"This phenomenon, where a change in the developmental timing of a creature produces morphological changes is called heterochrony, and paedomorphosis is one example of it," Abzhanov explained. "In the case of birds, we can see that the adults of a species look increasingly like the juveniles of their ancestors."
In the case of modern birds, he said, the change is the result of a process known as progenesis, which causes an animal to reach sexual maturity earlier. Unlike their dinosaurian ancestors, modern birds take dramatically less time just 12 weeks in some species to reach maturity, allowing birds to retain the characteristics of their juvenile ancestors into adulthood.
"This study is a prime example of the heuristic power in multidisciplinary, specimen-based, anatomical research," said Gabe Bever of NYIT's New York College of Osteopathic Medicine and a co-author of the paper. "That the mechanisms of evolutionary events millions of years old can be circumscribed with this combination of modern and fossil specimens is remarkable."
Ultimately, Abzhanov said, the way the bird skull evolved through changes in the developmental timeline highlights the diversity of evolutionary strategies that have been used over millions of years.
"That you can have such dramatic success simply by changing the relative timing of events in a creature's development is remarkable," he said. "We now understand the relationship between birds and dinosaurs that much better, and we can say that, when we look at birds, we are actually looking at juvenile dinosaurs."
"It shows that there's so much for evolution to act upon," Bhullar agreed. "When we think of an organism, especially a complex organism, we often think of it as a static entity, but to re
|Contact: Peter Reuell|