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Skin hair feathers scales

Source: TW

This work suggests that stem mammals had scaly skin like that seen in reptiles today. It seems that hair emerged only later in the mammalian lineage. But when exactly remains unclear. One possibility is that hair in pan-mammalia and feathers in pan-reptilia emerged relatively late and under the same selective pressures https://cell.com/current-biology/fulltext/S0960-9822%2825%2900574-3