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The platycerate gastropods Orthonychia yutaroi Ebbestad, sp. nov. (Ordovician, Boda Limestone, Sweden), O. enorme (Silurian, Sweden, Gotland), O. parva (Pennsylvanian, Finis Shale Member, USA), and Orthonychia sp. (Mississippian, Imo Formation, USA) are studied including their protoconch morphology. Orthonychia yutaroi is the oldest known species in Orthonychia. Platycerates contain species with both, openly and tightly coiled protoconchs. This is the first report that tightly coiled protoconchs occur in Orthonychia. This and previously published observations blur the diagnostic difference between orders Cyrtoneritimorpha (openly coiled protoconch) and Cycloneritimorpha (tightly coiled protoconch). We suggest to treat Cyrtoneritimorpha and Cycloneritimorpha as synonyms of Neritimorpha. The monotypic Devonian genus Pragoserpulina is morphological so close to the Orthonychia species reported herein that synonymy of both genera seems to be possible (and thus of the families Pragoserpulinidae and Orthonychiidae). Protoconch morphology and dimensions suggest that the studied platycerate species had planktotrophic larval development. By contrast, two studied Carboniferous euomphaloid species (one with an openly and the other with tightly coiled protoconch) have paucispiral, large protoconchs indicating non-planktotrophic larval development. We assume that openly and tightly coiled protoconchs were present in various Paleozoic gastropod clades and that selection acted against the openly coiled protoconch morphology. It has previously been proposed that increasing predation pressure in the plankton was the reason for the demise of openly coiled protoconchs (Paleozoic plankton revolution). The presence of larval planktotrophy in platycerates excludes the possibility that they belong to extant basal gastropod clades such as Patellogastropoda, Cocculiniformia, and Vetigastropoda. However, a previously proposed close relationship to Neritimorpha is corroborated. [ABSTRACT FROM AUTHOR]

With 1429 animal species, the Triassic Cassian Formation in the Dolomites, Southern Alps (Italy), yields the highest species richness reported from any spatially constrained pre‐Quaternary formation known to science. The high preserved diversity is partly attributable to a high primary diversity governed by the tropical setting, increasing alpha diversity, and the breadth of habitats spurring beta diversity. More important is the excellent preservation of fossils and the ease with which they can be extracted from the poorly lithified sediments. We propose the term 'liberation Lagerstätten' to capture this preservational window. In contrast to conservation Lagerstätten, liberation Lagerstätten like the Cassian Formation originate from normal marine conditions but low‐grade diagenesis. Molluscs contribute substantially to species richness, comprising 67% of all invertebrate species in the Cassian Formation. The gastropod dominance (39% of all species) is nearly as great as in Recent tropical settings, contradicting the concept of a substantial Cenozoic rise. [ABSTRACT FROM AUTHOR]

In a cenote formed in the limestone karst of Lifou (New Caledonia), more than 35 shells ofNautilus macromphaluswere discovered in 35–40 m water depth. Seven shells were recovered and subsamples of two shells were used for a study on microbial bioerosion. Both shells were intensively bioeroded and SEM-analyses revealed a total of six ichnotaxa with a dominance of the cyanobacterial traceScolecia filosa. Such a low diversity ichnocoenosis and the strong dominance of a single ichnotaxon indicate that the environment in the cenote was hostile for many euendolithic organisms. The unfavourable conditions were caused by (1) restricted water-mass exchange with the open ocean, limiting the chance of larvae being transported into the cenote; (2) intense fluctuations in fresh water influx in the karst system promoting traces of euryhaline euendoliths (Ichnoreticulina elegans, S. filosa, Scolecia serrata); and (3) very limited light availability, allowing the development of traces of organotrophs (S. serrata, Flagrichnus profundus) and the most effective among the photoautotrophs only (I. elegans, S. serrata, and ‘Conchocelis’-stages of bangiacean rhodophytes), indicating deep-euphotic to dysphotic conditions and leading to the observed low ichno-diversity. These results foster the knowledge on the environmental tolerance of microbioerosion trace makers, helping to draw conclusions regarding the characteristics of other extreme (palaeo)environments. [ABSTRACT FROM AUTHOR]