Fossil evidence from some ophiacodonts shows that parts of the skin was naked , but that the belly was covered in dermal scutes . These scutes looked like the scutes present in reptile groups , but they are of a different type of structure . Fossil evidence from some ophiacodonts shows that parts of the skin was naked , but that the belly was covered in dermal scutes , looking like the scutes present in other reptile groups , which are of a different type of structure .