A new Oligocene genus of the Spalacidae (Rodentia) from the Balkan – Anatolian biogeographic province: spalacid relationships and their dispersal through time

The Oligocene muroid Eucricetodon exhibits a wide Eurasian distribution. Numerous species have been described from an area encompassing at least four distinct biogeographic provinces. Its type species originates from Europe, a province that includes an estimated twenty-three formally described species, while ten species are known from Asia.

Two species previously assigned to Eucricetodon from the Oligocene of the Balkan – Anatolian biogeographical province are the focus of this study. Molars of Eucricetodon exhibit a mosaic of subtle morphological features with no clear polarity, making it difficult to define distinct groups within this large number of species. However, the enamel microstructure of its incisors, which is known to be of phylogenetic significance, displays two distinct types.

Eucricetodon from Balkan – Anatolia and Asia exhibits the derived K 10 microstructure, whereas European Eucricetodon possesses the distinctly different K 4 type. These differences likely reflect geographically separated evolutionary trajectories. The Anatolian species are therefore described here as Dekamyarion gen. nov.

The K 10 microstructure characterises the Spalacidae, a family that includes a few extant and numerous extinct taxa. Molecular studies estimate the origin of Spalacidae in the Late Eocene, while divergence of its extant subfamilies occurred in the Late Oligocene, a timing broadly consistent with the fossil record. Dekamyarion represents the oldest known genus possessing K 10 incisors and, together with several other taxa, forms part of the spalacid stem group.

We also discuss other extinct taxa that are phylogenetically related to the extant subfamilies, whereas others represent extinct branches of the family. Spalacidae occur in Eurasia and Africa, and extinct species are also known from North America.