Glirudinus aff. glirulus ( Dehm, 1935 )

Lu, Xiaoyu, Costeur, Loïc, Hugueney, Marguerite & Maridet, Olivier, 2021, New data on early Oligocene dormice (Rodentia, Gliridae) from southern Europe: phylogeny and diversification of the family, Journal of Systematic Palaeontology 19 (3), pp. 169-189 : 178-179

Glirudinus aff. glirulus ( Dehm, 1935)

( Fig. 4T)

Type locality. Gunzenheim, Germany (MP30).

Holotype. Slg. Munchen 1934 V21, fragment of the left lower jaw with incisor and m1.

Specimens and measurements. UCBL-FSL_218044, right m2, L = 0.97 W = 0.93 ( Fig. 4T); UCBL-FSL_218069, right m3, L = 1.10 W = 1.14.

Description of the specimens from Montalb́an 1D.

m2. Only one tooth was found in Montalb́an 1D. The occlusal surface is slightly concave. The anterotropid connects to the metalophid on its lingual side. The metalophid extends from the posterior arm of the metaconid to the protoconid with a gap near the lingual side. The centrolophid is weak and free. The entoconid is also free. The posterotropid is very weak, almost absent. All tropids and lophids are straight and form an angle of approximately 45 Ǫ to the longitudinal axis of the tooth, except the anterolophid and posterolophid.

m3. The pattern of m3 is similar to m2 and slightly concave. The talonid is noticeably narrower than the trigonid. The anterotropid is absent. The centrolophid is not connected to the metaconid. It is interrupted and more developed than in m2. The entoconid weakly connects with the mesolophid and the posterolophid at a low level. The posterotropid is well developed.

Remarks. The pattern is composed of an association of straight lophids with an oblique centrolophid, all forming a right triangle shape of the trigonid which is a typical character of the genera Glirudinus and Glirulus . In addition, Glirulus is only known in the Miocene and has more crests than Glirudinus , especially the existence of precentrotropid and postcentrotropid in lower molars, while Glirudinus traces back to the early Oligocene of Itardies (MP23) with fewer and more robust crests ( Vianey-Liaud 2003). Consequently, despite some variation of the anterotropid and metalophid observed in our specimens, we refer them to Glirudinus because of the lower number of crests and of their robustness. Glirudinus antiquus Vianey-Liaud, 2003 from Itardies is the only species known so far in the early Oligocene. The size of our m2 fits within the size range of the type population from Itardies (m2: mean length = 1.02; mean width = 0.98; Vianey-Liaud 2003); however, the m3s are much larger (m3: mean length = 0.89; mean width = 0.85; Vianey-Liaud 2003). Additionally, the metalophid is transverse and the trigonid is not triangular as in the type population. The interrupted centrolophid in m3 also occasionally appears in G. antiquus . Thus, considering both morphology and size, our specimen is more similar to the late Oligocene species Glirudinus glirulus (Gunzenheim, Dehm 1950; Pech Desse and Pech du Fraysse, Vianey-Liaud 2003). Even if the identification at specific level is uncertain and needs more specimens for a confirmation, the new specimens can without doubt be referred to the genus Glirudinus , which has never been identified in Montalb́an 1D before.