Were they developed anew or a heritage from fish?
Pangolin scales are certainly not retained from fish. Pangolins are within the clade Pholidota (Tree of Life page for Eutheria) and their nearest relatives are anteaters, sloths, and armadillos.
According to the University of California Museum of Paleontology, similarities between pangolin and armadillos are the results of convergent evolution. So the pangolin scales are a new feature that arose somewhere on the lineage leading to pangolins.
1$\begingroup$ were they developed from hair or from skin folds? $\endgroup$– AnixxFeb 23, 2012 at 2:05
1$\begingroup$ They are keratinous scales, like hair and claws/nails. I'd suspect similar development to nails, but I'm not sure. $\endgroup$– kmmFeb 23, 2012 at 3:41
$\begingroup$ Their closest relatives are carnivores, not anteaters, sloths, and armadillos. See DOI: 10.1186/1471-2148-6-93. $\endgroup$– mgkrebbsDec 22, 2015 at 17:23