Its type species is Rhamphosuchus crassidens, which is only known from incomplete sets of fossils, mostly teeth and skulls.

[3] Another crocodylian, Purussaurus, from the Miocene of Peru and Brazil, is known from an equally incomplete fossil set.

If the most recent estimate is correct, then several other extinct crcoodilians and crocodylomorphs likely surpassed Rhamphosuchus in weight , such as the Late Cretaceous alligatoroid Deinosuchus, the Early Cretaceous pholidosaurid Sarcosuchus and the Miocene gavialid Gryposuchus, at 10.6 m, 9.5 m and 10 m, respectively.

Rhamphosuchus was previously regarded as a close relative of the modern false gharial within the subfamily Tomistominae.

However, Tomistominae in its traditional sense is now known to be paraphyletic, and a 2022 study by Iijima and colleagues recovered Rhamphosuchus as a derived member of the subfamily Gavialinae instead.