Chicks (baby of chickens) and ducklings seem to have fine hairs, at least something that look like hairs to me. Most mammals have hairs, but reptiles, fish, or other animal groups do not have hairs as far as I know.
I have looked up the tree of evolution, and it looks like this.
So, the tortoises, crocodiles (I do not know what lepidosauria means but I guess it is reptiles other than the aforementioned), and birds diverged after their common ancestor was split from the common ancestor of mammals.
Since none of the tortoises, lepidosauria, or crocodiles have hairs now, does this mean that the hair of birds and mammalian hair is an example of convergent evolution? Or did these other taxa lose hair during evolution?