Miodyromys Kretzoi, 1943

Hír, J., 2013, Early and Middle Miocene (MN 5 - MN 6) transitional rodent fauna from Litke (North Hungary, Nógrád County), Fragmenta Palaeontologica Hungarica 30, pp. 101-137 : 110-115

Genus: Miodyromys Kretzoi, 1943

Miodyromys sp.

( Figs 9–20)

Material and measurements (mm) –

Locality No. inv. MMP. Position L W Figure Litke 1 2012.169. D4 0.70 0.90 9

Litke 1 2012.174. D4 0.63 0.74

Litke 1 2012.170. P4 0.66 0.90 10

Litke 1 2012.171. P4 0.73 0.90

Litke 1 2012.172. P4 0.63 0.85

Litke 1 2012.173. P4 0.71 0.88

Litke 2 2013.81. P4 0.67 0.84

Litke 1 2012.158. M1–2 1.13 1.27 11

Litke 1 2012.159. M1–2 1.05 1.26

Litke 1 2012.160. M1–2 1.06 1.19

Litke 1 2012.161. M1–2 0.97 1.13

Litke 1 2012.162. M1–2 1.06 1.23

Litke 1 2012.163. M1–2 fragm. – 1.19

Litke 1 2012.164. M1–2 0.95 1.12

Litke 1 2012.165. M1–2 1.06 1.18 12

Litke 1 2012.194. M1–2 0.94 1.12

Litke 2 2013.72. M1–2 0.98 1.25

Litke 2 2013.73. M1–2 0.94 1.12

Litke 2 2013.74. M1–2 1.02 1.12

Litke 2 2013.75. M1–2 0.95 1.08

Litke 2 2013.76. M1–2 0.99 1.20

Litke 2 2013.77. M1–2 0.92 1.13

Litke 1 2012.166. M3 0.80 0.98

Litke 1 2012.167. M3 0.85 0.99 13

Litke 1 2012.168. M3 0.78 0.99

Litke 1 2012.175. d4 0.7 0.56

Litke 1 2012.176. d4 0.78 0.57 14

Litke 1 2012.177. p4 0.70 0.70 15

Litke 1 2012.178. p4 0.76 0.73

Litke 1 2012.179. p4 0.73 0.73

Litke 1 2012.180. p4 0.71 0.71

Litke 2 2012.78. m1 1.06 1.01

Litke 2 2012.79. m1 1.16 1.05 16

Litke 1 2012.182. m1 1.09 1.00

Litke 1 2012.183. m1 1.05 0.98

Litke 1 2012.185. m1 1.09 0.99 17

Litke 1 2012.184. m1 1.16 1.05 18

Litke 1 2012.191. m1 1.15 0.98

Litke 1 2012.192. m1 1.18 1.09

Litke 1 2012.193. m1 1.08 1.01

Litke 1 2012.186. m2 1.13 1.08

Litke 2 2012.80. m2 1.15 1.02 19

Litke 1 2012.187. m3 0.91 0.91

Litke 1 2012.188. m3 0.99 0.95

Litke 1 2012.189. m3 – –

Litke 1 2012.190. m3 1.15 0.91

Litke 2 2012.82. m3 0.97 0.85 20

Litke 2 2012.83. m3 0.85 0.85

Description – D4 – Triangular outline. Four main ridges (homology is uncertain there): anteroloph, protoloph, metaloph and posteroloph. Anteroloph and posteroloph are connected in the lingual angle. The protoloph-metaloph connection is very close to the lingual angle but it is situated slightly labially. Anteroloph-protoloph and metaloph-posteroloph connection is found in the labial margin. A long isolated ridge (anterior centroloph?) is found in the centre of the occlusal surface.

P4 – Elliptic outline. Anteroloph is short and independent. Protoloph, metaloph and posteroloph merge in the protocone. An isolated anterior centroloph is developed in the centre of the occlusal surface. Two roots.

M1–2 – Rectangular outline, concave occlusal surface. The lingual and labial ends of the anteroloph are free. The protoloph, metaloph and posteroloph are lingually connected. The anterior centroloph is longer than the posterior one. The centrolophs are fused only in one molar (1 out of 14 specimens). In the juvenile unworn molars the lingual wall is ornamented. Occurrence of the extra ridges: no extra ridges (5/14), anterior extra ridge developed, no posterior extra ridge (8/14), anterior and posterior extra ridges equally found (2/14). Labial connection of the posterior centroloph is week (2/14).

M3 – Trapezoidal outline, the posterior margin is narrower. In contrast to the M1–2’s the lingual and labial ends of the anteroloph are not free. Lingually the anteroloph, the protoloph, the metaloph and the posteroloph are connected to an endoloph. Anterolabially the anteroloph, the metaloph and the anterior centroloph are connected. The posterior centroloph, the metaloph and the posteroloph are connected on the posterolabial side. The posterior centroloph is longer than the anterior one. A posterior extra ridge and another extra ridge between the anteroloph and protoloph are developed in specimen 2012.167.

d4 – Triangular outline. The anterior portion is variable. The posterior part consists of the lingually connected mesolophid, posterolophid and a posterior extra ridge between them.

p4 – The outline is triangular, but it has a wider posterior part than in d4. In the anterior portion an anterolophid and a strongly reduced metalophid are developed. In the posterior part the mesolophid and the posterolophulid are lingually connected. Posterior extra ridge is not developed.

m1, m2 – Rectangular outline. The constant elements of the occlusal surface are the four main ridges (anterolophid, metalophid, mesolophid, posterolophid) and a long posterior extra ridge (or named as extra ridge 4: following HEISSIG 2006). The anterolophid and the centrolophid are lingually connected to the metaconid. The lingual end of the metalophid is close to the metaconid but does not reach it. The mesolophid and the posterolophid are lingually connected. The labial end of the main ridge is free. The occurrence of the other extra ridges: extra ridge 1 (1 out of 11 specimens), extra ridge 2 (6/11), extra ridges 2+3 (1/11), posterior extra ridge is doubled (1/11). Three specimens have preserved roots. All of them are simple; those are not grooved and have not any tendency for bifurcation.

m3 – The basic structure is equal to the m1–m2 molars but the posterior part of the occlusal surface is narrower. Extra ridges 1+2 are developed only in the specimen 2012.188.

Comments – The relationship and possible synonymy of the genera Miodyromys Kretzoi, 1943 , Prodryomys Mayr, 1979 , Pseudodryomys de Bruijn, 1966 , Peridryromys Stehlin et Schaub, 1951 and Myomimus Ognev, 1924 is still un- der discussion. The morphology (two centrolophs in upper molars and one or more extra ridges in both upper and lower molars) of the Litke material refers to Miodyromys , which is the most frequent Myomiminae glirid in the Middle Miocene of Central Europe ( DAXNER-HÖCK 2010).

The Miodyromys finds from Litke 1–2 differ from M.aegercii Baudelot, 1972 in the smaller measurements and the less developed extra ridges in the M1–2 molars; from M. hamadryas Major, 1899 in the smaller measurements and in the presence of two roots in m1 molars and the less developed extra ridges in the M1–2 molars; from M. grycivensis Nesin et Kowalski, 1997 in the smaller mean measurements and the less developed extra ridges in the M1–2; from M. vagus Mayr, 1979 in the smaller measurements, in the merged protoloph and anterior centroloph in the labial side of the M1–2 molars and in the presence of two roots in the m1–2 molars; from M. biradiculus Mayr, 1979 in the smaller mean measurements, in the fewer and less developed extra ridges in the M1-M2-M3-m1-m2 molars; from M. asiamediae Maridet et al., 2011 in the smaller measurements, in the absence of the extra ridge between the anterolophid and the metalophid in m2; from M. aff. grycivensis of Comăneşti (HÍR et al. 2011) in the shorter anterior extra ridge in M1–2 molars.

The measurements of Miodyromys sp. 3 from Schellenfeld 4 (MN 5, ZIEGLER 1995) are similar to the Litke material; however, the morphology of the figured m2 molars (Taf. 4: 11, 12) strongly differs because the mesolophids are reduced. The measurements of Miodyromys sp. from Gratkorn (MN 7/8, DAXNER-HÖCK 2010) are very similar to the Litke material, but the extra ridges are less developed.

The best similarity in the morphology and in the measurements was found to the Miodyromys cf. biradiculus material from the Zaisan Depression, Eastern Kazakhstan ( KOWALSKI & SHEVYREVA 1997) although the published material is not abundant and it was collected from different localities. Miodyromys wesselsi has not been described in details from Tavnik (MN 9) in Serbia. KRSTIĆ et al. (2008) mentioned that this new species from the Middle Miocene sediments of Serbia shows a more complex molar morphology than the species Miodyromys aegercii . After this short discussion the identity of the Litke finds is uncertain.

The species M. praecox Wu, 1993 , M. prosper (Thaler, 1966) and M. hugueneyae Agusti et Arbiol, 1989 are out of consideration because of the significant age differences: these species are Late Oligocene – Early Miocene elements (up to MN3).

The taxonomy and evolution of the Miodyromys genus is best documented and studied in the Northern Alpine Foreland Basin ( MAYR 1979, HEISSIG 2006, WU 1990, 1993, KÄLIN & ENGESSER 2001). The population from Litke is not comparable to the evolutionary lines described from this region because all of the South German and Swiss late MN5 faunas with Cricetodon meini contain larger sized Miodyromys species. For instance: Edelbeuren-Maurerkopf, SACH (1999, MN5): M. aegercii , C. aff. meini ; Wannenwaldtobel 2, SACH (1999, MN6): M. aegercii , C. aff. meini ; Hohenraunau, SEEHUBER (2008, MN5+MN6): M. aegercii , C. cf. meini ; Unterneul 1a, HEISSIG (1989, MN5): M. aegercii , C. cf. meini , S. bredai ; Ebershausen, HEISSIG (2006, MN5): M. vagus , C. meini . Some early MN6 faunas are also known with C. aff meini (Sagentobel: M. aff. aegercii ; Rümikon: M. aegercii ; Gallenbach 2b: Miodyromys sp. ).

The same association was reported from the Middle Miocene of Serbia: Lazarevac, MARKOVIĆ (2008, MN6): M. aegercii , C. meini ; Bele Vode, MARKOVIĆ & MILIVOJEVIĆ(2010, MN6): M.aegercii , C.meini . In Austria and in Greece Miodyromys is substituted by other Myomiminae taxa: Mühlbach, DAXNER-HÖCK (2002, MN5): Prodryomys satus , C. meini ; Antonios, KOUFOS (2006, MN4-MN5 transition): Myomimus sp. , C. meini ; Thymiana A, KOUFOS (2006, MN5): Peridyromys sp. , C. meini .

The small-sized Miodyromys sp. is an immigrant at Litke localities and it is missing in Austria, Southern Germany and Western Europe. Its closest relative seems to be the M. cf. biradiculus from Kazakhstan. Without more detailed information we abstain from the classification on species level or description as a new species.