Spermophilus nogaici ( Topachevsky, 1957 )

Spermophilus nogaici ( Topachevsky, 1957)

Figs. 3 View Fig , 4 View Fig .

1957 Citellus (Urocitellus) nogaici sp. nov., Topachevsky 1957: 204– 208, figs. 1–13.

1965 Citellus nogaici W. Topacevski, 1957 ; Topachevsky 1965: 38–39.

1965 Citellus View in CoL (cf. Urocitellus ) nogaici Topatschevky, 1957 ; Gromov 1965: 178–181 (in part), fig. 36: 1–6.

1973 Citellus (Urocitellus) nogaici W. Topačevski, 1957 ; Topachevsky 1973: 13–21.

1987 Citellus nogaici Topachevsky, 1957 ; Topachevsky et al. 1987: 57–58.

Lectotype: NMNHU-P 27-190 (formerly NMNHU-P 27-189 ), right maxilla with P4 ( Topachevsky 1957: 204, fig. 3).

Type locality: Nogaisk, Zaporozhye Region, Ukraine.

Type horizon: Early Pleistocene, Calabrian, middle Biharian.

Material.— From Early Pleistocene, early–middle Biharian, Zhevakhova Gora 1: NMNHU-P ZG 1-1–2, DP4; NMNHU-P ZG 1-3, P4; NMNHU-P ZG 1-4–14, M1–M2; NMNHU-P ZG 1- 16–19, M3; NMNHU-P ZG 1-20–22, dp4; NMNHU-P ZG 1-

-22–24, p4; NMNHU-P ZG 1-1-25–34, m1–m2; NMNHU-P ZG 1-25–36, m3; NMNHU-P ZG 1-1-37, mandible with p4–m2. Tarkhankut: NMNHU-P 50-29/5–16, NMNHU-P 50-31/8–13, P3; NMNHU-P 50-29/68–72, NMNHU-P 50-31/14, DP4; NMNHU-P 50-29/17–67, NMNHU-P 50- 31/15–21, P4; NMNHU-P 50-27/1–122, NMNHU-P 50- 28/1–30, NMNHU-P 50-31/23–45, M1–M2; NMNHU-P 50-28/31–89, NMNHU-P 50-31/46–56, NMNHU-P 50- 31/97, M3; NMNHU-P 50-29/73–75, dp4; NMNHU-P 50- 26/61–128, NMNHU-P 50-31/57–68, p4; NMNHU-P 50- 25/1–145, NMNHU-P 50-31/69–89, m1–m2; NMNHU-P 50-26/1–60, NMNHU-P 50-31/90–96, m3; NMNHU-P 50- 29/1, NMNHU-P 50-31/3, maxilla with P4–M2; NMNHU-P 50-31/2, maxilla with P4; NMNHU-P 50-29/2, mandible with m1–m3; NMNHU-P 50-29/3, mandible with m2–m3; NMNHU-P 50-29/4, mandible with p4; NMNHU-P 50- 31/4, mandible with m1–m2; NMNHU-P 50-31/5, mandible with m2; NMNHU-P 50-31/6, mandible with m3. Nogaisk: NMNHU-P 27-227–233, P3; NMNHU-P 27-123–132, NMNHU-P 27-235–249, P4; NMNHU-P 27-85, NMNHU-P 27-110–119, NMNHU-P 27-148–158, NMNHU-P 27- 250–259, NMNHU-P 27-487–518, M1–M2; NMNHU-P 27-120–122, NMNHU-P 27-518–535, M3; NMNHU-P 27-104–109, NMNHU-P 27-538–552, p4; NMNHU-P 27- 133–147, NMNHU-P 27-176–188, NMNHU-P 27-571–638, m1–m2; NMNHU-P 27-159–175, NMNHU-P 27-639–667, m3; NMNHU-P 27-191, maxilla with M1–M2; NMNHU-P

27-224, mandible with p4–m3; NMNHU-P 27-738, mandible with p4–m2; NMNHU-P 27-733, mandible with p4. Babakh-Tarama 1: NMNHU-P BaT1-1–4, M1–M2; NMNHU-P BaT1-5, M3; NMNHU-P BaT1-6–8, m1–m2. Moiseevo 1: ZIN 105151/2–6, P4; ZIN 105151/7–21, M1–M2; ZIN 105151/23–27, M3; ZIN 105151/28, dp4; ZIN 105151/29–37, m1–m2; ZIN 105151/38, m3. Tsymbal: ZIN 105150/1–9, P3; ZIN 105150/10–15, DP4; ZIN 105150/16–26, P4; ZIN 105148/1–30, M1–M2; ZIN 105150/27–46, M3; ZIN 105149/1, dp4; ZIN 105149/2–9, p4; ZIN 105149/10–46, m1–m2; ZIN 105149/47–54, m3. Cherevichnoe 1: NMNHU-P Che1-1–4, P3; NMNHU-P Che1-5–6, DP4; NMNHU-P Che1-7–14, P4; NMNHU-P Che1-15–32, M1–M2; NMNHU-P Che1-33–40, M3; NMNHU-P Che1-41–43, dp4; NMNHU-P Che1-44–46, p4; NMNHU-P Che1-47–58, m1–m2; NMNHU-P Che1-59– 70, m3. Karai-Dubina: NMNHU-P KaD-1, P3; NMNHU-P KaD-2–6, P4; NMNHU-P KaD-7–14, M1–M2; NMNHU-P KaD-15–22, M3; NMNHU-P KaD-23, NMNHU-P KaD- 49–50, dp4; NMNHU-P KaD-24–28, p4; NMNHU-P KaD- 29–43; m1–m2; NMNHU-P KaD-44–46; m3; NMNHU-P KaD-47, mandible with m1–m3; NMNHU-P KaD-48; mandible with m3.

From early Middle Pleistocene, late Biharian, Tihonovka 1: NMNHU-P 29-206–212, P3; NMNHU-P 29-213– 218, P4; NMNHU-P 29-4037–4050, M1–M2; NMNHU-P 29-4051–4063, M3; NMNHU-P 29-4064, dp4; NMNHU-P 29-4065–4078, p4; NMNHU-P 29-4079–4093, m1–m2; NMNHU-P 29-4094–4104, m3; NMNHU-P 29-4036, maxilla with P3–M3; NMNHU-P 29-220, mandible with m2– m3. Bolshevik 1: NMNHU-P 45a-54, a damaged skull with P3–M3 and incisors; ZIN 105153/1–5, P3; ZIN 105153/6, P4; ZIN 105153/7–8, M1–M2; ZIN 105153/9, M3; ZIN 105153/10–12, p4; ZIN 105153/13–14, m1–m2. Bolshevik 2,I: NMNHU-P Bol2/1-1–14, P3; NMNHU-P Bol2/1-15, DP4; NMNHU-P Bol2/1-16–24, P4; NMNHU-P Bol2/1-25– 44, M1–M2; NMNHU-P Bol2/1-45–48, M3; NMNHU-P Bol2/1-49–65, p4; NMNHU-P Bol2/1-66–95, m1–m2; NMNHU-P Bol2/1-96–107, m3.

Emended diagnosis.—Medium-sized species of Spermophilus with elongated, low, and slightly domed skull having a shortened, evenly tapered anteriorly rostrum, a broad posterodorsal process of premaxilla, a perpendicularly oriented frontoincisive suture, elongated incisive foramen occupying about 45% of the diastemal length, broad hard palate, and small, knob-like facial tuberosity. The braincase is rounded with no sagittal crest and U-shaped temporal lines. The lower diastema is shorter than the lower dentition. The M3 exhibits a metaconule, metaloph, and metacone; the p4 trigonid is subequal or slightly (10–20%) narrower than the talonid and lacks a lingual anterolophid; the m3 possesses a prominent entoconulid and entolophid.

Medium-sized Spermophilus , larger than S. alashanicus , S. citelloides , S. citellus , S. dauricus , S. pygmaeus , S. suslicus , S. taurensis , and S. xanthoprymnus , and smaller than S. fulvus , S. major , S. polonicus , S. primigenius , S. ralli , S. relictus , S. superciliosus , and S. tologoicus . Differs from all species of the genus other than S. polonicus , S. praecox , and S. primigenius in the following combination of features: broad posterodorsal process of premaxilla that exceeds the width of the nasal at its midlength; subparallel upper toothrows; a relatively long posterior valley of M1–M2 that is only two times shorter than the central valley, more pronounced and tall hypocone, and the presence of a rudimentary endoloph of P4–M2; a well-developed M3 metaconule; narrower trigonid of p4 that generally lacks the lingual anterolophid; and salient entoconulid and entolophid of m3 delimited labially by a deep valley. Differs from S. polonicus , S. praecox , and S. primigenius in a larger P3 that has the anterior valley and prominent protocone; more expanded anterior valley, smaller metaconule, weaker endoloph, lower hypocone, and stronger lingual metaloph of P4–M2; lack of mesostyle on P4; presence of the metaloph on M3; more trapezoidal p 4 in occlusal outline, less pronounced anteroconulid, and stronger anterolophid of this tooth; a tendency to have more pronounced metalophids of p4–m3; and stronger m3 entoconulid and entolophid. Further differs from S. polonicus in the presence of prominent protocone and paracone of P3; a metaloph on M3; and in having less massive main cusps of P4–M3 and p4–m3.

Description.—The P3 is large ( Table 1), generally slightly longer than wide, and circular in occlusal outline ( Fig. 3A–E, Z View Fig ). About two-thirds of the specimens are gently flattened along the posterolabial face of the crown, where the tooth abuts P4. The crown is dominated by the paracone, protocone, and protoloph that extends transversally ( Fig. 3A, B View Fig ) or slightly obliquely across the crown ( Fig. 3C–E View Fig ) delimiting the smaller anterior valley from the larger posterocentral valley. In most specimens the anteroloph is present, but variably expressed; when present it occurs as either an extremely short or faintly elongated low crest, which exceeds two-thirds of the total crown width. The concavity of the anterior valley is discernible in most specimens. The paracone and protocone are nearly equal in size in the specimens from the mid- and late Biharian localities Tsymbal, Cherevichnoe 1, Karai-Dubina, Tihonovka 1, Bolshevik 1, Bolshevik 2,I ( Fig. 3D, E View Fig ); in those from stratigraphically older Tarkhankut and Nogaisk, however, the protocone appears to be one and a half times smaller than the paracone

Fig. 3A–C View Fig ). The lingual side of the paracone is continued into a massive protoloph that tapers lingually, terminating before the contact with the lingual arm of the protocone. The contact between these structures is defined by a sharp constriction; in heavily worn teeth the paracone and protocone become fused thus forming an asymmetric B-shaped wear facet. A long and prominent posteroloph defines the posterocentral valley. The ridge follows the entire posterior lobe of the tooth from the posterolingual wall of the protocone and gradually diminishes in width and height before reaching the base of the paracone. A small hypocone swelling at the lingual arm of the posteroloph is observable in three out of eight specimens from Nogaisk ( Fig. 3B View Fig ), in eight of seventeen teeth from Tarkhankut, in three of four teeth from Tsymbal, two of the four from Cherevichnoe 1, one of the five P3s from Tihonovka 1, six of the thirteen teeth from Bolshevik 2,I, and the only specimen from Karai-Dubina. The tooth has one labiolingually compressed root with a deep longitudinal groove on its labial surface.

The DP 4 is proportionally narrower labiolingually and distinctly smaller than the permanent premolar. The protocone, paracone, and metacone are distinct, with their apices substantially higher than the main lophs ( Fig. 3F, G View Fig ). The hypocone is indistinct. The anterior valley is strongly expanded anteriorly and lingually, which gives the crown a widely triangular to rectangular occlusal outline. The valley is bounded anteriorly by a well-developed and high anteroloph crowned with a barely distinct anterocone. The labial and lingual arms of the anteroloph do not extend to the anterior wall of the protoloph leaving both the antesinus and anterolabial sinus open in all examined specimens. A tiny cusplet on the labial end of the ridge, topographically equivalent to the parastyle, is evident in one of the two specimens from Zhevakhova Gora 1 ( Fig. 3F View Fig ), in three of the six DP4s from Tarkhankut, in three of the five teeth from Tsymbal, and one DP4 from Cherevichnoe 1. The anterostyle is discernible in most specimens as a minute isolated swelling on the anterolingual face of the protocone, level with the bottom of the anterior valley ( Fig. 3G View Fig ). The teeth from Zhevakhova Gora 1 do not show any traits of the cusplet ( Fig. 3F View Fig ). Protoloph and metaloph are both complete, roughly straight, and parallel to each other. The metaloph is slightly longer, but always lower than the protoloph, and bears one, rarely two constrictions that delimit the metaconule swelling labially and lingually. The metaconule is relatively larger in DP4s from the early Biharian localities and reduced to anteroposteriorly compressed swelling in those from the mid- and late Biharian assemblages. Two specimens ( NMNHU-P 50-29 /70, ZIN 105150 View Materials /14) present a small, albeit well-defined, second metaconule sitting on the medial portion of the labial metaloph. The central valley is symmetrical and trapezoidal; in three specimens from Tarkhankut ( NMNHU-P 50-29 /71), Tsymbal ( ZIN 105150 View Materials /13), Cherevichnoe 1 ( NMNHU-P Che1-5), and the teeth from Zhevakhova Gora 1 its sinus is occupied by a small, knoblike mesostyle ( Fig. 3F View Fig ). The posterior valley is short and shallow due to a reduction of the posteroloph. The endoloph is observable in one tooth from Zhevakhova Gora 1 ( Fig. 3F View Fig ), two from Tarkhankut, and in two of the five teeth from Tsymbal. The crown is supported by three widely spaced, divergent, and thin roots .

The P4 is triangular in occlusal outline, with a gently rounded to nearly flattened posterior lobe, and vast, asymmetrical anterior lobe ( Fig. 3H–M, Z View Fig ). The labiolingual width of the anterior lobe is greater than three-fourths of the total width of the crown. The only exception is the specimen from the early Biharian of Zhevakhova Gora 1 ( NMNHU-P ZG1-3), which possesses a slightly narrower anterior valley reaching approximately two-thirds of the crown width. A crescentic anterocone dominates the anterior lobe; the anterocone is about twice the height of the posterior lobe. An elongated lingual arm and short labial arm of the anteroloph descend posterolingually and posteriorly respectively from the anterocone to enclose the anterior valley. The anterostyle is variably present at the lingualmost portion of the anteroloph: it is moderately developed in the teeth from Zhevakhova Gora 1, Tarkhankut, Nogaisk, Moiseevo 1, and Tsymbal ( Fig. 3H–K View Fig ); and it is larger in P4s from Cherevichnoe 1, Karai-Dubina, Tihonovka 1, Bolshevik 1, and Bolshevik 2,I ( Fig. 3L, M, Z View Fig ). The cusplet is tightly appressed to the base of the protocone in most specimens. About half of P4s from the whole sample possess a tiny parastyle at the opposite, labial end of the anteroloph. The protoloph and metaloph are nearly equal in length and height. A slight constriction of the lingual metaloph is evident in the specimens from Zhevakhova Gora 1, Tarkhankut, Nogaisk, and Moiseevo 1 ( Fig. 3H–K View Fig ); in other localities, however, the metaloph of P4 is a massive ridge fused with the protocone ( Fig. 3L, M, Z View Fig ). Approximately halfway between the protocone and metacone is a metaconule swelling that varies in size from moderate (Zhevakhova Gora 1, Tarkhankut, Nogaisk, Moiseevo 1) to small and almost indistinct, subsumed into the metaloph (Tsymbal, Cherevichnoe 1, Karai-Dubina, Tihonovka 1, Bolshevik 1, Bolshevik 2,I). A small to moderately pronounced second metaconule is occasionally present in about one-third of the teeth ( Fig. 3H, J, L, Z View Fig ). The lingual metaloph narrows lingually, thus appearing somewhat thinner when compared with the same portion of the protoloph. A space between them, the central valley, is anteroposteriorly short, about 10–20% shorter than the anterior valley. The sinus is free from accessory cusplets, apart from two specimens ( NMNHU-P 50-31/15, NMNHU-P 27-123) that bear a tiny, knob-like mesostyle ( Fig. 3J View Fig ). Along the rear margin of the crown is a distinct, low, and evenly smooth posteroloph with a faint hypocone swelling on its lingual end. The posterior valley is labiolingually broader, but anteroposteriorly shorter than the central one. A low, reduced endoloph is present in the specimens from Zhevakhova Gora 1, seven out of 15 teeth from Tarkhankut, ten of the 18 from Nogaisk, one of the four from Moiseevo 1, three of six from Tsymbal, two of the five from Cherevichnoe 1, one of the five from Karai-Dubina, two of the nine from Bolshevik 2,I, and one of the four P4s from Bolshevik 1. The tooth has three roots: a stronger lingual root, more slender anterolabial root, and the thinnest posterolabial root.

The M1 and M2 are rectangular to roughly trapezoidal in occlusal outline ( Fig. 3N–S, Z View Fig ); the labial portion of the tooth is slightly longer anteroposteriorly, on average, than its lingual counterpart, although the difference is negligible in some specimens ( Fig. 3N, P, Q View Fig ). The anterior lobe is wide labiolingually, and forms about two-thirds of the anterior face of the tooth. The anterior valley, as in P4, is rimmed by a well-developed, salient anteroloph. The lingual portion of the anteroloph in unworn specimens protrudes farther lingually than the apex of the protocone. In 97% of the M1– M2s the anteroloph forms a teardrop-shaped anterostyle separated from the protocone base by the antesinus, which shows a tendency to deepening and widening in geologically younger specimens: from a barely discernible, diminutive depression in the early Biharian teeth from Zhevakhova Gora 1 ( Fig. 3N View Fig ) to a deeply excavated groove in those form the late Biharian localities. The anterolabial corner of the crown is accentuated by a sharp and high, anteroposteriorly compressed anterocone. In half of the M1–M2s the short labial anteroloph forms a diminutive, conical parastyle. Three specimens ( NMNHU-P 50-28/27, NMNHU-P 50-31/32, NMNHU-P 27-489) possess a second parastyle lying at the bottom of the anterolabial sinus. The trigon is narrowly V-shaped; it is formed by a well developed, high metaloph and protoloph, which converge lingually at an acute angle of 7–13°. The paracone is higher than the metacone. The protoloph is complete and evenly smooth with almost flat anterior and posterior walls. The metaloph, in contrast, is slightly restricted lingually and labially to the metaconule. The metaconule appears as a moderately developed, anteroposteriorly compressed cusp in most specimens.Those from Moiseevo 1, Cherevichnoe 1, Tihonovka 1, Bolshevik 1, and Bolshevik 2,I have a somewhat less developed metaconule. About 7–12% of M1–M2s bear the second metaconule sitting on the labial metaloph, adjacent to the metaconule. The percentage of the teeth with a mesostyle ranges from 65% in the early Biharian samples to 12% in late Biharian ones. The posteroloph is labiolingually short, about 20% shorter than the anteroloph, and similar to the posteroloph in P4. Its lingual arm may be free, separated from the protocone by the lingual posterosinus or may join with the protocone via a low endoloph ( Fig. 3N, P View Fig ), as seen in 40% of M1–M2s from Zhevakhova Gora 1, 37% from Tarkhankut, 35% from Nogaisk, 50% from Moiseevo 1, 38% from Tsymbal, 35% from Cherevichnoe 1, 10% from Tihonovka 1, 11% from Bolshevik 2,I, two of the four from Babakh-Tarama 1, one of the eight M1–M2 from Karai-Dubina, and one of the two specimens from Bolshevik 1. The hypocone is small to indistinct. Viewed posteriorly, the cusp appears much lower than the main labial cusps, and occurs at the same level as the bottom of the central valley. The root structure is as in P4, differing only in a more slender anterolabial root, comparable to the posterolabial root in size and morphology.

In occlusal outline, the M3 is a rounded triangle, approximately as long as wide, with a well-defined, gently tapering posterior lobe ( Fig. 3T–Y, Z View Fig ). The anterior lobe of the tooth is similar to the same structure of M1–M2; but in the M3 this lobe is less cuspate, slightly wider labiolingually, with anteroposteriorly longer labial portion. The anterostyle is smaller than in M1–M2. The antesinus, separating the anterostyle from the protocone is present in seven out of the 56 M3 from Tarkhankut, in eight of twenty from Nogaisk, in two of four from Moiseevo 1, in two of twelve from Tsymbal, if five of seven from Cherevichnoe 1, in five of six from Karai-Dubina, in four of six teeth from Tihonovka 1, in three of four from Bolshevik 2,I, and in the only M 3 specimen from Bolshevik 1. The anterocone is less pronounced than in M1–M2. In about 10% of the specimens the cusp is paired by a faint parastyle ( Fig. 3W View Fig ). The protocone is the tallest cusp on the crown. It is joined to the second tallest cusp, the paracone, by a strong protoloph ridge. The metacone is present in all teeth, except for one aberrant specimen from Tarkhankut ( NMNHU-P 50-28/33), but the cusp is substantially smaller than the paracone. A shallow ectoloph extends between the paracone and metacone. The mesostyle is observable in 5–12% of the teeth. The labial metaloph is variably developed. It is mostly incomplete in the majority of the specimens from early and Biharian assemblages and in about half of the mid Biharian teeth ( Fig. 3T, W, X View Fig ). In contrast, the loph is essentially complete, oriented posterolabially, and slightly convex anteriorly in M3s from the late Biharian localities ( Fig. 3Y, Z View Fig ). The metaconule is a swollen cusp connected by a compressed and short lingual metaloph to the posterior arm of protocone. Most specimens from Nogaisk and Tarkhankut, four from Karai-Dubina, five of the 21 M3s from Tsymbal, four from Tihonovka 1, and two from Bolshevik 2,I have a prominent anterior projection of the metaconule that, nevertheless, fails to reach the protoloph ( Fig. 3V–Y View Fig ). Three specimens from Tarkhankut possess a similar, but posterolingually directed projection of the metaconule that almost crosses the posterior valley to delimit it into two nearly equal-sized smaller basins. A prominent sinus indents the labial side of the crown between the protocone and hypocone. The hypocone is a diminutive conule in virtually all specimens. In about 65% of M3s from Tarkhankut, Nogaisk, and Moiseevo 1, in approximately 45% from Cherevichnoe 1, and in 70–90% of teeth from Tsymbal, Tihonovka 1, and Bolshevik 2,I the protocone and hypocone are connected by a narrow endoloph. A low, irregular posteroloph is extended along the posterior margin of the tooth; its labial end is usually free and does not merge with metacone in unworn and lightly worn specimens. The posteriormost apex of the loph is swollen and tends to form a cusp-like bulge (posterocone) that expands anteriorly in about 35% of the M3s to occupy the bottom of the posterior valley ( Fig. 3T, U, X View Fig ).

The deciduous p4 of S. nogaici is known only from fourteen specimens, nine of which are from Zhevakhova Gora 1, Tarkhankut, and Cherevichnoe 1. The tooth is characterized by a labiolingually narrow trigonid and wide, simple talonid, giving the crown a clearly triangular occlusal outline ( Fig. 4A, B View Fig ). A large metaconid and a somewhat smaller protoconid are closely spaced and separated by a narrow, anteriorly opened trigonid basin, with a well-developed metalophid between them. The anteroconulid is present in all dp4s as a rounded cusp; the specimen from Tihonovka 1 ( NMNHU-P 29-4064 ) shows an anterolophulid, which partly encloses the trigonid basin anteriorly. The ectolophid is a low, narrow crest occasionally ( NMNHU-P ZG1-20 , NMNHU-P Che1-41) bearing a gentle mesoconid swelling at its central part ( Fig. 4A View Fig ). The posterior portion of the tooth crown is represented by a strong, labially expanded hypoconid, solid posterolophid with indistinct hypoconulid, and a weak entoconid, which may be either isolated ( NMNHU-P ZG1-20 ; NMNHU-P 50-29 /74) ( Fig. 4A View Fig ) or fused with posteroloph ( Fig. 4B View Fig ). The tooth lacks any signs of ecto- and mesostylids. Two roots are present: a massive, anteriorly directed anterior root, and weaker posterior root .

The p4 varies in occlusal outline from being nearly triangular to almost rectangular; most specimens possess a relatively narrow and high trigonid that is about two times higher and on average about 7–3% narrower than the talonid ( Fig. 4C–M, Z View Fig ). The protoconid is slightly broader and lower than the metaconid, which is the tallest cusp in unworn specimens. The high labial anterolophid forms the anterolabial margin of a deeply excavated, asymmetrical trigonid basin. This lophid thickens into a weak anteroconulid defined in moderately worn p4s by an almond-shaped, compressed wear facet. The lingual anterolophid is absent in one ( NMNHU-P ZG1-1 - 22 ) of the three teeth from Zhevakhova Gora 1. When present, it varies from partially incomplete and low, in 36–62% of the teeth ( Figs. 4C, D, H, J View Fig ), to a strong ridge that closes the depression of the trigonid anterolingually. The posterior wall of the trigonid basin is formed by both a pronounced labial metalophid and a somewhat weaker lingual metalophid. The junction between these two is defined as a well-marked constriction roughly at the midline of the trigonid basin. In three specimens ( NMNHU-P 50-26 /122, NMNHU-P 50- 29 /27, ZIN 105149 View Materials /2-9) the ridges fail to connect leaving the basin open posteriorly ( Fig. 4F View Fig ). The ectolophid is a strong, albeit low, anteriorly tapering ridge comparable to the metalophid in width. The mesoconid is usually indistinct, although in two p4s from Tarkhankut ( NMNHU-P 50-26 /65; NMNHU-P 50-31 /59) a swelling of the ectolophid may represent this cuspid ( Fig. 4D View Fig ). The hypoconid ranges in shape and amount of labial expansion from a relatively large, moderately expanded cusp seen in the majority of the teeth from early and mid Biharian localities ( Fig. 4C–E, J, Z View Fig ), to a more derived condition with reduced hypocone that only slightly protrudes labially observed in the specimens from Bolshevik 1, three of eleven from Nogaisk, two of eight from Tsymbal, and two of 13 teeth from Tihonovka 1 Fig. 4F, H, I, K–M View Fig ). The entoconid is fully merged with the posterolophid. The posterolophid is straightened or slightly bowed posteriorly and labially, and lacks a distinct hypoconulid. The mesostylid is variably present midway between the metaconid and entoconid: it is observable in all p4 from Zhevakhova Gora 1, in about 55–70% of the specimens from Tarkhankut, Nogaisk, Cherevichnoe 1, and Tsymbal; and in about half of the teeth from Karai-Dubina, Tihonovka 1, Bolshevik 1, and Bolshevik 2,I ( Fig. 4C, D, F, G, J, L, M, Z View Fig ). NMNHU-P 50-26 /119 has an ectostylid-like projection on the anterolabial wall of the hypocone. The tooth is two-rooted in most cases: a roughly cylindrical anterior root supporting the trigonid, and a labiolingually widened posterior root beneath the talonid. In most p4s, the lingual side of the posterior root is complicated by a remnant of an additional root. In about two-thirds of the specimens from the late Biharian assemblages and about 10% of those from Nogaisk and Tarkhankut this structure is evident as a solitary, albeit underdeveloped, posterolingual root .

The m1 and m2 are virtually identical in size and morphology, so, similar to the upper counterparts, they are included in one category here. The only questionable distinction between m1 and m2 is a stronger metalophid on the first molar. The occlusal outline of the tooth is rectangular ( Fig. 4N–S, Z View Fig ). The two major trigonid cusps are subequal in size, the metaconid being slightly larger and taller than the protoconid. The trigonid is much taller than the talonid cusps, the hypoconid and reduced entoconid. A massive anterolophid continues labially along the anterior side of the tooth crown, where it bends posteriorly to fuse with the anterior wall of the protoconid. The anteroconulid is indistinct; some 5% of the m1–m2s from Nogaisk and Tarkhankut demonstrate a barely discernible anteroconulid expansion on the anterolabial corner of the anterolophid. The metalophid, either incomplete or complete, is present in six of the nine teeth from the early Biharian of Zhevakhova Gora 1; 81 of the 154 from the mid Biharian of Tarkhankut, 92 of the 115 from Nogaisk, one of the three from Babakh-Tarama 1, five of the eight from Moiseevo 1, 24 of the 30 from Tsymbal, eight of the 12 from Cherevichnoe, 11 of the 14 from Karai-Dubina; and 15 of the 16 from the late Biharian of Tihonovka 1, four of the five specimens from Bolshevik 1, and 23 of the 29 m 1–m2 from Bolshevik 2,I Fig. 4O–S, Z View Fig ). The ectolophid is prominent, low, and uniform throughout its length. The talonid portion of m1–m2 is marked by a well-developed hypoconid, a weak to indistinct entoconid, and a posteriorly convex posterolophid between them. The bottom of the lingual sinus bears a small to moderately developed mesostylid evident in 70–89% of the specimens; about 30% of specimens with the mesostylid show remnants of the metastylid crest ( Fig. 4O, S View Fig ) connecting the mesostylid to the base of metaconid. In three m1–m2s from Tarkhankut and two from Nogaisk there is a tiny cuspid sitting on the lophid, which we interpret as a metastylid ( Fig. 4Z View Fig ). The ectostylid-like structures are discernible in about one-third of m1–m2s ( Fig. 4O, R, Z View Fig ). The basins are covered with smooth rugosities, which became more pronounced on the posterolabial corner of talonid basin. The tooth has four roots: larger posterolabial and anterolingual roots, a smaller anterolabial, and the smallest posterolingual root.

The m3 is large and triangular to rectangular in occlusal outline with labially expanded hypoconid ( Fig. 4T–Y, Z View Fig ). The trigonid differs from that of m1–m 2 in being slightly lower and having a straighter, more uniform anterolophid with no signs of the anteroconulid. The metalophid is short in 40–65% of m3s ( Fig. 4U–X, Z View Fig ), moderately developed and incomplete in 40–65% ( Fig. 4Y View Fig ), or long and complete in the rest of the specimens. One tooth from Nogaisk ( NMNHU-P 27-164) and Tarkhankut ( NMNHU-P 50-31/93) lack the metalophid. The ectolophid forms a wide angle of 96–115° with the anterolophid. This ridge is massive, tapers both anteriorly and posteriorly, and shows a large, anterolingually expanded wear facet in moderately worn specimens. The sinusid is narrow, slit-like, and oriented anterolabially. About 25% of m3s demonstrate a low ectostylid on the anterolabial wall of a large, rounded hypoconid ( Fig. 4V, Z View Fig ). The mesostylid resembles that of m1–m2. There is a large, swollen hypoconulid on the posteriormost side of the crown, mostly isolated from the hypoconid by a strong postflexid. The posterolophid differs slightly in height and expression among the specimens. Most (about 75–80%) have a complete posterolophid enclosing the talonid posteriorly ( Fig. 4V, W, Y, Z View Fig ); others, however, possess a weaker lophid, with a sharp constriction at the base of the entoconid ( Fig. 4T, U, X View Fig ). The bottom of the talonid basin is uneven. The main part of the basin is occupied by a salient structure consisting of a massive, blunt entoconulid and a smoothened entolophid, which connects the entoconulid with a lophate entoconid. The entoconulid attains its greatest development in the specimens from Tihonovka 1 and Bolshevik 2,I in which it tends to fuse with the ectolophid, thus dividing the talonid basin into a larger anterior and smaller posterior depressions ( Fig. 4U View Fig ). A deep, crescentic valley delimits the lingual extension of the entoconulid from the hypoconid and hypoconulid. There are four roots similar to those in m1–m2.

Remarks. —The initial description of the lower dentition of S. nogaici was largely based on its holotype, a well-preserved right mandible with p4–m3 from Nogaisk ( NMNHU-P 27- 189). Currently, the exact location of this specimen is unknown, and it appears to be lost or destroyed. Nevertheless, the alpha taxonomy needs to be stabilized by selection of a lectotype from what remains of the topotypic material. We were able to find a right maxillary fragment with P4 ( NMNHU-P 27-190) listed by Topachevsky (1957: 204) as a cotype and here designate this specimen as the lectotype of S. nogaici .

The species was named based on 85 specimens from the Nogaisk ( Topachevsky 1957, 1965). Later, Gromov et al. (1965) documented additional specimens from the type locality,whichhavebeensupplementedbythedescriptionsofmore abundant S. nogaici fossils from Tarkhankut (Topachevsky 1973) and Cherevichnoe 1 localities (Topachevsky et al. 1987). Many new dental fossils have been discovered since those reports, including previously undocumented deciduous premolars, bringing the total sample from a few hundred teeth to almost one and a half thousand teeth.

This larger sample allows us to assess patterns of variability in dental traits suggested by previous workers to be characteristic of S. nogaici based on smaller samples. Topachevsky (1957, 1973) and Gromov et al. (1965) highlighted the following features of the upper dentition of S. nogaici as distinguishing the species from other early Spermophilus : relatively small size; anterior valley and lingual metaloph of P4 are more strongly developed than in S. primigenius ; and M3 is shorter, with either interrupted or, rarely, complete metaloph and weak metacone (originally “marginal tubercle”). Spermophilus nogaici remains the smallest early Pleistocene species of Spermophilus , although this difference is less marked compared to S. praecox sp. nov., which significantly overlaps in size with S. nogaici ( Tables 1, 2). However, S. nogaici is somewhat larger than the specimens of Spermophilus aff. primigenius from the late Biharian of Somssich Hill 2 locality ( Pazonyi et al. 2018), southern Hungary ( MVS, personal observation), which has smaller upper and lower premolars. Larger sample sizes do not support Gromov et al. (1965) observations of reduced metaloph and metacone on M3. The size of the metacone on this tooth varies from quite small in the specimens pertaining to the early Biharian assemblages to only slightly lower and narrower than the paracone in those from the late Biharian localities, and in most teeth it is not substantially more reduced than in S. primigenius , and appears to be consistently larger than in S. polonicus . Although nine specimens of S. nogaici from Nogaisk have an interrupted metaloph on M3, all other known teeth possess a complete crest connecting metaconule and metaloph (11 out of 20 M3s; 55%). The percentage of specimens possessing a complete metacone tends to increase in time, thus showing a clear evolutionary tendency toward the acquisition of a strong and even crest ( Fig. 3T–Y, Z View Fig ). Despite these problems, other diagnostic characters of S. nogaici listed by Gromov et al. (1965) appear to be valid for distinguishing this species from other early members of the genus.

The westernmost occurrences of S. nogaici are limited to southeastern Ukraine and Moldova. Several putative S. nogaici -like specimens from central Europe have been reported in the literature. Popov (2017) illustrated nineteen isolated teeth of a moderately-sized ground squirrel from the Early Pleistocene (late Biharian) of Futjova Cave in northern Bulgaria that he tentatively referred to “ Spermophilus cf. nogaici ”. Apart from slightly narrower p4s and somewhat shorter M1–M2s these specimens fall within the size variation of S. nogaici from Nogaisk. Their morphology, however, is not fully consistent with identification as S. nogaici . The p4, in particular, has an anteroposteriorly elongated crown with relatively wide trigonid, and a small, rudimentary hypoconid reminiscent of that in most living species of the genus. Although present in some specimens of S. nogaici , such a combination of features is unusual for this species, but is evident in a putative S. primigenius sample from the late Early Pleistocene of Somssich Hill 2. Other characters supporting the identification of Futjova Cave squirrels as S. primigenius include a weak entoconulid of m3 and weak hypocone of M1–M2. Furthermore, “ Spermophilus cf. nogaici ” from Futjova and Spermophilus aff. primigenius from Somssich Hill 2 appear to share the same structure of the M3 talon, with a small posterior lobe and weak metaloph bearing no signs of metaconule, although based on figures and the brief description ( Popov 2017) it is difficult to tell whether these features are real or artifactual. Given these observations, Spermophilus fossils from Futjova Cave are tentatively attributed here to Spermophilus aff. primigenius . It is quite possible that these late Biharian specimens of middle-sized Spermophilus from central Europe (including those from Somssich Hill 2) belong to a different yet undescribed species of Spermophilus that would fill the apparent stratigraphical gap between the typical S. primigenius and Late Pleistocene Spermophilus citelloides Kormos, 1916 . The discovery of more complete material is necessary to allow clarification of this taxon’s relationship to the mentioned species.

Stratigraphic and geographic range.—Early to Middle Pleistocene (Biharian) of southern Ukraine, Moldova, and southwestern Russia.