Switzerland – A research published Friday in the journal Science Advances has found that feathers and hair share a genetic origin, the same from the reptile scales. A single specimen seems to be the ancestor of all three structures: a reptile that lived more that 300 million years ago.
A team from the University of Geneva and the Swiss Institute of Bioinformatics found a series of similar microscopic structure on the skin of embryos of a bird, a hairy mammal, and a reptile. These structures are the placodes, which are minuscule bumps of thick tissue of the skin.
It was already known that mammalian hairs and avian feathers both developed from almost identical structures. This finding meant a mystery for scientists and biologists because mammals and birds evolved from reptilian lineages distant from each other, leading to the idea of these species independently developing placodes. Other studies on modern reptiles found no evidence of placodes on their skin.
Because of their delicate origin, there is a lack of samples of preserved skin, which had impeded deeper studies of the link between scales, feathers and hair. But the survey revealed on Friday shows that scales in reptiles do develop placode and that it shares the same anatomical and molecular signatures of placodes of feathers and hair. They found the structure on bearded dragons, Nile crocodiles, and corn snakes.
Common embryonic route between hairs, feathers and scales confirmed
Professor Michel Milinkovitch, the evolutionary geneticist leading the study, stated that their new data complements the study of last year made by a team at Yale, according to Daily Mail. The new findings include new molecular signatures in reptiles “that are identical to those observed during the development of hairs and feathers, as well as the presence of the same anatomical placode as in mammals and birds.” This shows that, regardless of their contrastive shape, feathers, hair, and scales evolved from the scales of a common ancestor, specifically a reptilian.
In the study, researchers focused on three varieties of bearded lizards: one with standard sized levels, one with smaller scales, and the third one without scales.
A gene called ectodysplasin-A (EDA) is the responsible for the development of the concentrations in the bearded lizards. In the lizard with standard sized scales, two functioning copies of the gene are present. In the lizard with smaller scales, there was found only one working copy. The third one does not have a functioning copy of EDA, which inhibits the develop of scales. Analysis showed later that in the third type of lizard, EDA failed to set in during the embryonic stage, impeding the formation of placodes.
EDA is also found in mammals and birds, and they can develop problems growing hair or feathers because of a genetic mutation as well. Mice and even humans present abnormalities in the development of teeth, nails and hair when a mutation on EDA occurs.
To Milinkovitch, this finding is particularly interesting because feathers, fur, and scales are essential features that allow the identification of the different species. But it was concluded that they have a common ancestor. Marcelo Sánchez-Villagra, a professor at the University of Zurich, told Discovery News that this common ancestor would not be precisely a reptile, but an animal with reptilian features that lived 330 million years ago, according to Seeker.com. The divergence of the structure came with evolution and mutation.
Evidence has been registered through the years that some species of dinosaur may have been covered in feathers.