M. validus was first described and named by Maurice G. Mehl in Mehl et al.,
in 1916 on the basis of the holotype UW 3807, a complete skull, and the two paratypes UW 3808 and UW 3809, partial skulls, from Norian-aged Upper Petrified Forest Member of the Chinle Formation, Coconino County of Arizona.
The skulls have been lost since the 1950s, and a line drawing in the original 1916 description is the only visual record of the specimen.
M. validus, once thought to be the type species of Machaeroprosopus, was suggested by some authors to represent the same species as Pseudopalatus pristinus.
If this is the case, the name Machaeroprosopus would have precedence over Pseudopalatus because Pseudopalatus was named in 1928, twelve years after Machaeroprosopus was named.
Long and Murry (1995) erected a new genus for Belodon buceros, not knowing that it was in fact the type species of Machaeroprosopus (and not M. validus), creating Arribasuchus buceros.
They also suggested that M. validus might be a junior synonym of A. buceros.

Until recently, M. validus was considered to be the only species of Machaeroprosopus that has not been reassigned.
Thus, Machaeroprosopus was considered to be a nomen dubium or "doubtful name" because of the lack of diagnostic specimens that can support its distinction from other phytosaur genera.
However, a taxonomic revision of Machaeroprosopus, conducted by Parker et al. (
in press), revealed that UW 3807 is not the holotype of Machaeroprosopus, while the previously named species Pseudopalatus buceros has priority as the type species of the genus.
Therefore, the name Pseudopalatus was considered a junior synonym of Machaeroprosopus, and all species of the former were reassigned to the later.
This revised taxonomy was already accepted in several studies, including Stocker and Butler (2013).
Stocker and Butler (2013) also treated M. validus as a possibly valid species, and not a junior synonym of Machaeroprosopus buceros as was previously suggested by Long and Murry (1995).
M. validus was first described and named by Maurice G. Mehl in Mehl et al., in 1916 on the basis of the holotype UW 3807, a complete skull, and the two paratypes UW 3808 and UW 3809, partial skulls, from Norian-aged Upper Petrified Forest Member of the Chinle Formation, Coconino County of Arizona. The skulls have been lost since the 1950s, and a line drawing in the original 1916 description is the only visual record of the specimen. M. validus, once thought to be the type species of Machaeroprosopus, was suggested by some authors to represent the same species as Pseudopalatus pristinus. If this is the case, the name Machaeroprosopus would have precedence over Pseudopalatus because Pseudopalatus was named in 1928, twelve years after Machaeroprosopus was named. Long and Murry (1995) erected a new genus for Belodon buceros, not knowing that it was in fact the type species of Machaeroprosopus (and not M. validus), creating Arribasuchus buceros. They also suggested that M. validus might be a junior synonym of A. buceros.
Until recently, M. validus was considered to be the only species of Machaeroprosopus that has not been reassigned. Thus, Machaeroprosopus was considered to be a nomen dubium or "doubtful name" because of the lack of diagnostic specimens that can support its distinction from other phytosaur genera. However, a taxonomic revision of Machaeroprosopus, conducted by Parker et al. (in press), revealed that UW 3807 is not the holotype of Machaeroprosopus, while the previously named species Pseudopalatus buceros has priority as the type species of the genus. Therefore, the name Pseudopalatus was considered a junior synonym of Machaeroprosopus, and all species of the former were reassigned to the later. This revised taxonomy was already accepted in several studies, including Stocker and Butler (2013). Stocker and Butler (2013) also treated M. validus as a possibly valid species, and not a junior synonym of Machaeroprosopus buceros as was previously suggested by Long and Murry (1995).
Machaeroprosopus