text:  Several groups of <unk> have large bony plates on their backs . One <unk> , <unk> , has armour @-@ like plating that covers both its back and underside . The <unk> <unk> also has extensive plating on its back . Most members of the family <unk> also have armor , although it only covers the midline of the back with two narrow rows of plates . Other <unk> , such as <unk> , have been found with small , disc @-@ like bony <unk> that were in life probably embedded in the skin . All of these <unk> were adapted to a terrestrial lifestyle . Armor may have offered protection from predators in the case of <unk> . The <unk> may have provided stability for the spine , as they would have limited flexibility and may have been connected by strong ligaments . <unk> such as <unk> and <unk> that may have been at least partly terrestrial also have long neural spines on top of their vertebrae that would have stabilized the spine . <unk> <unk> are also seen in <unk> , but unlike <unk> , <unk> , <unk> , and <unk> , these animals are thought to have been fully aquatic . <unk> may have inherited their armor from a terrestrial ancestor , as both <unk> and <unk> have been considered close relatives of the group . 
  