Usually scaled, the skin of fish can also be naked or made up of bony plates. Researchers have reconstructed the evolution of the skin structures in fish, going back to the common ancestor, more than 420 million years ago. They found that only fish that had lost their scales were able to develop a bony armor, and that the protective state of their skin influenced their choice of open water or sea floor habitats.
Click here for original story, Scaled, armored or naked: How does the skin of fish evolve?
Source: ScienceDaily