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The evolution of horny scales in the Permian era

A fossil from the Polish Permian reveals the common origin of horny scales among terrestrial vertebrates, supporting the importance of keratin in animal evolution.

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Published in 
 · 24 May 2024
The scales on this lizard playing dead look a lot like those left behind by a reptile and mammal anc
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The scales on this lizard playing dead look a lot like those left behind by a reptile and mammal ancestor.

Horny scales, commonly associated with reptiles, have played a crucial role in our evolution, contributing to the formation of fur and feathers. A new fossil discovery provides evidence that scales evolved in the Permian era, before the great divergence of land vertebrates.

Scales are essential for maintaining the separation between the inside of an organism and the outside world. In fish, this task is carried out by a layer of scales on the skin, adapted to their aquatic environment. In terrestrial vertebrates, diversity is greater, but a rich fossil record suggests a common origin for scales.

The Permian fossil from Bieganów, Poland is extraordinary for several reasons. The plate contains hundreds of belly prints, some so detailed that they clearly show the imprint of scaly skin. These footprints are attributed to a diadectid, ancestor of amniotes, which includes reptiles, mammals and birds.

Horny scales, composed mainly of keratin, appear to have been present since the beginning of amniotes. Keratin is a versatile protein, found in nails, hair, feathers, beaks and other structures of many animals. Without keratin, the animal world would be radically different.

Although most amphibians have developed other strategies for protection, some also have horny scales. This raises the question of whether scales appeared independently or predated the split between amphibians and amniotes.

Fossilized impressions of the scales suggest that they were hard and well-defined, typical of keratinous structures. This supports the hypothesis that horny scales have a common origin between diadectids and amphibian ancestors.

The study ( was published in Biology Letters and opens new perspectives on the evolutionary history of horny scales.

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