Incisor microstructures and significance of late Eocene-early Oligocene Muroidea (Rodentia) from the Balkans and Anatolia

Incisor microstructures are reliable but underused markers for distinguishing muroid subfamilies. Here, we document and illustrate incisor microstructures of isolated teeth from late Eocene – early Oligocene muroid assemblages of the Balkan – Anatolian palaeobiogeographical province. We discuss their taxonomic significance and illustrate emergence and decline of taxa bearing these structures. In our material, isolated muroid incisors can be consistently matched to molars of the same taxon. We document the primordial K1 and the derived K7, K8, and K10 structures, representing ten muroid genera and one dipodid. The K1 structure occurs in early-diverging genera that became extinct in the early Oligocene. Alongside them appear four derived clades that originated in the late Eocene. Melissiodontinae retained the K1 structure, while Pseudocricetodontinae possess the derived K7 structure; both subfamilies persisted into the Early Miocene. Paracricetodontinae, with the K8 structure, were short-lived. We propose that the K10 structure arose in the late Eocene or early Oligocene as a single event; it characterises a clade including extant Spalacidae and extinct Cricetodontinae and Eumyarioninae, among others. The clade also occurs in Asia, the Indian subcontinent, and Africa. In Balkan – Anatolia, it radiated in the late Oligocene, declined in the Miocene, and survives today with a single genus.