Micromys bendai van de Weerd, 1979

Colombero, Simone, Pavia, Giulio & Carnevale, Giorgio, 2014, Messinian rodents from Moncucco Torinese, NW Italy: palaeobiodiversity and biochronology, Geodiversitas 36 (3), pp. 421-475 : 439-440

Micromys bendai van de Weerd, 1979 ( Fig. 4 S-V)

Micromys bendai van de Weerd, 1979: 144 , pl. 3, figs 4, 5, 9, pl. 4, figs 6, 10. — Aguilar et al. 1989: 141, fig. 2. — Hordijk & de Bruijn 2009:41, pl. 12, figs 1-14.

OCCURRENCE IN THE STUDIED LAYERS. — MCC3, MCC4, MCC5, MCC7.

REFERRED MATERIAL. — Three mandibular fragments bearing m1 and m2; 13 isolated M1; five isolated M2; two isolated M3; ten isolated m1; four isolated m2.

MEASUREMENTS. — see Table 5.

DESCRIPTION

M1

t1 very close to or connected to t5;the t3 exhibits a short posterior spur; a small swelling of the enamel is present in most of the specimens on the anterior edge of the tooth between t1 and t2 or between t2 and t3;t3-t6-t9 are usually well aligned in an almost straight labial margin since the t6 can slightly protrude; t4-t5-t6-t7-t9-t8 are connected in a partially developed stephanodont crest since t7 is isolated from t4; t9 reduced; t12 moderately developed; five roots.

M2

t1 bis always present as an isolated cusplet or in a twinned complex formed by t1 and t1 bis t3 smaller than t1, usually connected to t5; t6 large, t9 reduced; t7 narrow or crest-like, isolated or weakly connected to t8; t12 present; four roots.

M3

t large; the t3 is a small swelling of the enamel; posterior complex connected to t6; t8 large and connected to the t6; three roots.

m1

Cuspids are pointed; small tma; longitudinal spur absent; a narrow labial cingulum departs from the c1 reaching the anteroconid without developing accessory cusplets; two main roots and one central rootlet.

m2

Anterolabial cuspid moderately or poorly developed; longitudinal spur absent; narrow labial cingulum departing from a rather small c1; posterior heel oval and poorly developed; two roots.

REMARKS

The average size of Micromys from MCC is slightly larger than that of Micromys bendai from Ptolemais 1 (type population, van de Weerd 1979) and Péage de Roussillon ( Aguilar et al. 1989). However, it falls in the size range of other assemblages from Greece such as Tomea Eksi 1 and 2, Prosilion-Mercurion ( Hordijk & de Bruijn 2009). Direct comparisons with molars of M. bendai from the type locality of Ptolemais 1did not reveal any relevant morphological difference suggesting that the material from MCC documented herein can be identified as Micromys bendai .

Micromys steffensi van de Weerd, 1979 , from the Early Pliocene of Greece ( Hordijk & de Bruijn 2009; Vasileiadou et al. 2012) displays larger dimensions even if the size range of m1 partially overlaps with that of M. bendai from MCC. Direct comparisons with specimens of M. steffensi from the type locality of Kardia, evidenced a great similarity with M. bendai . However, some small morphological differences can be detected, including the presence of a t1 bis in some M1 and the better development of the posterior spurs of t 3 in M1 of M. steffensi .

The Late Miocene to Early Pliocene Micromys paricioi Mein, Moissenet & Adrover, 1983 , known in Spain ( Mein et al. 1983; Adrover et al. 1988; García-Alix et al. 2008b) and Greece ( Vasileiadou et al. 2003), can be easily distinguished from M. bendai by its smaller size, less-developed t7 and less frequent t1 bis in M2.

Micromys cingulatus Storch & Dahlmann, 1995 from Maramena (Miocene/Pliocene boundary of Greece) is similar in size to M. bendai from MCC, but it exhibits less roots in M1 (three roots plus an extremely rare incipient fourth central rootlet), a reduced t7 and lacks the t1 bis in M2 ( Storch & Dahlmann 1995).

The molars of Micromys chalceus Storch, 1987 from the Late Miocene of Mongolia are evidently smaller than the material from MCC ( Storch 1987). Moreover, the M1 lacks a t7 and it usually displays a minor number of roots in M1 since a fifth rootlet is visible only in 11 out of 108 specimens ( Storch 1987). The earliest Pliocene Micromys kozaniensis van de Weerd, 1979 , from Ptolemais 3 ( van de Weerd 1979) and the Mongolian locality of Bilike ( Qiu & Storch 2000), differs from M. bendai in having narrower upper molars. From a morphological point of view, M. kozaniensis displays more posterior and slightly more developed t7 especially in the M2, more developed t12 and a deep inflexion in the outline of the M1 between t1 and t2 ( van de Weerd 1979).

M. bendai is reported in the latest Miocene-to- Early Pliocene of Greece ( de Bruijn 1989; Koufos 2006; Hordijk & de Bruijn 2009) and the Early Pliocene of France ( Aguilar et al. 1989).

Micromys minutus (Pallas, 1771) , the Eurasian Harvest Mouse,is the only extant species of the genus Micromys . Towards the end of the Miocene and during the Pliocene this genus exhibited a greater diversity with a higher number of species whose phylogenetic relationships are still not resolved. As a matter of fact, even if some species such as M. cingulatus from Greeceand M. chalceus from Asia exhibit less advanced morphological features (e.g., reduced number of roots, t7 absent or reduced), their presence in latest Miocene/earliest Pliocene localities of Europe and Asia indicates that they are contemporary to other species of this genus, namely M. bendai , M. paricioi , which, on the contrary, display more advanced morphological traits (e.g., higher number of roots and well developed t7) ( Hordijk & de Bruijn 2009). In summary, as already evidenced by some authors (van de Wteerd 1979; Storch & Dahlmann 1995; Hordijk & de Bruijn 2009), it is extremely problematic to define a single lineage leading to the extant M. minutus . The evolutionary lineage M. chalceus – M. cingulatus – M. paricioi proposed by Storch & Dahlmann (1995) seems to be not valid because M. paricioi appeared in Spain almost contemporaneously to the appearance in Greece of M. cingulatus (García-Alix et al. 2008b) . Micromys steffensi is reported from the Pliocene deposits of the Ptolemais basin ( Hordijk & de Bruijn 2009) and shows a strong similarity with M. bendai , but it differs in its larger size and in some morphological details. In our opinion, M. steffensi probably should be regarded as an endemic form within the Ptolemais basin.

Some other species appeared subsequently, such as Micromys caesaris Minwer-Barakat, García-Alix, Martín-Suárez & Freudenthal, 2008 , a form of small size reported in the Late Pliocene of the Guadix Basin, Spain (Minwer-Barakat et al. 2008) and Micromys praeminutus , known from some Pliocene localities of Europe ( Michaux 1969; van de Weerd 1979).

Figures

FIG. 4. — Isolated teeth of Paraethomys Petter, 1968, Occitanomys Michaux,1969, Centralomys De Giuli,1989 and Micromys Dehne, 1841 from Moncucco Torinese. A-F, Paraethomys meini (Michaux, 1969); A, MGPT-PU128032, M1 dex.; B, MGPT-PU128040, M2 sin.; C, MGPT-PU127602, M3 sin.; D, MGPT-PU127146, m1 sin.; E, MGPT-PU127302, m2 sin.; F, MGPT-PU127603, m3 sin.; G-L, Occitanomys brailloni Michaux, 1969; G, MGPT-PU127062, M1 sin.; H, MGPT-PU127447, M2 dex.; I, MGPT-PU127657, M3 dex.;J, MGPT- MGPTPU127166,m1 dex.; K, MGPT-PU127305,m2 dex.; L, MGPT-PU127658,m3 sin.;M-R, Centralomys benericettii (De Giuli, 1989); M, MGPT-PU128090, M1 sin.; N, MGPT-PU128278, M2 sin.; O, MGPT-PU128115, M3 sin.; P, MGPT-PU128272, m1 sin.; Q, MGPT-PU128321, m2 sin.; R, MGPT-PU128144, m3 dex.; S-V, Micromys bendai van de Weerd, 1979; S, MGPT-PU127434, M1 dex.; T, MGPT-PU127251, M2 dex.; U, MGPT-PU127600, m1 dex.; V, MGPT-PU127601, m2 sin. Scale bar: 1 mm.