In his landmark 1967 work "Systematics and Morphology of American Mosasaurs", Dale Russell performed a complete review and redescription of "Tylosaurus". In a taxonomic examination, Russell found little justification for recognizing the validity of "T. dyspelor" and declared it a "nomem vanum", along with recognizing "T. micromus" as a junior synonym of "T. proriger". Many of the complete skeletons formerly assigned to the former taxon were reassigned to the type species. "T. nepaeolicus" was affirmed as a distinct species. Russell (1967) provided extensive diagnoses of "Tylosaurus" that are still used by scientists today, and Everhart remarked that the work "remains the single best reference regarding the skeletons of the various mosasaur genera" like "Tylosaurus".