In this study we appraised the dental morphology and potential origin of two Neogene cricetodontine-like muroids, Pliotomodon primitivus from sediments in northern California and an undescribed muroid from central Oregon. Dental features of Pliotomodon are similar to those of Eurasian genera such as Byzantinia, Hispanomys and Ruscinomys, but the unusual morphology of M3/m3, with continuous enamel connections across their lingual surfaces closing the hypoflexus and posteroflexid, respectively, plus retention of only three roots on M1, suggests Pliotomodon arose from an ancestor distinct from the one that gave rise to the large late Neogene hypsodont cricetodontines of the Old World. Another archaic cricetodontine-like rodent, from the Warm Springs region of the John Day Formation in Oregon, is named as a new species of Deperetomys, D. dingusi, sp. nov. 

Supplementary file 1 (Supplementary Table 1) includes measurements and body mass data collected at museums to create equation 1 in the text. Supplementary file 2 (Supplementary Table 2) is a chronologically ordered summary of measurements and body mass estimates for cricetodontine and cricetodontine-like Old and New World rodents taken from the literature and generated for this study.

Supplementary data file 3 lists the characters and states for phylogenetic analysis using the TNT program of the Willi Hennig Society, determined through observation and coding of specimens. The characters and states are from López-Guerrero, P. 2014, Cricetodontini (Rodentia, Mammalia) del Mioceneo medio y superior del área de Daroca (Aragón, España): sistemática y filogenia.

Supplementary data file 4 represents the character and state matrix used by TNT, and Supplementary data file 5 provides the single most parsimonious tree from the TNT analysis and lists of hypothesized terminal taxa apomorphies and node synapomorphies.

MS Word, MS Excel, Adobe Acrobat, TextEdit