargas. “Not only do we know a great deal about bird development, but also about the dinosaur-bird transition, which is well-documented by the fossil record. This leads naturally to hypotheses on the evolution of development, that can be explored in the lab.”
The results of this study can be found in the academic journal Evolution.