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Middle Jurassic Gastropods from the Central High Atlas, Morocco
Abstract
This systematic study considers twenty-four gastropod species recovered in the Upper Aalenian-Lower Bajocian sediments of the Central High Atlas. Twenty-one species belong to archaeogastropod groups and three species are assigned to two caenogastropod families. A new genus, Sadkia nov. gen. (family Eucyclidae), and two new species, Sadkia richensis nov. sp. and Pirper ouchenensis nov. sp., are described. This gastropod fauna is compared with the coeval faunas known from other regions in order to define better the palaeobiogeographical history of the western Tethyan gastropods during the Jurassic. The generic/subgeneric and specific palaeogeographical distributions indicate a close resemblance between the gastropod faunas of the Central High Atlas and those of the European continental seas. On the other hand, there are no evidences of relationships with the faunas of the inner area of the western Tethys.
... Based on the change in coiling direction during ontogeny, Bandel (1993) united slit-less Cirridae and slitbearing Porcelliidae in the superfamily Cirroidea (¼Porcellioidea). It is debated whether Cirridae is related to Porcelliidae or Eucyclidae (see Conti & Monari, 2001;Karapunar & N€ utzel, 2021;Szab o et al., 2019); therefore, the family Cirridae was excluded from the list of pleurotomariidan genera. As a result of a revision, the current list consists of 283 pleurotomariidan genera (see Supplemental material, Appendix 6 for the complete list). ...
Evolutionary relationships of fossil gastropods have largely been inferred using taxonomic systematics. Phylogenetic relationships between extinct gastropod groups and their relationship to extant groups are largely unresolved. Here we reconstruct the phylogeny of Pleurotomariida, which has the longest fossil record among extant gastropod clades and represents one of the most diverse Palaeozoic gastropod groups. Bayesian (fossilized birth–death [FBD] model) and parsimony analyses were performed using 93 morphological shell characters comprising 109 pleurotomariidan species representing 80 genera/subgenera ranging from the Ordovician to Recent. Parsimony analysis failed to reconstruct stratigraphically congruent trees and many nodes have poor support. The FBD model incorporates the stratigraphical ages of taxa for tree reconstruction and therefore better fits the stratigraphical record. According to the FBD phylogeny, Pleurotomariida was represented by three distinct lineages during the Palaeozoic: Eotomariini, Wortheniellini and Pleurotomariini. Pleurotomariini and Wortheniellini survived the end-Permian mass extinction. Although Wortheniellini showed a higher diversification during the Triassic recovery period, only Pleurotomariini survived until the present day, suggesting that resilience to extinction was not dependent on diversification dynamics in this clade. The FBD analysis indicates that groups that have an exclusively Triassic fossil record originated during the Permian and that the origination and extinction rates increased from the Ordovician to the Jurassic and dropped subsequently. Sampling standardized diversity analysis of Pleurotomariida corroborates that they were one of the most diverse gastropod groups in the late Palaeozoic and that their diversity significantly dropped after the end-Permian mass extinction. Early ontogenetic shell characters are more conservative (phylogenetically more informative) compared to late ontogenetic shell characters. In contrast to previous assumptions, axial characters are not more homoplastic than spiral shell characters, as indicated by higher consistency index values. The data further revealed that adult gastropod shell size depends significantly on the protoconch size and the initial whorl size.
Systematic knowledge of Early and Middle Jurassic marine gastropods from Argentina has been supplied during the last decade through several contributions. The present paper describes a new marine gastropod fauna for the Jurassic of the Neuquén Basin, represented by four major taxa such as Patellogastropoda, Vetigastropoda, Caenogastropoda and Heterobranchia, including 14 new species of the genera Scurriopsis (Hennocquia), Eucyclus, Pleurotomaria, Laevitomaria, Obornella, Crossostoma, Palaeorissoina, Euconactaeon, Striactaeonina and Sulcoactaeon; members of Ambercyclus and Rhabdocolpus are also described from the studied area. Most of these taxa are first reported in the Jurassic of Argentina, extending their palaeobiogeographical distribution in South America at that time. Particularly, the genera Obornella, Palaeorissoina, and Euconactaeon also extend their chronostratigraphic distribution in the Jurassic marine deposits of the Neuquén Basin, from the late Hettangian (Palaeorissoina) and late Pliensbachian (Obornella) to the Aalenian–Bajocian (Euconactaeon). The new fossils described here expand the known diversity of the marine gastropod faunas in the Jurassic of Argentina and contribute to the paleontological knowledge of the group in the Mesozoic of the Southern Hemisphere.
A reef-associated mollusc fauna (gastropods and bivalves) and its facies context are described from latest Triassic (Sevatian–Rhaetian) reef carbonates of Austria (Rötelwand reef at Gaissau and Gosaukamm near Hallstatt). The studied carbonates from the Rötelwand reef consist of mollusc-rich rudstones, partly boundstones, which contain branched corals ( Cycliphyllia and Retiophylia, Pinacophyllum ), whereas coralline sponges are absent. The rich foraminiferid fauna that is associated with the reef builders consists of 11 genera; eight of these genera became extinct until the end of the Rhaetian. Associated with small patch reefs was a rich mollusc fauna with 19 gastropod species and 8 epifaunal bivalve species. The gastropod fauna is dominated by Microschiza rhaetica , Trochotoma praecursor , and the large growing Purpuroidea moosleitneri . Six gastropod species are new to science: Angulomphalus senowbarii sp. nov., Stuorella zapfei sp. nov., Hologyra callosa sp. nov., Microschiza rhaetica sp. nov., Angularia corallina sp. nov., and Purpuroidea moosleitneri sp. nov. Four Triassic gastropod species are placed in other genera (new combinations): Tylotrochus diversicostatus Wolff, 1967 and Eucycloscala epitoniformis Nützel and Senowbari-Daryan, 1999 are placed in Sadkia, Praelittorina sepkoskii Nützel and Erwin, 2004 in Microschiza , and Purpuroidea ? minioi Leonardi, 1935 in Angularia Koken, 1892. Reversal of precedence is proposed for Angularia Koken, 1892 (Gastropoda) and Angularia Busk, 1881 (Bryozoa) under ICZN Art. 23.9. Although reefs suffered a catastrophic decline at the end of the Triassic, most of the studied reef-associated bivalve and gastropod genera survived into the Jurassic, indicating a considerable ecological plasticity of these groups. Only 12 out of 47 reef-associated mollusc genera became extinct (25.5%). This observation is at variance with earlier suggestions that taxa that were associated with reefs and carbonate substrata had a significantly higher extinction risk than level-bottom dwellers. However, extinction at the species level appears more severe; only three bivalve species but no gastropod species recorded in this fauna have records from the Jurassic.
Whereas Middle Jurassic gastropods are very well known in Europe and other regions of the world, these faunas have been much less studied from northern Africa and most contributions available in literature have been based on relatively well preserved material. Except a little lower Bajocian fauna from the Central High Atlas (Morocco) described at the turn of the 21th century, nothing is known about the Middle Jurassic gastropods of the southwestern Tethyan margin. The present paper aims to update the systematics of two vetigastropod species: Obornella cf. granulata (Sowerby, 1818) and Ambercyclus ornatus (Sowerby, 1819) recently found in the upper Bajocian succession of the Ksour Mountains (Tniet el Klakh Formation) at western Saharan Atlas (northern Algeria). The new Ambercyclus material found in well preserved conditions confirms the absence of umbilicus in Ambercyclus; thus, we emend the original generic diagnosis. The specimens of Obornella cf. granulata and Ambercyclus ornatus represent the first occurrence of both genera and species in the upper Bajocian marine deposits of the western Saharan Atlas, and provide new taxonomic and palaeobiogeographic information about Middle Jurassic vetigastropods in Algeria.
The article is free to read at https://doi.org/10.1002/spp2.1258.
The gastropods from Jurassic neptunian sills of Rocca Busambra (Sicily, Italy) represent an extraordinary assemblage for richness and extremely high degree of novelty, consisting of about 250 species (two‐thirds of which are new) of 20 superfamilies. A total of 38 species and 18 genera of Lottioidea, Pleurotomarioidea, Scissurelloidea, Fissurelloidea and Eucycloidea are described. Of these, 30 species and 9 genera are new, namely Ramusatomaria nuda gen. et sp. nov., Trapanimaria gattoi gen. et sp. nov., Trapanimaria nicolosiensis gen. et sp. nov., Trapanimaria? pallinii gen. et sp. nov., Trochotomaria conoidea sp. nov., Trochotomaria polymorpha sp. nov., Laevitomaria babalusciae sp. nov., Pyrgotrochus vorosi sp. nov., Auritoma lenticula gen. et sp. nov., Busambrella fasciata gen. et sp. nov., Emarginula (Emarginula) burgioi sp. nov., Emarginula (Tauschia) acutidens sp. nov., Propeucyclus sicanus gen. et sp. nov., Propeucyclus obesus gen. et sp. nov., Propeucyclus? semireticulatus gen. et sp. nov., Eucyclomphalus? marenostrum sp. nov., Toronyella lineata gen. et sp. nov., Toronyella margaritata gen. et sp. nov., Zarnglaffia polygonalis sp. nov., Zarnglaffia palermitana sp. nov., Ambercyclus cratisculptus sp. nov., Elymicyclus alternatus gen. et sp. nov., Elymicyclus ietumensis gen. et sp. nov., Elymicyclus martae gen. et sp. nov., Elymicyclus garibaldii gen. et sp. nov., Jurassiscala sturanii gen. et sp. nov., Jurassiscala? tenuiretis gen. et sp. nov., Fischeriella sicula sp. nov., Retimusina poseidoni gen. et sp. nov. and Retimusina? tritoni sp. nov. The new scissurelloidean family Auritomidae fam. nov. is erected. A palaeobiogeographical analysis indicates close relationships with coeval faunas from condensed pelagic carbonates of the central region of western Tethys.
Two new species of calliotropid gastropods, Calliotropis (Riselloidea) faustiankensis sp. nov. and Calliotropis (Riselloidea) lukovensis sp. nov., are described from the Middle Jurassic (Middle Bathonian¡Upper Callovian) of Poland. Additionally, new excellently preserved shells of Calliotropis (Riselloidea) biarmata (M€unster) allow redefinition of this
species. The new morphological information obtained from these three fossil species of Calliotropis in combination with the dataset assembled from 20 extinct and 24 living calliotropids is here summarized in quantitative multivariate and principal component analyses suggesting an onshore-offshore trend in calliotropid gastropod evolution from the Triassic to Recent times. This trend, which is expressed in the morphology of shells, shows that the Mesozoic species are mostly shallow water, while Cenozoic and Recent taxa are mostly deep water. The distinction supports earlier suggestions that the genus Calliotropis can be subdivided into two temporal subgenera belonging to the family Eucyclidae Koken.
Vetigastropod and neritimorph species from Lower Bajocian (Middle Jurassic) sediments of south-western Luxembourg are described. Eighteen species are recognized. Two new genera – Szabotomaria gen. nov. and Fabercapulus gen. nov. – and four new species – Szabotomaria ziqquratiformis sp. nov., Colpomphalus thuyi sp. nov., Colpomphalus tigratus sp. nov. and Fabercapulus semisculptus sp. nov. – are erected. These species, together with other species recently described from the same strata, are part of a diverse assemblage consisting of 32 species belonging to 14 genera in six families and five superfamilies, representing the richest vetigastropod-neritimorph fauna currently known from Bajocian and sub-coeval deposits of western Europe. An analysis of the palaeoecological and palaeobiogeographical relationships of this fauna and those from other areas of the western European shelf was performed using cluster analysis and by comparison of the respective taxonomic structures. The former detected a major cluster composed of two distinct branches: the faunas of the northern Paris-Wessex Basin, including Luxembourg, and those of the southern Germany basin. These faunas have similar taxonomic structures and occur mainly in facies represented by condensed iron ooid-rich marls and limestones deposited in lower offshore to upper offshore-shoreface settings. The close relationship between the Luxembourg and other faunas of the Paris-Wessex Basin reflects free faunal exchange and facies similarities. Slight differences in the sedimentary context could explain the separation of the southern German from the Anglo-Paris branch, whereas similarities between Swabian and Franconian faunas most probably reflect the geographical continuity of these areas. The Early Bajocian fauna of the East Midlands Shelf comes from sediments deposited in a shallow-water, oolitic barrier complex and is different from other western European faunas in both species composition and taxonomic structure.
http://zoobank.org/urn:lsid:zoobank.org:pub:F4E70C4E-ECC3-49D9-9398-AC2C288F51A1
A new description of Discohelix calculiformis DUNKER, 1847, the type species of Discohelix DUNKER, 1847, is given on the basis of the original material (syntypes). Moreover, new diagnoses are given for Discohelix and some other genera of the Discohelicidae (Pentagonodiscus WENDT, 1968, Colpomphalus COSSMANN, 1916, Asterohelix SZABO, 1984, and Zardinihelix BANDEL, 1988). The Discohelicidae are a heterogenic, probably polyphyletic unit. In the group Discohelix/Pentagonodiscus/Colpomphalus/Asterohelix (Discohelicidae sensu stricto) the growth lines run opisthocyrt on the lateral side (prosoclin on the dorsal and opisthoclin on the under side). Within the group Zardinihelix/Platybasis/Nummocalcar the growth lines run straight and prosoclin from the adapical to the abapical suture. These genera are only tentatively assigned to Discohelicidae. Discohelix parvanodosa GRONDEL, 2000 and related species have strongly strengthened growth lines on the first teleoconch whorls. This is typical of Liotiidae, and they probably belong to this family. Triadodiscus BANDEL, 1993 and possibly also Triadoskenea BANDEL, 1993 are synonyms of Eudaronia COTTON, 1945 (like Levihelix GRUNDEL, 2000) and belongs to Eudaroniinae GRUNDEL, 2004 (related to Skeneidae?). Valamidiscus SZABO, 2002 is possibly a member of the Discohelicidae but rather isolated within this family.
The large bivalve limestones of the Grand Pic de l'Ouarsenis have yielded a gastropod fauna attributed to the Middle Carixian (Lower Pliensbachian) by Metaderoceras sp. and to the C1 biozone of the benthic foraminifer chart. Its palaeontological study allows to recognize and to describe eight species belonging to seven different superfamilies, despite their poor state of preservation. Some taxa are known on both sides of the Tethys (north-western and maghrebian margins). The environmental setting of the Ouarsenis fauna is mainly controlled by an insular palaeotopography and by autocyclic processes (tectonic and hydrodynamism). The deposit of the gastropod fauna has occurred during the transgressive phase of a 3rd order sequence (condensed interval sensu Vail et al., 1991). These events, occurring during the Late Carixian times, are well documented along the south-tellian border. The eustatic deepening is complicated by the local tilted-blocks tectonics. In these conditions, the gastropods level has been deposited in a weak sedimentation rate setting and its environment is located to the upper part of the photic zone and subjected to low hydrodynamic conditions. The marine waters were warm, calm, with a normal salinity.
The Mollusca are a large, diverse, and economically important group that ranges from slugs and snails through clams and oysters to octopus, squid, and cuttlefish. They are evolutionarily ancient and better known than most invertebrate groups because of their calcareous skeletons, which has led to their excellent preservation as fossils. This is a state-of-the-art summary of research into Molluscs and their evolution, including recent developments in phylogenetic analysis and molecular techniques. Since the last book on this topic was published in 1985, the vast amount of updated information found here should be on the bookshelf of every zoologist, evolutionary biologist, and taxonomist.
The euomphalids and the platyceratids are commonly found in faunas which are rich in calcitic shelled organisms such as the brachiopods, crinoids, and bryozoans but poor in molluscs. It is believed that molluscs were probably in the faunas originally but were not preserved because of their unstable aragonite shells, internal molds are commonly encountered. The euomphalids have an outer and inner layer composed of delicate, fibrous calcite; both layers are relatively thin compared to the middle crossed-lamellar layer. The upper Cretaceous euomphalid Weeksia, however, lacks a calcitic outer layer and may not be a euomphalid. In addition, it has transitional structure which suggests an origin for crossed-lamellar structure. -Author