The site of Moncucco Torinese is located in the Torino Hill, at the top of a gypsum quarry (Fig. 2). A detailed description of the geological setting and stratigraphy of the area and fossil site was provided by Dela Pierre et al. (2007) and Colombero et al. (2014b). The fossiliferous deposits belong to the Cassano Spinola Conglomerates Formation, the uppermost lithostratigraphic unit of the Messinian succession of the Tertiary Piedmont Basin (Fig. 3). Moreover, micropaleontological data indicate that the fossiliferous layers can be correlated to phase 3.2 (sensu Roveri et al., 2014) of the Messinian Salinity Crisis, chronologically constrained between 5.42 and 5.33 Ma (see Alba et al., 2014 and Colombero et al., 2014b).

The studied material consists of nine sciurid teeth including premolars and molars, selected from 2800 rodent teeth derived from the processing of 18 tons of sediment. Fossils are currently housed in the Museo di Geologia and Paleontologia, Università degli Studi di Torino. Nomenclature and measurement follow Casanovas-Vilar et al. (2015) except the definition of the mesoloph. Following Marivaux et al. (2004), the mesoloph is the short crest developing from the mesostyle, whereas the crest departing from the protocone between the protoloph and the metaloph is the protolophule. The tiny crest developing between anteroloph and protoloph is an anterior accessory ridge. Measurements are given in mm. All measurements provided herein and the pictures of Sciurus vulgaris have been taken with the Leica Application Suite V. 3.3 of a stereomicroscope Leica M205C, whereas dental remains from Moncucco Torinese were photographed with the Scanning Electron Microscope Cambridge S-360 of the Dipartimento di Scienze della Terra di Torino. Dental material of Sciurus warthae from the Early Pleistocene of Monte La Mesa (STUM), as well as of the extant Sciurus vulgaris (MCCI, DBIOS) and Sciurus carolinensis (MCCI) from Italy was examined for comparative purposes. As regards the taxonomic classification of Sciuridae, we follow Steppan et al. (2004), thereby implying that we consider Pteromyini and Sciurini as two closely related tribes within the subfamily Sciurinae. Fig. 4C and D (M3 and m1 of Sciurus warthae) and Fig. 4G and H (M3 and m1 of Pliopetaurista pliocaenica) were originally presented in Colombero et al. (2014b) with erroneously inverted captions; such a mistake is corrected herein.

Institutional abbreviations: DBIOS: Dipartimento di Scienze della Vita e Biologia dei Sistemi, Università degli Studi di Torino, Italy; MCCI: Museo Civico di Storia Naturale di Carmagnola, Carmagnola, Italy; MGPT-PU: Museo di Geologia e Paleontologia, Università degli Studi di Torino, Italy; STUM: Dipartimento di Studi Umanistici, Università degli Studi di Ferrara, Italy.

Order Rodentia Bowdich, 1821

Family Sciuridae Fischer, 1817

Subfamily Sciurinae Fischer, 1817

Tribe Sciurini Fischer, 1817

Genus Sciurus Linnaeus, 1758

Sciurus warthae Sulimski, 1964

Referred material and measurements: a right dP4 (MGPT-PU136604, L:? -W: 1.77), a left P4 (MGPT-PU136591, L: 2.13-W: 2.30), a right M3 (MGPT-PU128219, L: 2.84-W: 2.60), a right m1 (MGPT-PU 128221, L: 2.28-W: 2.42), a left m2 (MGPT-PU 136592, L: 2.35-W: 2.66).

Description

dP4 – (Fig. 4A). Completely unworn tooth, parastyle not preserved. Distinct paracone and metacone, well-developed protocone; hypocone tiny but distinct; anteroloph partially preserved and low; protoloph short and interrupted at its midlength by a deep notch; metaloph uninterrupted bearing a small metaconule; tiny mesostyle present; roots not preserved.

P4 – (Fig. 4B). Worn tooth with exposed dentine in some portions of the occlusal surface. Roughly triangular outline; large protocone; parastyle slightly more lingually positioned than paracone and metacone; paracone and metacone worn but evident; a trace of a small mesostyle is observable; anteroloph and posteroloph completely worn, metaloph and protoloph visible. Due to the poor preservation of this specimen, the presence of protoconule and metaconule cannot be observed; three roots.

M3 – (Fig. 4C). Triangular outline with expanded posterior basin; protocone large; paracone high and distinct; mesostyle small and distinct; continuous posterior rim enclosing the posterior basin; worn protoloph connecting protocone to paracone; metaloph absent; anteroloph low; three roots.

m1 – (Fig. 4D). Subtrapezoidal outline; high metaconid and hypoconid; protoconid smaller than hypoconid; evident entoconid; mesoconid small; metastylid partially merged with the metaconid and separated from the entoconid by a notch; metalophid partially observable due to wear, anterolophid low and connected to the anterolingual part of the protoconid; reduced trigonid basin; posterolophid continuous and not posteriorly projected; roots not preserved.

m2 – (Fig. 4E). Sub-rectangular outline; worn tooth especially along the labial margin; postero-lingual corner partially abraded, lacking the enamel; metaconid high; hypoconid and protoconid strongly worn; entoconid partially damaged but suggesting the presence of an angular postero-lingual corner; mesoconid not visible due to wear, metastylid well-developed and only partially connected to the metaconid; metalophid very low due to wear; anterosinusid absent; posterolophid low and lingually connected to hypoconid; four roots.

Remarks. The occurrence of an evident entoconid defining an angular postero-lingual corner in the lower molars is a typical feature of most of the squirrels within the subfamily Sciurinae. In particular, the simple pattern of the lower molars, devoid of marked enamel ornamentation and of evident anterosinusids, is strongly similar to that of extant Sciurini and more specifically, to that of the genus Sciurus. The dental remains from Moncucco Torinese are closed in size and morphology to the cheek teeth of the extant Eurasian Red Squirrel Sciurus vulgaris. In particular, the dimensions of the studied sample from MCC fall within the size range of S. vulgaris from northern Spain (Colección J.M. Rey, Universidad de Santiago de Compostela) (Cuenca-Bescós, 1988) and are also very similar to those of the studied collection of S. vulgaris from northern and central Italy (DBIOS collection) to which differ mainly for the slightly longer M3 (Fig. 5). The morphology of the teeth is strikingly similar and the sample from MCC differs from S. vulgaris only in the slightly less pronounced hypoconids of m1, in the more developed and isolated metastylid of m2, and in the slightly narrower M3 that displays a more elongated posterior basin. The evident morphological affinities with extant Sciurus support the attribution of the material from Moncucco Torinese to this genus. The Miocene record of the genus Sciurus is rather poor. In Asia, very scarce and poor samples of dental remains assigned to undetermined species of Sciurus have been found in the Late Miocene of China and Turkey (Bosma et al., 2013 and Qiu et al., 2008). In North America, Sciurus olsoni from the Late Miocene of Nevada is considered by many authors the oldest species of this genus (Oshida et al., 2009 and Pečneróva and Martínková, 2012), representing the earliest reliable record of Sciurus in the New World (Emry et al., 2005). The dental remains of this American species are considerably smaller but morphologically roughly similar to those of Moncucco Torinese. The described teeth from Moncucco Torinese represent the only European record of the genus Sciurus before the Pliocene. Among the Pliocene and Pleistocene Eurasian species, Sciurus maltei from the Early Pliocene of Wölfersheim (Germany) and Sciurus whitei from the Middle Pleistocene of Norfolk (UK) and Tarkö (Hungary) differ from the material from Moncucco Torinese in their notably smaller size (Dahlmann, 2001). The morphology of the teeth of Sciurus described herein fits well with Sciurus warthae, a species documented by sparse remains found in the Early Pliocene of Poland (Sulimski, 1964), Germany (Dahlmann, 2001) and in the Pleistocene of Monte La Mesa (Marchetti et al., 2000). Sciurus cf. warthae has been recorded in other Polish Pliocene localities (Black and Kowalski, 1974), as well as in the Pleistocene of northern Italy (Siori and Sala, 2007). The material from Monte la Mesa is nearly identical to that from Moncucco Torinese. The overall size of the specimens from Moncucco Torinese is very similar to or slightly smaller than that of S. warthae from its type population of Węże 1, Poland, and other localities (Dahlmann, 2001, Marchetti et al., 2000 and Sulimski, 1964).

Sciurus warthae from Moncucco Torinese represents the earliest European record of Sciurus. Sulimski (1964) indicated that S. warthae differs from S. vulgaris for the presence of four roots in the m3, remarkably shorter diastema, large and solid cusps, and greater overall dimensions. However, the dimensions of S. vulgaris are very similar to those reported for the known specimens of S. warthae (see Fig. 5 and data in Black and Kowalski, 1974, Cuenca-Bescós, 1988, Dahlmann, 2001, Marchetti et al., 2000 and Sulimski, 1964) and the cusps of S. vulgaris are as large and solid as in S. warthae. Our comparative observations revealed that this species is very close to S. vulgaris, suggesting that it pertains to the same evolutionary lineage. In particular, lower molars of S. warthae are remarkably similar to those of S. vulgaris, even if they differ in having a less labially extended hypoconid in the m1 and slightly more distinct metastylid in the m2. The P4 presents a triangular outline and a parastyle slightly more lingually placed than paracone and metacone, a morphological pattern that is can be also found in S. vulgaris. Moreover, the mesostyle present in the single M3 from Moncucco Torinese is also observed in some specimens of S. vulgaris. Finally, in many unworn upper cheek teeth of S. vulgaris, the lingual wall of the protocone displays a peculiar slight enamel ornamentation consisting of shallow but dense small pitts associated to a rugose surface (Fig. 6A), that are also documented in unworn specimens of S. warthae (e.g., Dahlmann, 2001).

As far as concerns the phylogenetic history of extant species of Sciurus, Mercer and Roth (2003) demonstrated that the earliest divergence within this genus occurred 8.6 ± 1.3 Ma, giving rise to the Eurasian lineage including S. vulgaris. More recent molecular analyses based on some extant species of Sciurini (Oshida et al., 2009, Pečneróva and Martínková, 2012 and Villalobos and Gutierrez-Espeleta, 2014) suggested a basal divergence of the “S. vulgaris clade”, followed by a colonization of the New World that led to the origin of the extant North American and Neotropical lineages whose speciation took place during the Pliocene-Pleistocene (Oshida et al., 2009). The close relationship between S. vulgaris and S. warthae interpreted on the basis of some shared morphological features, and the Messinian report of S. warthae at Moncucco Torinese strongly support the hypothesis of a Late Miocene divergence of the “S. vulgaris clade”. However, the occurrence of S. olsoni in the early Late Miocene of North America (Clarendonian, approximately 9.8 Ma) (Emry et al., 2005) and some sparse remains assigned to the genus Sciurus in the Miocene of Asia (Bosma et al., 2013 and Qiu et al., 2008) concur to indicate that the early evolutionary history of tree squirrels is rather complicated, and a North American origin of Sciurus cannot be definitely excluded.

Tribe Pteromyini Brandt, 1855

Genus Hylopetes Thomas, 1908

Hylopetes hungaricus (Kretzoi, 1959)

Referred material and measurements: a left M1 (MGPT-PU 136589, L: 1.49-W: 1.68)

Description

M1 – (Fig. 4F). Moderately worn tooth, subquadratic in outline; evident rugose enamel absent; slight wrinkles and deep short valleys developed on the walls of the lophes; distinct mesostyle, strongly developed parastyle; a short anterior accessory loph develops between anteroloph and protoloph; protolophule moderately developed; mesoloph weak; contacts of protoloph and metaloph with protocone characterized by marked constrictions; anteroloph and protoloph parallel to each other and orthogonal to endoloph; metaloph slightly oblique due to the posterior position of the metacone with respect to the protocone; sinuous endoloph with distinct constriction in front of the quite well-developed anteroconule; protocone massive and high; endoloph posteriorly thickened indicative of a small hypocone; paracone very robust; metacone slightly smaller than paracone; posteroloph worn and low. A single root preserved.

Remarks. The single upper molar described above pertains to a small sciurid characterized by short accessory lophes and very slight wrinkles associated to a rather distinct mesostyle, well-developed parastyle, quadratic outline and presence of constrictions on protoloph and metaloph. These features are indicative of Hylopetes, a genus of flying squirrel today widespread in South-East Asia with nine species (Thorington et al., 2012). As far as concerns the Late Miocene European pteromyin squirrels of Europe, Pliopetaurista, Miopetaurista and Albanensia clearly differ from the tooth from Moncucco Torinese due to their peculiar labyrinthic aspect, and larger size (Daxner-Höck and Mein, 1975, De Bruijn, 1995 and Mein, 1970), Forsythia lacks a mesostyle (Mein, 1970), and Blackia lacks accessory lophes and protolophule, a well-developed mesostyle, constrictions on protoloph and metaloph, and exhibits a less antero-posteriorly extended lingual margin (Daxner-Höck, 1975, Daxner-Höck, 2004 and Mein, 1970). Some small-to-medium sized species of sciurids from the Neogene of Europe have been assigned to the flying squirrel Neopetes or Hylopetes, including Neopetes hoeckarum, Hylopetes debruijni, Hylopetes macedoniensis, Hylopetes magistri and Hylopetes hungaricus. Neopetes hoeckarum represents the earliest record of this group in Eurasia and its biochronological range extends from MN4 (late Early Miocene) to MN11 (Late Miocene) (Daxner-Höck, 2004 and De Bruijn, 1998). This taxon differs from Hylopetes by lacking the accessory lophes and protolophule and having less distinct and lower cusp(id)s. Hylopetes debruijni is known from the Middle Miocene of France (?MN6–MN7) (Mein and Ginsbourg, 2002). This primitive species exhibits a large size, anterior accessory loph absent, protolophule absent or poorly developed and constrictions on protoloph and metaloph absent. Hylopetes macedoniensis is known from the Late Miocene of the Eastern Mediterranean in Greece (Maramena, MN13) and Turkey (Dűzyayla, MN10–12) (Bosma et al., 2013, Bouwens and De Bruijin, 1986 and De Bruijn, 1995). The upper teeth of H. macedoniensis differ from the single tooth of Moncucco Torinese in the slightly larger size, less developed protolophule, smaller parastyle, and in lacking anterior accessory lophes between anteroloph and protoloph. Hylopetes magistri, originally described as Hylopetes debruijni (see Reumer and Van den Hoek Ostende, 2003 and Van den Hoek Ostende and Reumer, 2011) is a sciurine recovered in the Pleistocene of Tegelen, The Netherlands. Colombero et al. (2014b) proposed that this species does not pertain to the genus Hylopetes and should be assigned to the genus Sciurus. They observed that the lower molars of this taxon are devoid of the typical morphological features of Hylopetes such as deep anterosinusids, distinct anteroconulids, posteriorly projected posterolophids and high and distinct labial cuspids (see Chaimanee, 1998 and Ellerman, 1940). Moreover, the upper molars from Tegelen lack the accessory lophes and the protolopules that can be observed in Hylopetes and the constrictions that are always present in metalophes and common in protolophes of Hylopetes. The presence of rare and barely observable enamel wrinklings as those described by Reumer and Van den Hoek Ostende (2003) in H. magistri is not a valid criterion to distinguish flying and tree squirrels (Thorington et al., 2005). As a matter of fact, even if enamel ornamentations are usually more common and developed among pteromyins, they can be also observed in sciurins, for example in the genus Sciurus where pitts and enamel crenulations can be observed in unworn lower molars and in the lingual wall of the protocones of Sciurus vulgaris (Fig. 6). Thorington et al. (2005) noted the presence of pitted enamel in Sciurus granatensis and S. vulgaris. Finally, it is worth noting that enamel ornamentations is a plesiomorphy, occurring in some early (Eocene to Oligocene) sciurid taxa (Cuenca-Bescós and Canudo, 1992, De Bruijn and Ünay, 1989 and Emry and Korth, 2007). Pteromyini and Sciurini are closely related to each other and grouped within the subfamily Sciurinae; they probably diverged in the Early Miocene (Mercer and Roth, 2003), thereby suggesting that the enamel ornamentations cannot be regarded as an apomorphy of Pteromyini. Since the morphological features of H. magistri are remarkably close to those of Sciurus (see Colombero et al., 2014b) we tentatively assign this species to Sciurus. Hylopetes hungaricus is a very rare species known only from sparse remains from the Pliocene (MN14–MN15) of central Europe (Black and Kowalski, 1974, Kretzoi, 1959, Kretzoi, 1962, Mörs et al., 1998 and Sulimski, 1964). Hylopetes cf. hungaricus has been also reported in the early Late Miocene (MN10–MN11) of Austria (Daxner-Höck, 1975 and Daxner-Höck, 2004), Late Miocene (MN13) of Greece (Bosma et al., 2013), and in the Pliocene (MN15) of Germany (Dahlmann, 2001). The morphology and the size of the tooth from Moncucco Torinese described herein fit well with those of the M1-2 of H. hungaricus from the Pliocene of Poland (Black and Kowalski, 1974), and Germany (Mörs et al., 1998) and also with those of H. cf. hungaricus from the Pliocene of Wölfersheim, Germany (Dahlmann, 2001). In particular, the short anterior accessory loph is characteristic of the upper molars of these taxa. The size and the morphology of the tooth from Moncucco Torinese are also similar to those of the early Late Miocene (MN10-MN11) specimens from Schernham and Kohfidisch identified as H. cf. hungaricus (Daxner-Höck, 1975 and Daxner-Höck, 2004) that solely differ in lacking the anterior accessory lophes. Therefore, morphological and biometrical evidences indicate that the single M1 from Moncucco Torinese described herein can be assigned to H. hungaricus. A single m1 from the locality of Brisighella 6 (Latest Miocene, Monticino Quarry, central Italy) was identified as Hylopetes sp. by De Giuli (1989). This tooth can be tentatively assigned to H. hungaricus based on its morphology and the small size that clearly differentiate it from the coeval H. macedoniensis. Hylopetes hungaricus was originally described as Pliopetes hungaricus and successively transferred to Hylopetes by Van de Weerd (1979). Such a generic assignment is justified by the morphological features of the upper teeth that are characteristic of the genus Hylopetes. Moreover, the lower molars of H. hungaricus display marked anterosinusids (Kretzoi, 1962) that are also usually well-developed in extant Hylopetes (Chaimanee, 1998, Colombero et al., 2014b and Ellerman, 1940). The morphology and dimensions of H. hungaricus are notably similar to those of the Pleistocene record of the extant Red-checked flying squirrel Hylopetes spadiceus from Thailand, a species currently widespread in south-east Asia (Chaimanee, 1998). The fossil record of H. spadiceus dates back to the Late Pliocene (Chaimanee, 1998), suggesting that a close relationship between these two species cannot be excluded.

Genus Pliopetaurista Kretzoi, 1962

Pliopetaurista pliocaenica (Depéret, 1897)

Referred material and measurements: a right M3 (MGPT-PU 128347, L: 2.84-W: 2.64); a left m1 (MGPT-PU 128218, L: 2.77-W: 2.51)

Description

M3 – (Fig. 4G). Subovoid outline with lophes and wrinkles providing a labyrinthic aspect to the occlusal surface; protocone rather posterior with respect to protoloph; distinct paracone connected to endoloph by a well-developed protoloph; anteroloph lower than protoloph; anteroconule slightly worn but large, hypocone slightly worn and represented by a marked enlargement of the endoloph; metacone represented by a slight and barely observable enlargement of the posteroloph; metaloph and metaconule absent.

m1 – (Fig. 4H). Subquadratic outline with lophids and wrinkles providing a labyrinthic aspect to the occlusal surface; protoconid and hypoconid well-developed, metaconid high, entoconid small but distinct; well-developed anterolophid connecting protoconid and metaconid; metalophid very short and interrupted, trigonid basin large, long posterior arm of the metaconid ending in a small metastylid; deep notch between the metastylid and the entoconid; posterolophid feebly enlarged near the hypoconid, suggesting the occurrence of a minuscule hypoconulid; distinct mesoconid.

Remarks. The teeth documented herein can be assigned to Pliopetaurista due to the typical labyrinthic morphology of the occlusal surface associated to a short hypolophid in the lower molar and the absence of metaloph in the M3. Size and morphological patterns of the molars from Moncucco Torinese are indicative of Pliopetaurista pliocaenica. In particular, the presence of a hypocone in the M3 and a very reduced metalophid are indicative of this taxon. As a matter of fact, the very similar Piopetaurista dehneli displays less developed or absent hypocones in upper molars and slightly more developed metalophids (Mein, 1970). The size of the specimens from Moncucco Torinese is intermediate between the mean values of Pliopetaurista dehneli and P. pliocaenica. The former species is common in the Early Pliocene of central and eastern Europe (Mein, 1970 and Sulimski, 1964), and has also been reported close to the Mio-Pliocene boundary at Maramena and Kessani (De Bruijn, 1995 and Vasileiadou et al., 2012); P. pliocaenica ranges chronologically from the Latest Miocene (in Spain; García-Alix et al., 2007) to the Plio-Pleistocene (in western and central Europe; Adrover et al., 1993, Black and Kowalski, 1974, Mein, 1970, Minwer-Barakat et al., 2012 and Mörs et al., 1998). Pliopetaurista kollmanni (Late Miocene) and Pliopetaurista bressana (Middle to Late Miocene) from central Europe are smaller with less pronounced ridges and tubercles (Daxner-Höck, 2004 and Mein, 1970). Pliopetaurista rugosa from the Latest Miocene of Eastern Asia does not have a hypocone also displaying a thinner endoloph (Qiu, 1991).

Sciurinae indet.

Referred material and measures: a fragmented left m1–2 (MGPT-PU 136590, L: 2.02-W:?)

Description

m1–2 – (Fig. 4I). Fragmented lower molar; protoconid and hypoconid completely abraded; small mesoconid preserved; prominent metaconid; large and cilindrical entoconid; metastylid partially merged with the metaconid and separated from the entoconid by a notch; a shallow flexus corresponding to this interruption can be observed in the lingual outline of the molar; posterolophid continous; metalophid interrupted before reaching the metaconid; trigonid partially preserved. Roots not preserved.

Remarks. This poorly preserved specimen displays a distinct entoconid defining an angular postero-lingual corner and a rather small mesoconid. A short metalophid, connected with the anterolophid, has been previously reported in the Early Pliocene species Sciurus maltei from Wölfersheim (Dahlmann, 2001), while an interrupted metalophid has been observed in the single m1 of Sciurus anomalus, the extant Persian Squirrel, from the Greek locality of Notio 1 (Hordijk and De Bruijin, 2009). However, the size of the tooth documented herein is slightly larger than that of S. maltei and smaller than S. anomalus and S. warthae preventing any possible attribution to these taxa. Moreover, this tooth does not belong to Hylopetes hungaricus, previously described in this paper, due to the much smaller size of this species. The dimensions of m1–2 of Hylopetes macedoniensis from the Late Miocene of Greece (Bouwens and De Bruijin, 1986 and De Bruijn, 1995) and Turkey (Bosma et al., 2013) are usually only slightly smaller than those of the specimen from Moncucco Torinese. Conversely, the morphology of the preserved portion of this molar is consistent with that characteristic of Hylopetes in some traits such as the distinct entoconid, prominent metaconid, and well-developed metastylid. However, the poorly developed mesoconid is an uncommon feature for H. macedoniensis. The described morphological features alone are not fully adequate to conclusively discriminate between Sciurus and Hylopetes. As a matter of fact, deep anterosinusids associated to variably developed anteroconulids and a posteriorly projected posterolophid are the main distinctive morphological traits of Hylopetes. Unfortunately, these features are not preserved in the studied specimen thereby preventing any conclusive and more detailed taxonomic attribution. Due to the morphological and biometrical differences with the sciurid species from MCC described above, this tooth represents an additional indeterminate taxon that is referred to as Sciurinae indet.

The fossil squirrels described herein provide useful information that improves our knowledge of the rodent bioevents at the end of the Messinian and, more generally, of the Neogene mammal biochronology of Europe. As previously evidenced by the analysis of fossil mammals from Moncucco Torinese, this locality can be referred to the Late Turolian (MN13) (Alba et al., 2014 and Colombero et al., 2014b). As far as the sciurids are concerned, the presence of H. hungaricus at Moncucco Torinese is consistent with the broad chronological range of this taxon and H. cf. hungaricus that spans from the late Vallesian to the Early Villanyian of central and south-eastern Europe (Daxner-Höck, 2004, Kretzoi, 1962 and Mörs et al., 1998). Pliopetaurista. pliocaenica appeared in south-western Europe during the Late Turolian (MN13), in the Spanish localities of Purcal 25 and 24A (García-Alix et al., 2007 and García-Alix et al., 2008) and it has been successively found in some Ruscinian, Villanyian and Biharian localities of western and central Europe (e.g., Adrover et al., 1993, Black and Kowalski, 1974, García-Alix et al., 2007, Mein, 1970, Minwer-Barakat et al., 2012 and Mörs et al., 1998). The occurrence of these taxa at Moncucco Torinese fits well with their known biochronological ranges. The occurrence of S. warthae, represents the earliest documented report of the genus Sciurus in Europe. This species and S. cf. warthae have been also found in some Ruscinian, Villanyian and Biharian localities of Poland, Germany, and Italy (Black and Kowalski, 1974, Dahlmann, 2001, Siori and Sala, 2007 and Sulimski, 1964). Tree squirrels of the genus Sciurus are extremely rare in the fossil record. High humidity in soil can lead to the corrosion and the breakage of the bones of small mammals (Andrews, 1990). Thus, densely forested areas, the typical habitat of tree squirrels, can be scarcely conducive to the preservation of fossil remains. Tree squirrels were probably less abundant than other rodents in the original biocenoses of Moncucco Torinese, probably representing rare elements of the original mammal communities as similarly hypothesized for other assemblages of fossil rodents (Emry et al., 2005). Moreover, considering the strong importance of nocturnal birds of prey as small mammal bone accumulators (Andrews, 1990) compared to other diurnal predators, the diurnal lifestyle of sciurids of the tribe Sciurini (see Thorington et al., 2012) may represent another factor that contributes to underestimate the abundance of tree squirrel within original rodent communities. As a matter of fact, diurnal predators, including both mammalian and avian taxa, have high corrosive digestive processes that do not favor the conservation of the bones in pellets and scats. On the contrary, in many species of nocturnal birds of prey, the digestion does not or can only partially affect mineralized components such as bones and teeth (Andrews, 1990). Since predation is one of the main cause of death for small mammals and probably the most important single factor that preside over the accumulation of small mammal bones (Andrews, 1989), the digestive processes of predators are among the most important biostratinomic events that affect the earliest taphonomic phases of the fossilization of the small mammal bones. Moreover, experimental evidences indicate that bones included in pellets and scats of predators are protected from weathering also for a long time (Andrews, 1990), thus increasing the potential of their successful fossilization. However, rather diverse sciurid assemblages, have been found within large rodent samples in fluviatile deposits (Cuenca-Bescós and Canudo, 1992), thus suggesting that inadequate sampling is probably one of the main biases in detecting rare taxa such as tree squirrels. As a matter of fact, the material of S. warthae collected at Moncucco Torinese consists of five teeth out of 2800 rodent teeth collected after washing and sieving more than 18 tons of sediments. Therefore, it appears that our knowledge about the evolutionary history of the genus Sciurus is negatively affected by paleoecological and taphonomical factors that, together with inadequate sampling, concur to compromise the reconstruction of the evolutionary events of this genus, including diversification and dispersal. Our data clearly indicate that Sciurus was already present in Europe in the Messinian, even though an earlier appearance cannot be excluded. The sciurids from the Late Turolian of Moncucco Torinese include some taxa that are also present in the Ruscinian of Europe such as S. warthae and P. pliocaenica, thereby suggesting that the sciurid communities of central Europe were not affected by any abrupt turnover at the transition between Turolian and Ruscinian. Similar conclusions are also drawn for other rodent taxa such as hystricids, murids, glirids and cricetids since several taxa common in the Early Ruscinian of Europe were already present at the end of the Turolian in NW Italy (Colombero et al., 2013 and Colombero et al., 2014b).

The scarcity of sciurid fossil remains prevent an accurate analysis of the paleobiogeographic history of this group. H. hungaricus (and/or H. cf. hungaricus) have been previously found in central, eastern and south-eastern Europe (Dahlmann, 2001, Daxner-Höck, 2004, Kretzoi, 1962 and Mörs et al., 1998). The report from Moncucco Torinese and its occurrence at Brisighella expand its paleogeographical range with the inclusion of north-western and central Italy. The occurrence of P. pliocaenica at the end of the Messinian in Italy confirms the expansion of this taxon from the Iberian Peninsula to the central-southern regions of Europe, slightly before the Mio/Pliocene boundary (see, e.g., Colombero et al., 2014b, García-Alix et al., 2007 and García-Alix et al., 2008). Finally, the occurrence of S. warthae at Moncucco Torinese suggests that the European distribution of this genus expanded at least during the latest part of the Miocene.

Flying squirrels of the genus Hylopetes are currently widely distributed in South-East Asia, inhabiting a variety of forested habitats. The morphology of the teeth of H. hungaricus seems to indicate a close relationship with H. spadiceus. This extant species inhabits a variety of closed biotopes including primary forests, as well as degraded and cultivated forests, thereby suggesting a certain degree of environmental tolerance (Thorington et al., 2012). Similar environmental requirements might be hypothesized for H. hungaricus. Although Pliopetaurista does not have a clearly defined extant relative, it belongs to the tribe Pteromyini, suggesting the presence of some kind of forested areas in the original paleobiotope. Sciurus warthae displays a dental morphology strongly reminiscent to that of S. vulgaris, the extant Eurasian Red squirrel to which is closely related. Sciurus vulgaris is an arboreal species that requires extended forested territories, decreasing in number or even disappearing in highly fragmented habitats. Sciurus lis, the Japanese Squirrel and the extant closest relative of S. vulgaris is also linked to the presence of primary and secondary forest. Similar environmental requirements can be confidently assumed also for S. warthae.

Remains of flying and tree squirrels are extremely rare in the Upper Miocene deposits of Moncucco Torinese (nine specimens out of more than 2000 dental remains), representing less than 5‰ of the total amount of recovered rodent teeth. However, they suggest that closed habitats or at least connected forested areas were present at that time in the north-western sectors of Italy. These conclusions are also supported by the occurrence of other arboreal rodents such as glirids, which are rather common at Moncucco Torinese, where are represented by four species (Eliomys aff. intermedius, Glirulus lissiensis, Glis minor and Muscardinus vireti) (Colombero et al., 2014b). Strongly humid conditions, however, were not postulated based on the composition of terrestrial gastropods assemblages (Harzhauser et al., 2015) that indicated mostly dry conditions and presence of rocky outcrops associated to rare moist habitats in the original paleobiotope. This view is perfectly consistent with the paleobotanical data that hypothesized the presence of extensive “sub-humid” forests in NW Italy during the latest part of the Messinian (Bertini and Martinetto, 2011).

The data reported herein expand our knowledge about the evolutionary history of the genus Sciurus supporting the hypothesis that the “S. vulgaris clade” arose during the Late Miocene (Mercer and Roth, 2003, Oshida et al., 2009, Pečneróva and Martínková, 2012 and Villalobos and Gutierrez-Espeleta, 2014). The material from Moncucco Torinese indicates that the genus Hylopetes was widespread in the emerging Italian Peninsula at the end of the Messinian, and that other pteromyine squirrels, such as P. pliocaenica, were present in NW Italy slightly before the Pliocene. The squirrel material from Moncucco Torinese documents the first reliable co-occurrence of Sciurini and Pteromyini (sensu Steppan et al., 2004) in the Late Miocene of Europe.

Squirrels are extremely fine proxies for paleoecological analyses due to their strict ecological requirements. As demonstrated herein, adequate sampling provided higher probability of detecting the rarest taxa allowing to refine the original paleobiodiversity spectrum, with the inclusion of uncommon and highly informative taxa such as the tree squirrels. As a final note, it is interesting to evidence that the occurrence of tree and flying squirrels in NW Italy strongly supports geochemical and paleontological evidence suggesting that increased humid conditions took place during the Lago-Mare phase at the end of the Messinian Salinity Crisis (Bertini, 2006, Bertini and Martinetto, 2011, Carnevale et al., 2006 and Roveri et al., 2014).