NESSOV, L. A. and A. O. AVERIANOV. 1996. Early Chimaeriformes of Russia, Ukraine, Kazakhstan and Middle Asia II. Description of New Taxa. Vestnik Sankt-Peterburgskogo Universitita, Ser. 7, Iss. 3(21):3-10.

Translated by Oleg LEBEDEV

New materials of the fossil chimaeriform fishes were collected in the Commonwealth of Independent States (CIS) recently (see locality overview in [1]). The most productive year was 1994; in this year, L. A. NESSOV, A. V. GRUBA and A. A. TIMOFEYEV collected about 1,000 chimaeriform tooth plates in the sands and sandstones of the Upper Albian-Cenomanian deposits in the Stoylo quarry close to the town of Gubkin (the Belgorod Region). A part of the material from the localities near Gubkin originates from unweathered and undisturbed deposits and is well dated. This new material is extremely important for the estimate of chimaeriform diversity at the Early-Late Cretaceous boundary, when this group flourished, and especially for the study of the morphology of the dentition of the rare chimaeriforms. New chimaeriform taxa from the Albian-Cenomanian of Russia (in the vicinity of the town of Gubkin) and the Oligocene of Kazakhstan are described below.

Order Chimaeriformes
Superfamily Callorhynchoidea
Family Callorhynchidae
Genus Callorhinchus Lacepede 1798
Callorhinchus borealis sp. nov.

Etymology
From the Latin borealis - northern.

Holotype
TsNIGR museum N 1/12963, a right palatine tooth plate (Text fig. 1: 3), the Stoylo quarry; Upper Albian, Lower Cretaceous.

Description
Palatine tooth plates (Text figs. 1: 2, 3) are wide, with a short symphyseal margin; the length of the latter is no longer than that of the lingual edge; these plates bear two tritors (internal and median) which may be completely isolated (two specimens, text fig. 1: 3a; and [2] text fig. 1:3) or connected to each other by a narrow bridge in the posterior part (one specimen, text fig. 1: 2). The median tritor is approximately twice as short as the internal one. There is a small oval-shaped median tritor on the mandibular tooth plate (text fig. 1: 4), as well as one or two short and narrow symphyseal tritors and a similar external one. The descending lamina [3] is well expressed on both the palatine and mandibular tooth plates. The vomerine tooth plates conditionally assigned to this species (text fig. 1: 1) bear three tubercles each close to a wide symphyseal surface; the anterolateral slope of each exhibits a short row of small rounded tritors. A field of closely spaced vertical "point" tritors, whose elements are only somewhat disposed in longitudinal rows is found over the wear surface.

Comparison
C. borealis is most close to the Late Cretaceous C. hectori Newton 1876 from New Zealand in its tooth plate construction [4], differing from that form by its shorter symphyseal margin and the lesser elongation of the junction of its internal and median tritors. From C. newtoni Ward 1973 (Paleocene, Thanetian) and C. regulbiensis Gurr 1963 (Lower Eocene, Sparnacian) of England [5,6] the new species differs in the comparatively smaller area occupied by tritors on the palatine tooth plate and in the greater isolation of the internal tritor from the median one. It also differs from the latter species by the oval shape and relatively smaller size of the median tritor on the mandibular tooth plate, as well as the smaller size of the external and posterior tritors on that plate. Compared to C. crassus Woodward and White 1930 from the Oligocene-Miocene of Argentina [7], the labial edge of the mandibular tooth plate in this species is more convex and rounded when viewed from below, the external tritor is comparatively shallower and placed closer to the lingual margin, and there are 1-2 symphyseal tritors.

In Recent adult callorhynchids, the internal and median tritors on the palatine tooth plate are usually fused over much of their length. This is true for Callorhinchus callorhynchus (L., 1758) from the coastal basins of South America, C. capensis Dumeril 1865 from the South African seas, and C. milii Bory 1823 from the South Australian and New Zealand waters [3: fig.3, 4, 8; Pl.6: fig. 1, 2, 5-7,9; fig.9]. However, in one of the modern Callorhinchus species, C. smithi Lay and Bennett 1939 from the coastal waters of South America [8: Pl.6, fig. 1], the internal and median tritors are completely separated and appear as two narrow parallel crests. In all extant species the palatine tooth plates are comparatively narrow (rostrocaudally elongated), their symphyseal margin being 1.5 to 2 times longer than the lingual one; only the median tritor is present on the mandibular tooth plate.

Comments
In the extant callorhynchids, the median and internal tritors on the palatine tooth plate are usually isolated in juvenile individuals and fuse at the later ontogenetic stages [9]. Possibly, in C. borealis n. sp. both tritors remained isolated in some individuals during their lifetime.

Fossil callorhynchid tooth plates are exceptionally rare. Callorhinchus remains compose only 0.83% of the total of 1,500 tooth plates collected by various authors in the Stoylo and Lebedi quarries [1]. It is interesting to note that Callorhinchus species have survived until now, being represented by solitary tooth plates found in Mesozoic and Cenozoic deposits, whereas Ischyodus and Edaphodon , dominant in the Cretaceous assemblages, became extinct in the Late Cretaceous and Neogene, respectively. Callorhinchus 's survival may be due to its insignificant dietary specialization [10], while the more specialized Ischyodus and Edaphodon possessed robust tooth plates and were more restricted to a durophagous and probably scavenging mode of eating [1]. Callorhinchus remains are found in the Northern Hemisphere only up to the Eocene; its extant members in the Southern Hemisphere are probably relicts forced out of northern waters.

The Callorhinchus collection described is the largest of those known from a single locality or a group of close localities. The new species from the vicinity of the town of Gubkin is the earliest species erected on tooth plate material.

Materials
Apart from the holotype (collected by E. B. Ivashintsova and Yu. V. Starikov), 2 palatine and 3 mandibular tooth plates, the Stoylo and Lebedi quarries.

Superfamily Rhinochimaeroidea
Family Rhinochimaeridae
Lebediodon , gen. nov.

Type Species
Lebediodon oskolensis sp. nov., Cretaceous (Late Albian-Cenomanian); Belgorod Region, Russia.

Diagnosis
Vomerine plates are small; the distance between the labial and lingual edges is short. The tooth plates are thin and bear a deep symphyseal surface, as well as a small projection at the labial margin situated quite far from the symphyseal area. A faintly expressed gentle crest runs across the oral surface posteriorly from this projection. The anterior internal tritor is situated at the tip of the symphyseal projection and consists of several vertical tubes disposed in a short longitudinal row. The anterior external tritor is composed of similar tubes also forming the same kind of row. A row of separate tritoral tubes, up to 33 in number, runs practically without interruption along the whole of the labial margin. The descending lamina is quite short and the pocket posterior to it is very shallow. The parasymphyseal furrow on the basal side is almost unexpressed. The palatine tooth plates are long (anteroposteriorly), rather thin and possess a wide symphyseal surface; the plane of the latter forms an obtuse angle with the oral side of the tooth plate. The anterior internal tritor dominates the others; it is very narrow, and it extends a long distance close to the symphyseal edge of the oral surface. The external tritor partly occupies a small projection of the labial edge anteriorly. The latter is also very narrow; it turns posteriorly into a set of isolated tubes occupying a rather long labial cutting edge. The descending lamina on the basal side is short, oblique and is accompanied by a shallow pocket. It crosses a wide and shallow longitudinal parasymphyseal furrow. The mandibular tooth plates are strongly elongated; the distance between the labial and lingual edges is short. The anterior external and posterior internal tritors are very narrow; a gentle longitudinal low ridge runs posteriorly from the latter. The anterior tritor represented by a row of isolated tubes follows the cutting edge. The external posterior tritor consists of a row of isolated tubes. The symphyseal surface is narrow.

Comparisons
The new genus differs from Rhinochimaera Garman 1901 [8] by the presence of tritors on the labial margin of the tooth plates; from Neohariotta Bigelow and Schroeder 1950 [11, fig. 4] by the presence of only two, not three or four, longitudinal tritor lines and the absence of a deep longitudinal furrow on the oral side of the palatine tooth plate; from Hariotta Goode and Dean 1895 [8, Pl.5; 12, fig. 1F; 13, fig. 2; Pl. 1B] by a considerably narrower posterior internal tritor on the mandibular tooth plate.

Generic Composition
Type species.

Lebediodon oskolensis sp. nov.

Etymology
The generic name originates from the former Lebedi village and the specific one from the Oskol River.

Holotype
TsNIGR museum N 6/12963, a left palatine tooth plate (Fig. 1-5), Stoylo quarry; Cretaceous (Upper Albian-Cenomanian).

Description
A shallow longitudinal furrow runs along the symphyseal margin on the basal surface of the palatine tooth plate (Fig. 1: 6). Incremental lines on the oral surface (Fig. 1: 6A) are inclined at about 40 degrees to the symphyseal margin. There may exist a point (single tube) median tritor (specimen no. 8/12963). The anterior external and anterior internal tritors of the vomerine tooth plate consist of 2-5 tubes each. The symphyseal surface of the mandibular tooth plate bears one to two longitudinal grooves (Fig. 1: 7). The descending lamina is not expressed on the basal surface of the mandibular plate (Fig. 1: 7).

Comments
The individual body size was small. The dentition is sectorial. Only about 2.1% of the chimaeroid tooth plates from the localities near the town of Gubkin belong to Lebediodon . The vomerine tooth plates of L. oskolensis are somewhat similar to the presumed mandibular of Elasmodectes willetti (NEWTON 1878) from the Upper Cretaceous of England; (this tooth plate may turn out to be a vomerine and belong to Rhinochimaeridae). However, in contrast to E. willetti , in L. oskolensis the anterior internal tritor is short and the anterior external one is elongated longitudinally.
The Ischyodus sp. cf. I (?) incisus Newton 1878 tooth plates from the Albian-Cenomanian near the town of Gubkin (12 tooth plates) differ from L. oskolensis by the presence of a well defined, although narrow, posterior external tritor on the mandibular plate. This tritor in L. oskolensis disintegrates into a set of "point" tritors [tritoral rods]. The tooth plates of L. oskolensis differ from those of I. (?) incisus f rom the Upper Cretaceous of England [4: Pl. 12, fig. 10] not only by having these tritoral rods instead of an anterioposteriorly elongated posterior external tritor but also by lacking a descending lamina on the mandibular tooth plate.

Materials
Three palatine, 9 vomerine and 20 mandibular tooth plates from the Lebedi and Stoylo quarries.

Stoilodon , gen. nov.

Type Species
Stoilodon aenigma sp. nov., Cretaceous (Late Albian- Cenomanian) of the Belgorod Region, Russia.

Diagnosis
Presumably vomerine or, less probably, mandibular tooth plates possess no tritors, with the exception of tritoral rods exposed as "points" at the cutting edges. The plates possess a very long, narrow parasymphyseal process, as well as a narrow second one strongly projecting anteriorly and situated at the labial edge of the tooth plate. These projections, when viewed from the oral surface, are separated by a very deep labial notch, the angle between its margins being less than 90 degrees. The tooth plate margin between the projections mentioned above and laterally from the second projection is sectorial. The symphyseal surface is deep and significantly flattened. The descending lamina is absent.

Comparisons
The genus differs from other known Rhinochimaeridae [8; 11; 12] by its very large size, strongly expressed labial projections on the vomerine (?) tooth plate and the deep notch between these projections.

Generic Composition
Type species.

Stoilodon aenigma sp. nov.

Etymology
From the former Stoylo village and aenigma (Latin) - a puzzle.
Holotype: TsNIGR museum, N 10/12963; a left vomerine (?) tooth plate (Fig. 2: 1), the Stoylo quarry; Cretaceous (Upper Albian- Cenomanian).

Description
The tooth plates are large. A short anterior part of the symphyseal surface probably includes a contact area for the counterpart tooth plate. The angle between the symphyseal plane and the labial edge of the parasymphyseal projection of the holotype (Fig. 2: 1) is approximately 30 degrees, whereas in two other specimens (N11/12963 and N12/12963) it is close to 35 degrees; the angle between the edges of the labial projection is approximately 50 degrees and the edges of the labial notch diverge 58-60 degrees. The unworn part of the oral surface of the tooth plate has incremental lines resembling gentle folds which follow an arch-shaped course from the symphyseal region toward the labial surface and somewhat backwards. Those folds are crossed by equally gentle folds and striations situated parallel to the symphyseal margin. The wear surface in the area of the labial notch occupies slightly less than a third of the distance from this notch to the lingual tooth plate margin. The lateral region of the tooth plate (specimen N11/12963) bears a short obtuse lateral margin and a sharpened edge with a narrow wear surface. A narrow shallow groove runs along the lower edge of the symphyseal surface at approximately 1/6-1/8 of its depth. Two wide striated stripes parallel to the symphyseal margin are situated on the basal surface of the tooth plate (Fig. 2: 1b) in the symphyseal area and immediately lateral to the labial projection. The width of the medial stripe constitutes approximately 2/5-3/5 of the width of the area between the symphyseal plane and the labial notch. Sigmoid-shaped incremental lines running parallel to the lingual edge form a prominent ornamentation between the above mentioned stripes and also on the lateral part of the basal surface of the tooth plate. The wear surface is widest at the parasymphyseal and anterolateral projections on the anterior part of the basal surface of the tooth plate, and narrowest close to the labial notch. When viewed from the lingual (posterior) side (Fig. 2: 2) the tooth plate can clearly be seen to consist of three layers. The basal layer consists of vascularized pleromin in which the canals, about 0.2-0.3 millimeter in diameter, are approximately parallel to the symphyseal plane when viewed from the abrasion surface. The layer close to the oral surface includes similar canals which are approximately parallel to the incremental lines on the oral surface of the tooth plate. These canals and those of the basal layer become significantly narrower at a distance of 1 centimeter from the lingual margin of the tooth plate. A very thin third layer, situated between the first two, includes canals 1 mm. in diameter that are slightly compressed dorsoventrally close to the lingual edge. These canals are disposed in a single sheet, closely spaced, and oriented in an intermediate fashion relative to those of the other two layers. When the broken surface of the tooth plate, which is approximately parallel to the symphyseal plane, is examined in labial view (specimen N12/12963), it may be seen that the canals of the intermediate layer become narrower at a distance of about 1 centimeter in the anterior direction, decreasing to 0.1 millimeter in diameter; the pleromin around these canals is especially dense and may be regarded as constituting "point" tritors. This kind of pleromin forms a cutting edge as the tooth plate wears. It may also be observed at the broken surface mentioned above that the canals in the upper layer of the tooth plate are also directed from the oral surface anteriorly and towards the intermediate layer, while the ones in the basal layer are directed from the basal surface anteriorly and towards the intermediate layer. This orientation of the canals probably provided self-sharpening of the labial edge as wear occurred parallel to the canals simultaneously from the oral and basal sides. Similar "point" tritors [tritoral rods] are also found on the labial edges of the tooth plates in Rhinochimaera [8; p.225].

Comments
If all the collected tooth plates of S. aenigma are really vomerine, ---and the vomerine in Rhinochimaera does have a labial notch , although not as deep as the one in Stoilodon--- then, on the basis of the vomerine tooth plate/ body length ratio in Rhinochimaera , the body length in Stoilodon from the mouth opening to the tip of the tail could have attained 5 meters. Nevertheless, in Stoilodon the proportion of the body length to that of the vomerine tooth plate could differ from that of the Recent Rhinochimaera . Even so, it is apparent that Stoilodon was one of the largest species in the assemblage of fishes from the vicinity of the town of Gubkin. The dentition of this fish was specialized to cut soft tissues, an action facilitated by the strongly sharpened labial edge of the tooth plate and also by the prongs on either side of the notch. This species was very rare: its remains constitute only about 0.26 % of all tooth plates found. Stoilodon aenigma and Lebediodon oskolensis are probably the earliest known members of the Rhinochimaeridae.

Materials
Four vomerine (?) tooth plate fragments, Stoylo quarry.

Superfamily Chimaeroidei
Family Edaphodontidae
Genus Amylodon Storms 1895
Amylodon emba sp. nov.

Etymology
Species name from the Emba River near which the holotype was found.
Holotype: TsNIGR museum N 13/12963, a left palatine tooth plate (Fig. 2: 3), Kolenkaly Mts., Aktyubinsk Region, Kazakhstan; Paleogene, Middle Oligocene, beds containing Pinna .

Description
Anterior and posterior internal tritors are found on the narrow palatine tooth plate; the posterior one consists of two parallel "columns" (Fig. 2: 3).

Comparisons
A large posterior internal tritor, but one that is not divided into two parts, is present in A. venablesae Casier 1966 from the Lower Eocene of England [15] and in A. delheidi Storms 1895 from the Lower Oligocene of Belgium [6]. In A. eocenica (Woodward and White 1930) from the Eocene of England [7] and Amylodon sp. nov. from the Upper Cretaceous of the Volgograd Region, the posterior internal tritor is completely absent. The new species from Kazakhstan differs from all known Amylodon species by its relatively much narrower palatine tooth plate.

Materials
Holotype.

Family Chimaeridae
Genus Belgorodon , gen. nov.

Type Species
"Chimaera " bogolubovi Nessov 1986; Cretaceous (Late Albian-Cenomanian); Belgorod Region, Russia.

Diagnosis
The distance between the labial and lingual margins of the palatine and mandibular tooth plates is small, but it is much larger between the symphyseal and lateral margins. There are two to three long bar-like tritors on the palatine tooth plate anteriorly; the external tritor is long and undivided; the posterior internal and median ones are small and widely separated; the median tritor is close to the external one. The mandibular tooth plate has a narrow symphyseal margin. This tooth plate is rather thin in its symphyseal part but is strongly thickened more laterally where the narrow, longitudinally elongated anterior external and posterior internal tritors lie close to one another or interconnect. The anterior [parasymphyseal] tritor is large and has a long narrow projection extending laterally along the labial margin. The posterior external tritor is small and short; sometimes it becomes subdivided into two or three parts.

Comparisons
Belgorodon differs from Chimaera L., 1758 and Hydrolagus Gill, 1862 [3,6,9,14,16] in having smaller posterior internal and median tritors on the palatine tooth plate; the extent of its anterior tritor; the smaller length and larger width of the tooth plate itself; and the presence of a strong swelling along the main tritoral zone on the mandibular plate.

Comments
The new species is similar to Elasmodectes Woodward 1888 [4, 14] in the small depth of the symphyseal surface of the mandibular tooth plate, but differs in the presence of the posterior internal tritor and the strong swelling of the tooth plate in the area of this tritor and the anterior external tritor.

Generic Composition
Type species.

Belgorodon bogolubovi (Nessov 1986)

"Chimaera " bogolubovi : NESSOV et al., 1986, p. 128, Text-fig. 1, fig. 3.

Etymology
The generic name after the Belgorod Region in which the material was found; the specific one after N.N. Bogolyubov.
Holotype: TsNIGR museum, N 3/12292, a left palatine tooth plate [2], Lebedi quarry; Cretaceous (Upper Albian-Cenomanian).

Description
The basal surface of the palatine dental element (Fig. 2: 4) bears a short subtransverse descending lamina in the wide parasymphyseal furrow; the symphyseal surface is deep. The median tritor on this tooth plate has a posterolateral projection. The wear surface on the palatine (Fig. 2: 4) and the mandibular (Fig. 2: 5) tooth plates occupies about half of the length of the plate, measured rostrocaudally.

Comments
Belgorodon bogolubovi is probably the earliest member of the modern family Chimaeridae. Belgorodon remains constitute 0.46 % of the tooth plates collected.

Materials
Three palatine and four mandibular tooth plates; Lebedi and Stoylo quarries.

Conclusions
Only 3.35 % of all the tooth plates from the chimaeriform fishes that inhabited the territory of the Belgorod Region about 105-99 million years ago can be assigned to the modern families Callorhynchidae, Rhinochimaeridae and Chimaeridae; the rest belong to the family Edaphodontidae (the dominant genus Ischyodus and Edaphodon ). A trend in callorhynchid evolution from the Cretaceous to the present time seems to be the decrease in tritoral material on the mandibular plates. A similar trend in all components of the dentition was expressed especially in rhinochimaerid history. The comparison of the Albian-Cenomanian genus Belgorodon to the extant Chimaera demonstrates that a similar tendency was present in chimaerid evolution as well.

Summary
Cretaceous chimaeroids Callorhinchus borealis , sp. nov. (the most ancient Callorhynchidae known from dental plates), Lebediodon oskolensis , gen. et sp. nov., Stoilodon aenigma , gen. et sp. nov. (the oldest forms of Rhinochimaeridae), Belgorodon bogolubovi (Nessov 1986) gen. nov., (the most ancient member of the Chimaeridae) and Oligocene Amylodon emba , sp. nov. (Edaphodontidae) are described.

Bibliography
1. NESSOV, L.A. and A.O. AVERIANOV 1996. Ancient chimaeroid fishes of Russia, Ukraine, Kazakhstan and Central Asia. I. Some ecological characteristics of chimaeroids and a summary of their occurrence. Bull. St. Petersburg Univ., ser. 7, no. 7, pp. 11-19.

2. NESSOV, L.A., R.A. MERTINIENE, L.B. GOLOVNEVA et al. 1986. New finds of the ancient organisms' remains in the Belgorod and Kursk regions. In: Comprehensive studies of the biogeocenoses of the wood-steppe oak forests, pp. 124-131 (Leningrad St. Univ. Publishers) Leningrad (St. Petersburg).

3. PATTERSON, C. 1992. Interpretation of the tooth plates of chimaeroid fishes. Zool. J. Linn. Soc., 106(1).

4. NEWTON, E.T. 1878. Chimaeroid fishes of the British Cretaceous rocks. Mem. Geol. Surv. U.K., Monogr. 4.

5. GURR, P.R. 1963. A new fish fauna from the Woolwich Bottom Bed (Sparnacian) of Herne Bay, Kent. Proc. Geol. Assoc., 73, pt.4.

6. WARD, D.J. 1973. The English Paleogene chimaeroid fishes. Proc. Geol. Assoc., 84, pt.3.

7. WOODWARD, A.S. and E.I. WHITE 1930. On some new chimaeroid fishes from Tertiary formations. Ann. Mag. Nat. Hist., Ser. 10, 6(35).

8. GARMAN, S. 1901. The chimaeroids (Chismopnea Raf., 1815; Holocephala Mull., 1834), especially Rhinochimaera and its allies. Bull. Mus. Comp. Zool., 41(2).

9. DIDIER, D.A., B.J. STAHL and R. ZANGERL 1994. Development and growth of compound tooth plates in Callorhinchus milii (Chondrichthyes, Holocephali). J. Morphol., 222(10).

10. RIBBINK, A.J. 1971. Contributions to the functional morphology of fishes. Pt. VI: The jaw mechanism and feeding of the holocephalan, Callorhynchus capensis Dumeril. Zool. Africana, 6(1).

11. BULLIS, H.R. and J.S. CARPENTER 1966. Neohariotta carri ---a new species of Rhinochimaeridae from the southern Caribbean Sea. Copeia, No. 3.

12. GARRICK, J.A.F. 1971. Hariotta raleighana , a long-nosed chimaera (family Rhinochimaeridae), in New Zealand waters. J. Roy. Soc. New Zealand, 1, No.3/4.

13. WERDELIN, L. 1986. A new chimaeroid fish from the Cretaceous of Lebanon. Geobios, No. 19, fasc.3.

14. WOODWARD, A.S. 1891. Catalogue of the fossil fishes in the British Museum (Natural History), Pt. 2. London.

15. CASIER, E. 1966. Faune ichthyologique du London Clay. London.

16. DEAN, B. 1906. Chimaeroid fishes and their development. Publ. Carnegie Inst. Washington, No. 32.

Figure Captions:
Fig. 1. Tooth plates of chimaeriforms Callorhynchidae (1-4) and Rhinochimaeridae (5-7) from the Upper Albian-Cenomanian of the Belgorod Region, Russia. (1: 4) Callorhinchus borealis sp. nov.: (1) a left vomerine tooth plate: 1a- from below, 1b- in anterior view; (2) a left palatine tooth plate from below; (3) a right palatine tooth plate (holotype): 3a- from below, 3b- in anterior view, 3c- in posterior view; (4) a left mandibular tooth plate: 4a- from above, 4b- in anterior view; (5-7) Lebediodon oskolensis gen. et sp. nov.: (5) a right vomerine tooth plate: 5a- from below, 5b- in anterior view, 5c- from above; (6) a left palatine tooth plate (holotype): 6a- from below, 6b- in anterior view; (7) a left mandibular tooth plate: 7a- from above, 7b- in anterior view. Scale bar: 1 centimeter. Dotted lines indicate the approximate position of the symphyseal plane (also in Fig. 2).

Fig. 2. Chimaeriform tooth plates of the families Rhinochimaeridae (1, 2), Edaphodontidae (3) and Chimaeridae (4, 5) from the Upper Albian-Cenomanian of the Belgorod Region, Russia (1, 2, 4, 5) and the Oligocene of the Aktyubinsk Region, Kazakhstan (3). (1, 2) Stoilodon aenigma gen. et sp. nov.: (1) a right vomerine tooth plate (holotype): 1a- from below, 1b- from above, outline reconstructed after specimen no. 12/12963, 1c- in anterior view; (2) a left vomerine tooth plate (specimen no. 12/12963) in posterior view (broken line inside tooth plate image shows the position of an intermediate layer of dentine); (3) Amylodon emba sp. nov., a right palatine tooth plate (holotype): 3a- from below, 3b- in anterior view; (4, 5) Belgorodon bogolubovi (Nessov): (4) a left palatine tooth plate: 4a- from below, 4b- the medial part of the tooth plate from above, 4c- in anterior view; (5) a left mandibular plate: 5a- from above, 5b- from below.