Palaeozoic Gastropods Research Articles

Permian gastropods from the Ratburi Limestone, Khao Phrik, Central Thailand

A new silicified Middle Permian gastropod fauna is reported from Central Thailand. It is the first diverse Permian gastropod assemblage described from the Sibumasu terrane. The gastropod fauna comes from fore-reef shallow water carbonates of the Middle Permian (Wordian) limestones of the Ratburi Group exposed at Khao Phrik, Ratchaburi Province. Thirty-four gastropod species are reported, 17 nominate species and 17 in open nomenclature. Nine species are new to science: Retispira khaophrikensis, Amaurotoma? multispirata, Eoplatyzona ratchaburiensis, Hesperiella cyrtocostata, Worthenia? waterhousei, Stegocoelia centrosinuata, Procerithium? inaequetuberculata, Chlorozyga asiatica and Hyphantozyga? khaophrikensis. The gastropod assemblage is strongly dominated by bellerophontids (especially Warthia and Retispira). The fauna shares only a few species with faunas from other Permian deposits in Thailand and elsewhere, namely the previously described gastropod fauna of the Tak Fa Limestone. The fauna shows relationships to Late Palaeozoic gastropod faunas from the Palaeo-Tethys, such as those of Australia and Malaysia.

Carboniferous platyceratid gastropods from Western Australia and a possible alternative lifestyle adaptation

Cook, A.G. & Jell, P.A., September 2015. Carboniferous platyceratid gastropods from Western Australia and a possible alternative lifestyle adaptation. Alcheringa 40, XX–XX. ISSN 0311-5518Platyceratid gastropods, common and in many cases abundant as elements of middle Palaeozoic gastropod faunas worldwide, are rare or absent in Australian Devonian faunas. In Australia, the earliest abundant platyceratids occur in the Lower Carboniferous (Tournaisian) echinoderm-rich Septimus Limestone and Enga Sandstone in the Bonaparte Gulf Basin, Western Australia. Four taxa, each with significant morphological plasticity, are recognized. In Platyceras (Platyceras) tubulosus (de Koninck, 1883), three rows of long radially arranged spines and common pentameral symmetry of re-entrants on the aperture suggest an alternative possibility that a relationship between echinoderms and platyceratids developed, and that this may be with archaeocidaroids that are commonly preserved with the gastropods. Similarly in the singly spinose Platyceras (Platyceras) emmemmjae sp. nov., re-entrants suggest an echinoderm relationship. It is proposed that an echinoderm–Platyceras relationship possibly developed in Australia only after a suitable echinoid host had evolved allowing an alternative way for a gameto- or coprophagous habit to be exploited fully.Alex G Cook [alex.Cook@y7mail.com] and Peter A. Jell [p.jell@uq.edu.au], School of Earth Sciences, The University of Queensland, Queensland 4072, Australia.

Septate gastropods from the Upper Devonian of the Canning Basin: implications for palaeoecology

Cook, A.G., Jell, P.A., Webb, G.E., Johnson, M.E. & Baarli, B.G., 21.4.2015. Septate gastropods from the Upper Devonian of the Canning Basin: implications for palaeoecology. Alcheringa 39, 519–524. ISSN 0311-5518Septate murchisoniid gastropods are documented from the Upper Devonian (Frasnian) Pillara Limestone, Canning Basin, Western Australia. Two localities were investigated corresponding to a peri-island and back reef setting. Extensive septation is reviewed for Palaeozoic gastropods and is interpreted to be an adaptation to shallow water, apical breakage in non-euomphaloidean gastropods, or combined with the possible need to adjust calcium levels in the mantle. Fletcherviewia from the Middle Devonian of north Queensland is reassigned to the Murchisoniidae.Alex G. Cook [alex.cook@y7mail.com], Peter A. Jell [p.jell@uq.edu.au] and Gregory E. Webb [g.webb@uq.edu.au], School of Earth Sciences, The University of Queensland, Queensland, 4072, Australia; Markes E. Johnson [mjohnson@williams.edu] and B. Gudveig Baarli [gbaarli@williams.edu], Department of Geosciences, Williams College, Williamstown, MA 01267, USA. Received 7.2.2015; revised 16.4.2015; accepted 21.4.2015.

Operculum regeneration following failed predation in the Silurian gastropodOriostoma

Regeneration of the calcareous rigiclaudent operculum following severe, non-lethal, predatory attacks is described in two specimens of the characteristic Silurian gastropod Oriostoma from the English Midlands. This is the first record of the regeneration of opercula in Palaeozoic gastropods and of opercula conjoined with shells that have been repaired after significant, failed, durophagous attacks. In one specimen, a series of repaired injuries culminates in a repaired aperture closed by the operculum. In the second specimen, new shell growth has failed to recover the full extent of the original broken whorl, and the new aperture and operculum, though well developed, are smaller than the originals. Both opercula are unusually thin centrally when compared to other, strongly domed, Oriostoma opercula.

Affinities of the alleged earliest Cambrian gastropodAldanella

Unlike true Palaeozoic gastropods, but similar to some coeval hyoliths, the cup-like hemispherical embryonic shell of Aldanella attleborensis (Shaler and Foerste, 1888) from the earliest Cambrian (early Tommotian) Erkeket Formation of northern Siberia bears a mucro. Also, the pattern of mortality, with right-skewed distribution and a peak at about 1.0 mm diameter, is not similar to that of early Palaeozoic gastropods; there is no evidence of metamorphosis that would end the pelagic larval stage of ontogeny. Specimens of larger size are rare in samples of phosphatized “small shelly fossils” but are known in related species of the genus, of up to 3–5 mm diameter. A phosphatized soft body is preserved in a few specimens of A. attleborensis, one bearing possible chaetae of about 5 μm diameter. Such bunches of chaetae arming locomotory organs were earlier identified in the genus Pelagiella Matthew, 1895, a more derived member of the same lineage. It shares with the genus Aldanella Vostokova, 1962 also the mucronate embryonic shell and acicular aragonitic shell wall microstructure. The presence of chaetae-bearing organs suggests pelagic mode of life of pelagiellids at maturity. Middle Cambrian Pelagiella shells reached 7 mm in diameter, suggesting evolutionary increase in mature size. Embryonic shell morphology, wall microstructure, and the presence of locomotory organs with a fan of chaetae contradicts gastropod, and even conchiferan affinity of the pelagiellids, but together with the pattern of ontogeny conforms to the enigmatic Palaeozoic hyoliths. They differ in having opercula closing the shell apertures and in lacking evidence of chaetae. The helens, paired apertural appendages of possible locomotory function occurring in apertures of some of them, do not reveal any similarity to chaetae in their development. We propose classifying the order Pelagiellida in the class Hyolitha rather than in the class Gastropoda, until its phylogenetic position is clarified. Such understood hyoliths may represent the earliest stage in evolution of molluscs, immediately following initial diversification of the spiralians (lophotrochozoans) into phyla.

The effects of taxonomic standardization on sampling-standardized estimates of historical diversity.

Occurrence-based databases such as the Palaeobiology database (PBDB) provide means of accommodating the heterogeneities of the fossil record when evaluating historical diversity patterns. Although palaeontologists have given ample attention to the effects of taxonomic practice on diversity patterns derived from synoptic databases (those using first and last appearances of taxa), workers have not examined the effects of taxonomic error on occurrence-based diversity studies. Here, we contrast diversity patterns and diversity dynamics between raw data and taxonomically vetted data in the PBDB to evaluate the effects of taxonomic errors. We examine three groups: Palaeozoic gastropods, Jurassic bivalves and Cenozoic bivalves. We contrast genus-level diversity patterns based on: (i) all occurrences assigned to a genus (i.e. both species records and records identifying only the genus), (ii) only occurrences for which a species is identified, and (iii) only occurrences for which a species is identified, but after vetting the genus to which the species is assigned. Extensive generic reassignments elevate origination and extinction rates within Palaeozoic gastropods and origination rates within Cenozoic bivalves. However, vetting increases generic richness markedly only for Cenozoic bivalves, and even then the increase is less than 10%. Moreover, the patterns of standing generic richness are highly similar under all three data treatments. Unless our results are unusual, taxonomic standardization can elevate diversity dynamics in some cases, but it will not greatly change inferred richness over time.

Recovery of gastropods in the Early Triassic

Gastropod rebound from the end-Permian mass extinction event initiated in the Olenekian and diversification continued until the Carnian. The most diverse and abundant Early Triassic gastropod faunas are from the Moenkopi Formation (Utah) and the Upper Werfen Formation (Europe, Alps), which contribute as much as 50% to the reported global gastropod diversity of the Early Triassic. Gastropod faunas with more than 10 to 15 species are unknown from the Induan. However, the Olenekian fauna from the Sinbad Limestone (Moenkopi Formation) comprises 26 species. Faunas with more than 100 gastropod species have not been reported prior to the Late Anisian. The number of reported gastropod taxa continues to rise until the Carnian. Several caenastropod groups and the opisthobranchs have their first occurrence in the Olenekian, which indicates a major turnover within the Gastropoda. Typical Palaeozoic gastropod groups were rapidly replaced and Early Triassic gastropod faunas are distinct form Late Palaeozoic faunas. Zygopleura rugosa Batten and Stokes is transferred to the genus Ampezzopleura and its diagnostic larval shell is reported for the first time. It corroborates the view that the highly diverse pseudozygopleurids became extinct at the end-Permian mass extinction event and were replaced by the superficially similar Mesozoic Zygopleuridae. To cite this article: A. Nützel, C. R. Palevol 4 (2005) .

Shell repair and shell form in Jurassic pleurotomarioid gastropods from England

Traces of unsuccessful predatory attacks can be found in the hard parts of shell-bearing organisms as repaired shell injuries and are often preserved in the fossil record. These repaired shell injuries can help to deduce the relationship between predator and prey in the past. Gastropods afford an excellent opportunity for study since their shells are easily recognized from the Cambrian onwards, and usually preserve a full record of their life history. Predation is a phenomenon which has led to a great variety of adaptations among prey organisms in their quest to avoid being eaten. Increased predation pressure seems to have been one of the factors that has fueled the evolution of predation-resistant shell morphologies.Individual case studies examine the frequency of shell repair in assemblages of Palaeozoic gastropods from different geological periods. The Silurian species Poleumita discors showed a shell repair frequency of 10 %, while only 4 % of the Devonian species Praenatica gregaria have been repaired. The Palaeozoic bilaterally symmetrical bellorphontiform molluscs also showed low levels of shell repair.Similar shell morphologies in the long-lived group of pleurotomarioid gastropods were examined and shell repair frequenceis calculated to investigate potential variation through geological time. The Palaeozoic species showed repair frequencies of 17.1 % and 4.2 %. The frequency increased in the Mesozoic to between 28.8 % and 46.6 %, while all shells of Recent pleurotomarioids in the study showed repaired injuries. The repaired injuries found do not change in appearance through time, which is probably a reflection of the presence of the slit in the apertural margin. Which type of injury is the most abundant can be seen to change with time, and there is also an increase in size with time. This may be a defensive strategy taken up by the pleurotomarioids as a response to more abundant predators.

Larven-Gehäuse und Gehäuse-Mikrostrukturen von außergewöhnlich gut erhaltenen unterkarbonischen Gastropoden vom Buckhorn-Asphaltlager (Oklahoma, USA)

Gastropods from the mid-Pennsylvanian Buckhorn Asphalt Quarry in Oklahoma (U.S.A.) are very well preserved. Commonly, protoconchs and original shell microstructure are present and unaltered. Two pleurotomarioid gastropod species of the generaSalterospira andParagoniozona are preserved with the early ontogenetic shell and with a nacreous shell structure. Two other nacreous archaeogastropods with a rotelliform shell lack a selenizone and are closely related to the Anomphalidae. They are tentatively assigned to the genusAnomphalus. A fifth tiny archaeogastropod lacks nacre and has exclusively crossed lamellar shell microstructure. It represents the oldest known archaeogastropod that lacks nacre.Microdoma conicum represents the trochomorph archaeogastropods; it has an inner nacreous layer, a crossed acicular layer, and an outermost thin calcitic layer. The protoconch ofMicrodoma is typical for archaeogastropods. The construction of the shell indicates that most archaeogastropods from Buckhorn Asphalt deposit have a nacreous inner layer, but one type has a crossed lamellar microstructure, like the modern Phasianellinae and Fissurelloidea, indicating the antiquity of this structural type within the Vetigastropoda (Archaeogastropoda). The Neritimorpha are present with the two neritopsid generaNaticopsis andTrachydomia. Naticopsis has a thick inner crossed lamellar layer and a thin prismatic outer calcitic layer. The families Goniasmidae, Orthonemidae, Pseudozygopleuridae, and Meekospiridae represent the Caenogastropoda. All reported species of these families have a crossed lamellar shell structure and a caenogastropod-type protoconch. There is now clear evidence that the Goniasmidae are Caenogastropoda, though they have a selenizone, a feature that is almost unknown in modern caenogastropods. Only a few modern caenogastropods have slit-like structures in their shell, e.g. the heteropodAtlanta and the worm snailSiliquaria. Both are distantly related to the slit-bearing Goniasmidae and it is unlikely that the slit is homologous in these groups. The fact that these ancient caenogastropods had a slit in the outer lip is most important for the reconstruction of the phylogeny of the Gastropoda. The Goniasmidae are present with the generaGoniasma (one species),Stegocoelia (three species), andCerithioides (one species). The Orthonemidae are represented by the generaOrthonema andPalaeostylus. The genusOrthonema is present with a dextral species and the sinistral speciesO. sinistrorsa. Species ofOrthonema have the same type of a heliciform larval shell that is present in the Goniasmidae. Therefore, the two families are probably closely related.Palaeostylus is present with a newly described species,Palaeostylus batteni n. sp. The Pseudozygopleuridae are present with a single species,Pseudozygopleura peoriense. The common speciesGirtyspira minuta belongs to the family Meekospiridae. The teleoconch has a faint spiral striation and a polished surface The protoconch/teleoconch transition indicates that its protoconch is paucispiral and ends with a faint, straight prosocline thread. The Heterostropha are present with the order Allogastropoda represented by two species of the generaDonaldina andPseudaclisina, of whichPseudoaclisina is reported from North America for the first time. The exceptional preservation increases the number of shell characters considerably (protoconch, shell microstructure, micro-ornaments), even for seemingly well established taxa. The knowledge of these features greatly improves the systematics of several major groups of Late Palaeozoic gastropods and represents an important source of information for future phylogenetic analyses.

An Evaluation of the Recently Proposed Palaeozoic Gastropod Subclass Euomphalomorpha

The recently proposed subclass Euomphalomorpha Bandel and Frýda, 1998 was primarily based on an openly coiled, planispiral initial whorl. Here, the protoconch of Carboniferous euomphalids is described and figured in detail previously unknown. This protoconch comprises distinctly less than one planispiral whorl with an abrupt transition to the telecoconch. It is umbilicate or openly coiled. Umbilicate or bilaterally symmetrical protoconchs are still present in Recent species of the Cocculiniformia, the Neomphalidae and the Docoglossa. A previously suggested close phylogenetic relationship between the euomphalids and primitive gastropod limpets is therefore corroborated by the protoconch morphology. The fact that several Palaeozoic gastropods, unlike most modern gastropods, have an openly coiled initial whorl is highly remarkable, but the meaning of this feature for the phylogeny and the systematics of the Gastropoda is not yet clear.

Shell Repair and Failed Predation in Lower Palaeozoic Gastropods from Sweden

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The geographic, taxonomic and temporal distribution of determinate growth in marine gastropods

Many marine gastropods are characterized by determinate growth, as inferred from the presence of unique terminal elaborations of the shell's aperture. Although determinate growth has evolved repeatedly in most major gastropod clades, it is especially frequent among siphonate caenogastropods. Analyses of shallow-water assemblages show that the incidence of species with determinate growth is far higher in the tropics (especially the tropical Pacific and Indian Oceans) than at higher latitudes. Compilations of fossil assemblages from warm-water environments indicate that, although determinate growth occurred in some Palaeozoic gastropods, it became widespread only in the Neogene. In some groups, terminal apertural elaborations arose in lineages whose growth was more or less continuous and indeterminate, but in others it was derived either from or was ancestral to episodic growth. The hypothesis that periodic or terminal apertural elaborations evolved as a means to dispose of calcium carbonate once growth in the spiral direction ceased is rejected in favour of functional interpretations. Among the latter, the roles of modified apertures in defence and in mate recognition are explored, but no firm conclusion regarding the latter possibility can be drawn owing to our ignorance of mate recognition in gastropods.