Spermophilus praecox, Sinitsa & Pogodina, 2019

Sinitsa, Maxim V. & Pogodina, Nataliya V., 2019, The evolution of early Spermophilus in eastern Europe and the antiquity of the Old World ground squirrels, Acta Palaeontologica Polonica 64 (3), pp. 643-667 : 654-660

Spermophilus praecox sp. nov.

Figs. 5–7 .

ZooBank LSID:urn:lsid:zoobank.org:act:9EC89A65-A40E-42FC-8418-

55A8DA818088

1965 Citellus (cf. Urocitellus ) nogaici Topatschevky, 1957 ; Gromov et al. 1965: 178–181 (in part), fig. 36: 7.

1989 Citellus (Urocitellus) cf. nogaici Topachevski,1957 ; Topachevsky and Nesin 1989: 23–25, fig. 5.

2007 Spermophilus cf. nogaici Topachevski, 1957 ; Stadnik and Dema 2007: 361–364.

Etymology: From the Latin praecox , premature or precocious; in reference to the early occurrence of the species in the fossil record.

Holotype: NMNHU-P 41-5598 , left M1–M2.

Type locality: Kotlovina 2, Reni District, Odessa Region, Ukraine.

Type horizon: Early Pleistocene, Gelasian, late Villanyian.

Material.—From late Pliocene, middle Villanyian, Kryzhanovka 2: ZIN 105160/1, P3; ZIN 105160/2, P4; ZIN 105160/3– 5, M1–M2; ZIN 105160/6, M3; ZIN 105160/7–8, m3.

From Early Pleistocene, late Villanyian, Kotlovina 2: NMNHU-P 41-5588–5590, P4; NMNHU-P 41-5591–5600, M1–M2; NMNHU-P 41-5601–5602, M3; NMNHU-P 41- 5603–5605, p4; NMNHU-P 41-5606–5608, NMNHU-P 41- 5610, m1–m2; NMNHU-P 41-5609, m3; ZIN 105163/2, M1– M2; ZIN 105163/3, m1–m2; ZIN 105163/4, m3; Kotlovina 3: NMNHU-P 41 5611, P4; NMNHU-P 41-5612–5615, M1– M2; NMNHU-P 41-5616, M3; NMNHU-P 41-5617–5618, p4; NMNHU-P 41-5619–5625, m1–m2; NMNHU-P 41-5626– 5628, m3; ZIN 105163/1, mandible with p4–m3; Yuzhny: GIN 1166/1, P3; GIN 1166/2–3, P4; GIN 1166/4–9, M1–M2; GIN 1166/10–12, M3; GIN 13–17, m1–m2; GIN 1166/18, m3.

From Early Pleistocene, early Biharian, Morskoy: NMNHU-P MoT-1–4, P3; NMNHU-P MoT-6–10, P4; NMNHU-P MoT-11–30, M1–M2; NMNHU-P MoT-31–33, M3; NMNHU-P MoT-34–44, p4; NMNHU-P MoT-45–57, m1–m2; NMNHU-P MoT-58–61, m3; NMNHU-P MoT-62, mandible with p4–m3; NMNHU-P MoT-63, mandible with incisor, NMNHU-P MoT-64, edentulous mandible.

Diagnosis.—Medium-sized, primitive species of the genus with small P3 having a diminutive protocone and lacking the anteroloph; P4–M2 that consistently exhibit the endoloph and mesostyle, large metaconule, and rudimentary lingual metaloph; M3 is simple with smoothened metacone, metaconule, and labial metaloph; p4 trigonid is 12–23% labiolingually narrower than talonid, lacking lingual anterolophid and lingual metalophid; and m1–m2 with weak, shortened metalophid.

Cheek teeth similar in size to S. nogaici , smaller than S. fulvus , S. major , S. polonicus , S. primigenius , S. ralli , S. relictus , S. superciliosus , and S. tologoicus , but larger than S. alashanicus , S. citelloides , S. citellus , S. dauricus , S. pygmaeus , S. suslicus , S. taurensis , and S. xanthoprymnus . Differs from all species of the genus other than S. polonicus and S. primigenius in retaining relatively lower crowned premolars and molars; small, simple P3 with rudimentary protocone and anterior valley; weak anterior valley, anterostyle, metaloph of P4–M2 accompanied by enlarged posterior valley, salient and circular metaconule, more inflated hypocone, and consistently present endoloph and mesostyle; primitively shortened metalophid of p4–m3; and elongated p4 with labiolingually compressed trigonid, cuspate anteroconulid, weak to indistinct lingual anterolophid and lingual metalophid. Differs from S. polonicus and S. primigenius in being smaller; having stronger endolophs and more globular metaconules of P4–M2; larger M3 metaconule and wider metaloph; and possessing a p4 hypoconulid. Further differs from S. polonicus in having lightly-built, less cuspate dentitions with more trenchant ridges; longitudinally oriented endolophs of P4–M2; more pronounced M3 metacone; stronger metalophid of p4–m3; and posteriorly tapered talonid of m3 that lacks a hypoconulid and postflexid.

Description.— Mandible: Four partial mandibles referable to S. praecox sp. nov. have been recovered from Kotlovina 2 (ZIN 105163/1) and Morskoy (NMNHU-P MoT-62, NMNHU-P MoT-63, NMNHU-P MoT-64), preserving the main portion of the mandibular body with most of the ramus and diastema being missing ( Fig. 5 ). The body is very deep and narrowed mediolaterally and the diastemal portion is robust. The diastema seems to be relatively shallow ( Fig. 5A ), and forms no acute transition between the horizontal and vertical edges of the diastemal depression seen in most Spermophilus . Dorsally, the depression is marked by a well-defined shelf for the attachment of the anterior mandibular part of the buccinator muscle (buccinator ridge) that extends anteriorly from the lingual rim of the p4 posterior alveolus along the dorsal margin of the bone ( Fig. 5A 2 ). The area of the mental foramen is missing in all specimens. The preserved posterior rim of the foramen, preserved in ZIN 105163/1 ( Fig. 5A 1 ), suggests that the species had a relatively small mental foramen placed roughly at the middle of the diastema, about 2.41 mm anterior to p4. The masseteric fossa is a vast area with widely rounded anterior edge terminating below the posterior root of p4 ( Fig. 5A 1, B 1, C 1 ). The anterior extent of the fossa is not marked by either a prominent crest or bulging for the anterior fibers of the anterior deep masseter muscle observable in some primitive marmotines ( Sinitsa 2018). The fossa is floored by a pronounced lower masseteric ridge, although the ridge does not project strongly laterally. The upper masseteric ridge is smooth but well-elevated above the lateral surface of the bone. The ascending ramus rises gradually opposite the m1–m2 embrasure. The medial surface of the mandibular body is noticeable for an ellipsoidal mylohyoid depression, the anterior and dorsal edge of which is rimmed by a strong mylohyoid line ( Fig. 5A 2, B 2, C 2 ). The ventral part of the depression bears five to seven diminutive venous foramina and a set of irregular grooves marking the paths of accessory veins on the bony surface. As seen in NMNHU-P MoT-64 ( Fig. 5C ) the angular process of S. praecox was relatively large and only slightly inflected inwards.

Dentition: The P3 is a small peg-like tooth with simple, gently ellipsoidal crown ( Fig. 6A–D ). The posterolabial flattening, marking the contact with P4, is very slight, presumably due to the small size of the tooth. As in S. nogaici and other derived marmotines, the crown is formed by two major cusps, the protocone and paracone. In contrast to S. nogaici and all extant species of the genus, however, the protocone in S. praecox sp. nov. is a diminutive cusp, more than three times smaller than the paracone. The protoloph appears to be a massive, uninterrupted ridge when unworn, which is particularly the case of the P3s from Morskoy ( Fig. 6B–D ), showing nearly fused protocone and paracone connected by a massive protoloph. A small anterocone, forming a recessed anterior valley, is present at the anteriormost margin of the crown. The anteroloph is not defined in all but one specimen (NMNHU-P MoT-3) whose anterior portion bears an extremely short, cuspate anteroloph. The posterior valley is simple, surrounded by a crescent-shaped posteroloph with no recognizable cusps. The tooth possesses a strong endoloph between the protocone and posteroloph. The crown is narrowed toward its base and continues into a simple root with a deep longitudinal groove on the labial surface.

The P 4 is a rounded triangle in occlusal outline ( Fig. 6E– I ). The anterior lobe is relatively small, always narrower labiolingually than half of the total crown width. The anteriormost edge of the lobe is topped with a well-developed, conical or, rarely ( NMNHU-P MoT-6, NMNHU-P MoT-10), comblike anterocone ( Fig. 6H, I ). The lingual arm of anteroloph consists of two sections of nearly equal length: the higher and bulky labial portion adjacent to the anterocone, and the much lower and narrower lingual portion. In most specimens the anteroloph fails to connect with the base of the protocone, thus leaving the anterior valley opened lingually. Apart from three specimens ( NMNHU-P MoT-8– 10) the anterostyle is weak to nearly absent. On the opposite, labial side of the anterior valley, the labial arm of the anteroloph extends posterolabially from the anterocone and terminates abruptly at the bottom of the labial anterosinus. The parastylar cusplet is present in all but two P4s ( NMNHU-P MoT-8, NMNHU-P MoT-10). The protocone is the tallest principal cusp followed by the metacone and paracone. The paracone and metacone are less closely spaced than in S. nogaici , resulting in a much anteroposteriorly longer central valley, which exceeds the anterior valley in both length and width. There is a prominent mesostyle at the central part of the central sinus. The protoloph is straight, uninterrupted, and decreases in width and height at its midlength. The metaloph, in contrast, is slightly longer, narrower, and about two to three times lower than the protoloph in unworn specimens. A salient, large, rounded to slightly anteroposteriorly compressed metaconule is well-bounded from the metaloph by abrupt constrictions; it is closely appressed to the lingual wall of the protocone but separated from it by a strong groove. On NMNHU-P MoT-9 the labial metaloph bears a faint second metaconule. The posterior valley is roughly subequal in size to the central one ( Fig. 6E–G ), or slightly shorter in the specimens from Yuzhny and Morskoy Fig. 6H, I ). The endoloph is a strong longitudinally oriented crest that extends posteriorly from the protocone to the hypocone, from which also extends a strong posteroloph. The rudimentary hypocone appears well elevated above the base of the crown: in direct posterior aspect the apex of the cusp is aligned with the tip of the metacone .

The M1–M2 is triangular in outline ( Fig. 6J–P ). The labial part of the crown is markedly longer than the lingual part. The anterior lobe, as in P4, is relatively short labiolingually, constituting 65.5–76.9% (mean 71.6%) of the total width of the crown. A moderately developed anterostyle is present on the anterior slope of the protocone in most specimens and defines the lingual end of the anteroloph that runs across the anterior lobe, ending labially just before reaching the deepest point of the anterolabial sinus. A shallow indentation on the anterolingual side of the crown, just between the anterostyle and protocone, represents a rudimentary antesinus. The anterocone is pointed but weak; posterior to it a diminutive parastyle is observable in one of the three from Kryzhanovka 2, five of seven M1–M2s from Kotlovina 2, two of four teeth from Kotlovina 3, one of five from Yuzhny, and nine of the 18 from Morskoy ( Fig. 6K, M, O ). The central valley, formed by a complete and straight protoloph, and rudimentary metaloph is substantially longer anteroposteriorly than the anterior valley. At the labial side of the central valley is a knob-like, pointed mesostyle that partially dams the exit of the central sinus. The angle between the protoloph and metaloph ranges from 8.5 to 11.7°. The rudimentary and narrow metaloph with restricted lingual and labial portions is dominated by a large metaconule. The cusp appears to be more pronounced and globular in the specimens from Kotlovina 2 and 3 ( Fig. 6K ), and slightly compressed anteroposteriorly in those from Kryzhanovka 2, Yuzhny, and Morskoy ( Fig. 6N, O ). The posterior valley is somewhat anteroposteriorly shorter than the central valley. It is rimmed posteriorly by a massive, albeit low, posteroloph that extends labially from a high hypocone bulging and fades out before the contact with the base of the metacone. The endoloph is consistently present in all specimens, while showing some signs of reduction in those from Morskoy.

The M 3 is slightly (7–14%) shorter than wide and resembles a rounded triangle in occlusal outline ( Fig. 6Q–W ). The posterior lobe is relatively small and weakly defined. The anteroloph is low lingually but continuous from the anterior wall of the protocone to the narrow anterolabial sinus, closing off a vast anterior valley labially. Both the anterostyle and antesinus are weak to indistinct. The anterocone is a small and pointed cusplet barely discernible from the anteroloph. One specimen from Yuzhny ( GIN 1166 /10) possesses a very faint parastyle. The protocone and metacone are nearly equal in height and connected by a massive, straight protoloph. The posterior and central basins are partially separated by a moderately developed metacone, from the lingual side of which departs a short, but prominent labial metaloph terminating roughly at the center of the tooth crown. In one M3 ( NMNHU-P 41-5602 ) the crest is complete, albeit shallow, and continuous from the metacone to the metaconule ( Fig. 6R ). The metaconule is a salient but low cusp just labial to the posterolabial side of the protocone. There is no hypocone or true endoloph distinguishable. The posteroloph generally runs from the metaconule along the posterolingual margin of the crown to the voluminous posterocone, then curves around the posterolingual edge of the tooth, and diminishes gradually before reaching the metacone. On the lightly worn specimens from Morskoy ( NMNHU-P MoT-31, NMNHU-P MoT-32) the loph fails to connect to the metaconule, leaving the posterior valley opened lingually ( Fig. 6V, W ). The three roots are ellipsoidal to circular in cross section, with the posterior root being only slightly larger than the anterolabial and, especially, anterolingual roots .

The p4 of S. praecox sp. nov. is clearly premolariform and similar to the deciduous lower premolars of S. nogaici in overall proportions ( Fig. 7A–G, Z ). The trigonid is moderately compressed labiolingually, about 12–23% narrower than the talonid, which gives the tooth crown a subtriangular to subrectangular occlusal outline. The two anterior cusps, metaconid and protoconid, are the tallest of the main cusps and are closely appressed; the metaconid is slightly taller than the protoconid. The metaconid is anterolingual in position, and is distinctly separated from the protoconid by a slit-like posterior portion of the trigonid basin. A widely triangular anterior side of the crown bears a weak anteroconulid, which is aligned with a shallow and smoothened labial anterolophid. There is no lingual anterolophid in any of the p4s. The metalophid is thin, tapering lingually, and low. All examined specimens, except two teeth from Morskoy (NMNHU-P MoT-34, NMNHU-P MoT-43) lack the lingual metalophid ( Fig. 7D, G ) seen in more derived members of the genus, including S. nogaici . A low ectolophid is present along the labial margin of the tooth, in four out of 18 specimens displaying a small mesoconid at the central part of the ridge ( Fig. 7B, D, F, Z 1 ). The hypoconid protrudes more anterolabially than it does in S. nogaici and other Spermophilus , thus causing the posterolingual expansion of the sinusid. The entoconid is distinct as a labiolingually compressed ridge-like cuspid. A transition from the entoconid to posterolophid is well defined due to the presence of a massive hypoconulid that forms the entire posterior wall of the crown. A small mesostylid is connected to the base of the metaconid by a faint metastylid crest. The tooth possesses two roots supporting the trigonid and talonid; the posterior root is thicker and expanded lingually.

The m1–m2 is a rectangle with a slightly narrower anterior portion and a gently curved posterolingual angle Fig. 7H–S, Z ). The trigonid is about one and a half times the height of the talonid. Both the metaconid and protoconid are narrow and pointed in unworn teeth. The metaconid is notably taller but appears to be narrower at its base than the protoconid. The anterolophid connects the labial base of the metaconid to the anteriormost side of the protoconid, forming the anterior wall of the tooth crown. The anteroconulid is missing in all examined specimens. An elongated metalophid that at least partially dams the trigonid basin posteriorly is observable in three out of the seven m1–m2s from Kotlovina 2, in four of the seven teeth from Kotlovina 3, in three of the five specimens from Yuzhny, and in seven of 15 m 1–m2s from Morskoy, suggesting that the ridge was present in all m1s ( Fig. 7M, N, Q, S ), while being deeply reduced to absent in m2s ( Fig. 7Z 1 ). A small to moderately developed mesostylid is variably present immediately posterior to the metaconid. Three of six teeth from Kotlovina 2, three of four from Kotlovina 3, one of three specimens from Yuzhny, and five of 17 teeth from Morskoy demonstrate a weak metastylid crest between these two cusps ( Fig. 7J, K, N–P, R, Z 1 ). The ectolophid is a straightened ridge that joins the posterior part of the protoconid and the anterolingual base of the hypoconid. It varies slightly in shape among specimens from evenly smooth and uniformly thick to slightly tapered and gradually narrowed both anteriorly and posteriorly. Some specimens ( Fig. 7K, O, Q, R ) appear to retain a more primitive morphology with a narrow ectolophid that gently arcs lingually. The hypoconid is only slightly lower than the protoconid, and about 20–40% taller than the rudimentary, lophate entoconid. The crescentic posterolophid is as high as the primary lophids; it continues along the posterior margin of the crown to merge with the entoconid, and encloses the talonid basin. Two specimens (NMNHU-P 41-5608, NMNHU-P 41-5621) show a diminutive hypoconulid on the posteriormost extent of the crest ( Fig. 7J ). The root system consists of four slender roots, of which the posterolabial one is the longest and the strongest root.

The m3 has a distinctly triangular crown with narrow talonid due to a weak labial expansion of the hypocone Fig. 7T–Y, Z ). The trigonid is about 25% taller than the talonid. The metaconid and protoconid are of similar size, and the two cusps are connected by a continuous anterolophid. A very faint anteroconulid sitting directly anterior to the protoconid is present in two teeth (NMNHU-P MoT-58 and NMNHU-P MoT-60; Fig. 7V, X ). The metalophid is strongly reduced: it is completely absent in two out of the four specimens from Kotlovina 2, two of the three teeth from Kotlovina 3, and three of the five m3s from Morskoy Fig. 7U–W, Z 1 ). The other m 3 specimens possess an extremely shortened crest evident as a lingual protrusion of the protoconid. The ectolophid is a straight or slightly arcuate crest that extends from the anterolingual wall of the hypoconid to the posterolingual base of the protoconid. The anterior and posterior constrictions, seen in most species of the genus, are not as pronounced, and become evident only in heavily worn specimens. A poorly-defined ectostylid, partially incorporated with the hypocone, is present in about half of m3s ( Fig. 7T, V, Z 1 ). The hypoconid and a somewhat lower entoconid are located at the posterolabial and posterolingual extremes of the crown, respectively, and dominate the talonid portion of the tooth. The hypoconid varies in size from a rather small cusp, comparable to the protoconid in the teeth from Kryzhanovka 2, Kotlovina 2, and 3 ( Fig. 7U, V, T, Z 1 ), to a more voluminous, labially expanded cusp in those from Yuzhny and Morskoy ( Fig. 7W–Y ). The entoconid is very shallow and reduced with barely discernible entoconulid and entolophid; it fades out gradually labially. The groove between the entoconulid and the hypoconid is only barely discernible in m3s from Kotlovina and Yuzhny ( Fig. 7U, V, Z 1 ); whereas the groove is more pronounced in the two molars from Kryzhanovka 2 and Morskoy ( Fig. 7T, W–Y ). Apart from NMNHU-P MoT-59 showing a sign of postflexid barely separating the remnant hypoconid from the main portion of the posterolophid, there is no sign of either the postflexid or the hypoconulid in any of the m3s. The root structure is similar to that in S. nogaici with four distinct roots that diminish in size from the largest posterolabial to the smallest posterolingual root.

Remarks. —The recognition of this new species helps to resolve the dilemma faced in previous studies of late Pliocene and Early Pleistocene Spermophilus from eastern Europe ( Gromov et al. 1965; Topachevsky and Nesin 1989; Stadnik and Dema 2007), the extensive variability in dental morphology among Villanyian and Biharian specimens attributed to S. nogaici . Presumably because of the lack of diagnostic specimens, primarily the P3s, Topachevsky and Nesin (1989) cited Spermophilus cf. nogaici as occurring at Kotlovina 2 and 3, noting that these specimens were among the earliest records of this taxon, slightly differing from the type material by having more pronounced mesostyles, mesoconids, and mesostylids. Subsequently, Spermophilus cf. nogaici has also been reported from the middle Villanyian of Zhevakhova Gora 4 (originally Zhevakhova Gora 15) in southern Ukraine ( Stadnik and Dema 2007). Based on the limited sample available to them, the authors noted that the specimens of Spermophilus cf. nogaici may have represented a new species, which is described here as S. praecox . It is perhaps not surprising that among the species of the genus S. praecox sp. nov. shows closest resemblance to S. nogaici in known parts of the dentition, and it seems obvious that these two species are closely related. In contrast to S. nogaici , however, S. praecox has substantially smaller P3, while being slightly larger in most other tooth dimensions ( Tables 1–3), and retaining what appears to be a more primitive dental morphology.

The more primitive traits of S. praecox sp. nov., as compared with S. nogaici , involve both upper and lower premolars and molars. The P3 of S. praecox , apart from its smaller size, possesses a relatively smaller protocone and larger paracone, and lacks a distinct anterior valley. The P4 is less molariform, with smaller anterior valley hardly reaching two-thirds of the transversal width of the tooth; it has a more cuspate anterocone, weaker anterostyle, stronger endoloph, proportionally larger central valley, consistently present mesostyle, larger metaconule, and more rudimentary metaloph mostly lacking its lingual portion. The M1–M2 of S. praecox differ from those of S. nogaici in possessing a primitively smaller anterior valley that, viewed occlusally, appears to be narrower transversally than the posterior valley; it also lacks a furrow-like antesinus and enlarged anterostyle. As in P4, the M1–M2s of S. praecox are notable in having a mesostyle, larger central valley, complete and strong endoloph with elevated hypocone, and a much weaker and reduced metaloph that yields a voluminous metaconule. Similarly, the M3s of S. praecox are separable from the same teeth of S. nogaici in having a less expanded anterior valley with extremely shallow antesinus and indistinct anterostyle; and a weaker metacone, metaloph, and metaconule, with the latter closely appressed to the protocone.

Compared to S. nogaici , the p4 of S. praecox is more longitudinally elongated and trapezoidal with distinctly narrower trigonid, consistently present anteroconulid, more massive hypocone and hypoconulid, stronger mesoconid, and fainter anterolophid that consists only of a rudimentary labial portion and lacks the lingual portion. The m1–m2 and m3 of S. praecox and S. nogaici are similar in most respects. However, in S. praecox the metalophids are lacking on m2–m3; and the talonid of m3 is relatively weaker and is characterized by a small hypoconid not shifted labially, a weak entoconulid and posterolophid, and no distinct hypoconulid or postflexid.

The dentition of Spermophilus praecox shows resemblances to the cheek teeth of S. primigenius and, especially, S. polonicus in possessing a small P3 with rudimentary anterior valleys, less molariform P4 and p4, inflated metaconules, and stronger mesostyles on P4–M2. Similarities to S. polonicus are certainly plesiomorphic retentions, indicating that S. praecox is more primitive than S. nogaici , in agreement with its earlier occurrence.

Despite these similarities, however, S. praecox clearly differs from S. polonicus in having relatively lightly-built cheek teeth with slender lophs, less stout, cone-shaped major cusps, and more inflated conules ( Gromov et al. 1965; Black and Kowalski 1974; MVS, personal observation). In particular, the upper third premolar of S. praecox , although represented by only a few specimens, has less elongated and narrowed anteriorly occlusal surface, with much larger paracone separated from the protocone by the protoloph ( Fig. 6A, C ). The P4 and M1–M2 are proportionally shorter anteroposteriorly, less cuspate, and show somewhat larger anterior and posterior valleys. The metaconules of these teeth are salient, more globular, and buttressed by a relatively weaker metaloph with deeply reduced lingual portions. Furthermore, the mesostyles and endolophs appear to be stronger in S. praecox than in S. polonicus . The unique configuration of the trigon in S. polonicus , with a more labially positioned hypocone relative to the protocone, further distinguishes this species from S. praecox , which shows a nearly longitudinally oriented endoloph.In contrast to S. polonicus the M3 of S. praecox possesses a salient metaconule, metacone, posterocone, and a distinct, albeit low, metaloph.

Perhaps the most pronounced differences between S. praecox and S. polonicus are in the lower dentition. The p4–m3 of S. praecox are less cuspate, and have much stronger metalophids, particularly in p4 and m1, contrasting with the more cuspate lower cheek teeth of S. polonicus , with no clearly discernible metalophids. The p4 of S. praecox has a stronger anteroconulid, mesoconid, and hypoconulid. The m3 of S. praecox differs noticeably from that of S. polonicus in having a lighter talonid that does not exhibit a clear hypoconulid, postflexid, or the labial expansion of hypoconid seen in S. polonicus . Finally, the bases of the protoconid and hypoconid of m1–m 3 in S. praecox are not so closely spaced as they are in S. polonicus .

Specific distinction of S. praecox from S. primigenius ( Kormos 1934; Gromov et al. 1965; MVS personal observations) is supported by its smaller size, larger posterior valleys, stronger endolophs with more elevated hypocones, larger metaconules, narrower anterior valleys, and incomplete metalophs of P4–M2. The M3 of S. praecox has larger metaconules and relatively broader, albeit constricted, metalophs. Differences in the lower dentition are equally apparent; for example, in comparison to S. primigenius , the p4 of S. praecox is notable in being clearly premolariform, having a labiolingually narrow trigonid, exhibiting strongly appressed metaconid and protoconid, and displaying a weaker anterolophid topped by a cuspate anteroconulid. Further, the p4 of S. praecox possesses a mesoconid and strong hypoconid, which are lacking in S. primigenius .

The dentition of S. praecox also differs from that of S. tologoicus ( Gromov et al. 1965; Erbajeva and Pokatilov 1966; MVS personal observations), the most poorly known early Old World ground squirrel from the Early Pleistocene Gelasian) of the western Transbaikal area in eastern Asia Alexeeva and Erbajeva 2008). Compared with S. tologoicus , the teeth of S. praecox are substantially smaller in size and are more cuspate; the P3 is weaker with a reduced anterior valley and protocone; the P4–M2 exhibit anteroposteriorly shorter anterior valleys; stronger endolophs, mesostyles, and metaconules; the p4 is less molariform with labiolingually narrower trigonid; and the m1–m2 exhibit shorter metalophids.

In summary, comparisons between S. praecox and the other early species of Spermophilus reveal that S. praecox is one of the most, if not the most primitive member of the genus, which is consistent with its status as the oldest known member of the genus, documented from the middle Villanyian and earliest Biharian, ca. 2.6–1.7 Ma.

Stratigraphic and geographic range.—Late Pliocene (middle Villanyian) to Early Pleistocene (earliest Biharian) of southern Ukraine.

Figures

Fig. 5. Ground squirrel Spermophilus praecox sp. nov. from the Early Pleistocene of southern Ukraine: Kotlovina 3 (A) and Morskoy (B, C); mandibles in lateral (A1–C1), and medial (A2–C2) views. A. ZIN 105163/1. B. ZIN NMNHU-P MoT-63 (inverted). C. NMNHU-P MoT-64.

Fig. 6. Ground squirrel Spermophilus praecox sp. nov. from the late Pliocene and Early Pleistocene of southern Ukraine: Kryzhanovka 2 (A, J), Kotlovina 2 (E, F, K, L, Q, R), Kotlovina 3 (G, M, S), Yuzhny (B, N, T, U), Morskoy (C, D, H, I, V, W); upper cheek teeth (A–D, P3; E–I, P4; J–P, M1–M2; Q–W, M3), in occlusal views. A. ZIN 105160/1. B. GIN 1166/1. C. NMNHU-P MoT-2. D. NMNHU-P MoT-4. E. NMNHU-P 41-5588. F. NMNHU-P 41-5589. G. NMNHU-P 41-5611. H. NMNHU-P MoT-6. I. NMNHU-P MoT-10. J. ZIN 105160/5. K. NMNHU-P 41-5598 (holotype). L. NMNHU-P 41-5599. M. NMNHU-P 41-5613. N. GIN 1166/4. O. NMNHU-P MoT-14. P. NMNHU-P MoT-16. Q. NMNHU-P 41-5601. R. NMNHU-P 41-5602. S. NMNHU-P 41-5616. T. GIN 1166/11. U. GIN 1166/12. V. NMNHU-P MoT-31. W. NMNHU-P MoT-32. C, J, K, O, Q, S (inverted).

Fig. 7. Ground squirrel Spermophilus praecox sp. nov. from the late Pliocene and Early Pleistocene of southern Ukraine: Kotlovina 2 (A, B, H–J), Kotlovina 3 (C, J–L, U, V, Z), Kryzhanovka 2 (T), Yuzhny (M–O), Morskoy (D–G, P–S, W–Y); lower cheek teeth (A–G, p4; H–S, m1–m2; T–Y, m3; Z, p3–m3), in occlusal (A–Z1), labial (Z2), and lingual (Z3) views. A. NMNHU-P 41-5603. B. NMNHU-P 41-5604. C. NMNHU-P 41-5617. D. NMNHU-P MoT-34. E. NMNHU-P MoT-36. F. NMNHU-P MoT-39. G. NMNHU-P MoT-43. H. NMNHU-P 41-5606. I. NMNHU-P 41-5610. J. NMNHU-P 41- 5621. K. NMNHU-P 41-5622. L. NMNHU-P 41-5624. M. GIN 1166/13. N. GIN 1166/15. O. GIN 1166/16. P. NMNHU-P MoT-48. Q. NMNHU-P MoT-47. R. NMNHU-P MoT-50. S. NMNHU-P MoT-57. T. ZIN 105160/7. U. NMNHU-P 41-5627. V. NMNHU-P 41-5626. W. NMNHU-P MoT-58. X. NMNHU-P MoT-60. Y. NMNHU-P MoT-61. Z. ZIN 105163/1. B, G, Q, R, X, Y (inverted).

Fig. 2. Upper (A) and lower (B) sciurid cheek teeth illustrating the terminology employed here (after Marivaux et al. 2004; Comte et al. 2012; Vianey- Liaud et al. 2013; and Maridet et al. 2017; with modifications). Abbreviations: aam, anterior arm of metacone (premetacrista sensu Comte et al. 2012; Vianey-Liaud et al. 2013); aap; anterior arm of protocone; aapa, anterior arm of paracone; alas, anterolabial sinus; anl, anteroloph; ansd, anterosinusid; ant, anterocone; ants, antesinus; ast, anterostyle; antd, anteroconulid; anv, anterior valley; cev, central valley; ecl, ectoloph; ecld, ectolophid; encd, entoconulid; end, entoconid; endr, entoconid ridge; enl, endoloph; enld, entolophid; esd, ectostylid; hyd, hypoconid; hyld, hypoconulid; hyld II, hypoconulid II (second hypoconulid); hyp, hypocone (hypostyle sensu Popova 2016); hyst, hypostyle (hypostyle 2 sensu Popova 2016); lamtl, labial metaloph; lamtld, labial metalophid; lanld, labial anterolophid; laprl, labial protoloph; lianld, lingual anterolophid; liansd, lingual anterosinusid; limtl, lingual metaloph; limtld, lingual metalophid; liprl, lingual protoloph; mecd, mesoconid; med, metaconid; mes, mesostyle; mesd, mesostylid; mesl, metastyle; met, metacone; metd, metastylid; metdtc, metastylid crest; metl, metaconule; metl II, metaconule II (second metaconule); mtld, metalophid; pap, posterior arm of paracone (postparacrista sensu Comte et al. 2012; Vianey-Liaud et al. 2013); par, paracone; parl, paraconule; pasl, parastyle; pasl II, parastyle II (second parastyle); plas, posterolabial sinus; poc, posterocone; pofd, postflexid; pol, posteroloph; pold, posterolophid; pov, posterior valley; prd, protoconid; pro, protocone; prst, protostyle; sd, sinusid; sin, sinus; talb, talonid basin; trdb, trigonid basin.

Fig. 1. Geographic location of Spermophilus-bearing fossil localities (stars) discussed in the text.