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The Link Between Fur, Feather And Scales

A close-up photo on feathers going many different directions

Scales, feathers, and fur seem so different from each other. So how could have mammals, birds, and reptiles evolved from a common ancestor?

In 2016 a duo of European scientists published findings showing that scales, feathers, and fur, are different forms of the same structure. They found out by studying embryos.

Embryonic development can often reveal hidden similarities between animals that seem very different. Scientists have known for a long time that both bird and mammal embryos develop a pattern of specialized thickenings on their skin called placodes.

And Reptiles Too

Scientists know they really are similar because placodes in birds and mammals express some of the same genes and signaling pathways. The placodes in birds develop into feathers, and those in mammals develop into hair. The European researchers found that placodes in some reptiles were also the same.

Using special molecular probes to label them, they found that there are also placodes in the skin of the embryos of crocodiles, lizards, and snakes. They were hard to find, because scales develop quickly, so the placodes only last for just a short time.

The findings show that the common ancestor of modern reptiles, birds, and mammals, 350 million years ago, already had these placodes. This means that fur and feathers are heavily modified scales.

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