Abstract of Smith, G.R., and R.K. Koehn. 1971. Phenetic and cladistic studies of biochemical and morphological characteristics of Catostomus. Syst. Zool. 20:282-297.

Mountain suckers are the sister group to Catostomus catostomus. The Columbia river form is the next branch, Rio Grande next, Great Basin next, Santa Ana form next, and upper and lower Colorado River species pair most terminal.