 Such was the case when Herbert E. Gregory referred "Rutiodon gregorii" to "Nicrosaurus".In the early 1960s, Gregory did not recognize the differences among phytosaurs like "Machaeroprosopus", "Leptosuchus" and "Rutiodon" and attributed the variance to growth, sexual dimorphism or individual variance.Most of the species of "Machaeroprosopus" were assigned to "Rutiodon" except for "M. gregorii" which was assigned as "Phytosaurus gregorii" because of the attributes it shared with European phytosaurs.