 However, at the time specimen were often referred to specific genera based on character similarities without giving much regard to the differences.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.