Diverse Molluscan Fauna Research Articles

Under-documented micro species and the end of Carolinian endemism: bivalves of the Waccamaw Formation (basal Pleistocene, S.E. USA)

ABSTRACT The Waccamaw Formation is a Gelasian (basal Pleistocene, 2.5–1.8 Ma) muddy shell-sand found in patches in southeastern North Carolina and northeastern South Carolina, USA. It has a diverse molluscan fauna but has never been monographed. Previous studies documented about 650 species of molluscs, including about 215 bivalves. Extensive sampling of three sites and examination of other unpublished collections has increased those figures to 1,250 and 335 species, respectively. In addition to numerous geographical and chronological range extensions, this study has also discovered 52 undescribed species of bivalves and 8 apparently undescribed genera of bivalves (two of those are extant and known from previous studies) and 9 families of bivalves new to the formation. Galeommatoidea has seen the greatest increase in documented diversity, going from 21 to 53 species known from the formation; the next most dramatic is Anomalodesmata, going from 14 to 32 species known to be present. The molluscan fauna of the Waccamaw Formation has a species richness more typical of tropical areas, but with a distinctive mix of subtropical shallow to mid-shelf taxa, and a few typically cold-water groups. The Recent fauna in the region with the most comparable average water temperature, South Carolina to northern Florida, has much lower diversity (about 775 species of molluscs, with about 280 of them bivalves) and lower endemism (almost no recent endemics) in a comparable amount of geographic area to the Waccamaw Formation deposits. A dramatic drop in typical winter water temperatures c. 1.8–1.7 Ma seems to be the most likely cause for these changes. Bivalve groups which have had the greatest drop in regional diversity are Noetiidae, Carditidae, Astartidae, Galeommatoidea, Ungulinidae and Pandoridae. Contrastingly, the local diversities of Arcidae, Mytiloidea, Lucinidae, Cardiidae and Pholadidae have all increased between the Gelasian and the recent, overwhelmingly through northwards range expansions.

Revisiting the molluscan fauna from the Cambrian (Series 2, stages 3–4) Xinji Formation of North China

AbstractA diverse group of molluscs from the Cambrian Series 2, Stages 3–4 Xinji Formation of the North China Block (NCB) is described, based on more than 4500 specimens from three well‐studied sections in Shaanxi and Henan provinces, along the southern and southwestern margin of theNCB. Twenty molluscan species are identified, including one bivalve, three stem group gastropods, and 16 additional helcionelloids. Among these, six helcionelloid species are reported from theNCBfor the first time, and one new species,Parailsanella luonanensissp. nov. is proposed. This diverse molluscan fauna shares a large number of species with contemporaneous faunas of South Australia (15), Antarctica (7), Laurentia (6), Siberia (3) and South China (1). Faunal similarities are even greater on a generic level. The striking similarities of the molluscan faunas of North China, South Australia and Antarctica strongly support the hypothesis that theNCBwas situated close to Eastern Gondwana, most likely close to South Australia in the Cambrian Epoch 2. In addition, well‐preserved shell attachment muscle scars were observed in the helcionelloidFigurina figurina, with two pairs of symmetrical, continuous, band‐like muscle scars, which are obviously different from the musculature of both gastropods and monoplacophorans. Because of this unique musculature, these characteristic Cambrian cap‐like molluscs are assigned to the Helcionelloida rather than to the Gastropoda or Monoplacophora.

Living in a swampy paradise: Paleoenvironmental reconstruction of an African Humid Period lacustrine margin, West Turkana, Kenya

The African Humid Period (AHP), spanning ∼15-5 ka, was characterize across East Africa by increased precipitation. Wetter climate conditions created environments favorable to human occupation in what are today harsh, resource-limited places to inhabit. The Turkana Basin is a striking example of this. Throughout the AHP, lake levels intermittently rose ∼100 m establishing hydrologic connectivity from Lake Turkana into the Nile drainage system via an outlet to the northwest. This study presents new, high-resolution data from West Turkana outcrops of the Late Pleistocene/Holocene Galana Boi Formation. This research complements existing lake-level curves and allows for landscape reconstruction through lateral facies associations. The Kabua Gorge area contains both well-exposed stratigraphic sections and multiple archaeological sites to the north and west of the outcrops. This creates the opportunity to tie the archaeology closely to paleoenvironmental reconstructions from the geological record. The depositional environment is characterized by a dynamic fluctuating lake margin, consisting of at least four phases of inundation. Highstand Phase 4 is distinct within the Kabua Gorge sequence because it is comprised of black clay containing 2–10% total organic carbon, pedogenic overprinting, pedogenic carbonate nodules, and a diverse molluscan fauna. Deposition of this unit is indicative of an organic-rich, reducing lacustrine environment that was subsequently overprinted by pedogenesis. This unit grades laterally basinward from organic-rich paleosols to lacustrine silts characterized by abundant freshwater diatom taxa. By coupling sedimentology, diatom assemblage data, δ13C and δ18O isotope geochemistry of pedogenic carbonates, and a radiocarbon chronology for the area, the paleoenvironment of Kabua Gorge is interpreted as a shallow marshy embayment connected to the main body of a freshwater Lake Turkana. The landscape is a highly dynamic one, varying on a scale of 100s of meters. Sediments were deposited during periods of inundation and then pedogenically modified during brief periods of subaerial exposure to form Vertisols. Archaeological sites in the early part of the AHP at Kabua Gorge are closely associated in age with lacustrine highstands. Hence, we propose that the lagoonal marsh environment of Phase 4 would likewise have been a resource-rich area for human occupation during the AHP. Potential resources drawing humans to the area include access to fresh water and fishing grounds. Ultimately, understanding the paleoenvironmental dynamics at Kabua Gorge provides a window into the broader ecosystems in which humans culturally evolved from the Late Pleistocene to present.

A national checklist of marine Mollusca in Spanish waters

A checklist of marine Mollusca recorded in Spanish jurisdictional waters is presented, based on a thorough literature search and a limited input of recent field work. The list is detailed according to the five demarcations of the Marine Strategy Framework Directive (NOR, Spanish north coast; SUR, Spanish coast of the Gulf of Cádiz; ESAL, Strait of Gibraltar and Alboran Sea; LEBA, East coast of Spain and Balearic Islands; CAN, the Canary Islands). The list differentiates coastal species living from the supralittoral zone to the shelf break, deep-sea benthic or demersal species, and holoplanktonic species, and also distinguishes between non-indigenous species and species endemic to a particular demarcation. A total of 2466 marine Mollusca species have been reported from Spanish waters, of which 1126 are recorded only from waters surrounding the Iberian Peninsula, 498 are recorded from the Canaries only, and 842 are shared. That total number represents around 5.5% of the global marine molluscan richness. Shore and shelf species are the most numerous (1837), followed by deep-sea benthic species (490) and pelagic species (139), but the contribution of the deep-sea species is most noteworthy in NOR. All eight molluscan classes were represented, but solenogastres and scaphopods were notably more represented than usual in NOR. Species richness in SUR and ESAL was higher than would be expected from their areas, supporting the claim that Andalusian waters have an exceptionally diverse molluscan fauna. Thirteen species collected from INDEMARES cruises are here reported for the first time in Spanish waters. The species recorded in Spanish seas represent more than half of the 4340 species of Mollusca recorded within the scope of the European Register of Marine Species, making this the highest species count in European seas. The Canary Islands demarcation holds by far the largest number of endemic species (127), but special mention is needed regarding the ca. 20 species endemic to the Strait of Gibraltar, a highly anomalous chorotype in the marine realm. The number of non-indigenous species (38) is surprisingly low compared with that of species known in the Mediterranean Sea, amounting to hardly 1.5% of the total and supporting the view that a high number of native species tends to reduce invasion success. The list is seen as a much needed tool for the identification of priority areas for biodiversity conservation, but requires permanent attention and curating in order to remain up-to-date.

Shoal-water dynamics and coastal biozones in a sheltered-island setting: Upper Devonian Pillara Limestone (Western Australia)

Along the Canning Basin's Lennard Shelf in Western Australia, the 80-km-long Oscar Range is composed of folded Palaeoproterozoic quartzite and phyllite and surrounded by limestones of the Great Devonian Barrier Reef including reef complex, related back-reef and lagoonal deposits of the Frasnian Pillara Limestone. The range represents an exhumed cluster of palaeoislands. Near the east end of the Oscar Range, a palaeoislet is encircled by the Pillara Limestone showing outward dips that dramatically shallow to expose nearly horizontal bedding planes offshore. From shore and outward, the facies zones observed in the Pillara Limestone include unfossiliferous laminated sediments followed by biozones with abundant Amphipora and Stachyodes, and domal stromatoporoids. An additional outermost lagoonal facies with a diverse molluscan fauna preserved in fine limestone/dolostone is described in this study. High-spired Murchisonia in a time-averaged assemblage with other gastropods, bivalves, brachiopods and scaphopods dominate this zone. Uneven distribution of biozones is due to intermittent shoals controlled by the complex relief of basement rocks or recent erosion into underlying layers. The orientations of dendroid stromatoporoids and high-spired gastropods were analysed to appraise the dynamics of prevailing shoal-water settings on the inner, more sheltered side of the Oscar Range facing the Devonian mainland to the north. Oscillatory wave action is interpreted as the main agent of transport. Palaeocurrent data for the lighter dendroid stromatoporoids suggest that fair-weather prevailing winds originated from the SE. Pebble clasts, oncoids, bivalves and gastropods indicate episodes of wave agitation and stronger wind from a SE and southerly direction.

ASSESSMENT OF SPECIES STATUS OF MOLLUSCA IN THEMID-LOWER YANGTZE LAKES

The mid-lower Yangtze River basin has the most diverse molluscan fauna in China.However,owing to the increasing human activities during past decades,molluscs are highly imperiled in this region.Aiming at systematic assessment of status quo of mollusc species,investigations in 13 lakes of mid-lower Yangtze River basin were conducted during May,2003 to June,2005.69 species-were identified,of which 44 species were endemic to China.The diversity differed greatly between river-connected and-isolated lakes.Connected lakes were most speciose,especially potamophilus taxa,such as Rivularia spp,Semisulcospira spp and-Unionidae.In the two largest connected lakes,Lake Poyanghu and Lake Dongtinghu,the species numbers were 53 and 57,accounting for 76.8% and 82.6% of the total,respectively.In contrast,molluscs in isolated lakes were very species-poor,each with 4—19 species.Quantitative analysis indicated changes on relative abundance of two predominant species(Bellamya purificata and Corbicula fluminea) were consistent with connectivity of research lakes.By calculation of conservation value indices,threatened status of 67 species was evaluated.The results showed that the current status of molluscan fauna in Yangtze Lakes was grim.Of 67 species evaluated,58.2% were considered near threatened or threatened,of which 26 species were threatened,13 species were near threatened,and only 37.3%(25 species) were able to maintain stable populations.In comparison with historical records,it was found that the fauna had deteriorated significantly,and the dominant taxa of bivalves had changed from large-sized unionids to the small-sized clam,Corbicula fluminea.The deterioration is considered to be attributed to river-lake isolation,overharvest and water pollution.

Influence of Size-sorting on Diversity Estimates from Tempestitic Shell Beds in the Middle Miocene of Austria

Paleontological data frequently are extracted from genetically and stratigraphically complex shell beds. It is therefore important to recognize taphonomic biases that can lead to major errors in paleoecological interpretations (e.g., on ancient local biodiversity). The strong influence of transport-related shell-size sorting on diversity estimates from single samples was studied in a transect of the middle Miocene Grund Formation (Lower Austria), which contains allochthonous, psammitic event beds with channel structures, sharp erosional bases, and graded bedding. These event beds are interpreted as proximal tempestites, and contain densely packed, polytaxic molluscan assemblages. The faunal composition and taphonomic features of shells indicate that transport occurred from wave- or current-agitated nearshore habitats into a pelitic, inner-shelf environment. The different skeletal concentrations contain a highly diverse molluscan fauna with 130 species identified from more than 4200 individuals. Although the quantitatively most-important species are the same in standardized samples from five different shell beds, species richness differs significantly among the three samples from the base of the transect and the two samples from its top. Diversity depends on size-sorting and therefore reflects the transport history of the individual tempestites, not the species richness of the original paleocommunity. Poorly sorted samples (indicating relatively minor transport) approximate the diversity of single samples of that environment better than well-sorted samples (which indicate stronger transport). Diversities of shelly assemblages from parautochthonous and allochthonous assemblages cannot be compared directly. Even comparisons among tempestites are problematic because transport intensity governs diversity. The intensity of any taphonomic process, however, is difficult to predict without detailed investigations. The use of samples from taphonomically complex shell beds for diversity comparisons can bias results, especially on the fine-scale level of local diversity patterns. Studies at such fine scales of resolution should consider the taphonomic framework of assemblages, which is necessary to recognize the dominant taphonomic factors and their intensities.

Deep sea molluscan fauna of the Cretan Sea (Eastern Mediterranean): Faunal, ecological and zoogeographical remarks

The deep sea molluscan fauna of the Cretan Sea (Eastern Mediterranean) was investigated from living material collected by the R/Vs“AEGAEO” and“PHILIA” cruises in the framework of the MTP/MAST EU research programme CINCS, carried out by the I.M.B.C. Examination of the deep sea benthos, with particular reference to the phylum Mollusca, over a grid of stations from depths between 40 and 1570 m, revealed the presence in the area of a diverse fauna consisting of 147 species belonging to 6 different classes. Large numbers of species (44) are new elements of the molluscan fauna of the Cretan Sea while another 4 species (1 Polyplacophora, 2 Gastropoda, and 1 Bivalvia) have not been reported so far from the Aegean or the Eastern Mediterranean. The majority of the species exhibit a wide bathymetrie distribution, from the continental shelf region to the bathyal slope, and only a few species are considered as deep sea species (reported only from the latter). The faunal composition of the collected material from the studied area (in depths over 200 m) clearly demonstrates the presence in the Cretan Sea of theAbra longicallus-association, already reported in other deep basins of the Mediterranean where similar research has been carried out. However, the presence of the bivalveNuculoma aegeensis even in the shallow waters of the continental shelf strengthens the opinion of other authors (Janssen 1989;Dounas &Koukouras 1992) that theNuculoma aegeensis “facies” of the above association is not found as deep asdi Geronimo (1974) had claimed (1500 m). Most of the deep sea mollusc species collected from the Cretan Sea are distributed from the Mediterranean to the Atlanto-Mediterranean and Boreal province while no species with an Indo-Pacific origin (Lessepsian immigrants) were found. Taking into consideration results of studies on the molluscan fauna from shallow waters of the Cretan Sea (Koutsoubas et al. 1992) it can be concluded that this part of the Mediterranean could not be considered as an impoverished system, as it hosts a rather enriched and diverse molluscan fauna numbering more than 400 species.

Holocene environmental changes in the Whitefish Dunes Area, Door Peninsula, Northern Lake Michigan Basin, USA

A two meter sediment core taken from an inter-dune pond in Whitefish Dunes State Park, Door Peninsula, Wisconsin, provides a record of paleoenvironmental changes in the area from approximately 3600 RCYBP to 5100 RCYBP. The hydrology of the Whitefish Dunes pond is now apparently dependent on ground water recharge from local precipitation that infiltrates into the dunes and from Clark Lane, making it very sensitive to low magnitude, short term climate fluctuations. Changes in lithology, molluscan species diversity, oxygen isotopes from gastropod shells, and sediment organic content permit division of the core into several intervals representing different environmental regimes. The basal sediments are older than 5130 RCYBP and resemble those of the Liberty Grove Member of the Pleistocene Horicon Formation. The oldest Holocene sediments recorded in the core are an organic rich layer dated at 5130 RCYBP, which accumulated in a depression on the surface of a sand bar. Continued rise in the local water table during the Nipissing Transgression produced paludal conditions in the area, which were followed by the onset of lacustrine conditions. During this interval, the area supported a diverse molluscan fauna. Minor, short term climate fluctuations are reflected in sediment and oxygen isotope changes which are absent from the record in deep water cores from Lake Michigan. This phase in the history of the area ended with the eutrophication of the pond and the development of dunes. Information from Whitefish Dunes pond and other onshore sites within the Lake Michigan basin are an important source of data for reconstructing the history of water levels and climate changes for this area of the Great Lakes drainage.

Early Holocene pollen and molluscan records from Enfield Lock, Middlesex, UK

Pollen, molluscan data, and sediment analyses, are presented from Enfield Lock, Middlesex, UK. The pollen data, from organic muds, show similarities with Pre-boreal and Boreal pollen spectra at other sites in the Thames basin; an overlying non-polleniferous marl yielded a diverse molluscan fauna. Radiocarbon dates on organic sediments at the site confirm the pollen records are from the early Holocene, but the shelly marl is less easily dated; there are affinities with molluscan records of the early to mid Holocene from sites elsewhere in southeast England. The biological and sedimentological data chronicle the changing depositional environments of the floodplain of the River Lea during four millennia of the early to mid Holocene. Charcoal records imply that fire was, at times, a significant influence on early Holocene vegetation, but a lack of local human artefacts contrasts with evidence for Mesolithic sites elsewhere, and has implications for the interpretation of early Holocene pollen assemblages from charcoal-rich sediments.

A diverse Holocene molluscan fauna including Anadara trapezia from Royal Park, Launceston, Tasmania

Estuarine sediments exposed during road construction at Royal Park in the city of Launceston, northern Tasmania, were found to contain a diverse molluscan fauna with some 40 species identified. An unusual occurrence was the presence of six specimens of Anadara trapezia, a species not previously encountered in situ in Quaternary marine or estuarine deposits in Tasmania. Amino acid racemisation and electron spin resonance, calibrated against radiocarbon dating, point to a late Holocene age for this estuarine sequence. A numeric age of 2600 ±400 yrs BP was derived for a specimen of A. trapezia, based on the extent of leucine and valine racemisation. Electron spin resonance data are consistent with this age assessment. The presence of A. trapezia in late Holocene sediments at Launceston may imply slightly warmer water temperatures during the late Holocene.

Neotectonics and Taphonomy: Pleistocene Molluscan Shell Accumulations in the Northern Gulf of California

Late Middle to early Late Pleistocene shallow marine deposits west of Bahia Adair, to the northern Gulf od California, have been exposed by tectonic uplift along the coast. Represented sedimentary environments include shallow subtital, tidal falt, tidal estuary, tidal channel and shoreface. The deposits contain a diverse molluscan fauna, often concentrated in shell beds. Based on taphonomic data, stratigraphic geometry and faunal composition, the shell beds are identified as beach berm accumualtions, tidal channel lags, subtidal community beds, or unconformity beds. While the first three types of shell beds form on many continental margins, the unconformity beds reflect the active tectonic setting of the northern Gulf of California

A new section in the Elsworth Rock (Jurassic, Oxfordian) at Papworth Everard, near Cambridge, England

Recent deepening and widening of a stream section at Papworth Everard exposed a good section through the Elsworth Rock Formation. Detailed bed by bed collecting has provided a diverse molluscan fauna, including abundant ammonites. These indicate a zonal range from cordatum to tenuiserratum Subzones. An abundant Cardioceratid fauna from one horizon shows characters intermediate between those typical of the maltonense and tenuiserratum Subzones.