Skull Island is home of a tribe of lizardfolk who have mastered the domestication of many ancient creatures, such as the woolly rhino, the triceratops, and the tyrannosaurus rex. How they did so was a mystery, especially given that they are, individually, extremely physically weak.
Their leader was a summoner with three times the power of a single lizardfolk. Shortly before his death at the hands of Riz Xepiroth, he was able to summon a pair of powerful elementals, who were also killed by Riz, Balkaran, and Kiroku.
The current power structure on Skull Island is unknown, as no non-lizardfolk have set foot upon sit since their leader was killed.