Unification of Criteria for Distinguishing Morphotypes of Cheek Teeth in Lemmings (Lemmini, Arvicolinae, Rodentia)

The missing Myopus: plugging the gaps in Late Pleistocene small mammal identification in western Europe with geometric morphometrics

“…For Myopus, teeth tend to be stockier and simpler in shape. This increased complexity of the anterior m1 loop in Lemmus, always absent in Myopus, and the organization of the buccal triangles shifting anteriorly on Lemmus, are congruent with the taxonomic literature (Chaline et al, 1988;Markova et al, 2018;Smirnov et al, 1997;Ponomarev et al, 2013b). Some of these authors also noted that on the M3, the T3/T4 alternation and asymmetry could be used to distinguish the two genera.…”

“…For these two molars, some authors note a high variation in the outer loops (anterior loop for m1, posterior loop for M3), which exhibit different stages of complexity, with the development of supplementary re-entrant angles on both labial and buccal sides (e.g. Markova et al, 2018;Ponomarev et al, 2013b). In general, Lemmus shows a higher tendency to complexity (i.e.…”

“…This last work shows that the frequency of cementum deposits in the last re-entrant angles of the outer loops of both M3 and m1 (LRA3 and BRA4 of m1) differs between the two genera. The cementum deposits are absent in Myopus teeth, whereas they are present in 40-70% of Lemmus individuals (Cheprakov, 2016;Markova et al, 2018;Ponomarev et al, 2013).…”

“…This problem of differentiation has therefore greatly reduced the palaeoecological utility of these taxa, which is particularly problematic considering their occurrence in many Quaternary deposits. Several authors have accordingly attempted to separate these two genera through morphometrical analysis of the first lower molar (m1) and the third upper molar (M3) but with varying degrees of accuracy (Chaline et al, 1988;Markova et al, 2018;Ponomarev et al, 2013b;Smirnov et al, 1997).…”