The Plesiosauria are a group of aquatic reptiles lived from the Late Triassic to the latest Cretaceous. Their four limbs were modified into flippers, and there are no significant differences in the size and shape of fore and hind limbs. Due to this unique body structure, it has been assumed that plesiosaurs may have performed a unique swimming style. However, the adaptive locomotor patterns of plesiosaurs is still unclear. To reveal their locomotion, we introduce a perspective of control principle underlying adaptive animals’ behaviors. This is because producing adaptive behaviors that respond to surrounding environments and morphology could be indispensable for animals of any era to survive. In this approach, we develop extinct-animal-like robots and establish a control mechanism which can create physically rational locomotor patterns for unique morphologies of extinct animals through robot experiments. In this paper, we have constructed a platform as the first step to investigate coordination mechanism between flippers in plesiosaur locomotion.