Abstract
Among the flourishing Muroidea, the Eucricetodontinaeconstitute the most diversifi ed subfamily of the EurasianPalaeogene. Early representatives, such as Atavocricetodonand Eucricetodon, are notably characterized by their simpleand primitive dental morphology. As a result, it appearsvery diffi cult to discriminate these genera according to theirdental morphology, and that is emphasized by their imprecisediagnosis. Here, we aim at challenging the taxonomic validityof Atavocricetodon, frequently considered as a grade ofEucricetodon. We chose to investigate the outline of fi rstupper molars for four species of Atavocricetodon and sevenof Eucricetodon, to avoid confusions made by their occlusaldental characters. The outline analysis involves samplesof ten molars, and was realized by using Elliptic FourierTransforms. Incisor enamel microstructures were investigatedas well in four species, because this dental character appearshighly useful in rodents to solve taxonomic issues. Resultsrevealed that if a signifi cant difference exists between the global dental shape of Atavocricetodon and Eucricetodon,outline morphospaces of the considered species generallyoverlap as displayed by the multivariate analysis and thehierarchical clustering. This is partly explained by the highintrageneric shape variation, which might correspond todifferent Oligocene lineages of Eucricetodontinae. Suchvariation is also due to Atavocricetodon paaliense, whichcould rather belong to another genus, the pseudocricetontineKerosinia. More generally, there is no discrete character or realapomorphy which permits to distinguish these genera, becauseincisor enamel microstructure patterns are highly variable anda few types are shared by both genera. Atavocricetodon cannotthus be retained neither as a genus, nor as a morphosubgenusof Eucricetodon. Further studies, including much more fossilmaterial, are needed to accurately identify the various lineagesof Eucricetodon and to potentially defi ne new genera on afair basis.