Re-investigation of fossil Lemmini specimens from the early and Middle Pleistocene of Western and Central Europe: Evolutionary and paleoenvironmental implications

Abstract

The current study focuses on the emblematic Myopus/Lemmus species complex (tribe Lemmini) in the European Pleistocene fossil record. The members of the two genera occupy distinct ecological niches and have different external appearances, but they are remarkably similar in their dental morphology, so that they were commonly thought of as undistinguishable in the fossil record. Thus, more or less all European Lemmini fossils have been assigned to the genus Lemmus. In the Early Pleistocene site of Schernfeld (Germany), the species Lemmus kowalskii had been described. It was thought by some authors that all Lemmini from Early to late Middle Pleistocene belong to this species.In the current study, we investigated Lemmini molar morphology from Western and Central European sites including Schernfeld (Early Pleistocene), Sackdillinger Höhle (Sackdilling Cave), and Koněprusy C718 (both early Middle Pleistocene), as well as other fossil localities with fewer specimens, formerly assigned to Lemmus kowalskii. Using an extensive modern referential material of Lemmus and Myopus, this study proposes to re-evaluate taxonomic status of the Middle and Early Pleistocene Lemmini. This modern referential also allows a better understanding of the morphology of Lemmus kowalskii specimens and its variability.Our results highlight the very high variation within fossil populations, as well as significant statistical differences between populations of the Early and Middle Pleistocene localities. A large part of these fossil specimens is firmly identified as Myopus sp., including the L. kowalskii holotype. Our identifications demonstrate that in most Early and Middle Pleistocene sites considered in this study, both genera (Lemmus and Myopus) are present. Possible interpretations and consequences for current view of lemming history are discussed, as well as some of the paleoecological and paleoenvironmental implications.