No link has been found from fish to amphibians, amphibians to reptiles, reptiles to mammals, etc. It is impossible, given the evolutionists' time scale of millions of years, that not one intermediate could be found. Examples of animals once held up as intermediates have systematically been thrown out. Archaeopteryx is now widely admitted to be a bird, plain and simple, complete with feathers. Using Archaeopteryx as an example, scientists now know that the problem of getting a reptile to evolve into a bird is horrendously problematic.
Scales are merely folds in the epidermis, while feathers and hairs develop from follicles.
To get from a reptile to a bird, you need more than feathers. A bird has very different respiratory, cardiovascular, muscular, and gastrointestinal systems than a reptile. At this point one has run into the problem of irreducibly complex systems. But the problem is more than just a few critters in the fossil record that don't appear to fit neatly into well-defined classifications. Darwin's theory implied not merely that fossil transitionals would be found, but it predicted that a truly complete fossil record would be mostly transitionals.