Family BRONTOTHERIIDAE Marsh 1873

Discussion: Mader (1989; 1998) divided the Brontotheriidae into two relatively large monophyletic subfamilies: the Dolichorhininae and the Brontotheriinae (= Telmatheriinae, sensu Mader 1989). Eotitanops and Palaeosyops were resolved as sister genera to these subfamilies, but were not found to comprise a monophyletic taxon. Recent phylogenetic analyses by Mihlbachler (2008) generally support this conclusion. Eotitanops and Palaeosyops are accorded their own subfamilies in the present revision.