On this entry of Prehistoric Kingdom Candidates, some of the most well-known creatures from the early Palaeozoic; Pterygotus, Arthropleura, Ichthyostega and Stethacanthus. Description and poll in the comments.
@ChIkEn NuGrEt I must admit that, with one exception, I mostly focused on non-dinosaurian animals. But adding some lesser-known species, especially from Gondwana, is a good idea, definitely worth considering.