Stefano Monari

Middle Jurassic Gastropods from the Central High Atlas, Morocco

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.

Phylogeny and Biogeography of Pholadid Bivalve Barnea (Anchomasa) with Considerations on the Phylogeny of Pholadoidea

The paper examines the systematics, phylogeny and biogeographical history of Barnea (Anchomasa), which is one of the most abundant and diversified of modern pholadid bivalves. The range of morphology of its distinctive characters and comparisons with other pholadoidean taxa are described in detail. An extensive cladistic analysis based on morphological characters at genus and subgenus levels allowed the inclusion of B. (Anchomasa) into the phylogeny of Pholadoidea and the establishment of its most appropriate taxonomic position. The analysis confirms that Barnea s.s. and B. (Umitakea) are its closest relatives and that the morphological similarities to other taxa are mainly due to plesiomorphies. The fossil record and the data on the present-day distribution contributed to trace the biogeographical history of B. (Anchomasa). The present-day biogeography is marked by the disjunct distribution of species. Species are distributed mainly either along the Atlantic and Pacific coasts of the American continent (American group) or in the Indo-West Pacific region (Indo-West Pacific group). Both these groups have distinct morphological features and biogeographical structures. The fossil record and the known geodynamic scenario suggest a relationship of direct derivation between the Indo-West Pacific group and a stock of north-eastern Atlantic to Paratethyan species. This reflects a vicariant event related to the closure of the connection between western Tethys and the Indian Ocean in the middle Miocene. The American group presumably arose from the European stock during the Late Pliocene by dispersal towards the eastern coasts of North America and rapid southward diffusion. A relative differentiation within the American group is probably related to the last phases of emergence of the Panama Isthmus. The cladistic analysis also gives suggestions for the reconstruction of the phylogeny of the superfamily Pholadoidea. It confirms the interpretation of several characters sustained by previous authors. However, it also shows remarkable differences to the previous taxonomic arrangements. Pholadinae includes only taxa having the protoplax and it appears to be the sister-group of a major clade composed mainly of two groups, namely Martesiinae-Jouannetiinae and Xylophagainae—Teredinidae. The Martesiinae are paraphyletic whereas the obligate wood-boring Xylophagainae and Teredinidae form a well-supported monophyletic group.

Earliest Jurassic patellogastropod, vetigastropod, and neritimorph gastropods from Luxembourg with considerations on the Triassic–Jurassic faunal turnover

The Hettangian to earliest Sinemurian Vetigastropoda, Patellogastropoda, and Neritimorpha housed in the National Museum of Natural History of Luxembourg are studied. Most of the species comes from the Luxembourg Sandstone Formation. This deposit formed along the southern margin of the London-Brabant-Ardennes Landmass, in a region that during the earliest Jurassic constituted a seaway connecting the Paris Basin with the epicontinental seas of the Netherlands and northern Germany. The systematic analysis revealed high diversity of the studied fauna; we identified twenty-two species, eleven genera, nine families, and six superfamilies. A new genus, Meiersia gen. nov., and three new species, Anodomaria schroederi sp. nov., Meiersia disarmata sp. nov., and Spirocirrus weisi sp. nov. are described. The fauna is dominated by pleurotomarioideans representing the genera Ptychomphalus, Pleurotomaria, and Trochotoma, and by the patellogastropod genus Scurriopsis both in number of species and specimens. The neritimorph genus Neridomus is also well represented. Among the accessory taxa, Anodomaria and Spirocirrus first appeared in the Late Hettangian of the Luxembourg area. Most of these genera show a species radiation in the Early Jurassic and are distributed over the western European epicontinental shelf, probably favoured by an east to west marine transgression which influenced wide areas from the basins of the northern Germany to the Paris Basin through the Luxembourg seaway. The evolutionary and palaeobiogeographical data demonstrate that this radiation was already considerably advanced in the Late Hettangian. This suggests that the recovery of the gastropod diversity after the end-Triassic crisis was relatively fast in western Europe.

A new genus and species of fimbriid bivalve from the Kimmeridgian of the western Pontides, Turkey, and the phylogeny of the Jurassic Fimbriidae

A new lucinoidean genus and species, Cerkesia contiae gen. et sp. nov., from the Kimmeridgian carbonate platform deposits of the Cerkes area (western Pontides, Turkey), is described and placed in the family Fimbriidae. Morphological comparisons reveal similarities with Fimbria, Cyclopellatia and Sphaera. A phylogenetic analysis supports the monophyly of the family. Similarities between Cerkesia and Fimbria determine inclusion of these genera in the same clade. The unusual features characterizing Cerkesia closely relate it to Cyclopellatia. Sphaera belongs to a different clade and its similarities with Cerkesia are owing to convergent and plesiomorphic characters. Cerkesia was a slow and shallow burrower. The morphology of the anterior adductor scar suggests a mode of life comparable to that of Fimbria but other features indicate adaptive strategies typical of the Lucinidae. The associated fossils and facies reveal that Cerkesia lived in soft and sandy substrates of quiet and protected areas of the carbonate platform under stressful environmental conditions. The appearance of Cerkesia in the western Pontides marks the eastward expansion of a clade that developed principally in the European seas during the Late Jurassic while the Sphaeriola-Sphaera clade was confined to the southernmost Tethyan margin.

Gastropods from upper Pliensbachian–Toarcian (Lower Jurassic) sediments of Causses Basin, southern France and their recovery after the early Toarcian anoxic event

A gastropod fauna has been studied from upper Pliensbachian – upper Toarcian deposits of two sections of the Causses Basin (southern France) in order to investigate the mode of recovery after the early Toarcian anoxic event. The fauna consists of 15 species, one of which is new (Bathrotomaria kronzwilmesorum sp. nov.). Their stratigraphical distribution shows two peaks of diversity – in the Bifrons Zone (Bifrons Subzone) and in the Aalensis Zone (Mactra Subzone) – which reflect brief times during which the oxygen content and bottom consistency favoured the settlement of a relatively diversified fauna. In the Variabilis–Pseudoradiosa zones, gastropods are only represented by two species. This probably indicates more severe and unstable environmental conditions, only allowing the survival of gastropod taxa with wide adaptive capacities. The very low species diversity and the discontinuous and slow faunal recovery were probably determined by physiographic factors. The Causses area was a small basin confined by exposed lands and open towards the central part of western Tethys. Gastropods described here occur exclusively in the Toarcian – early Aalenian communities of the European epicontinental seas, whereas species from the central region of western Tethys are absent. Geographic isolation and marginal location of the Causses Basin restricted faunal exchange with the western European epicontinental seas, preventing fast recovery after the anoxic event. Gastropods of the central region of the western Tethys were probably unable to settle and colonize that area due to the strongly different environment.

AN OVERVIEW OF THE JURASSIC GASTROPODS FROM ROCCA BUSAMBRA (NORTH-WESTERN SICILY, ITALY)

This paper is an overview of the gastropods from the Toarcian to Lower Kimmeridgian fissure fillings of Rocca Busambra. They are the most diverse and richest Jurassic faunas known from the pelagic sediments of the western Tethys. 224 species, 137 of them new, were recognized. The main feature of the structure of these assemblages is the high number of new taxa and the concomitant presence of an archaic stock with Triassic affinities, and a group advancing the appearance of the modern caenogastropod taxa. These features give these assemblages an important place in the reconstruction of the evolution of the whole class.

The genus Leptomaria E Eudes-Deslongchamps, 1864 (Gastropoda, Pleurotomariidae) from the Early Bajocian of Luxembourg: systematics and paleobiogeography

Four species of the pleurotomariid genus Leptomaria E Eudes-Deslongchamps, 1864 are reviewed based on previously undescribed material from Bajocian deposits of the eastern Paris Basin. One of them, Leptomaria nicsimonisp. nov., is introduced as a new species. A critical revaluation of the literature shows that Leptomaria has been broadly interpreted in the past, in contrast with the rather detailed description given by its author. This focused on shell characters, such as the width and position of the slit and selenizone, which have been overlooked by most subsequent authors. A revised diagnosis that reintroduces these characters is presented on the basis of the Bajocian material studied and of a survey of the relevant literature. This diagnosis, which is based also on other characters not considered before, excludes from Leptomaria several species previously assigned to it. The genus occurred from the Middle Aalenian to the Cenomanian mainly in the epicontinental seas of western Europe. It experienced a peak of diversity in the Bajocian, followed by a slow decline in Bathonian to Callovian times concomitantly with the appearance of the genus in the south-eastern margin of Tethys. Records in Upper Jurassic to Cretaceous sediments are sparse. http://www.zoobank.org/urn:lsid:zoobank.org:pub:FDAE7E20-F314-4FE2-902B-D9FFA195AC2E

The Jurassic Pleurotomarioidean Gastropod Laevitomaria and Its Palaeobiogeographical History

The genus Laevitomaria is reviewed and its palaeobiogeographical history is reconstructed based on the re-examination of its type species L. problematica, the study of material stored at the National Natural History Museum of Luxembourg, and an extensive review of the literature. The systematic study allows ascribing to Laevitomaria a number of Jurassic species from the western European region formerly included in other pleurotomariid genera. The following new combinations are proposed: Laevitomaria allionta, L. amyntas, L. angulba, L. asurai, L. daityai, L. fasciata, L. gyroplata, L. isarensis, L. joannis, L. repeliniana, L. stoddarti, L. subplatyspira, and L. zonata. The genus, which was once considered as endemic of the central part of the western Tethys, shows an evolutionary and palaeogeographical history considerably more complex than previously assumed. It first appeared in the Late Sinemurian in the northern belt of the central western Tethys involved in the Neotethyan rifting, where it experienced a first radiation followed by an abrupt decline of diversity in the Toarcian. Species diversity increased again during Toarcian—Aalenian times in the southernmost part of western European shelf and a major radiation occurred during the Middle Aalenian to Early Bajocian in the northern Paris Basin and southern England. After a latest Bajocian collapse of diversity, Laevitomaria disappeared from both the central part of western Tethys and the European shelf. In the Bathonian, the genus appeared in the south-eastern margin of the Tethys where it lasted until the Oxfordian.

Vetigastropoda and Neritimorpha from the Lower Bajocian of Luxembourg and palaeobiogeography of Aalenian–Bajocian (Middle Jurassic) gastropods of western Europe

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