M. pristinus was first described and named by Maurice G. Mehl in 1928 as the type species of Pseudopalatus, Pseudopalatus pristinus, on the basis of the holotype MU 525, nearly complete skull.
It was collected, from the Norian-aged Upper Petrified Forest Member of the Chinle Formation, near Adamana, Arizona.
Additional skulls and postcranial material, some articulated skeletons, from the same member were referred to this species by Colbert (1946) and Long and Murry (1995) from Arizona, and by Lawler (1979), Ballew (1986) and Long and Murry (1995) from New Mexico.
Charles Camp (1930) described and named Machaeroprosopus tenuis on the basis of UCMP 27018, a nearly complete skull, lower jaws, and some complete postcranial material, from the Billings Gap locality (UCMP 7043, Upper Petrified Forest Member), Apache County of Arizona.
This specimen was occasionally referred to as Rutiodon tenuis, although since Long and Murry (1995) it is considered to be a junior synonym of M. pristinus.
Long and Murry (1995) also suggested that Redondasaurus gregorii from the Redonda Formation of New Mexico is a junior synonym of M. pristinus, although this was not accepted by subsequent authors.
Other, then unnumbered, specimens from the upper Church Rock Member (Chinle Formation, Utah), Bull Canyon Formation and Travesser Formation (New Mexico) and Cooper Canyon Formation (Texas), were referred to M. pristinus by Long and Murry (1995), although recent studies suggest that M. pristinus is currently known only from the Upper Petrified Forest Member of Arizona and New Mexico.
M. pristinus was first described and named by Maurice G. Mehl in 1928 as the type species of Pseudopalatus, Pseudopalatus pristinus, on the basis of the holotype MU 525, nearly complete skull. It was collected, from the Norian-aged Upper Petrified Forest Member of the Chinle Formation, near Adamana, Arizona. Additional skulls and postcranial material, some articulated skeletons, from the same member were referred to this species by Colbert (1946) and Long and Murry (1995) from Arizona, and by Lawler (1979), Ballew (1986) and Long and Murry (1995) from New Mexico. Charles Camp (1930) described and named Machaeroprosopus tenuis on the basis of UCMP 27018, a nearly complete skull, lower jaws, and some complete postcranial material, from the Billings Gap locality (UCMP 7043, Upper Petrified Forest Member), Apache County of Arizona. This specimen was occasionally referred to as Rutiodon tenuis, although since Long and Murry (1995) it is considered to be a junior synonym of M. pristinus. Long and Murry (1995) also suggested that Redondasaurus gregorii from the Redonda Formation of New Mexico is a junior synonym of M. pristinus, although this was not accepted by subsequent authors. Other, then unnumbered, specimens from the upper Church Rock Member (Chinle Formation, Utah), Bull Canyon Formation and Travesser Formation (New Mexico) and Cooper Canyon Formation (Texas), were referred to M. pristinus by Long and Murry (1995), although recent studies suggest that M. pristinus is currently known only from the Upper Petrified Forest Member of Arizona and New Mexico.
Machaeroprosopus