Studies show that hairs, feathers and scales aren't so different at all.
The potential evolutionary link between mammal's hairs, bird's feathers, and reptile's scales has been debated for decades. However, today's researchers of the University of Geneva, and the SIB Swiss Institute of Bioformatics, Switzerland, demonstrated that all these skin appendages are homologous or share a common ancestry.
Swiss biologists discovered that the molecular and micro anatomical signatures are identical between hairs, feathers and scales at their early developmental stages.
These observations were published today in Science Advances, which indicated that the three structures evolved from their common reptilian ancestor.
Mammalian hairs and avian feathers develop from a similar primordial structure caled a 'placode', a local thickening of the epidermis with columnar cells that reduce their rate of proliferation and express very specific genes.
But birds and mammals are not sister groups since they evolve from the different reptilian lineages. According to previous studies, reptiles' scales do not develop from an anatomical placode, which implies that birds and mammals have independently 'inverted' placodes during their evolution.
They also identified in reptiles new molecular signatures 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 indicates that the three types of skin appendages are homologous, which also proves that the avian feathers and the mammalian hairs, despite their very different features, evolved from the scales of their reptilian common ancestor.
During the new study, researchers investigated the bearded dragon, a species of lizard that comes in three variants. The first is the normal wild-type form. The second has scales of reduced size because it bears one copy of natural genetic mutation. And the third has two copies of the mutation which lacks all scales.
By comparing the genome of those three variants, it was identified that the peculiar look of these naked lizards is due to the disruption of the ectodysplasin-A (EDA), a gene whose mutations in humans and mice are known to generate substantial abnormalities in the development of teeth, glands, nails and hairs.
The Swiss researchers have demonstrated that, when EDA is malfunctioning in lizards, they fail to develop proper scale placode, exactly as mammals or birds affected with similar mutations in that same gene develop proper hairs or feathers placodes.
These future studies will hopefully give us further understanding on the complexity and the diversity of life during evolution.
Source: PHYS ORG Science Daily
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