Tonomochota khinganica, Gusev & Tiunov, 2023

Gusev, Alexander E. & Tiunov, Mikhail P., 2023, New finds of the fossil genus representatives of Tonomochota Tiunov et Gusev, 2021 (Lagomorpha, Ochotonidae) in Korydornaya Cave (Jewish Autonomous Oblast, Far East of Russia), Amurian Zoological Journal XV (4), pp. 894-906 : 898-903

Tonomochota khinganica sp. nov.

https://zoobank.org/ NomenclaturalActs/3EB8153A-D728-4F72-B5AE-

B3DF32E35717

Fig. 4. Occlusal views of P 3, Tonomochota khinganica sp. nov. A — FSC RJARV–KorC–02, left P 3; B — FSC RJARV–KorC–03, right P 3; C — FSC RJARV–KorC–04, right P 3; D — FSC RJARV–KorC–05, left P 3; E — FSC RJARV–KorC–06, left P 3; F — FSC RJARV–KorC–07, right P 3; G — FSC RJARV–KorC–08, left P 3; H — FSC RJARV–KorC–09, right P 3; I — FSC RJARV–KorC–10, left P 3; J — FSC RJARV–KorC–11, right P 3. Scale bar = 0.5 mm

Рис. 4. ЖеватеΛьная поверхность P 3 Tonomochota khinganica sp. nov. A — FSC RJARV–KorC–02, Λевый P 3; B — FSC RJARV–KorC–03, правый P 3; C — FSC RJARV–KorC–04, Λевый P 3; D — FSC RJARV–KorC–05, Λевый P 3; E — FSC RJARV–KorC–06, Λевый P 3; F — FSC RJARV–KorC–07, Λевый P 3; G — FSC RJARV– KorC–08, Λевый P 3; H — FSC RJARV–KorC–09, правый P 3; I — FSC RJARV–KorC–10, Λевый P 3; J — FSC RJARV–KorC–11, правый P 3. Масштабная Λинейка 0,5 мм

Table 1 Teeth measurements (mm) of Tonomochota khinganica sp. nov., T. khasanensis ,

Ochotona hyperborea and O. hyperborea (recent)

ТабΛица 1 Измерения (мм) зубов ΑΛя Tonomochota khinganica sp. nov., T. khasanensis ,

Ochotona hyperborea и O. hyperborea (современный)

Tooth Measurements n khinganica

Tonomochota Mean SD nov ±. Min Max sp. ‒ n Tonomochota khasanensis Mean SD ± Min Max ‒ n hyperborea Mean Ochotona SD ± Min Max ‒ n hyperborea Ochotona Mean (recent SD ±) Min Max ‒ 1 2 3 4 5 6 7 9 10 11 12 13 14 15 1.56 ± 1.50 ‒ 1.39 ± 1.31 ‒ 1.34 ± 1.23 ‒ 1.33 ± 1.16 ‒ 1

0.06 1.66 0.06 1.53 0.05 1.41 0.08 1.44 1.40 ± 1.35 ‒ 1.38 ± 1.30 ‒ 1.32 ± 1.21 ‒ 1.26 ± 1.06 ‒ 2

0.04 1.46 0.06 1.47 0.06 1.39 0.10 1.36 1.12 ± 1.05 ‒ 1.01 ± 0.96 ‒ 1.02 ± 0.90 ‒ 1.07 ± 0.96 ‒ 1/2

0.05 1.22 0.03 1.08 0.05 1.12 0.07 1.23 0.64 ± 0.60 ‒ 0.62 ± 0.55 ‒ 0.56 ± 0.48 ‒ 0.54 ± 0.32 ‒ 3

0.02 0.66 0.03 0.69 0.04 0.63 0.09 0.66 0.18 ± 0.14 ‒ 0.15 ± 0.10 ‒ 0.16 ± 0.05 ‒ 0.16 ± 0.08 ‒ 4

0.06 0.31 0.03 0.22 0.05 0.26 0.04 0.24 P3 5 9 0.54 ± 0.49 ‒ 24 0.53 ± 0.40 ‒ 20 0.48 ± 0.41 ‒ 19 0.42 ± 0.22 ‒ 0.04 0.61 0.08 0.78 0.05 0.62 0.10 0.56 1.10 ± 1.00 ‒ 1.04 ± 0.94 ‒ 0.95 ± 0.84 ‒ 0.92 ± 0.76 ‒ 6

0.05 1.18 0.07 1.18 0.06 1.03 0.09 1.06 0.79 ± 0.72 ‒ 0.71 ± 0.65 ‒ 0.70 ± 0.61 ‒ 0.68 ± 0.60 ‒ 7

0.05 0.87 0.05 0.83 0.05 0.80 0.05 0.76 0.63 ± 0.58 ‒ 0.60 ± 0.53 ‒ 0.59 ± 0.53 ‒ 0.55 ± 0.46 ‒ 8

0.03 0.67 0.05 0.75 0.03 0.66 0.05 0.60 0.96 ± 0.86 ‒ 0.92 ± 0.78 ‒ 0.84 ± 0.74 ‒ 0.84 ± 0.70 ‒ 9

0.06 1.03 0.07 1.09 0.05 0.95 0.11 1.00

1.46 ± 1.45 ‒ 1.28 ± 1.12 ‒ 1.25 ± 1.00 ‒ 1 ‒ 1.64

0.01 1.48 0.09 1.38 0.11 1.40

0.66 ± 0.63 ‒ 0.66 ± 0.56 ‒ 0.61 ± 0.44 ‒ 2 ‒ 0.74

0.02 0.69 0.05 0.71 0.06 0.76 P 2 1 4 12 103

0.36 ± 0.28 ‒ 0.34 ± 0.22 ‒ 0.37 ± 0.24 ‒ 3 ‒ 0.35

0.08 0.43 0.05 0.38 0.05 0.50

0.68 ± 0.66 ‒ 0.62 ± 0.53 ‒ 0.58 ± 0.40 ‒ 4 ‒ 0.82

0.01 0.69 0.07 0.74 0.07 0.76 2.47 ± 2.40 ‒ 2.32 ± 2.23 ‒ 2.14 ± 1.83 ‒ 2.07 ± 1.70 ‒ 1

0.07 2.56 0.05 2.39 0.15 2.38 0.14 2.38 1.13 ± 1.06 ‒ 1.16 ± 1.10 ‒ 1.07 ± 0.94 ‒ 1.02 ± 0.82 ‒ 2

0.04 1.17 0.04 1.25 0.05 1.16 0.06 1.14 P 3 7 11 48 108

1.33 ± 1.14 ‒ 1.29 ± 1.10 ‒ 1.25 ± 0.92 ‒ 1.20 ± 0.82 ‒ 3

0.13 1.47 0.17 1.56 0.19 1.68 0.14 1.52 0.54 ± 0.48 ‒ 0.56 ± 0.48 ‒ 0.43 ± 0.34 ‒ 0.58 ± 0.44 ‒ 4

0.04 0.58 0.06 0.66 0.05 0.63 0.06 0.75

ТабΛица 1. Окончание

Fig. 5. Occlusal views of P 2 and P 3, Tonomochota khinganica sp. nov. A — FSC RJARV–KorC–12, right P 2; B — FSC RJARV–KorC–13, left P 3; C — FSC RJARV–KorC–14, left P 3; D — FSC RJARV–KorC–15, left P 3; E — FSC RJARV–KorC–16, right P 3; F — FSC RJARV–KorC–17, right P 3; G — FSC RJARV–KorC–18, right P 3; H — FSC RJARV–KorC–19, left P 3. Scale bar = 0.5 mm

Рис. 5. ЖеватеΛьная поверхность P 2 и P 3 Tonomochota khinganica sp. nov. A — FSC RJARV–KorC–12, правый P 2; B — FSC RJARV–KorC–13, Λевый P 3; C — FSC RJARV–KorC–14, Λевый P 3; D — FSC RJARV– KorC–15, Λевый P 3; E — FSC RJARV–KorC–16, правый P 3; F — FSC RJARV–KorC–17, правый P 3, G — FSC RJARV–KorC–18, правый P 3; H — FSC RJARV–KorC–19, Λевый P 3. Масштабная Λинейка 0,5 мм

Etymology. The name of the species is related to the Greater Khingan Mountain Range.

Type locality. Korydornaya Cave

Holotype. FSC RJARV –KorC–02

Age. Late Pleistocene.

Other material. Collected together with the holotype: five left P 3 and five right P 3; one left P 2; seven P 3, eleven M 2 (Fig. 4, Fig. 5, Fig. 6).

Diagnosis. A medium-sized pika. The ratio of width to length of the occlusal surface is on average 1.13 mm, which makes the tooth look slightly flattened.

Description. A medium-sized pika. The occlusal surface of the third lower premolar tooth has a triangular shape. The width of the occlusal surface of the tooth is greater than its length ( Table 1). The ratio of width to length of the occlusal surface varies from 1.05 to 1.22 mm, on average 1.13 mm (n=8). The anteroconid is variable in its shape, it can be triangular, diamond-shaped or trapezoidal (Fig. 4). The labial fold on the anteroconid is filled with cement. This fold together with the cement is clearly visible in FSC RJARV–KorC–08 and

Fig. 6. Occlusal views of M 2, Tonomochota khinganica sp. nov. A — FSC RJARV–KorC–20, right M 2; B — FSC RJARV–KorC–21, right M2; C — FSC RJARV–KorC–22, right M 2; D — FSC RJARV–KorC–23, left M 2; E — FSC RJARV–KorC–24, right M 2; F — FSC RJARV–KorC–25, right M 2; G — FSC RJARV–KorC–26, right M 2; H — FSC RJARV–KorC–27, right M 2; I — FSC RJARV–KorC–28, right M 2; J — FSC RJARV–KorC–29, right M 2; K — FSC RJARV–KorC–30, right M 2. Scale bar = 0.5 mm

Рис. 6. ЖеватеΛьная поверхность M 2 Tonomochota khinganica sp. nov. A — FSC RJARV–KorC–20, правый M 2; B —FSC RJARV–KorC–21, правый M 2; C —FSC RJARV–KorC–22, правый M 2; D —FSC RJARV–KorC–23, Λевый M 2; E — FSC RJARV–KorC–24, правый M 2; F — FSC RJARV–KorC–25, правый M 2; G — FSC RJARV– KorC–26, правый M 2; H – FSC RJARV–KorC–27, правый M 2; I — FSC RJARV–KorC–28, правый M 2; J — FSC RJARV–KorC–29, правый M 2; K — FSC RJARV–KorC–30, правый M 2. Масштабная Λинейка 0,5 мм

FSC RJARV –KorC–09, unlike the rest of the specimens (Fig. 4G, 4H). In the three specimens FSC RJARV–KorC–02, FSC RJARV– KorC–05 and FSC RJARV–KorC–06 cement is almost invisible on the occlusal surface of the tooth, yet, it is present when viewing the specimens from the side. All the studied specimens also have a lingual fold, but only FSC RJARV–KorC–05, FSC RJARV–KorC– 07, and FSC RJARV –KorC–09 have it filled with cement. The isthmus connecting the anteroconid with the posteroconid is variable, its width varies from 0.14 to 0.31 mm ( Table 1). 7 out of 8 specimens have a weakly pronounced mesoflexid, which is noticeable only when viewing the lateral wall of the tooth. Of all the specimens, only FSC RJARV –KorC–05 has it filled with cement. Two specimens , FSC RJARV–KorC–10 and FSC RJARV–KorC–11, were not included in the statistical analysis because the width of their occlusal surface is smaller than that in the remaining specimens. At the same time, the ratio of the width of the tooth to its length in these specimens is the same as in the other teeth assigned to the species that we describe, T. khinganica sp. nov. (Fig. 4I, 4J).

The occlusal surface of the second upper premolar P 2 has an elongated oval shape with a narrow paraflexus filled with cement (Fig. 5A). The paraflexus originates from the upper part of the hypercone and is directed towards the posterior cheek area. The width from the very lingual point of the hypercone to the deepest point of the paraflexus is equal to half the width of the tooth itself (Fig. 3B). The enamel is thin (narrow) along the entire border of the occlusal surface.

The occlusal surface of the premolar P 3 is trapezoidal (Fig. 5B–H). The anteroloph is approximately 54% of the tooth width (N = 7). The U-shaped paraflexus starts from 1/4 and ends at 1/3 or 1/2 of the width of the occlusal surface of the tooth relative to the cheek area. The hypercone is narrow, short, filled with cement.

The second upper premolar M 2 is wide, the length varies from 1.52 to 1.66 mm, on average 1.55 mm ( Table 1). The process on the posteroloph of M 2 is large and well-developed (Fig. 6A–K).

The other teeth of the upper and lower jaws are morphologically similar to the corresponding teeth of the genus Ochotona . The upper molars P 4 -M 1 consist of two lophs separated in the middle by a deep hypoflexus filled with cement. The teeth of the lower jaw P 4 -M 2 are formed by two lophs (trigonid and talonid) connected by cement.

Comparisons. In size and shape of the occlusal surface P 3, the new species is the closest to P 3 T. khasanensis . It should be noted that the main measurements of P 3 (length and width of the tooth) of T. khasanensis from the deposits of Korydornaya Cave are smaller than those from the deposits of Sukhaya Cave ( Table 1, 2). That can be due to the geographical variability of this species. In T. major and T. sikhotana , this tooth is larger than in T. khinganica sp. nov. The most important is the ratio of width and length of the third lower premolar in T.khinganica sp. nov., which is of the greatest importance among the species of this genus.

According to the morphological structure of individual isolated third lower premolars, the presence of two more species of the pika was established in the cave deposits: T. khasanensis и O. hyperborea . It should be noted that in addition to P 3, a significant number of other teeth were collected. In this regard, an attempt was made to determine their species. Considering that the size of P 3 T. khinganica sp. nov. is larger than the corresponding tooth in T. khasanensis and O. hyperborea from the deposits of this cave ( Table 1), it is obvious that the rest of the teeth in this species should be larger.

To compare the groups, we conducted a discriminant analysis based on the metric features P 3, P 3 and M 2. The percentage of correctly identified instances for P 3 was 81% (Wilk’s = 0.04, R = 0.93, Χ 2 = 271.10, p <0.01), for P 3 70 % (Wilk’s = 0.47, R = 0.93, Χ 2 = 127.3, p <0.01), for M 2 77 % (Wilk’s = 0.33, Χ 2 = 205, p <0.01). The dispersion graphs of the first and second canonical roots are shown in Figure 7A-7C. According to the analysis results, measurements 1, 2, 3, 4, 5 for P 3 (Fig. 3A), measure-

Table 2

Teeth measurements (mm) of Tonomochota khinganica sp. nov., T. major , T. sikhotana ,

T. khasanensis (from Sukhaya Cave)

ТабΛица 2

Измерения (мм) зубов ΑΛя Tonomochota khinganica sp. nov., T. major , T. sikhotana ,

T. khasanensis (from Sukhaya Cave)

3

ments 1, 2, 3, 4 P 3 (Fig. 3C), and measurements 1, 4, 5, 7 M 2 (Fig. 3D) were essential to the species discrimination.

By metric parameters, P 2 T. khinganica sp. nov. is larger than P 2 T. khasanensis and O. hyperborea ( Table 1). According to the occlusal surface morphology, P 2 T. khinganica sp. nov. is similar to T. khasanensis , they have a round- ed anterior edge on the hypercone but are distinguished by a paraflexus reaching up to half of the tooth. The anterior edge of hypercone P 2 Ochotona hyperborea differs from T. khinganica sp. nov. in a pointy shape. Specimens of O. hyperborea , in which the anterior edge of the hypercone was erased, differed well in smaller tooth proportions ( Table 1).