On the status of early Eucricetodontinae (Muroidea, Rodentia) with a special focus on the Atavocricetodon vs Eucricetodon issue: morphometrical aspects
Résumé
Among the flourishing Muroidea, the Eucricetodontinae
constitute the most diversifi ed subfamily of the Eurasian
Palaeogene. Early representatives, such as Atavocricetodon
and Eucricetodon, are notably characterized by their simple
and primitive dental morphology. As a result, it appears
very diffi cult to discriminate these genera according to their
dental morphology, and that is emphasized by their imprecise
diagnosis. Here, we aim at challenging the taxonomic validity
of Atavocricetodon, frequently considered as a grade of
Eucricetodon. We chose to investigate the outline of fi rst
upper molars for four species of Atavocricetodon and seven
of Eucricetodon, to avoid confusions made by their occlusal
dental characters. The outline analysis involves samples
of ten molars, and was realized by using Elliptic Fourier
Transforms. Incisor enamel microstructures were investigated
as well in four species, because this dental character appears
highly useful in rodents to solve taxonomic issues. Results
revealed that if a signifi cant difference exists between the
global dental shape of Atavocricetodon and Eucricetodon,
outline morphospaces of the considered species generally
overlap as displayed by the multivariate analysis and the
hierarchical clustering. This is partly explained by the high
intrageneric shape variation, which might correspond to
different Oligocene lineages of Eucricetodontinae. Such
variation is also due to Atavocricetodon paaliense, which
could rather belong to another genus, the pseudocricetontine
Kerosinia. More generally, there is no discrete character or real
apomorphy which permits to distinguish these genera, because
incisor enamel microstructure patterns are highly variable and
a few types are shared by both genera. Atavocricetodon cannot
thus be retained neither as a genus, nor as a morphosubgenus
of Eucricetodon. Further studies, including much more fossil
material, are needed to accurately identify the various lineages
of Eucricetodon and to potentially defi ne new genera on a
fair basis.