 <unk> larvae are often distinguished by poorly developed bones and the presence of a <unk> apparatus , a series of bones that gills would attach to in life . However , some fully mature <unk> also possess <unk> bones but did not have external gills . A dense covering of scales is also seen in larvae and adults . Major body changes occur in <unk> , including the <unk> and strengthening of skull bones , the <unk> of <unk> bones , and an increase in body size . 
