Complex sentence: A varanid lizard fossil sampled for the study showed isotopic variation consistent with being an heterothermic ectotherm, whereas that of the dinosaurs, including "Achelousaurus", it was consistent with them being homeothermic endotherms.
Split into simpler sentences: A varanid lizard fossil sampled for the study showed isotopic variation consistent with it being an heterothermic ectotherm. The variation of the dinosaurs, including "Achelousaurus", was consistent with them being homeothermic endotherms.