Sciurus warthae Sulimski, 1964

Colombero, Simone, Pavia, Giulio & Carnevale, Giorgio, 2014, Messinian rodents from Moncucco Torinese, NW Italy: palaeobiodiversity and biochronology, Geodiversitas 36 (3), pp. 421-475 : 454-457

Sciurus warthae Sulimski, 1964

( Fig. 8A, B )

Sciurus warthae Sulimski, 1964: 162 , text fig. 3, pl. 3, figs 1-4. — Marchetti et al. 2000: 90, figs 3, 9-14. — Dahlmann 2001: 49, pl. 7, figs 20-27.

Sciurus cf. warthae – Black & Kowalski 1974: 465, pl. 12, figs 1, 2. — Siori & Sala 2007: 210, figs 2, 1-2.

TYPE LOCALITY. — Węże 1, Poland.

OCCURRENCE IN THE STUDIED LAYERS. — MCC5.

REFERRED MATERIAL. — A single isolated M3; a single isolated m1.

MEASUREMENTS. — M3:MGPT-PU 128219 (2.84 × 2.60); m1: MGPT-PU 128221 (2.28 × 2.42).

DESCRIPTION

M3

Triangular in outline; central basin deep and broad, moderately expanded posteriorly without evidence of crenulation; large and rounded protocone gradually rising from the endoloph; anteroloph lower than protoloph; paracone high and vertical; central basin bordered by a continuous rim interrupted just behind the paracone, where a cusplet occurs; three roots.

m1

Rhomboid in outline; molar basin without crenulation; the metaconid constitutes the higher cuspid followed by the hypoconid; protoconid less developed than hypoconid; well-developed and distinct entoconid resulting in an angular postero-lingual outline; anterolophid low; metalophid scarcely visible due to wear; mesostylid very poorly marked and represented by a weak enamel swelling; a notch is present anterior to the entoconid; mesoconid very low and separated from protoconid and hypoconid by two notches; roots not preserved.

REMARKS

The postero-lingual outline of the m1 is notably angular with a distinct entoconid, a feature present in tree squirrels and most of the flying squirrels ( de Bruijn 1999). Among flying squirrels the morphology of the teeth of the genera Hylopetes Thomas, 1908 and Neopetes Daxner-Höck, 2004 is the most similar to the studied material. However, the dental morphology of the extant species of Hylopetes (see Bouwens & de Bruijn 1986 and Thorington et al. 1996, 2002), and comparison with some teeth of Hylopetes lepidus Horsfield, 1822 (IVAU and UCBL collections) evidenced the existence of some differences with the studied material. In particular, the m1-2 of extant Hylopetes are characterized by protoconid and hypoconid of roughly similar size and structure; both cuspids are high, distinctly vertical, remarkably protruding over the labial margin and from the postero-labial corner of the tooth; the protolophid can be easily distinguished from the hypoconid because it extends slightly posteriorly. In the single m1 from MCC the protoconid is less developed than the hypoconid; the hypoconid does not protrude over the postero-labial corner; the labial cuspids are not as distinct from the cingulids as in extant Hylopetes , the posterolophid constitutes a lingual extension of the hypoconid and does not extends posteriorly as in Hylopetes . In addition, in extant Hylopetes the anterolophid is well developed, always forming an evident anterosinusid and usually a distinct anteroconulid that is absent in the studied specimen; the mesostylid of extant Hylopetes is usually present and somewhat isolated whereas it is barely sketched in the single m1 from MCC. In the M3 of extant Hylopetes the protocone is well distinct from the endoloph, whereas in the specimen from MCC the protocone is broader and more rounded, gradually rising from the endoloph. Moreover, the enamel of the studied teeth is not sculptured as it usually occurs in unworn teeth of Hylopetes . In summary, Hylopetes displays more isolated, distinct and higher tubercles, a pronounced anterosinusid and more sculptured and crenulated enamel with respect to the studied molars. Daxner-Höck (2004) included some Neogene species of sciurids previously assigned to the genus Hylopetes , such as Hy- lopetes macedoniensis Bouwens & de Bruijn, 1986 and Hylopetes hoeckarum de Bruijn, 1998 , within the genus Neopetes . Neopetes differs from Hylopetes in having extremely low tooth-crowns and almost no sculptured enamel on unworn teeth; the lower teeth differ considerably by their rhomboid outline and by the presence of pronounced entoconids and mesostylids separated by a wide notch (Daxner-Höck 2004). Direct examination of material belonging to Neopetes macedoniensis ( Bouwens & de Bruijn, 1986) from the latest Miocene of Maramena revealed that this species differs from the material of MCC also in the presence of better developed anterolophulids, commonly present anteroconulids and anterosinusids and more distinct labial cuspids in the lower molars. A very well-defined mesostylid is also present in Neopetes hoeckarum ( de Bruijn, 1998) from Lower and Middle Miocene of Central Europe (see Daxner-Höck 2004). Therefore, the studied molars cannot be assigned to Neopetes especially because of the absence of mesostylid and anterosinusid and the presence of less distinct tubercles.

The morphology of the studied lower molars is remarkably similar to that of Sciurus vulgaris Linnaeus, 1758 , type species of the genus Sciurus Linnaeus, 1758 , with a well-developed metaconid and a distinct entoconid. Moreover, the lower teeth of S. vulgaris do not display strongly developed anterolophulids and they lack anterosinusids and anteroconulids. In addition, the m1 and m2 of S. vulgaris display a more quadrangular outline. The M3 from MCC is also very similar to that of Sciurus vulgaris in certain dental structures, including the large protocone, high paracone, very narrow basin between anteroloph and protoloph, and presence of a notch on the rim just behind the paracone.We therefore assign the studied specimen to the genus Sciurus .

The size of the teeth from MCC agrees very well with that of Sciurus warthae Sulimski, 1964 from Podlesice ( Black & Kowalski 1974), being slightly smaller than those from younger localities as Węże 1 (type locality, Sulimski 1964), Zamkowa Dolna ( Black & Kowalski 1974), Monte la Mesa ( Marchetti et al. 2000), Wölfersheim ( Dahlmann 2001), and Castagnone ( Siori & Sala 2007). The material from MCC was compared with some teeth of S. warthae from Monte La Mesa where unfortunately no M3 was found; the morphology of the m1 from the two localities is strikingly similar, especially in the well-developed metaconid, in the poorly developed mesostylid and in the isolation of the low mesoconid. According to the original description of the type assemblage from Węże 1, S. warthae does not exhibit a mesostylid or it is very weak. The material from MCC is therefore assigned to S. warthae because of its remarkable similarity to the specimens from the type locality and from the other localities of Europe.

The material of MCC was compared with Hylopetes magistri van den Hoek Ostende & Reumer, 2011 from the Pleistocene of Tegelen ( Reumer & van den Hoek Ostende 2003; van den Hoek Ostende & Reumer 2011). This species was originally identified as Hylopetes debruijni Reumer & van den Hoek Ostende, 2003 name already preoccupied by a different species, Hylopetes debruijni Mein & Ginsburg, 2002 , and for this reason subsequently modified to H. magistri (see van den Hoek Ostende & Reumer 2011 for further details). The specimens from MCC differ from H. magistri in having a slightly smaller size and in the absence of enamel crenulation that barely affects two teeth from Tegelen. The overall morphological pattern of the lower molars is very similar since m1 and m2 display a well-developed entoconid, small and isolated mesoconid, absence of anterosinusid and anteroconulids, well-developed metaconid, absence or strong reduction of mesostylid in the lower molars. Moreover, the specimens of M3 from Tegelen are also very similar to those from MCC since they show a high paracone and a low and rather continuous rim from which a large protocone arises. In our opinion, the absence of well developed anterosinusids, anteroconulids and mesostylids as well as the occurrence of poorly isolated cuspids in the material from Tegelen do not support their assignment to Hylopetes or Neopetes . In addition, feeble crenulations as those affecting two teeth (upon 17 specimens) from the collection of Tegelen represent a weak diagnostic character for ascribing this material to Hylopetes or Neopetes . In fact, the presence of crenulations and ornamented enamel is not an exclusive feature of flying squirrels, but it can occur also in many genera of ground and tree squirrels ( Thorington et al. 2005). The overall morphology of H. magistri fits better with that of the genus Sciurus Linnaeus, 1758 . Moreover, pitted enamel can be observed in Sciurus granatensis and Sciurus vulgaris ( Thorington et al. 2005: 954) thus suggesting that moderate enamel ornamentation could also rarely affect the teeth of Sciurus . Therefore, we tentatively assign H. magistri to the genus Sciurus . The new combination is therefore Sciurus magistri ( van den Hoek Ostende & Reumer, 2011) . The size and the morphological pattern of the teeth are very similar to S. warthae thus suggesting that S. magistri may be considered a junior synonym of S. warthae . Nonetheless, the presence of the slight enamel ornamentations, up to date unknown in S. warthae , prevents us to definitely synonymize these two taxa.

The record of S. warthae from MCC represents the oldest report of the genus Sciurus in Europe. S. warthae was previously known from the slightly younger fissure fillings of Podlesice (MN14) ( Black & Kowalski 1974). To date S. warthae has been reported from some Pliocene and Pleistocene localities of Poland ( Sulimski 1964; Black & Kowalski 1974), Germany ( Dahlmann 2001) and Italy ( Marchetti et al. 2000; Siori & Sala 2007). The few known specimens of this poorly documented taxon do not allow tracing its relationships within the genus Sciurus whose paleontological record is very scarce before the Pliocene ( Emry et al. 2005). Sciurus sp. from the latest Miocene of Ertemte 2 ( Qiu 1991) differs from Sciurus warthae in having a slightly better developed mesostylid, mesostyle in P4 absent and a weaker parastyle in the M1-2. The strong morphological affinities existing between S. warthae and S. vulgaris seem to indicate a close phylogenetic relationship between these two species. The earliest record of S. vulgaris is probably that from the Middle Pleistocene of Hórvölgy Cave, Hungary ( Lurz et al. 2005). The first reliable records of the genus Sciurus are those of Sciurus lii Qiu & Yan, 2005 from the Early to Middle Miocene locality of Shanwang ( China) ( Qiu & Yan 2005) and Sciurus olsoni Emry, Kort & Bell, 2005 from the Clarendonian (early-Late Miocene) of Nevada ( Emry et al. 2005).? Sciurus sp. is reported in the Late Miocene of Anatolia ( Bosma et al. 2013) thus suggesting that the genus Sciurus was already present in western Asia before the end of the Miocene. The record of MCC testifies that Sciurus entered Europe at least slightly before the beginning of the Pliocene.

Figures

FIG. 8. — Isolated teeth of Sciuridae Fischer,1817 from Moncucco Torinese:A, B, Pliopetaurista pliocaenica (Depéret,1897);A, MGPT- PU 128220,M3 dex.; B, MGPT-PU 128221,m1 dex.; C, D, Sciurus warthae Sulimski, 1964; C, MGPT-PU 128347, M3 dex.; D, MGPT- PU 128218, m1 sin. Scale bar: 1 mm.