Eutheria

Ecology

Biology

Incisor

Evolutionary biology

Paleontology

Structural basin

Maxillary central incisor

Lateral incisor

Orthodontics

Medicine

Phanerozoic

Cenozoic

Relationships of the specialized eutherian family Zalambda− lestidae (Late Cretaceous, Asia) have long been debated. Begin− ning with suggestion of Van Valen (1964) and including the re− cent phylogenetic analysis of Archibald et al. (2001), a possible close relationship of Zalambdalestidae to Glires (Lagomorpha + Rodentia) has been repeatedly suggested (but see Meng and Wyss 2001). One of the characteristics of Glires is the structure of the lower incisor, which is enlarged and open−rooted. An open−rooted incisor has been documented in the oldest known zalambdalestid, Kulbeckia, but structure of this tooth has re− mained unknown for the Mongolian representatives of this family, Zalambdalestes and Barunlestes. Here we present evi− dence on the presence of an open−rooted first lower incisor in Zalambdalestes lechei and Barunlestes butleri; we argue, how− ever, that structure of this incisor does not necessarily indicate relationship of Zalambdalestidae to Glires.

Lower incisor in zalambdalestid mammals (Eutheria) and its