Stenopterygius Quadrisicissus is a specific species of ichthyosaur, a type of prehistoric marine reptile. As such, there are no direct synonyms for this specific name. However, there are other ichthyosaur species that may be referred to by similar names, such as Stenopterygius longifrons or Stenopterygius quadriscissus. Additionally, there are many other prehistoric marine animals with similar names and appearances, such as the Plesiosaur and Mosasaur. While there are no direct synonyms for this specific species, there are many fascinating creatures from the prehistoric ocean that can be explored and studied.