V. V. Mitta

Late Volgian Kachpurites Spath (Craspeditidae, Ammonoidea) of the Russian platform

Ammonites of the genus Kachpurites are characteristic of the lower part of the Upper Volgian Substage of the Russian Platform. K. fulgens fulgens (Trautschold), K. fulgens tscheremkhensis Mitta et al., K. subfulgens (Nikitin) are established in the fulgens zone. The genus Kachpurites also includes ammonites previously described as Anivanovia mola Kiselev. The holotype of Volgidiscus singularis Kiselev belongs to K. mola, wheras some of its paratypes belong to Craspedites krylovi Prigorovsky. The generic name Anivanovia Kiselev, 2003 is considered as a junior subjective synonym Kachpurites Spath, 1924. The beds with Kachpurites mola are in the basal part of the Upper Volgian subditus Zone. Species of the genus Kachpurites are described, and macro- and microconchs are established within the species.

A new morphotype of lower jaw associated with Calliphylloceras (Cephalopoda: Ammonoidea) from the Middle Jurassic of the Northern Caucasus

The body chamber of an ammonoid of the genus Calliphylloceras (Suborder Phylloceratina) containing its lower jaw is reported from the Upper Bajocian (Strenoceras niortense Zone) of the Northern Caucasus. The arrangement, state of preservation, and size of the lower jaw suggest preservation in situ. The general morphology of the lower jaw strongly resembles the chitinous inner lamella of the aptychus-type lower jaws, because it is divided into two almost symmetric parts by a median harmonic midline joint termed symphysis. However, outer bivalved calcitic plates (apytchus sensu stricto) cannot be recognized in the present lower jaw. Early Jurassic Phylloceratina are known to have had lower jaws of the anaptychus-type, whereas Late Cretaceous taxa had lower jaws of the rhynchaptychus-type. It appears that in the Middle Jurassic a third morphotype of lower jaws was present in Phylloceratina, for which we introduce the new term ‘phyllaptychusʼ.KurzfassungAus dem Ober-Bajocium (Strenoceras niortense-Zone)) des Nordkaukasus wird die Wohnkammer eines Ammoniten der Gattung Calliphylloceras (Unterordnung Phylloceratina) mit einem Unterkiefer vorgestellt. Die Einbettungslage, Erhaltung und die Größe des Unterkiefers deutet auf einen in situ-Fund. Die allgemeine Morphologie dieses Unterkiefers erinnert stark an die chitinige Innenlamelle des Aptychus-Typs von Unterkiefern, da er von einer mittigen Sutur, Symphyse genannt, in zwei beinahe symmetrische Hälften geteilt wird. Äußere doppelklappige calcitische Platten (Aptychus im strengen Sinn) sind bei diesem Unterkiefer jedoch nicht erkennbar. Von frühjurassischen Phylloceratina sind Unterkiefer des Anaptychus-Typs bekannt, wogegen die spätkretazischen Arten Unterkiefer des Rhynchaptychus-Typs besaßen. Offenbar existierte während des Mittleren Juras bei den Phylloceratina noch ein dritter Unterkiefer-Morphotyp, für den wir den neuen Namen „Phyllaptychus“einführen.

Ammonite distribution across the Jurassic-Cretaceous boundary in central russia

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.

Ammonites of Tethyan origin in the Ryazanian stage of the Russian platform: Genus Riasanella gen. nov.

A new ammonite genus Riasanella is described from the Ryazanian Stage of the Russian Platform (type species R. rausingi sp. nov.). The new species R. plana sp. nov., R. olorizi sp. nov., and R. riasanitoides sp. nov. are described. These species come from the lower, strongly condensed beds of the Riasanites rjasanensis Zone of the Moscow Region. The upper subzone of this zone in the Ryazan Region contains specimens of Riasanella, identified in open nomenclature. The new genus is assigned to the family Himalayitidae; one of its species is a possible ancestor of Riasanites Spath.

Ammonites of Tethyan origin from the Ryazanian of the Russian platform: Genus Subalpinites Mazenot

The genus Riasanites, represented in Central Russia by two successive dimorphic species, is revised. R. swistowianus is found in the basal beds of the rjasanensis Zone. Its descendant R. rjasanensis is also found in this zone, but upwards in the section, including the beds with Surites spasskensis and Externiceras solowaticum. The representatives of Riasanites from the Crimea and Northern Caucasus are assigned to two species, R. crassicostatus and R. maikopensis, respectively. It is suggested that Riasanites evolved from Sub-Mediterranean Himalayatidae, which migrated from the Western Tethys via the Polish Passage into the Central Russian Basin, and from there to Mangyshlak, the Northern Caucasus, and the Crimea.

The ammonoid genus Spiroceras (Spiroceratidae, Ammonoidea) from the Upper Bajocian of the Northern Caucasus

Ammonites of the genus Spiroceras are described from the Upper Bajocian of the Kyafar River Basin (Karachay-Cherkessia), including macroconchs with preserved apertures and (for the first time in the entire history of the study of Middle Jurassic heteromorphs) microconchs with lateral lappets. The microconchs of S. bispinatum (Baugier et Sauzé), mainly represented by cyrtocones with one ventral row of nodes, correspond to microconchs with a gyroconic shell and a single row of nodes. Macroconchs and microconchs of S. annulatum (Deshayes), the ribs of which lack prominent nodes or spines, are found together. The assemblage also contains small-sized slightly uncoiled shells of Spiroceras aff. S. fourneti Roman et Pétouraud with widely spaced ribs and two prominent rows of large nodes, presumably macro- and microconchs. The ornamentation of this species resembles that of the monomorph Bajocia rarinoda Sturani from the upper part of the Lower Bajocian; perhaps the latter was ancestral to the Middle Jurassic heteromorph. The above species of Spiroceras, as well as S. obliquecostatum (Quenstedt), are figured.

Genus Oraniceras (Parkinsoniidae, Ammonoidea) from the Lower Bathonian of southern European Russia

This paper discusses members of the genus Oraniceras from the Lower Bathonian of the Saratov Volga Region (Oraniceras mojarowskii (Masarowič), O. besnosovi Mitta et Seltzer, and the Northern Caucasus (O. gyrumbilicum (Quenstedt), O. fretense (Wetzel), and O. wuerttembergicum (Oppel)). A new species O. scythicum sp. nov. is described, represented by macro- and microconchs from the Kuban River basin (Bolshoi Zelenchuk River, Karachay-Cherkessia).

On some Rarecostites (Parkinsoniidae, Ammonoidea) from the Upper Bajocian Parkinsoni zone of the Northern Caucasus

The ammonites of the genus Rarecostites (subfamily Parkinsoniinae) are studied from the lower part of the Upper Bajocian Parkinsonia parkinsoni Zone of the Kyafar River (Bolshoi Zelenchuk River Basin, Karachai-Cherkessia, Russia). The locality contains numerous microconch shells of R. subarietis (Wetzel). We follow de Grossouvre (1919) in considering the names R. acris (Wetzel) and R. arietis (Wetzel) to be subjective synonyms of R. subarietis and, thus, the standard Acris should be replaced by the Subarietis Subzone. The lower part of the section also contains numerous microconchs of R. sherstyukovi sp. nov. and, less commonly, macroconchs of R. kyafarensis sp. nov. The phylogeny of Rarecostites species is reconstructed; the above species are described and figured and the sherstyukovi and subarietis faunal horizons are established.

Ammonites of Tethyan origin in the Ryazanian Stage of the Russian Platform: Genus Mazenoticeras and other Neocomitidae

Ammonites from the Riasanites rjasanensis Zone (Ryazanian Stage of the Russian Platform) of the family Neocomitidae are considered. The new species Mazenoticeras robustum sp. nov. and M. ceccai sp. nov. are described. Other members of this genus and of the genera Malbosiceras and Pomeliceras are identified in open nomenclature.

The genus Keppleritiana gen. nov. (Stephanoceratidae, Ammonoidea) from the Upper Bajocian of the Northern Caucasus

A new ammonite genus of the subfamily Garantianinae, family Stephanoceratidae, from the Upper Bajocian Strenoceras niortense Zone in the Bolshoi Zelenchuk River basin (Karachay-Cherkessia), with two new species from two different localities, is established. The type species Keppleritiana rostovtsevi gen. et sp. nov. is homeomorphic to some species of the Upper Bathonian–Lower Callovian genus Kepplerites (Fam. Kosmoceratidae) but is distinguished by the presence of a ventral furrow in adults. An isolated valve of an aptychus possibly belonging to this species is illustrated. Keppleritiana graebensteini sp. nov. has a more archaic morphology and is apparently ancestral to the type species. The macroconchs and microconchs of both species are described.