Acanthodians

Acanthodii or acanthodians (sometimes called spiny sharks) is a paraphyletic class of extinct fish, sharing features with both bony fish  and cartilaginous fish. In form they resembled sharks, but their epidermis was covered with tiny rhomboid platelets like the scales of holosteans (gars, bowfins). They represent several independent phylogenetic branch of fishes leading to the still-extant Chondrichthyes.