Molecular experiment reverses evolution in birds obtaining a dinosaur-like lower leg
|Portrait of a chickensaur [Credit: Christopher Smka]|
Botelho and collaborators believe that early maturation at the lower end of the fibula occurs because of the influence of a nearby bone in the ankle, the calcaneum. Unlike other animals, the calcaneum in bird embryos presses against the lower end of the fibula: They are so close they have even been confused with a single element by some researchers. Botelho proposes that at this stage, the lower end of the fibula receives signals more like those at the bone shaft. In normal development, the calcaneum then becomes detached from the fibula. However, its distal end has already become committed to shaft-like development, and matures early. In the chickens with experimentally dinosaur-like lower legs, the calcaneum was still attached to the fibula. Botelho also confirmed the calcaneum strongly expresses PthrP, a gene that allows growth at the ends of bones.
The results of the entire study have been published in the journal Evolution. This is the second time Botelho has achieved an experimental reversal to a dinosaur-like trait in birds. Previously, he had managed to undo the evolution of the perching toe of birds, to produce a non-twisted, non-opposed toe, as in dinosaursand another lab at Yale obtained a dinosaur-like snout by altering gene expression in embryonic chickens. However, these studies are not aimed to producing dinosaurs for commercial or non-scientific purposes, as in the "Jurassic Park" movie series.
"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."
Source: Universidad de Chile [March 08, 2016]