Messinian rodents from Moncucco Torinese, NW Italy: palaeobiodiversity and biochronology Author Colombero, Simone Author Pavia, Giulio Author Carnevale, Giorgio text Geodiversitas 2014 2014-09-01 36 3 421 475 http://dx.doi.org/10.5252/g2014n3a4 journal article 6393 10.5252/g2014n3a4 08337548-044b-4fce-8702-fe17f207d9a2 1638-9395 4538563 Muscardinus vireti Hugueney & Mein, 1965 ( Fig. 6 F-P) Muscardinus vireti Hugueney & Mein, 1965: 118 , figs 64- 78. Muscardinus aff. vireti – Engesser 1983: 776 , fig. 6. — Colombero et al. 2013: 122, fig. 5E, F. Muscardinus cf. vireti – Angelone et al. 2011: 99 , fig. 6 (16). TYPE LOCALITY . — Lissieu, France . OCCURRENCE IN THE STUDIED LAYERS. — MCC3, MCC4, MCC5, MCC7. REFERRED MATERIAL. — A single maxillary fragment bearing M1 and M2; two isolated P4; 18 isolated M1; 15 isolated M2; three isolated M3; a single isolated p4; 22 isolated m1; 25 isolated m2; 9 isolated m3. MEASUREMENTS. — Table 9. DESCRIPTION P4 Ovoid in outline; three main ridges; first and second ridges connected on the lingual side. M1 Six main ridges; first ridge convex and lingually bent forming a “crochet” ( sensu Hugueney & Mein 1965 ); second ridge lingually inclined; all ridges but the first one connected by an elongate endoloph; a single specimen possesses small labial and lingual portions of an extra ridge situated between the third and fourth crests; four roots, three specimens with a supplementary anterolabial rootlet. M2 Eight main low ridges; a complete endoloph connects all the ridges; half of the specimens exhibit a small labial portion of an extra ridge; usually arising as a bifurcation of the sixth ridge; three or four roots. M3 Trapezoid or triangular in outline; eight main ridges connected by a complete endoloph; half of the specimens with a small labial portion of an extra ridge; usually as a bifurcation of the fifth or the sixth ridge; rare specimens with two labial portion of extra ridges; three roots. p4 Ovoid in outline; three main ridges weakly connected on the labial side. m1 Six main ridges; first and second ridges connected both on labial and lingual sides; third ridge convex or straight; forth, fifth and sixth ridges slightly convex; fifth and sixth ridges sometimes connected on the labial or lingual side; three roots. m2 Six main ridges; lingual side of the molar slightly longer than labial one; a swelling of the enamel occasionally occurs on the anterolabial border of the molar; ridges frequently connected on the labial side, most notably between first and second and between fifth and sixth ridges; a lingual portion of an extra ridge regularly present between the third and fourth ridges; in half of the specimens a smaller labial portion of an extra ridge is present between the third and fourth ridges; four roots. m3 Trapezoid in outline; lingual side longer than labial one; six main ridges; first and second ridges and fifth and sixth ridges occasionally connected on the labial and lingual side; 60% of specimens with a small lingual portion of an extra ridge between third and fourth ridges. REMARKS The flattened molars bearing a high number of roughly parallel ridges clearly support the attribution of the material documented herein to the genus Muscardinus Kaup, 1829 . The measurements of the studied material fit well with those of Muscardinus helleri Fejfar & Storch, 1990 from the Ruscinian locality of Gundersheim 4, even if the width of this latter species is generally larger. The morphology of the teeth from MCC is roughly similar to that of M. helleri primarily concerning the presence of six main ridges on the lower molars and M1, eight ridges on M2 and M3, as well as small lingual and labial extra ridges on the m2. However, some minor differences can be recognized, including the presence of a short endoloph in the M1 and M 2 in M. helleri not reaching the last two ridges, the absence of extra ridges in the M2, and the presence in fewer specimens with a lingual “crochet” on the first ridge of M1. The European Plio-Pleistocene Muscardinus pliocaenicus Kowalski, 1963 and the Late Miocene Muscardinus pliocaenicus austriacus Bachmayer & Wilson, 1970 from Austria (see also Daxner-Höck & Höck 2009 ) are slightly smaller than M. vireti from MCC. Moreover, these taxa are characterized by a minor number of ridges in the M1 and M2 and by the absence of extra ridges in the lower molars. Muscardinus dacicus Kormos, 1930 from the Plio-Pleistocene of Europe shows a larger size and can be easily distinguished from the material of MCC by its simplified dental pattern without extra ridges on the m2 and with less developed ridges separated by larger valleys in the M1. The Late Miocene species Muscardinus davidi Hugueney & Mein, 1965 from Lissieu is characterized by a size comparable to that of MCC from which it differs in having less seven ridges in the M2. The measurements of Muscardinus meridionalis García-Alix, Minwer-Barakat, Martín-Suárez & Freudenthal, 2008 from the localities Purcal 24 (Late Turolian) and Purcal 4 (Early Ruscinian) in the Granada Basin (García-Alix et al. 2008c) are only slightly larger than those of the studied material from MCC. The general pattern of the molars is rather similar in displaying a similar number of main ridges in each dental element. However, in M. meridionalis extra ridges are not present on M2 and M3, the endoloph of upper molars seems to be weaker, the “crochet” on the first ridge of the M1 only rarely occurs and the extra ridges on the lower molars are extremely infrequent in the m2 and completely absent in the m3. Compared with Muscardinus vireti Hugueney & Mein, 1965 from Lissieu, the specimens from MCC display slightly larger mean lengths and widths even if the size ranges partially overlap and also show a very similar morphology. In M. vireti the number of ridges is identical for each dental element (six in M1 and lower molars, eight in M2 and M3), the endoloph is well-developed and connects the last five ridges of M1, lingual and labial portions of extra ridges occur in many m2 and, finally, some M2 and M3 exhibit incomplete extra ridges very similar in shape to those observed in the specimens from MCC. A few specimens assigned to Muscardinus aff. vireti were reported from Baccinello V3 ( Engesser 1983 ). The measurements of that material are intermediate between those from MCC and Lissieu except for the m3 that are smaller. From the morphological point of view, the arrangement of the ridges of the molars is remarkably similar to that from MCC and no reliable differences can be detected. The Muscardinus material from MCC is therefore assigned to M. vireti . The slight size differences with the material from Lissieu can be explained by the different age of the two localities, since Lissieu is probably slightly older than MCC ( Gómez Cano et al. 2011 ). The intermediate size of the teeth from Baccinello V3 confirms that slight size differences are to be expected in assemblages of different age and geographic provenance. According to García-Alix et al. (2008c), M. vireti should be considered the ancestor of M. meridionalis . This interpretation is followed herein, justified by several relevant morphological features that are shared by these two taxa, including the number of crests in upper and lower molars. Actually, M. meridionalis only differs in having a slightly modified dental pattern with very uncommon extra ridges, a much rarer occurrence of the “crochet” on the M1, and the weaker endoloph. García-Alix et al. (2008c) considered M. helleri as the descendant of M. meridionalis . Such hypothesis appears to be weak considering that M. helleri displays a slightly more complicated dental pattern than M. meridionalis , with more developed extra ridges in the m2. Therefore, the lineage M. vireti – M. meridionalis – M. helleri seems to be dubious since it would imply a simplification of the dental pattern ( M. vireti – M. meridionalis ) followed by a reversal of this trend ( M. meridionalis – M. helleri ). Muscardinus meridionalis possibly represents a taxon exclusive from southern Spain .