Scientists at Tohoku University say they have resolved the biggest bone of contention in the theory that birds evolved from dinosaurs.
Koji Tamura, a professor of life sciences, led the group that found similar finger configurations between birds and dinosaurs. Their findings will be posted from Friday on the electronic version of the U.S. journal Science.
The theory that birds evolved from dinosaurs, particularly two-legged theropods, had been widely accepted. However, questions remained because the fingers of the theropods and birds did not match up.
Studies of fossils have led researchers to conclude that the ring and little fingers of theropods had gradually degenerated over time, leaving them with only three fingers–the thumb, index and middle fingers.
However, from an embryological standpoint and based on the position of the original form of the fingers in the wings of birds, the three fingers of the birds are believed to be the index, middle and ring fingers.
The different views of the fingers based on the paleontological and embryological viewpoints have been a key argument against concluding that birds evolved from dinosaurs.
Tamura’s group, which studied the development of and gene movement in chicken eggs from about the third day after fertilization, say they have resolved the discrepancy.
The group found that in the initial stages of development, clusters of cells that become the original form of fingers in the wing are located in the positions for the index, middle and ring fingers.
Although scientists believed the fingers grew in those positions, Tamura’s group confirmed that as the chicken’s fingers in the wing were developing, they shifted by one position and grew into the thumb, index and middle fingers, similar to the finger configuration of dinosaurs.
“By clarifying the ‘shift,’ we were able to resolve the embryological discrepancy in the theory about the origin of birds and were able to show a smooth evolution from dinosaurs to birds,” Tamura said.
Makoto Manabe, a senior researcher at the National Museum of Nature and Science, said about the finding: “This resolves the largest issue that still remained about the theory that birds evolved from dinosaurs. It is also important because it clarified the evolutionary process through an embryological manner that would not have been discovered through fossils.”
Author: Ryolo Takeishi | Source: Asahi [February 12, 2011]