The exposures of the Tithonian-Berriasian succession of the Vaca Muerta Fm in Caj & oacute;n de Almanza (Neuqu & eacute;n Basin) are extensively covered by modern material. This condition hampers the bed by bed collection of ammonites which, consequently, have never been sampled as successions of assemblages. The fine preservation and abundance of the local fauna makes of Caj & oacute;n de Almanza a locality of choice for expanding the knowledge of Tithonian-Berriasian ammonite fauna and its succession in this deep sector of the basin. Recently we have collected small assemblages from three successive horizons within the interval Altenans-Damesi zones (upper Tithonian-upper Berriasian). (BEHRENDsEN), Leonardia almanzaensis n. gen., n. sp., Substeueroceras koeneni (sTEuER), and Subthurmannia boissieri (PicTET). From this material plus a published list, and a number of few sets of ammonites formerly collected in isolation, we have pieced together a new chronostratigraphic and palaeontologic scheme for the study area, including the confirmation of the stratigraphic position of the holotype of Pliosaurus almanzaensis O'GORMAN, GAsPARiNi & sPALLETTi in the upper Alternans Zone.

The Late Jurassic aspidoceratoid genus Pseudhimalayites Spath is scarcely recorded but widely distributed in the Andean basins, the Caribbean region, and in the European Tethys. From Ponti Zone (Lower Tithonian) rocks of the Betic Range in Carchelejo we describe here the new species Pseudhimalayites carchelejensis, based on a macroconch (female) holotype. The corresponding microconch (male), described from the same ammonite assemblage, would belong to the morphogenus Simocosmoceras Spath which groups the microconchs of Pseudhimalayites. P. carchelejensis n. sp. differs from the coeval Pseudhimalayites steinmanni (Haupt) by lacking ventral tubercles in the phragmocone and by bearing umbilical tubercles only from the adult whorl of the phragmocone. These differences illustrate a significant morphologic divergence between the Andean and the Tethyan lineages.

The family Simoceratidae Spath, 1925, lumps various forms belonging to lineages with different roots and is clearly paraphyletic. One of its genera is Lytogyroceras Spath, 1924, which stands apart from the typical forms of the family bearing strong ribbing and tubercles. The sexual dimorphism of Lytogyroceras was supposed to be based only on adult size differences. Here we describe a recently collected lappeted microconch of Lytogyroceras subbeticum (Ol & oacute;riz, This microconch shows that the sexual dimorphism in the genus Lytogyroceras is not only characterized by different adult size of the sexes as formerly assumed, but also by different adult peristome morphology.

Three adult specimens of the rare lower Oxfordian ammonite species Protophites insociale (Bukowski) are described from two sections of southern Poland, Ogrodzieniec and Zalas. Based on their globular phragmocone, geniculate body chamber, suture line, looped ribs, and age, they have been included in the Pachyceratidae. In the present study Protophites (microconch) and Tornquistes (macroconch) are considered as a sexual dimorphic pair.

The Global Stratotype Section and Point (GSSP) for the base of the Kimmeridgian Stage (Jurassic System), at Flodigarry, Staffin Bay, Isle of Skye, Scotland, UK Journal Item How to cite: Wierzbowski, Andrzej; Barski, Marcin; Coe, Angela L.; Hounslow, Mark W.; Matyja, Bronisław A.; Price, Gregory D.; Wierzbowski, Hubert; Wright, John K.; Atrops, with contributions from Francois; Grabowski, Jacek; Mattioli, Emanuela; Morton, Nicol; Ogg, James G.; Olóriz, Federico; Page, Kevin; Parent, Horacio; Przybylski, Piotr; Schweigert, Guenter and Villaseñor, Anna Bertha (2023). The Global Stratotype Section and Point (GSSP) for the base of the Kimmeridgian Stage (Jurassic System), at Flodigarry, Staffin Bay, Isle of Skye, Scotland, UK. Episodes (Early Access).

The ancient hydrocarbon seep deposits at the La Elina Ranch, Neuquen Basin, northern Patagonia, Argentina, are the only Mesozoic seep site in South America yielding metazoan fossils. Apart from benthic mollusc shells and worm tubes, they yielded a number of nektonic ammonoids. Four species of ammonoids were identified: Hildaitoides retrocostatus, Hammatoceras ex gr. insigne, Calliphylloceras cf. nilssoni, and Phylloceras sp. The occurrences of three species (H. ex gr. insigne, C. cf. nilssoni, and Phylloceras sp.) probably are fortuitous, while H. retrocostatus might have actually thrived in, or around the seep, as indicated by numerous well-preserved juveniles, in addition to some adult specimens. The bathymetric estimates indicate a depth not greater than 200 m, while the benthic molluscs, typical of hydrocarbon seeps, indicate a much greater depth. It is hypothesized that the deep-water taxa might have occurred in a shallower setting, owing to rising anoxia and/or strong input of continental waters from the eastern and/or southeastern deltaic system. The ammonite assemblage indicates that the seep at La Elina is (Andean) Middle Toarcian, probably Chilensis Zone, in age.

Among the ammonite collection from the Neuquen and Mendoza provinces made by G. Bodenbender, stands Aspidoceras bodenbenderi Behrendsen. This rare aspidoceratid is assigned to the lower Alternans Zone because of the associated Parodontoceras calistoides (Behrendsen), and can be most likely attributed to the recently established genus Hypowaagenia Schweigert & Schlampp.(c) 2022 Elsevier Masson SAS. All rights reserved.

Fossils from the Jurassic succession of the Neuquén Basin (Argentina) were analysed for their stable isotope (δ 13 C, δ 18 O) and elemental (Mg/Ca, Sr/Ca) composition. Mg/Ca ratios point to comparatively stable temperature conditions from the Bajocian to Early Oxfordian and during the Tithonian, but do not allow a reliable reconstruction of absolute water temperatures. Sr/Ca ratios follow the general global pattern, indicating water exchange between the basin and the open ocean. The δ 18 O values can be translated into water temperatures between 20 and 25°C for most of the studied intervals with possible shorter cold spells in the Late Pliensbachian, Bajocian and Late Tithonian. However, precise temperature reconstructions are complicated by bivalve shells from the northern–central part of the basin pointing to local fluctuations in the δ 18 O values of seawater. Potential reasons for these variations are discussed, but it seems most likely that they are caused by phases of enhanced freshwater input leading to meso- to brachyhaline conditions in the northern study areas. This paper therefore exemplifies the particular challenges for temperature reconstructions in marginal seas and highlights the opportunities of combining different geochemical proxies to disentangle the influence of different environmental parameters. Supplementary material: Detailed results of the geochemical analyses, geographical coordinates and information on biostratigraphy are available at https://doi.org/10.6084/m9.figshare.c.5173466

A new bed-by-bed collection of samples of Stehnocephalites gerthi (SPATE') throughout its stratigraphic range has been studied in order to characterize the variation and phyletic evolution of this Jurassic ammonoid. The study was conducted adopting a partition of the morphologic variation within a species as transients for the phyletic changes in the lineage, and as morphs for the individual variation within the transients. The results of the study show that the phyletic evolution of the species can be described as three transients, which include wide variations in adult size, shell shape and ornamentation. This variation could be studied in detail from the transient III. The variation is very wide and can be described by means of four morphs. These morphs are interpreted as the result of the operation of different developmental heterochronic processes over different sets of charaters in different individuals. It is possible that the conspicuous morphology and ornamentation of the transient II, which correlates with lithogical changes, have originated in environmental changes.

The external area-to-volume ratio of the ammonite shell has been held to be related to morphology but never evaluated quantitatively. A dimensionless ratio, the Vogel number, was computed for large samples of Devonian to Cretaceous ammonites with a new method based on the ADA-model. The estimated ratios range from 2.4 to 3.4. The highest values are exhibited by uncoiled serpenticone ammonites, lowering in the sequence serpenticone-oxycone-spherocone. It is shown that the area-to-volume relationships are controlled by the involution (degree of overlapping) and the relative width of whorl section. The typical evolutionary trends serpenticone-spherocone and/or serpenticone-oxycone, broadly documented through the history of the Ammonoidea, could have been driven, at least in part, by the lowering of the area-to-volume ratio.

The aspidoceratid ammonites have been traditionally included in the superfamily Perisphinctoidea. However, the basis of this is unclear for they bear unique combinations of characters unknown in typical perisphinctoids: (1) the distinct laevaptychus, (2) stout shells with high growth rate of the whorl section area, (3) prominent ornamentation with tubercles, spines and strong growth lines running in parallel over strong ribs, (4) lack of constrictions, (5) short to very short bodychamber, and (6) sexual dimorphism characterized by miniaturized microconchs and small-sized macroconchs besides the larger ones, including changes of sex during ontogeny in many cases. Considering the uniqueness of these characters we propose herein to raise the family Aspidoceratidae to the rank of a superfamily Aspidoceratoidea, ranging from the earliest Late Callovian to the Early Berriasian Jacobi Zone. The new superfamily includes two families, Aspidoceratidae (Aspidoceratinae, Euaspidoceratinae, Epipeltoceratinae and Hybonoticeratinae), and Peltoceratidae (Peltoceratinae and Gregoryceratinae nov. subfam.). The highly differentiated features of the aspidoceratoids indicate that their life-histories were very different from those of the perisphinctoids; these ammonites show great promise for studies of developmental and evolutionary patterns and processes, and can be used for bio­stratigraphic-chronostratigraphic purposes and interprovincial correlations.

New ammonite collections from the lower part of the Vaca Muerta Formation (Portada Covunco Member) at Picún Leufú, Estancia María Juana and Carrín Curá provided new data about the species of the lower Tithonian Picunleufuense Standard Zone in the southern margin of the Neuquén Basin. The fauna is consistently composed of the four typical species (Indansites picunleufuense, Choicensisphinctes platyconus, Catutosphinctes guenenakenensis, and Cienguiticeras perlaevis), and here we add the aspidoceratid Physodoceras cf. neoburgense which is described based of two specimens from the new collections. The successive assemblages composed of different morphotypes (transients) of those species characterize the three biohorizons of the lower Picunleufuense Zone: picunleufuense alpha Hz. (base of the zone), picunleufuense beta Hz., and picunleufuense gamma Hz. (new). A new, earlier transient of Indansites picunleufuense is described, but the material is still scarce for the characterization of the adult macroconch. The ammonites from the locality Carrín Curá were collected from a section of the lower Vaca Muerta Formation: 17.1 m of sandy shales with thin intercalations of calcareous sandstones indicating a near-shore environment. Ammonites and bivalves occur in the calcareous sandstone levels.

In the late Pleistocene, Panochthus was the most diverse genus of glyptodontids with five species: P. jaguaribensis, endemic to the intertropical region of Brazil, P. hipsilis from Bolivia, P. greslebini from Brazil and Argentina, P. tuberculatus from Uruguay and Argentina and P. frenzelianus, probably from the Pampean region, Argentina. In this paper we describe the robust caudal tube of a new species, Panochthus florensis n. sp., that inhabited the center of the Pampean region of Argentina at the end of the Pleistocene. The reduction in the number of central figures, a single apical figure, the absence of an apexian figure, and the lack of figures between the first pair of dorsal figures allow a rapid differentiation from the already known species. The striking diversity of Panochthus contrasting with that of other late Pleistocene glyptodontids, lead us to propose hypotheses for explaining this fact.

A new collection of ammonites from the Picunleufuense Zone (standard base of the Andean Tithonian) of the locality Estancia Maria Juana (southern Neuquen Basin, Argentina) has provided abundant and well preserved material of new transients of Indansites picunleufuense and Choicensisphinctes platyconus. These transients are described and a detailed review of the early evolution of the Indansites lineage is presented. The meaning of changes in rib density, variations within the microconchs (males) and the length of the bodychamber in Indansites picunleufuense are discussed. It is concluded that the changes in rib density which characterize the successive macroconchs of the transients indicate changes in the rate of shell-growth. The more densely ribbed phragmocone of later transients would have had lower growth rates, which would also explain their smaller adult size. The microconchs show high variation in adult size suggesting high plasticity in the size-age maturation, most likely caused by influence of seasonal environmental conditions. A large small-macroconch-like lapetted microconch, coming from the close locality Picun Leufu, is interpreted as a new case of sex-change.

In the Cerro Mallín Quemado area (Sierra de la Vaca Muerta) the three members of the Vaca Muerta Formation (Portada Covunco, Los Catutos and Pichi Moncol) can be recognized, including the whole of the Tithonian rock-record. The ammonite fauna does not show significant differences with respect to that of the nearby locality Pampa Tril, but the record of faunal horizons is patchier. Eighteen species of ammonites were recorded through the studied sections, covering the whole of the Andean Tithonian. The current chronostratigraphic zonation of the Andean Tithonian is briefly discussed, updated and correlated with the most recent literature. From the current succession of ammonite bio-horizons previously defined in the basin, only three (picunleufuense alpha, picunleufuense beta and falculatum) were recognized definitely. Four other bio-horizons (perlaevis, erinoides, internispinosum alpha and vetustum) were recognized only tentatively, because the typical assemblages of morphotypes (morpho-species) were not clearly or completely recognized. The current regional time-correlation chart dated by the ammonite bio-horizons of the Neuquén Basin along a 70°W transect is updated with the results of the present study and additional information recently obtained from other localities.

The ammonite fauna of the Tithonian–Berriasian of the Vaca Muerta Formation in Pampa Tril has been recently described in detail. New important specimens and additional information are presented in this paper. The phyletic evolution of Choicensisphinctes, passing from C. platyconus to C. erinoides is confirmed, as well as the sexual dimorphic correspondence of this latter with C. mendozanus. A microconch of the genus Krantziceras is described for first time. New specimens of Substeueroceras koeneni identical to the paralectotype, along with material already described from the koeneni Hz. (Koeneni Zone), point to the fixation of this horizon as the type horizon of the species. New specimens of Subthurmannia boissieri from the Damesi Zone match clearly the range of variation of this species in Spain, thus providing an element for time-correlation with the Tethyan standard scale. Additional material from the internispinosum alpha Hz. confirms the origin of W. internispinosum from C. proximus by the inception of an evolutionary innovation in the juvenile ontogeny.

The recent recognition of the earliest Andean Tithonian ammonite fauna (Picunleufuense Zone) has allowed a balanced classification of the ataxioceratid ammonites, reflecting their phylogenetic relationships. The Picunleufuense Zone fauna, first recognized in the Neuquén Basin at the base of the Vaca Muerta Formation, is represented by numerous records of sparse ammonite faunas from Antarctica, the Austral Basin and the Tarapacá Basin (N. Chile and S. Peru). These Southeastern Pacific faunas include the Tithonian genera Indansites, Choicensisphinctes, Zapalia, Krantziceras (Tithonian–lower Berriasian) and Platydiscus. These five genera are grouped in a new subfamily established in this paper: Zapaliinae subfam. nov. (type genus: Zapalia). The origin of Indansites and Choicensisphinctes (possibly via Indanistes) from Lithacoceras is discussed. Zapalia must have been originated from Indanistes in the upper Proximus Zone. Platydiscus could have been originated from Krantziceras. The Tithonian Southeastern Pacific ataxioceratids (Zapaliinae subfam. nov.) form a group well separated from the Tithonian Indo-Madagascan Virgatosphinctinae.

New data are presented in relation to the worldwide definition of the Oxfordian/Kimmeridgian boundary, i.e. the base of the Kimmeridgian Stage. This data, mostly acquired in the past decade, supports the 2006 proposal to make the uniform boundary of the stages in the Flodigarry section at Staffin Bay on the Isle of Skye, northern Scotland. This boundary is based on the Subboreal-Boreal ammonite successions, and it is distinguished by the Pictonia flodigarriensis horizon at the base of the Subboreal Baylei Zone, and which corresponds precisely to the base of the Boreal Bauhini Zone. The boundary lies in the 0.16 m interval (1.24–1.08 m) below bed 36 in sections F6 at Flodigarry and it is thus proposed as the GSSP for the Oxfordian/Kimmeridgian boundary. This boundary is recognized also by other stratigraphical data – palaeontological, geochemical and palaeomagnetic (including its well documented position close to the boundary between magnetozones F3n, and F3r which is placed in the 0.20 m interval – 1.28 m to 1.48 m below bed 36 – the latter corresponding to marine magnetic anomaly M26r).The boundary is clearly recognizable also in other sections of the Subboreal and Boreal areas discussed in the study, including southern England, Pomerania and the Peri-Baltic Syneclise, Russian Platform, Northern Central Siberia, Franz-Josef Land, Barents Sea and Norwegian Sea. It can be recognized also in the Submediterranean-Mediterranean areas of Europe and Asia where it correlates with the boundary between the Hypselum and the Bimmamatum ammonite zones. The changes in ammonite faunas at the boundary of these ammonite zones – mostly of ammonites of the families Aspidoceratidae and Oppeliidae – also enables the recognition of the boundary in the Tethyan and Indo-Pacific areas – such as the central part of the Americas (Cuba, Mexico), southern America, and southern parts of Asia. The climatic and environmental changes near to the Oxfordian/Kimmeridgian boundary discussed in the study relate mostly to the European areas. They show that very unstable environments at the end of the Oxfordian were subsequently replaced by more stable conditions representing a generally warming trend during the earliest Kimmeridgian. The definition of the boundary between the Oxfordian and Kimmeridgian as given in this study results in its wide correlation potential and means that it can be recognized in the different marine successions of the World.

Asphinctites tenuiplicatus [M] and Polysphinctites secundus [m] from the Asphinctites tenuiplicatus Zone (Early Bathonian), are usually considered as a sexual dimorphic pair, although authors describe them as separate species.We used statistical methods to test the sexual dimorphic correspondence between those morphospecies, based on a rather large sample of well-preserved macro-and microconchs derived from a single horizon of calcareous concretions in the Polish Jura.Our results indicate that both dimorphs or sexes have identical ontogeny up to a critical diameter, from which they diverge towards the characteristic morphology and sculpture of each dimorph.Thus, both dimorphs are described as a single species: Polysphinctites tenuiplicatus [M and m].After review of the several nominal species usually assigned to the genera Asphinctites and Polysphinctites throughout their stratigraphic and biogeographic range in the Early Bathonian of the Tethys, it is concluded that they actually correspond to only two species of a single lineage.The corresponding name for the lineage should be Polysphinctites (= Asphinctites as a junior synonym).