ISSN 0031 0301, Paleontological Journal, 2011, Vol. 45, No. 4, pp. 379–389. © Pleiades Publishing, Ltd., 2011. Original Russian Text © V.V. Mitta, Jingeng Sha, 2011, published in Paleontologicheskii Zhurnal, 2011, No. 4, pp. 26–34.
Ammonite Distribution Across the Jurassic–Cretaceous Boundary in Central Russia V. V. Mittaa and Jingeng Shab aBorissiak Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya ul. 123, Moscow, 117997 Russia e mail: [email protected] bLPS, Nanjing Institute of Geology and Paleontology, Chinese Academy of Science, No. 39 East Beijing Road, Nanjing, 210008 China e mail: [email protected] Received November 9, 2010
Abstract—The distribution of ammonites across the Jurassic–Cretaceous boundary of the central part of the Russian Platform is discussed. The nomenclature of Craspedites nodiger (Eichwald, 1962) and Hectoroceras tolijense (Nikitin, 1881) is updated. A new species, Craspedites ultimus sp. nov., is described from the basal horizons of the rjasanensis Zone (Ryazanian Stage). The Hectoroceras tolijense and Hectoroceras kochi faunal horizons lying between the nodiger and rjasanensis zones are united in the kochi Zone of the basal Ryazanian. Previous opinions suggesting a hiatus between the Volgian and Ryazanian stages are reviewed and rejected.
Keywords: ammonites, Craspedites, Hectoroceras, Ryazanian Stage, Volgian Stage, Russian platform. DOI: 10.1134/S0031030111040083
INTRODUCTION of different authors on the correlation of the Boreal scales with the presumably uninterrupted Tithonian– The Boreal–Tethyan correlation has been a major Berriasian zonation. However the continuous succes problem for Mid Mesozoic biostratigraphy. The sepa sion in the interval is not confirmed, as the upper ration of marine basins at the end of the Jurassic led to Tithonian zone (Durangites) is insufficiently studied in the formation of strongly differentiated faunas of dif the stratotype region and still has no index species. ferent origins, Boreal and Tethyan (Submediterra The taxonomic composition and distribution of nean). This presents considerable difficulties for cor ammonites in the jacobi Zone, which is presently con relation of the terminal Jurassic and basal Cretaceous. sidered to be the basal Berriasian zone, are also insuf Consequently, two parallel stages are recognized in the 1 topmost Jurassic (Tithonian in the submediterranean ficiently studied. paleogeographic regions and Volgian in the Boreal Realm); and in the lowermost Cretaceous (Berriasian Mesezhnikov and his colleagues from Leningrad in Submediterranean Province and Ryazanian in the (now St. Petersburg) and Novosibirsk came to a differ Boreal Realm). To reliably establish correlation mark ent conclusion in the 1970s after paleontological and ers, the primary task is to examine the systematic com stratigraphic study of the Jurassic–Cretaceous beds in position and stratigraphic distribution of the guide fos the Ryazan Region. In several outcrops near the vil 2 sils (primarily ammonites, the most important orthos lage of Kuzminskoe in the basin of the Oka River, his tratigraphic group) in regions with the highest group found Late Volgian Garniericeras subclypeiforme potential for Boreal–Tethyan correlation. (Milaschevitsch) in association with the Ryazanian Most authors studying the biostratigraphy of the Riasanites rjasanensis (Nikitin), and R. cf. swistow Jurassic–Cretaceous boundary beds suggest a hiatus between the Volgian and Ryazanian stages (Casey, 1 This Zone in its modern understanding unites the jacobi Zone 1973; Sasonova, 1977; etc.). This hypothesis is based (previously considered to be terminal for the Tithonian) and the grandis Zone (basal Berriasian Zone) of the standard scale. Tak on sharp differences in the composition of the ammo ing priority into account, the zone in its new definition should nite faunas in the Upper Volgian (the fauna repre have been assigned to the Tithonian, and the Berriasian begun sented solely by craspeditids of Boreal origin, i.e., from the occitanica Zone Craspedites and Garniericeras) and at the beginning of 2 These outcrops have been known in the geological literature for the Ryazanian (where ammonites of Tethyan origin a long time. However Pavlow (1894) and Bogoslowsky (1896) indicated the presence of “Oxynoticeras” subclypeiforme and are found in association with younger craspeditids). Craspedites spp. below beds with Riasanites. For a more detailed The duration of this interval in the Russian Platform is historical review and a scheme showing the locations see Mitta estimated differently, depending on the interpretation (2007).
379 380 MITTA, JINGENG SHA
(a) (b) М Bed Stage Surites 1.5 spasskensis 6 Riasanites
Valanginian rjasanensis 5 5 Riasanites Rjasanensis 4 swistowianus 4 3 Ryazanian Hectoroceras Ryazanian 3 kochi 2c 2 Kochi Hectoroceras 2b 0.5 tolijense 2a 1 Craspedites milkovensis 1
Volgian Craspedites Volgian Nodiger nodiger
Fig. 1. Diagrams showing (a) section of the Jurassic and Cretaceous boundary beds near the village of Kuzminskoe, Ryazan Region and (b) ammonoid based biostratigraphic scale of the upper part of the Volgian–lower part of the Ryazanian. Explana tion: (1) quartz sand, (2) glauconitic sand, (3) clayey sand, (4) sandstone, and (5) phosphorites. ianus (Nikitin) in a thin (up to 0.3 m) sandstone bed RESULTS AND DISCUSSION (Casey et al., 1977; Mesezhnikov et al., 1979). Sum marizing these results, it was suggested that the lower Lithological Description of the Section zone of the Ryazanian Stage (Riasanites rjasanensis) Several exposures dug 5–6 m apart approximately should be interpreted as a “hyperzone” with three 200 m upstream of a dam, near the village of Kuzmin included zones: (1) rjasanensis/subclypeiforme Zone, skoe on the right bank of the Oka River open the fol with Riasanites spp., Euthymiceras spp., Garniericeras lowing beds (from bottom to top, Fig. 1a): subclypeiforme (Milaschevitsch), Craspedites ex gr. (1) Greenish dark gray glauconitic sand. Visible kaschpuricus (Trautschold); (2) rjasanensis/kochi thickness 0.35 m. Zone, with Hectoroceras kochi Spath, Schulginites sp., Craspedites ex gr. kaschpuricus (Trautschold), Riasan (2) Indistinctly bedded reddish brown sandstone, ites spp., Euthymiceras spp.; (3) rjasanensis/spassken ochreous on the weathered surface and black or dark sis Zone, with Surites (Surites) spasskensis (Nikitin), gray on the freshly broken surface. Thickness 0.3 m. S. (Caseyiceras) spp., Externiceras solovaticum (Bog The bed consists of three smaller beds, each 0.1 m thick. oslowsky), Borealites suprasubditus (Bogoslowsky), The lower bed (2a), is strongly ferruginous and almost Riasanites spp., Euthymiceras spp. (Mesezhnikov, completely covered by a continuous iron oxide film on 1984). Taking into account the association of late Vol the freshly broken surface. The bed contains infrequent gian and Ryazanian ammonites, Mesezhnikov con Craspedites ex gr. nodiger (Eichwald)/kaschpuricus cluded that there was no gap between these two stages. (Trautschold) (Pl. 3, figs. 1, 2), and Garniericeras sub However his research, primarily on the taxonomy of clypeiforme (Milaschewitch) (Pl. 3, fig. 3). The middle these ammonites and their description, was not con bed (2b) did not contain fossils. The upper (2c) bed tinued, and in the later papers (Abbink et al., 2001; contained numerous poorly preserved R. swistowianus Wimbledon, 2008) a gap between the Volgian and Rya (Nikitin) (Pl. 3, figs. 5, 6), a few R. cf. rjasanensis zanian stages was still assumed. (Nikitin) and Chetaites sibiricus Schulgina (Pl. 3, fig. 7), and a fragment of Craspedites cf. ultimus sp. nov. In 2006, Russian and Chinese workers undertook joint field work studying the Ryazanian Stage and (3) Brownish gray and brown clayey sand in places underlying beds in the Moscow and Ryazan regions. becoming sandy clay. Thickness 0.0–0.15 m. Repeated collection in the outcrops near the village of (4) Phosphoritic, stained brown and gray sand Kuzminskoe supported the conclusion of Mitta (2006) stone conglomerate. The fossils are usually poorly about the immediate contact of beds with the Late Vol preserved and are represented by fragments. A few rel gian and Ryazanian ammonites. In this paper we will atively complete specimens of Riasanites rjasanensis discuss these and other recent data. (Pl. 3, fig. 4) were also found. Thickness 0.1–0.35 m.
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(5) Brownish yellow loosely cemented quartz zanian Stage of the Moscow Basin. The morphology sandstone. Thickness 0.15–0.2 m. of the new species suggests such a close relationship (6) Light colored and yellow, quartz sand. The vis with the Jurassic C. nodiger, that it removes any doubt ible thickness under the layer of soil is 0.45 m. that there was not a significant gap between the nodiger In bed 1, previous workers (Pavlow, 1894; Bog and rjasanensis zones. oslowsky, 1894, 1896; Mesezhnikov et al., 1979) found The Volgian Craspedites, as noted previously by Kachpurites, Garniericeras catenulatum (Fischer) and Mitta (2010), requires revision. Note that the repre other Late Volgian craspeditids, which indicated the sentatives of this genus in the Upper Substage of the Upper Volgian fulgens Zone (and, possibly, the subditus Volgian Stage of the Russian Platform in fact belong to Zone). the same phylogenetic lineage. The macroconchs of Bed 2a also contains the Upper Volgian fauna Craspedites [C. okensis (auct.) C. subditus (Traut (upper part of the nodiger Zone). In Bed 2b we found schold) C. nodiger (Eichwald)] reach 150–200 mm no fossils, although Hectoroceras tolijense (Nikitin) in diameter and are characterized by a pronounced recorded by Pavlow (1894) and housed in the Vernad trend towards elongation and coarsening of primary sky State Geological Museum, Russian Academy of ribs, from weakly developed umbilical nodes to coarse Sciences (GGM) (Mitta, 2007, pl. 1, figs. 2–5), pos rib folds, whereas the secondary ribs smoothen with sibly comes from this level. Bed 2c predominantly age. The process of transformation of ribs is gradual, contains Riasanites swistowianus. It is possible that and although each of the above listed macroconchs is Hectoroceras specimens figured as having come from characteristic of one of three Upper Volgian zones, Kuzminskoe (Casey et al., 1977; Mesezhnikov et al., transitional morphs are commonly present in the adja 1979) also come from this level. The presence of one cent zone. Figure 2 shows a specimen of C. nodiger specimen of Chetaites sibiricus, and also different state with a type of preservation characteristic of the nodiger of preservation of fossils suggests strong condensation; Zone of Moscow and its vicinity (a mold in the red Bed 2c supposedly correlates with the interval of the dish brown ferruginous sandstone), displaying a not kochi and swistowianus faunal horizons. particularly strongly inflated shell and long, but not Bed 4 (and apparently Bed 3) belongs to the mid very coarse ribs, which are usually found in C. subditus. dle–upper part of the rjasanensis Zone. The lithology Microconchs of Craspedites are half the diameter of of Bed 5 is similar to that of the tzikwinianus Zone of macroconchs and are far more diverse morphologically, the Ryazanian Stage in sections downstream on the which explains why a greater number of species are estab river (village of Nikitino, Staraya Ryazan), which lished based on microconchs. Nevertheless, many of agrees with its position in the section. Bed 6 is appar these species replace each other in an evolutionary suc ently an equivalent of sands with phosphorites of the cession, even though constituting dimorph pairs with the Valanginian Stage exposed downstream. same macroconch. Apparently, in this group of ammo Thus, the sandstone of Bed 2 is subdivided into nites the rate of morphological evolutionary change was three smaller beds with a distinct ammonite assem slower in macroconchs than in microconchs. blage each. The lower bed contains taxa exclusively characteristic of the nodiger Zone of the Russian Plat The nomenclature of the index species of the ter form. For comparison, Craspedites and Garniericeras minal Volgian zone is clarified below. It is widely from the vicinity of Syzran (sections of the Kashpir accepted that the specific name Ammonites nodiger Group) are figured in Pl. 3, figs. 8 and 9. The field Eichwald was established by Eichwald (1868) in results obtained by Mesezhnikov’s group were errone Lethaea Rossica. However there are considerably ear ous with regard to the association of the Late Volgian lier references to and descriptions of this species. The and Ryazanian ammonites. However, is there evidence name Ammonites nodiger (nom. nudum) was first men for a hiatus between the Volgian and Ryazanian, and if tioned in Geognosia by Eichwald (1846, p. 515). Sub so, for how long did it last? sequently Eichwald described A. nodiger found as The major argument supporting the hypothesis of a molds in sandstone in the Kotelniki locality near Mos gap is the fact that the ammonite faunas in the Upper cow (Eichwald, 1861, p. 297; this issue of the Bulletin Volgian and Ryazanian are completely discrete at the was signed by the censor for publication in January generic level. This is also supported by data on the 1862), with a list of synonymies including Ammonites sharp increase in taxonomic diversity in the Ryaza koenigi Sowerby sensu Auerbach and Frears (1846, nian, exceeding that of the Late Volgian by orders of p. 491, pl. 6, figs. 1–3). The differences between magnitude. The latter change was mainly produced by A. koenigi (now classified as Proplanulites koenigi a marine transgression from the west, which was not (Sowerby), family Perisphinctidae, Early Callovian] only responsible for an influx of migrants of Tethyan and A. nodiger are discussed later (Eichwald, 1862, origin, but also gave a natural impetus to the develop p. 388). In the latter paper the synonymy list of nodiger included specimens figured by d’Orbigny (1845, ment of the local faunas in the changing environment. 3 Considering the question of the continuity of the fau pl. 35, figs. 1–6) from Khoroshovo in Moscow cited nas, a new species Craspedites ultimus sp. nov. of a as A. koenigi. Only after all that, the species description genus previously regarded as exclusively Volgian is described below from the rjasanensis Zone of the Rya 3 These illustrations show Craspedites subditus (Trautschold).
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*
(a) (b)
Fig. 2. Craspedites nodiger (Eichwald), specimen PIN, no. 3990/406, ×0.6: (a) lateral view, (b) ventral view; Moscow, old collec tions, donated by A.E. Serbarinov. was published by Eichwald (1868, p. 1126, pl. 36, (1972, p. 202) as the lectotype. Later Casey (1973, fig. 3). In the latter monograph two specimens were p. 239) established the new genus Schulginites, with figured under the name Ammonites nodiger. Of these, the type species Oxynoticeras tolijense Nikitin, 1884. one (3b) is certainly not this species and does not This genus and the publication date of its type species belong to Craspedites, a fact mentioned by all subse were accepted by all subsequent workers (Sasonova, quent workers starting with Nikitin (1885). In fig. 3a 1977; Mesezhnikov et al., 1983; Schulgina, 1985; Eichwald figured a small specimen of C. nodiger, Klein, 2006; etc.). which is a microconch, judging from the uncoiling of the outer whorl and presence of expressed secondary In 1884, Nikitin, while describing Oxynoticeras ribs (Fig. 3c). The ammonite figured by Auerbach and tolijense, referred to the figured specimen of Ammo Frears (macroconch) provides a much more data on nites catenulatus Eichwald, 1868 [non Fischer, 1837 the species (Figs. 3a, 3b), and can be designated as the =Garniericeras catenulatum (Fischer)]. However, a few 4 years earlier, he (Nikitin, 1881, p. 83) while describing lectotype (however the whereabouts of this specimen 5 are not known, and it is likely to have been lost). Thus, the new genus Neumayria wrote: “… ammonite from the correct publication date of the name North Urals, described by Eichwald as catenulatus (Leth. Craspedites , pl. 35, fig. 4. pag. 1110), … for which I propose the (Eichwald) is 1862. ross. nodiger specific name Toliensis after a river, on the banks of which The situation with the nomenclature of Hectoro such unusual Jurassic species as the one listed here, have ceras tolijense (Nikitin), the index species of the next been found.” Further on he wrote “… N. Toliensis was biostratigraphic unit, is somewhat more complicated. poorly figured by Eichwald. I re examined Eichwald’s It is accepted that the correct publication date of this specimen in the Mining Museum and found that the ribs name is 1884 when Nikitin (1884, p. 65, pl. 2, fig. 7) and the acute siphonal surface [venter] are exaggerated published a description and a drawing of Oxynoticeras on his drawing, but the completely rounded last whorl, tolijense, a specimen later designated by Klimova the most interesting feature, is not shown at all” (Nikitin, 1881, p. 84). According to the International Code of 4 Klein, 2006 indicated that the lectotype of C. nodiger (Eichwald, 1868, p. 1126, pl. 36, fig. 3a) was designated by Nikitin (1885, 5 The generic name was preoccupied, and in a subsequent paper p. 133). However Nikitin (1885) only gave a synonymy list and a Nikitin (1884) assigned species of the genus “Neumayria” to description of this species. Oxynoticeras.
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(b)
(a) (c)
Fig. 3. Craspedites nodiger (Eichwald), original illustrations, ×0.8: (a, b) a reproduced figure of Ammonites koenigii Sow. (from Auerbach and Frears, 1846, pl. 6, fig. 1.2); (c) reproduced figure of Am. nodiger (from Eichwald, 1868, pl. 36, fig. 3a).
Zoological Nomenclature, this makes the name Neu diate link between the Volgian members of Garni mayria toliensis Nikitin, 1881 available. ericeras and Ryazanian representatives of Hectoroceras The description of the species in 1884 is supple (group H. kochi). Garniericeras shows, to a varying mented by data on its distribution but it is worded extent, morphological features observed in Schulg almost identically, i.e., there is no doubt that in both inites, i.e. a rounded venter in adults (G. interjectum cases it concerns with the same species based on the (Nikitin)), or replacement of the striated ornamenta same material. According to the International Code of tion by threadlike ribs (in some morphs of G. catenula Zoological Nomenclature (Article 58.13.), transcrip tum (Fischer)). The genus Schulginites was established tion of the semivowel i as y, ei, ej, or ij is deemed to be by Casey as monotypical; another species S. pseudoko identical. Taking into account the tradition (from chi Mesezhnikov, 1983 was described later from the 1884) of spelling this species name, is should be Mauryn’a River. The latter, being half the size of the referred to as Hectoroceras tolijense (Nikitin, 1881). type species, and having a wider umbilicus and more Figure 4 reproduces the first images of this species. discernible ornamentation at comparable sizes, may The origins of the type collection of this species are be a microconch of Hectoroceras tolijense. described below. Mesezhnikov et al. (1983) while Only the above mentioned collection of A.P. Pav describing “Schulginites” tolijense indicated the low from Kuzminskoe can be considered as providing “exact” locality and interval of the occurrence of the well documented records of H. tolijense from the Rus lectotype (Mauryn’a River, Chetaites sibiricus Zone). sian Platform. Taking into account a small number of The footnote says that all ammonite shells of this spe species in the genera Hectoroceras and Schulginites cies housed in the Mining museum were brought by and their phylogenetic affinity, I consider Schulginites the expedition of E.R. Fedorov, not from the Tol’a as a junior subjective synonym of Hectoroceras. Tiver, but from its tributary Mauryn’a. This is certainly Hectoroceras kochi, the index species of the next confusing. Fedorov’s first expedition to the eastern subdivision, is more widespread and is represented by slope of the Urals was in 1884–1886, but as noted a larger number of specimens. It was originally above, Eichwald described this genus in 1868 as described from eastern Greenland (Spath, 1947), but Ammonites catenulatus Fischer. Nikitin used the same was later found in Siberia (Schulgina, 1972), England collections, before Fedorov’s expeditions. Expeditions (Casey, 1973), and Central Russia (Casey et al., 1977). to the North Urals led by M.I. Protasov, N.l. Stra Nevertheless, it still insufficiently studied and not all jevsky, and E.K. Hofmann took place in the 1830s– of its illustrations are suitable for identification 1840s (Ilovaisky, 1915, and others). It is most likely because some do not show the shape of its cross sec that the material used by Eichwald and Nikitin were tion or shape of the venter, or lack measurements and brought to the Mining Museum by one of these. proportions. I assigned to H. kochi Spath only those The species Hectoroceras tolijense is also interesting specimens from Central Russia, which come from a because, in my opinion (Mitta, 2007), it is an interme thin (up to 0.05 m) bed of black sandstone under the
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basal sandstone of the rjasanensis Zone. These are flat tened shells with a narrow umbilicus and relatively thin ribs (Pl. 2, fig. 1; also Mitta, 2007, pl. 1, figs. 6–8). The sandstone of the rjasanensis Zone contains shells of a different kind (Pl. 4, fig. 2), showing wider whorls, considerably wider umbilicus, coarser ribs. Previously similar specimens from the same part of the sections were identified as Hectoroceras cf. kochi (Mitta, 2005, pl. 1, fig. 3; 2007, pl. 1, fig. 10). Apparently, this is another, as yet undescribed species of this genus. However the limited material and the lack of a speci men suitable for a holotype designation does not allow us from introducing a new species name. In addition, there is still some room for doubt as it is theoretically possible that this is a microconch of H. kochi, although specimens from the rjasanensis Zone in my collection represent the same morphotype. (a) (b) However, the fact that the beds with H. tolijense and those with true H. kochi occur in the interval directly below the rjasanensis Zone allows us to give a name to this “unnamed” Zone (Mitta and Bogomolov, 2008; Mitta and Sha, 2009). Correspondingly, we recognize the Hectoroceras kochi Zone between the nodiger Zone and rjasanensis Zone of the Russian Platform, which includes the previously established faunal horizons H. tolijense and H. kochi (Fig. 1b). This Zone is an approximate equivalent of the zone with a same name recognized in eastern Greenland and England, and possibly northern Siberia. The occurrence of these ammonites at the Jurassic–Cretaceous boundary in northern Siberia needs revision and is beyond the scope of this paper. The kochi Zone of the Russian Platform occurs in the boundary interval between the Volgian and Ryazanian Stages, and historically does not belong to these stages. Considering that in other regions of the Boreal Realm, the kochi Zone is referred (c) (d) to the Boreal Berriasian, we place it in the scale of the Russian Platform at the base of the Ryazanian Stage. Fig. 4. Hectoroceras tolijense (Nikitin), original illustra However, the ultimate placement of this interval as tions: (a, b) reproduced figures of Ammonites catenulatus either Jurassic or Cretaceous will depend on where the (according to Eichwald, 1868, pl. 35, figs. 3a, 3b); boundary between the two systems will be drawn in the (4c, 4d) reproduced figures of Oxynoticeras tolijense (according to Nikitin, 1884, pl. 2, fig. 7). standard scale.
Explanation of Plate 3 All sizes are natural. The beginning of the body chamber is marked with an asterisk. Fig. 1. Craspedites nodiger (Eichwald), phragmocone, specimen PIN, no. 3990/295: (1a) lateral view, (1b) ventral view. Fig. 2. Craspedites nodiger (Eichwald), phragmocone, specimen PIN, no. 3990/296: (2a) lateral view, (2b) apertural view. Figs. 3 and 9. Garniericeras subclypeiforme (Milaschewitch): (3) phragmocone, specimen PIN, no. 3990/297, lateral view; (9) phragmocone, specimen PIN, no. 3990/302: (9a) lateral view, (9b) apertural view. Fig. 4. Riasanites rjasanensis (Nikitin), a phragmocone with a half of a body chamber whorl; lateral view, specimen PIN, no. 3990/299. Figs. 5 and 6. Riasanites swistowianus (Nikitin): (5) phragmocone of a macroconch with an early part of the body chamber; lateral view, specimen PIN, no. 3990/298; (6) phragmocone of a microconch; lateral view, specimen PIN, no. 3990/393. Fig. 7. Chetaites sibiricus Schulgina, a phragmocone with a part of the body chamber, specimen PIN, no. 3990/300: (7a) lateral view, (7b) ventral view. Fig. 8. Craspedites parakaschpuricus Gerasimov, a phragmocone with a half of a whorl of a body chamber, specimen PIN, no. 3990/301: (8a) lateral view, (8b) ventral view. (1–7): bank of the Oka River near the village of Kuzminskoe, Ryazan Region; (1–3): Volgian, nodiger Zone; (4–7): rjasanensis Zone; (8–9) Ulyanovsk Region, bank of the Syzranka River, gully near the villages of Mar’evka and Rep’evka; Volgian, nodiger Zone; coll. by V.V. Mitta and A.V. Stupachenko
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Plate 3 *
1a 1b 2a 2b
*
4 3 *
5
* 6 7b 7a
8b * 8a 9b 9a
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Plate 4
1a 1b 3c 3b
2a 2b
3a
5b
4b 4a 5a
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SYSTEMATIC PALEONTOLOGY fluctuations of the density of the secondary ribs. Our Family Craspeditidae Spath, 1924 collection contains specimens with a higher, more oval cross section and more closely spaced ribs. Genus Craspedites Pavlow, 1892 Craspedites ultimus Mitta et Sha, sp. nov. C o m p a r i s o n. In its shell shape and ornamen Plate 4, figs. 3–5 tation, this species is most similar to C. subditus (Trautschold) and C. nodiger (Eichwald), index spe Etymology, From the Latin ultimus (ultimate). cies of two successive zones in the top of the Upper H o l o t y p e. PIN, no. 3990/315; Moscow Volgian. The new species differs from the above two in Region, Quarry no. 12 2 of the Lopatinskii Phospho the whorl shape and the wider umbilicus, and in the rite Mine; Ryazanian Stage, Riasanites rjasanensis higher ribbing coefficient in adult whorls. Zone, Riasanites swistowianus faunal horizon. D e s c r i p t i o n. The shell is large (phragmocone R e m a r k s. Apparently, the new species repre over 100 mm in diameter). Adult whorls are moder sents a connecting link between the Jurassic (Late Vol ately wide (early whorls are compressed or slightly gian) Craspedites and Cretaceous (Ryazanian) inflated), rounded trapezoid in cross section, with a Pseudocraspedites. Variations of this species include maximum width near the umbilicus. The width specimens with a relatively high whorl section and decreases towards the rounded venter. The umbilicus more densely spaced ornamentation resembling is moderately wide. The umbilical wall is steep in P. bogomolovi Mitta, but lacking constrictions charac young whorls, and is more gently sloping in adults. teristic of the latter species. The body chamber is not known. O c c u r r e n c e. Central Russia, Ryazanian Stage, The early whorls (Dm = 20–40 mm) possess thin lower part of the Riasanites rjasanensis Zone. evenly prominent bipartite and tripartite subradial ribs Material. Twenty eight specimens in various with a bifurcation point in the lower third of the flank. states of preservation from the type locality; one spec As the shell grows, the umbilical portions of the ribs imen comes from the basal part of the rjasanensis Zone become raised and are transformed into thickened pri in the gully near the village of Svistovo, Ryazan mary ribs, reaching the mid flank. As this happens the Region; several more specimens come from a number ribs become weaker and are hardly visible on the mold; of localities in the Oka River basin and are assigned to although in places with a preserved shell in large spec this species provisionally because of their poor preser imens, the venter possesses thin threadlike ribs. The vation. number of secondary ribs changes with age: ribbing coefficient gradually increases from 2.5 in young whorls to 4.5 in adult whorls. ACKNOWLEDGMENTS Measurements in mm and ratios: Geologist A.V. Stupachenko (Moscow), and Profs. Speci Wan Xiaoqiao and Yin Jiarun (Beijing) participated in Dm WH WW UW WH/Dm WW/Dm UW/Dm men no. the field work. I.A. Starodubtseva (Moscow) helped 3990/317 100 39 37 28 0.39 0.37 0.28 with the historical research. The photographs were 83 34 29 22 0.41 0.35 0.27 provided by V.T. Antonova (Paleontological Institute, Russian Academy of Sciences). T.B. Leonova and 3990/407 78 30 29 24 0.38 0.37 0.31 A.P.Rasnitsyn (both Paleontological Institute, Rus Holotype 56 22 23 17 0.39 0.41 0.3 sian Academy of Sciences) provided helpful sugges 3990/315 tions. The field work of 2006 was funded by grant 44 19 18 13 0.43 0.41 0.29 no. 04 05 39022 RFBR NSFC of China; the study is 3990/316 35 15 17 10 0.43 0.2 0.29 supported by the Program of the Presidium of the Rus 29 13 13 8 0.45 0.45 0.28 sian Academy of Sciences “Origin of the Biosphere and the Evolution of Geo biological Systems”, Variability. The variably is primarily observed project “Geo biological events in the evolution of the in the degree of steepness of the umbilical wall and pelagic biota based on cephalopods and radiolarians.”
Explanation of Plate 4 All images are natural size. Fig. 1. Hectoroceras kochi Spath, specimen PIN, no. 3990/394, cast of an imprint of a phragmocone: (1a) lateral view, (1b) ventral view. Fig. 2. Hectoroceras sp. nov., phragmocone, coll. by A.V. Stupachenko, specimen ABC/1070: (2a) lateral view, (2b) ventral view. Figs. 3–5. Craspedites ultimus sp. nov., phragmocone: (3) holotype PIN, no. 3990/315: (3a) lateral view, (3b) inner whorls, lateral view, (3c) the same, apertural view; (4) specimen PIN, 3990/317: (4a) lateral view, (4b) ventral view; (5) specimen PIN, no. 3990/316: (5a) lateral view, (5b) ventral view. All specimens come from the quarry of Lopatinskii Phosphorite Mine no. 12 2, Moscow Region; (1) kochi Zone, kochi faunal horizon; (2–5) rjasanensis Zone, rjasanensis Subzone, swistowianus faunal horizon; coll. V.V. Mitta and A.V. Stupachenko.
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