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1
Content available A new species of Pseudhimalayites (Ammonitina, Aspidoceratoidea) from the Lower Tithonian of the Betic Range, Southern Spain
Parent Horacio, Ramos-Agustino Enrique, Scherzinger Armin, Schweigert Günter
Volumina Jurassica
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2023
|
Vol. 21
19--26
EN
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.
2
Content available Structure of the calcitic layer of the aptychus of the ammonite genus Peltoceras
Mironenko Aleksandr A.
Annales Societatis Geologorum Poloniae
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2021
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Vol. 91, No. 4
397--404
EN
The aptychi of ammonites combined the functions of lower jaws and protective opercula. They consist of two parts: an inner organic layer and an outer calcitic lamella. In different evolutionary lineages of ammonites, the shape of aptychi, the sculpture of their surface and the microstructure of the calcitic layer vary greatly. However, the structure of the aptychi is not known for all evolutionary lineages of ammonites. Although numerous aptychi have been described for the Jurassic family Aspidoceratidae, almost all of them belong to only one evolutionary branch of this family – the Aspidoceratinae (sensu lato). For the second branch – the Peltoceratinae, only one aptychus had been described to date and the structure of its calcitic layer remained unknown. In this article, for the first time, the structure of the aptychus of the Peltoceratinae (upper Callovian Peltoceras) is described. The surface of this aptychus is covered with rough ribs and the calcitic part consists of only one layer of dense calcite. The thickness of the aptychus is much greater than that of the aptychi of supposed ancestors of the Peltoceratinae. The increase in the thickness of the aptychi in both the Aspidoceratinae and the Peltoceratinae, contemporaneously with the appearance of spines on their shells, is most likely related to increasing the protective function of the aptychi of these ammonites in the late Callovian.
3
Content available Hypowaagenia nov. gen., a rare genus of giant aspidoceratid ammonite from the Upper Jurassic of Southern Germany
Schweigert Günter, Schlampp Victor
Volumina Jurassica
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2020
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Vol. 18, no. 1
23--36
EN
A new genus, Hypowaagenia (type species: H. endressi nov. sp.), is introduced for previously unknown large-sized macroconchiate aspidoceratid ammonites with an umbilical and a ventrolateral row of spines. In the medium and adult stages irregular ribs interconnect these spines. The oldest unequivocal record of this genus comes from the Early Kimmeridgian Planula Zone, whereas the type material of H. endressi nov. sp. comes from the upper Platynota Zone/? lowermost Hypselocyclum Zone. Corresponding microconchs have not yet been identified. Although all unequivocal records come from Southern Germany, a Tethyan origin is most likely for these aspidoceratids. Another, stratigraphically younger species tentatively included in Hypowaagenia is Aspidoceras acanthomphalum (Zittel, 1870), which is, however, only recorded yet by mesoconchiate specimens. The ammonite fauna of the type horizon of H. endressi nov. sp. is briefly characterized and termed as the geniculatum Biohorizon of the late Platynota Zone.
4
Content available A review of the classification of Jurassic aspidoceratid ammonites – the Superfamily Aspidoceratoidea
Parent Horacio, Schweigert Günter, Scherzinger Armin
Volumina Jurassica
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2020
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Vol. 18, no. 1
47--52
EN
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.
5
Content available A microconchiate Hypowaagenia Schweigert and Schlampp, 2020 (Aspidoceratidae, Hybonoticeratinae) from the Upper Jurassic of Southern Germany
Schweigert Günter, Schlampp Victor
Volumina Jurassica
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2020
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Vol. 18, no. 2
115--120
EN
The previously unknown microconch which corresponds to the recently introduced Late Jurassic aspidoceratoid ammonite genus Hypowaagenia Schweigert and Schlampp, 2020, is reported from beds of the topmost Platynota Zone or basal Hypselocyclum Zone of Franconia. This record indicates that these exotic ammonite findings are not of long-drifting necroplanktonic shells, but stem from animals that have spread over this area after immigration from the Tethys
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