Apodemus atavus Heller, 1936

Colombero, Simone, Pavia, Giulio & Carnevale, Giorgio, 2014, Messinian rodents from Moncucco Torinese, NW Italy: palaeobiodiversity and biochronology, Geodiversitas 36 (3), pp. 421-475 : 443-446

Apodemus atavus Heller, 1936

( Fig. 5 G-L)

Apodemus atavus Heller, 1936: 126 , pl. 10, fig. 2. — Rietschel & Storch 1974: 495, text figs 1-3, pls 1-4. — Fejfar & Storch 1990: 147, figs 39-50. — Bolliger et al. 1993: 1045, figs 9, 10. — Marchetti et al. 2000:98, figs 6, 17-40, 42-48. — Martín-Suárez & Mein 2004:116, fig. 1. — Minwer-Barakat et al. 2005: 432, fig. 3A-F. — García-Alix et al. 2008b: 192, fig. 3M-R. — Hordijk & de Bruijn 2009: 36, pl. 10, figs 5-12.

Apodemus dominans Kretzoi, 1959: 243 . — van de Weerd 1976: 87, pl. 8, figs 6-10; 1979: 138, pl. 2, figs 1-9. — Sen 1977: 105, pl. 3, figs 7-10 (cum syn.). — Aguilar et al. 1986: 131; 1991: 159. — Adrover et al. 1988: 108, figs 3, 1-7. — Sesé 1989: 193. — Hordijk & de Bruijn 2009: 37, pl. 10, figs 1-4.

Apodemus cf. dominans – Adrover et al. 1988: 107, figs 2, 9, 10; 1993a: 69, pl. 8, figs 10-13. — Storch & Dahlmann 1995: pl. 1, figs 8-14. — Mörs et al. 1998: 151, fig. 10. — Vasileiadou et al. 2012: 222, fig. 7d.

Sylvaemus dominans – Popov 2004: 26 , figs 28, 29.

Apodemus cf. etruscus – Angelone et al. 2011: 99, figs 6, 12.

TYPE LOCALITY. — Gundersheim 4, Germany.

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

REFERRED MATERIAL. — Twelve isolated M1; seven isolated M2; four isolated M3; 17 isolated m1; six isolated m2; three isolated m3.

MEASUREMENTS. — see Table 7.

DESCRIPTION

M1

The t1 is close to but isolated from the t5; t1-t2 connection low; t3 small; 75% of the specimens exhibit a posterior spur on the t3 not connecting to t5, 25% of specimens with very reduced or absent posterior spur; t7 always present; t4-t7 connection absent in 50% of the specimens; t7-t8 connection absent in 20% of the specimen; t12 well-developed.

M2

t1 completely isolated; the t7 is always present and isolated from the t4; t7-t8 connection absent in 25% of the specimens and low and weak in the others; t9 and t12 well-developed.

M3

t1 strong; the posterior complex, formed by the t8 and t9, is bilobed and elliptic occasionally connected with the t6 but isolated from the t4.

m1

tma always present and well-developed; posterior heel ovoid or rounded; c1 isolated from hypoconid; labial cingulum composed by several cusplets, generally two or three in addition to the c1.

m2

Anterolabial cuspid well-developed and isolated; labial cingulum with two or three cusplets in addition to the c1.

m3

Anterolabial cuspid formed by a small swelling of the enamel; posterior complex rounded.

REMARKS

The medium-sized Apodemus present at MCC is smaller than A.gudrunae . From a morphological point of view A. atavus differs in the regular presence of a well-developed and frequently isolated t 7in both M1 and M2, more developed posterior spurs in the t3 of M1 and more developed t12.

In a previous cursory analysis of the vertebrate assemblage of MCC( Angelone et al. 2011), some of the specimens referred herein to as A. atavus were erroneously identified to as Apodemus cf. etruscus Engesser, 1989, a species reported only from the Late Miocene of Baccinello V3, central Italy.This species differs from A.atavus in having a poorly developed t 7 in the upper molars and poorly developed spurs on the t3 of M1.

The measurements of the specimens of the medium-sized Apodemus from MCC fit well with those of Apodemus atavus from the Pliocene localities of Gundersheim (type locality) ( Fejfar & Storch 1990), Saint Vallier (Martín-Suárez & Mein 2004), La Dehesa 1 (García-Alix et al. 2008b), Komanos 1 (low and high), Tomea Eksi 3, Vorio 3a and Notio 1 ( Hordijk & de Bruijn 2009), and Willerhausen ( Rietschel & Storch 1974). They are slightly smaller than A. atavus from the latest Miocene and Pliocene localities of Purcal 7, 13, Calicasas 3, 3B, 4B, Cerro del Águila 1C (García-Alix et al. 2008b), Vue-des- Alpes ( Bolliger et al. 1993) and the Pleistocene locality of Monte La Mesa ( Marchetti et al. 2000). The size ranges of the specimens belonging to A. atavus from the Pliocene localities of Tollo de Chiclana (Tollo de Chiclana 1, 1B, 3 and 13) (Minwer-Barakat et al. 2005) are very similar to those of MCC, even if the maximum values of M1 and m1 are slightly higher. The morphology of the studied material is perfectly consistent with that of A. atavus from Gundersheim, in particular as far as regards the development of t7 (which is isolated in half of the available M1), low t1-t2 connection, presence of spurs on t3 of M1, and well-developed tma in the m1.

The average size of Apodemus dominans Kretzoi, 1959 , a species reported in Europe since the latest Miocene to the Pleistocene, from the type locality of Csarnota 2 (see van de Weerd 1976) is similar to that of MCC except for the M1 and m2 that are slightly larger than those from MCC.The size of A. dominans from the Pliocene localities of Escorihuela, Orrios ( van de Weerd 1976), Castelnou 3 ( Aguilar et al. 1991), Mont-Hélène ( Aguilar et al. 1986, Concud Estación 3 and Concud Pueblo 3 ( Adrover et al. 1988) is extremely similar to that of MCC, whereas that from Çalta ( Sen 1977), Concud Estación 1 ( Adrover et al. 1988), Hambach ( Mörs et al. 1998), Muselievo ( Popov 2004), Notio 1 ( Hordijk & de Bruijn 2009), the latest Miocene locality of Bacochas 1 ( Sesé,1989), the Late Miocene-Early Pliocene of Maramena ( Storch & Dahlmann 1995); is only slightly larger. The lower molars of A. dominans from Celadas 9 and la Gloria 4 (Pliocene of Spain) ( Adrover et al. 1993a) are slightly smaller than those from MCC. The separation between A. atavus and A. dominans based on morphology is highly problematic ( Popov 2004; Hordijk & de Bruijn 2009; Vasileiadou et al. 2012). Fejfar & Storch (1990) suggested that putative distinctive characters of A. dominans such as the presence of a strong t 12 in M1-2, three radiculated upper molars, and the presence of rearward c 1 in m1-2 should be regarded as symplesiomorphies. The size differences between A. dominans from the type locality of Csarnota 2 ( van de Weerd 1976) and A. atavus from the type locality of Gundersheim-4 ( Fejfar & Storch 1990) are very slight; the mean values of M1 and m2 from Csarnota 2 are slightly larger than those from Gundersheim-4 but the size ranges partially overlap; the average sizes of M2, M3, m1, and m3 are very close and the size ranges are nearly identical. However, some authors (e.g., Storch & Dahlmann 1995; Mörs et al. 1998; Popov 2004; Hordijk & de Bruijn 2009; Vasileiadou et al. 2012) assigned some specimens from Maramena and Kessani (Miocene/ Pliocene boundary of Greece), Hambach (Pliocene of Germany), Muselievo (Pliocene of Bulgaria), Notio 1 (Pliocene of Greece) to A. dominans and A. cf. dominans because of their slightly larger mean values with respect to those of A. atavus from Gundersheim-4. These slight size differences, however, should not be regarded as reliable criteria to discriminate between these two taxa. The size of other species of Apodemus such as Apodemus sylvaticus (Linnaeus, 1758) (see Cuenca Bescós et al. 1997; Renaud & Michaux 2003, 2007) and Apodemus flavicollis (Melchior, 1834) (see Michaux & Pasquier 1974; Capizzi & Filippucci 2008) is characterized by considerable variation through time and space due to the interrelationship of multiple factors involving climatic and/or latitudinal variations and interspecific competition ( Renaud & Michaux 2007). Small differences in size between material from different regions and ages, as for example those reported for A. atavus and A. dominans , are to be expected and may be related to intraspecific variability. For these reasons, as already pointed out by several authors (Martín-Suárez & Mein 2004; Minwer-Barakat et al. 2005; García-Alix et al. 2008b), it is not possible to conclusively separate A. atavus and A. dominans from both a morphological and biometrical point of view and we follow the suggestions of these authors in considering A. dominans a junior synonym of A. atavus . As a consequence, the material from MCC is referred to A. atavus .

According to many authors ( Rietschel & Storch 1974; Fejfar& Storch 1990; Martín-Suárez & Mein 1998), A.atavus should be considered as the ancestor of the extant species A. sylvaticus . This relationships might be corroborated by some remains of A. atavus from Willerhausen ( Rietschel &Storch 1974), where the exceptional preservation of bones and soft tissues allowed the authors to note that the habitus and size of the two species are similar and that A. atavus solely differs for a few characters such as the shorter ulna and femur and the stronger t 12 in M1 and M2.

Figures

FIG. 5. — Isolated teeth of Apodemus Kaup, 1829 from Moncucco Torinese:A-F, Apodemus gudrunae van de Weerd,1976; A, MGPT- PU127084, M1 dex.; B, MGPT-PU127731, M2 sin.; C, 127661, M3 dex.; D, MGPT-PU127974, m1 sin.; E, MGPT-PU127475,m2 dex.; F, MGPT-PU127665, m3 sin.; G-L, Apodemus atavus Heller, 1936 from Moncucco Torinese; G, MGPT-PU127659, M1 dex.; H, MGPT- PU127660, M2 sin.; I, MGPT-PU127661, M3 sin.; J, MGPT-PU127180, m1 sin.; K, MGPT-PU127662, m2 sin.; L, MGPT-PU127663, m3 dex. Scale bar: 1 mm.