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Scientists have found the link between mammal hair, bird feathers, and reptile scales, which they say resolves the decades-long scientific debate as to how these skin coverings evolved. 

Previously, according to a report on the PBS NewsHourscientists were divided over how feathers, scales and hair evolved. The community knew that birds and mammals developed so-called placodes, thick skin in which feathers and hair grow out of, but reptiles didn’t have such a feature on its skin, creating a kink in the evolution of skin coverings.


Because of the lack of the placode in reptiles, two views in the scientific community emerged (but of course). One view was that hair, scales, and feathers developed independently in the animal world, while the other camp said that all species have a molecular placode in their genetic makeup, genes that enable a given species to grow hair, feathers, or scales. 

These two camps had divergent views for decades until researcher and geneticist Michel Milinkovitch of the University of Geneva happened upon a naked lizard, a bearded dragon (Pogona vitticeps) that completely lacked scales, PBS NewsHour reported. 

Milinkovitch and Biologist Nicolas Di-Poï of the Institute of Biotechnology at the University of Helsinki researched the naked reptile and determined that it lacked ectodysplasin-A (EDA), the placodes that forms skin appendages, or in the case of the naked beardie, scales.

The two scientists then did a comparison of three bearded dragons. They looked at a “normal” bearded dragon that has scales, a cross between a normal bearded dragon and a scale-less bearded called a heterozygous mutant, and a homozygous mutant, which completely lacks scales.

They found that the naked bearded dragon has no EDA at all, while the normal bearded dragon possessed the highest concentration of EDA. This threw the previous notion that reptiles lack placodes on its head. They determined that reptiles do in fact have physical placodes. 


Milinkovitch told PBS News Hour that the placodes were always present in reptiles. Science just had to find them. 

The study notes that all amniotes, those animals whose eggs feature an extra layer of protection, can be traced back to a common reptilian-like ancestor. 

“We have this deep heritage between reptiles, birds and mammals — a 320 million year old heritage,” Milinkovitch told PBS News Hour

Of course many things in science has its detractors. Jacob Musser, an evolutionary biologist with the European Molecular Biology Laboratory in Germany, says that while the Milinkovitch and Di-Poï findings are important with regard to the evolutionary development of placodes, the notion that all three skin appendages (feathers, scales, and hair) come from a common reptilian ancestor may not necessarily be true. 


“Their findings suggest that even though these structures look very different, they may have evolved from a common structure in the ancestor of reptiles and mammals,” Musser told PBS NewsHour. “But what this structure actually looked like is unclear. It may not have been a scale.”​​