Microtus (Terricola)

Agadjanian, Alexander K. & Kondrashov, Peter, 2020, Late Pleistocene (Eemian) Mollusk And Small Mammal Fauna From Mikhailovka- 5 (Kursk Oblast, Central Russia), Fossil Imprint 76 (1), pp. 17-39 : 25-27

Microtus (Terricola) ex gr. subterraneus (SELYS- LONGCHAMPS, 1836)

M a t e r i a l. PIN 4970/253–260, 8 m1; PIN 4970/261–

262, 2 m2; PIN 4970/263–268, 6 M3.

D e s c r i p t i o n. Small vole teeth, rootless, with crown cement.

The opposing angles of the m1 paraconid complex are fused. The shape of the anterior part of the paraconid is variable ( Text-fig. 6 ). The simplest morphotype has a single incoming angle on the medial side ( Text-fig. 6 ). These teeth have a well-developed incoming angle on the lingual side of the paraconid head unlike Microtus (Terricola) gregaloides . This m1 structure in Microtus (Terricola) voles is found in the populations of M. (Terricola) duodecimcostatus and M. (Terricola) lusitaniсus from the Late Pleistocene of southwestern Europe ( Chaline 1972). Other variations in the m1 structure include two incoming angles on the lingual and labial sides of the paraconid head that can be either weak or well developed. In the latter case, the distance between the apices of the angles is less than the anterior width of the paraconid head, which is more typical for modern M. (Terricola) subterraneus . See Table 3 for measurements.

The m2 structure is typical of most Microtus sensu lato except for the fusion of the first pair of the opposing triangles and, in one case, of the second pair also, which is characteristic of Terricola.

The M3s are the smallest teeth of all arvicoline M3 from Mikhailovka-5. Some of them show fusion of paracone with the hypocone and/or hypocone with the metacone. Few specimens have a simple posterior loop without the incoming angles, which is more typical of early Middle Pleistocene Microtus (Terricola) .

C o m p a r i s o n a n d c o m m e n t s. Microtus (Terricola) voles were widely distributed in the Russian Plain during the Middle Pleistocene ( Gromov and Polyakov 1977). Small populations persist in this region still today, which allows detailed morphological comparisons. Middle Pleistocene Microtus (Terricola) are mostly represented by the Microtus (Terricola) gregaloides morphotype, which is characterized by a small rounded paraconid head with a small incoming angle on the lingual side on m1 ( Agadjanian 2009). However, this morphotype has not been found in Mikhailovka-5 and is not present in the modern populations of Microtus (Terricola) .

Late Middle Pleistocene populations of Microtus (Terricola) are characterized by morphotypes similar to Microtus (Terricola) gregaloides and Microtus (Terricola) arvaloides , but the latter is more common ( Agadjanian 2009), which is also the case for the Terricola from Mikhailovka-5. In addition to the above-mentioned morphotypes, Likhvinian populations of Microtus (Terricola) (Vladimirovka locality on the Don River) also contain the Microtus (Terricola) duodecimcostatus morphotype. The dental morphology of the modern pine vole Microtus (Terricola) subterraneus is significantly different. Their m1 is similar to Microtus (Terricola) arvaloides , but the incoming angles on the paraconid head are much better developed. Modern Terricola also have a different m2 structure, where the dentine fields of the opposing triangles merge with each other. Moreover, the M3 of modern Microtus (Terricola) often has fused opposing triangles and paracone and hypocone are also fused. This m2 and M3 morphology does not occur in Middle Pleistocene Microtus (Terricola) ( Agadjanian 2009) . Thus, Microtus (Terricola) from Mikhailovka-5 differs significantly from the Middle Pleistocene Microtus (Terricola) in the structure of m1, m2, and M3. Its morphology is overall similar to the

Figures

Text-fig. 6. Molars of Microtus from Mikhailovka-5. Microtus ex gr. agrestis LINNAEUS, 1761: a–l: M2, m–s: M3; Microtus (Terricola) ex gr. subterraneus (SELYS-LONGCHAMPS, 1836): t–z: m1, aa–ab: m2, ac–ag: M3.