text:  In the <unk> stage of the Late <unk> ( 228 @.@ 0 - 216 @.@ 5 <unk> ) , <unk> were joined by the superficially very similar <unk> . <unk> are distinguished from <unk> by the positioning of their eye <unk> near the front of their skulls . Another group of <unk> , the <unk> , had wide heads with external gills , and adapted to life at the bottom of lakes and rivers . By this time , <unk> had become a common and widespread component of <unk> ecosystems . Some <unk> , such as <unk> and <unk> , even inhabited Antarctica , which was covered in temperate forests at the time . 
  