Size relationships help distinguish small and large groups of lower molars in Trinity Group tribosphenidan mammals, some of which can be associated with the upper molars of the type specimens of Pappotherium pattersoni and Holoclemensia texana, respectively.
Holoclemensia texana is distinctly larger and the lower molars referred to this taxon share a coherent suite of characters including enlarged metaconid, small anteriorly tilted paraconid, and robust hypoconid. They lack the "mesial" or "antero-lingual" cuspule beneath the paraconid.
A single lower molar (PM 965) is nearly the size of the smallest H. texana molars, but differs in the relative size of its paraconid, metaconid, and hypoconid. It also differs in possession of a distinct anterolingual cingular cusp on the paraconid (as does PM 948). PM 965 is not H. texana and may represent a new genus or a new species of Pappotherium.
The first molar of Slaughteria eruptens fits the size predicted for lowers of P. pattersoni, and is compatible in structure with the upper molars of the latter. It is distinctly different from smaller, more primitive, lower teeth that are referred to other genera (Trinititherium, Kermackia, Comanchea). These more primitive teeth are less compatible with the upper molar structure of P. pattersoni, although they should be evaluated as possible deciduous teeth. Morphological variation associated with sequential molar position and variation within a tooth position cannot be adequately constrained in most Trinity Group mammals. Despite the potential to underestimate species diversity without cognizance of variation, size, and structure unite S. eruptens and P. pattersoni. It is most parsimonious to regard S. eruptens as a junior synonym of P. pattersoni, pending discovery of more complete specimens.
Type: SMU 61725
Butler 1978, syn. n.
Pappotherium pattersoni thus shares with the trechnotherian clade and early eutherians the replacement of multiple deciduous precursor premolars and the alternate premolar eruption sequence of p3->p2->p4, but differs from eutherians in the lack of molarization of the lower premolars.