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Giant Middle Coniacian to Lower Campanian Platyceramus Seitz is among the largest Cretaceous bivalves, commonly reaching an axial length of over 1 m, and occasionally over 2-3 m in size. The genus is characterized by its large size, very low convexity, normal inflation limited mostly to the umbonal area, and flattened flanks. It is especially common in moderately deep calcareous shale facies, as well as in chalks and limestones of the Niobrara Formation and equivalents. Preferred facies contain abundant pyrite, elevated total organic carbon (TOC), and very low biotic diversity. The genus maintains its giant size in these facies, and becomes more abundant. It clearly prefers dysoxic facies. As such, it probably is chemosymbiotic; photosymhiosis is almost ruled out because of inferred water depths of 200-350 m. It is also found more sparsely, and of smaller size, in oxygenated facies, including shoreface sandstone. The study area contains over 81 giant-sized Platyceramus platinus (Logan, 1898) on a single bedding plane; there are very few small ones. This allows spacing, orientation, and size analysis to be performed on an adult population.

Recently, the first late Miocene--Pliocene eolian deposits from the western Chinese Loess Plateau have been reported. These deposits would complement the eolian record between Quaternary loess-paleosol sequences and Miocene loess sequences, if their wind-blown origin could be documented. However, although several lines of evidence indicate the eolian origin of this sequence, it is still necessary to address this issue through further efforts. Among these, biological approaches are of particular value. Here we analyze the composition and preservation conditions of mollusk assemblages in the Dongwan section. Our results show that all mollusk fossil individuals are preserved in perfect condition without indicating any reworking. All identifiable mollusk species are terrestrial, and are mostly identical to those identified in the Quaternary loess-paleosol sequences of the Chinese Loess Plateau. Generally, the cold-aridiphilous species are dominant in the loess layers, while thermo-humidiphilous species are mostly encountered in the paleosols. The close similarity of the mollusk record in both the Dongwan late Miocene--Pliocene deposits and the Quaternary loess sequence in the Chinese Loess Plateau supports the supposition that the Dongwan section is a typical loess-paleosol sequence, and is, without any doubt, of wind-blown origin. Keywords: terrestrial mollusk fossils, loess, Chinese Loess Plateau, late Miocene, Pliocene.

Recently, the first late Miocene-Pliocene eolian deposits from the western Chinese Loess Plateau have been reported. These deposits would complement the eolian record between Quaternary loess-paleosol sequences and Miocene loess sequences, if their wind-blown origin could be documented. However, although several lines of evidence indicate the eolian origin of this sequence, it is still necessary to address this issue through further efforts. Among these, biological approaches are of particular value. Here we analyze the composition and preservation conditions of mollusk assemblages in the Dongwan section. Our results show that all mollusk fossil individuals are preserved in perfect condition without indicating any reworking. All identifiable mollusk species are terrestrial, and are mostly identical to those identified in the Quaternary loess-paleosol sequences of the Chinese Loess Plateau. Generally, the cold-aridiphilous species are dominant in the loess layers, while thermo-humidiphilous species are mostly encountered in the paleosols. The close similarity of the mollusk record in both the Dongwan late Miocene-Pliocene deposits and the Quaternary loess sequence in the Chinese Loess Plateau supports the supposition that the Dongwan section is a typical loess-paleosol sequence, and is, without any doubt, of wind-blown origin. Keywords: terrestrial mollusk fossils, loess, Chinese Loess Plateau, late Miocene, Pliocene.

Size bias in the fossil record limits its use for interpreting patterns of past biodiversity and ecological change. Using comparative size frequency distributions of exceptionally good regional records of New Zealand Holocene and Cenozoic Mollusca in museum archive collections, we derive first-order estimates of the magnitude of the bias against small body size and the effect of this bias on completeness of the fossil record. Our database of 3907 fossil species represents an original living pool of 9086 species, from which ~36% have been removed by size culling, 27% from the smallest size class ( Keywords: fossil record, Mollusca, New Zealand, paleontologic record, size distribution.

Myophorellid bivalves (Trigonioida, Myophorellacea) with conspicuously tuberculate shells are abundant in Lower Cretaceous rocks of the Neuquen Basin represented by the Gondwanian genus Steinmanella Crickmay, 1930. Publications concerning Neuquen trigonioids deal only with taxonomy, and until now the sedimentary environments of the Steinmanella bearing facies have not been interpreted. The present study analyzes morphology, taxonomy, stratigraphy, and paleobiology of Steinmanella species collected from five sections of the Lower Member of the Agrio Formation, including the type locality. Two species are differentiated: Steinmanella pehuenmapuensis (Leanza, 1998) from the lower part of the member (Pseudofavrella angulatiformis Zone) and Steinmanella transitoria (Steinmann, 1881) from the middle and upper part of the member (Holcoptychites neuquensis, Hoplitocrioceras gentilii, and Weavericeras vacaensis Zones). Specimens of both species have been recorded in intermediate to high-energy shoreface and low-energy offshore deposits. The inferred paleoecologic model is that Steinmanella lived semi-infaunally and burrowed on sandy substrates in the shoreface and on muddy substrates in the offshore. Colonization of low-energy subenvironments in the offshore probably occurred during increased seafloor oxygenation and reduced net sedimentation or brief omission periods.

Seven new monoplacophoran genera and species are described and figured from Cambrian and Lower Ordovician strata of the Ozark Uplift of Missouri; Biloboconus frizelli, Ulrichoconus bonneterrense, Potosiplina delorensis, Gayneoconus echolsi, Irondalia irondalensis, Titanoplina meramecensis, and Wildernessia inexpectans. A new species of Kirengella, K. oregonensis, is described, and Hypseloconus compressus (Ulrich and Bridge, 1930, and H. expansus Stinchcomb, 1986, are assigned to the genus Kirengella. The morphology of Kirengella is compared to highly arched forms of the plated mollusk genus Preacanthochiton and is found to converge with them. Association with stromatolite reefs of both Kirengella and plated mollusks is noted.

Rare to abundant silicified polyplacophoran faunas occur in the late Wolfcampian Bird Spring Formation and the Leonardian Pequop and Loray Formations in Nevada, the Leonardian Arcturus Formation in Utah, and the early Leonardian Ft. Apache Limestone Member of the Supai Formation in Arizona. The faunas associated with the polyplacophorans are dominated by molluscs. New species include Gryphochiton distinctus, Acutichiton gracilis, A. nevadensis, and Arcochiton richardsoni. Traces of color patterns are present on Arcochiton richardsoni.

The Pliocene interchange of North Pacific and North Atlantic marine faunas via the Arctic Ocean was long thought to have been a single episode of faunal exchange between the northern oceans that took place as soon as the Bering Strait first opened. New evidence implies that there were two northern migration events instead of one, and that the second phase of migration was much later than the first. The migration of Atlantic-Arctic mollusks into the Bering Sea and North Pacific when the Bering Strait first opened at 4.8-5.5 Ma constituted the initial phase of this interchange, but the abrupt appearance of North Pacific mollusks in the North Atlantic at 3.6 Ma postdated the first opening of the Bering Strait by 1.2-1.9 m.y. This second phase of trans-Arctic migration was also coeval with shoaling of the Central American seaway between North and South America. This late Pliocene trans-Arctic migration of North Pacific mollusks is evidence for the reversal of marine flow to northward through the Bering Strait, which was one consequence of the reorganization of Northern Hemisphere ocean circulation caused by substantial closure of the Central American seaway. This inferred causal link between the histories of the Beringian and Panamanian ocean gateways is in agreement with ocean circulation models. Keywords: Bering Strait, Central America, mollusks, Pliocene, oceanography.

St/Ca and Mg/Ca ratios in biomineral CaCO(sub 3) have recently been regarded as more reliable than (delta)(super 18)O values as proxy for paleotemperature because they are less affected by salinity or polar ice volume. We argue, however, that vital effects can exert a greater control than paleotemperature over fossil Sr/Ca. Seasonal perturbations in isotopic data from the Eocene bivalve Venericardia planicosta reveal a gradually decreasing annual growth rate through ontogeny. High-resolution Sr/Ca ratios, analyzed with a new proton-microbe technique, increase markedly through ontogeny, however, suggesting that more Sr was incorporated as growth rate slowed rather than as a result of changing paleotemperature. Comparative (delta)(super 18)O and Sr/Ca data from the broadly coeval marine gastropod Clavilithes macrospira, which exhibits a linear growth rate through ontogeny, also shows a significant increase in Sr concentration with age as well as seasonal, possibly temperature-related variations. Our observations show that neither growth, calcification rate, nor temperature can be the sole factor controlling Sr incorporation into molluscan aragonite. Metabolic activity, related to factors such as temperature, salinity, age, and growth rate, is likely to exert the primary control over Sr/Ca ratios in aragonitic mollusks.

Two new cirroidean gastropod genera, Alaskiella (family Porcelliidae) and Alaskacirrus (family Cirridae), from the Emsian (late Early Devonian) of west-central Alaska (Medfra B-4 quadrangle) are described. The shell of Alaskiella medfraensis new genus and species exhibits inclined heterostrophic coiling. This shell character is known among other members of the subclass Archaeogastropoda, but is recorded for the first time within members of the superfamily Cirroidea. Inclined heterostrophic coiling of the shell was probably developed independently in several different groups of the subclass Archaeogastropoda. The new genus Alaskacirrus, represented by Alaskacirrus bandeli new species, is the oldest and only known Paleozoic member of the family Cirridae. This suggests that the family Cirridae was separated from the family Porcelliidae since at least Early Devonian time and that it most probably developed from the subfamily Agnesiinae of the family Porcelliidae. Thus, the stratigraphic range of the family Cirridae is at least from Lower Devonian to Cretaceous, an interval of about 350 million years.

The bivalve molluscs Colpomya? sp. and Goniophorina (Cosmogoniophorina)? tenuicostata Harrington are recorded for the first time in the Arenigian Suri Formation (Famatina Range, western Argentina), and the new taxa Suria ovalis new genus and new species, and Redonia riojana new species are proposed. Additionally, the rostroconchid Ribeiria spinosa Babin and Branisa is also described. Some taxa shared with the Acoite Formation (Cordillera Oriental, Northwestern Argentina) and the Sella Formation (Cordillera Oriental, Bolivia) suggest that the Suri Formation was geographically related to these basins, and consequently, it could likewise be considered as a peri-Gondwanan area.

Mobergellans are a distinctive group of Lower Cambrian breviconic shells with a prominent set of internal scars, presumably representing sites of former muscle attachment. Shells grew by accretion and appear to have secreted primary phosphate. Here a redescription is given of mobergellans, assigned to Hippoklosma new genus, from the Khairkhan Formation (Botomian-age equivalent) of southwest Mongolia. Hippoklosma mongolica (Missarzhevsky) is bilaterally symmetrical, with five pairs of radiating structures. These are presumably homologous with the muscle scars of other mobergellans, but in contrast consist of a series of disks (herein fibroplacodes) each containing a characteristic fibrous structure capped externally by a smooth lid. The apical region of the shell is domelike with transverse segmentation. A review of other mobergellans, including new data on Mobergella holsti from Sweden and Discinella micans from New York, and possibly related taxa concludes that although their affinities are problematic, a relationship with the Mollusca may be the most plausible hypothesis on existing evidence.

Researchers have been able to reconstruct the fossil Kimberella quadrata as a bilaterally symmetrical, benthic animal with a non-mineralized, univalved shell. There were found to be many similarities with a mollusc, although it was not possible to produce conclusive evidence of a molluscan affinity. These findings go against the view that the Ediacara biota represents an extinct grade of non-metazoan life. It seems that there may be a pre-Ediacaran origin for major metazoan clades.

Echinus gyracanthus Eaton, 1832, was the first tentaculitid reported from North America, but the original description and illustration are vague by present-day standards. Study of the type material and topotypes from the Lower Devonian Manlius Limestone in the Town of Schoharie, New York, suggests that Tentaculites gyracanthus (Eaton) is a discrete species, but one with pronounced and remarkable intraspecific variability. Tentaculites simmondsi new species also occurs in the same unit and locality.

Five species of nuculoid bivalves are described from Pennsylvanian outcrops of the Ixtaltepec Formation, Oaxaca, Mexico: Nuculopsis sp., Palaeoneilo sinuosus new species, Paleyoldia sp., Phestia bellistriata, and Phestia sp. have been collected in clastic rocks and in association with other marine invertebrate groups, which represent a peri-reefal environment.

Incompleteness of the fossil record has confounded attempts to establish the role of the end-Cretaceous bolide impact in the Late Cretaceous mass extinctions. Statistical analysis of latest Cretaceous outer-shelf macrofossils from western European Tethys reveals (i) a major extinction at or near the Cretaceous-Tertiary (K-T) boundary, probably caused by the impact, (ii) either a faunal abundance change or an extinction of up to nine ammonite species associated with a regression event shortly before the boundary, (iii) gradual extinction of most inoceramid bivalves well before the K-T boundary, and (iv) background extinction of approximately six ammonites throughout the latest Cretaceous., The end Cretaceous is marked by the extinction of 70% of species worldwide (1), which apparently coincided with the large bolide impact that created the 180-to 300-km-wide Chicxulub impact structure [...]

Hispanosinuites peeli new genus and species from the Lower Oretan shales (Middle Ordovician) of central Spain is described and placed in the new subfamily Hispanosinuitinae of the family Sinuitidae. This new subfamily is considered to represent a highly specialized phylogenetic lineage, which probably separated from the morphological range of the genus Sinuites during the Early Ordovician. The outer shell surface of Hispanosinuites peeli is entirely covered by secondary shell layers, which are interpreted as perinductura, inductura and coinductura. The similarity of these shell deposits in Hispanosinuitespeeli and species of Euphemites suggests that these layers were secreted by mantle flaps having the same form in both genera. Hispanosinuites peeli is interpreted as a mobile mollusc with an internal shell adapted to an infaunal mode of life. Discovery of this unusual mollusc reopens the question of the phylogenetic relations of the families Sinuitidae and Euphemitidae, which are often assigned to different molluscan classes.

The genus Baffinicythere is a northern high-latitude marine ostracode, which includes four species: B. howei Hazel, B. ishizakii new species, B. reticulata new species, B. robusticostata new species. The first species occurs only in late Pliocene to Recent sediments of the Arctic and northern Atlantic Oceans. The remaining three species are abundant in the Plio-Pleistocene formations of northern Japan, which yield cold-water molluscan faunas. Detailed morphological analyses and paleogeographic distribution of the three new species indicates that: 1) B. reticulata has some primitive characters relative to the other two species; 2) B. ishizakii and B. robusticostata seem to have had different strategies as regards rate of ontogenetic size increase; 3) the left valve outlines can be resolved into two components, ontogenetic shape changes and species-specific distinctions among the species; and 4) B. robusticostata invaded areas inhabited by B. reticulata and may have excluded it during the late Pleistocene. The Atlantic species B. howei has not been recorded from northern Japan. Comparisons of B. reticulata and B. howei, based on their pore distribution and reticulate sculptures, suggest that B. reticulata could have migrated to the Arctic Province after the Bering land barrier had been breached and then evolved rapidly into B. howei.

The emended descriptions of the genus Amphitriscoelus and the species A. waringi Harris and Hodson are given, and a new species is proposed (A. pluriloculata). These rudist bivalves are derived from a thick Lower Cretaceous sequence of carbonate sediments interlayered with siliciclastic, volcaniclastic, and volcanic rocks in southwestern Mexico, near Huetamo, in the State of Michoacan. The species belong to a recently discovered rich fauna containing other rudists, nerineid gastropods, orbitolinid foraminifers, and calcareous algae. The fauna shows a close affinity with the Amphitriscoelus fauna of northern South America. Similar assemblages are also present in Texas, Cuba and other Mexican localities. The wide distribution of the fauna allows interpretation of paleogeographic relations among all the regions as well as interpretation of paleoecological similarities. The existence of an homogeneous large faunistic province during the Early Cretaceous is suggested.

Small holes of irregular outline and mainly 0.2 to 1.5 mm in diameter are present in the exteriors of molluscan shells obtained from the latest Quaternary transgressive sequence on the Orange Shelf, Benguela region, off southwestern Africa. In shell interiors, the shell surrounding the holes is broken out to form flaring, conical spalls. The holes are clearly not borings, but are punctures caused by a small, pointed object having been forcefully driven into the shell. The holes in bivalves occur preferentially in small, thin-shelled tellinids and are nonrandomly placed in the central portions of valves. It is proposed that the holes are praedichnia produced by the rapid, ballistic-like raptorial strikes of spearing stomatopods, the pointed dactyl tips having penetrated the shells. Associated evidence of shell smashing, consisting of large holes in valves and gastropod whorls, supports the suggestion of stomatopod activity. The only stomatopod that inhabits the Benguela ecosystem, the spearer Pterygosquilla armata capensis Manning, 1969, is the probable tracemaker. Although shell nearly 1 mm thick has been pierced, the apparent selection of thin-shelled tellinids (0.14 to 0.34 mm thick) may reflect the requirement of shelling smashing in order to access the tissues. Nevertheless, the spearing of shelled prey is atypical for stomatopods and therefore confirmatory zoological observations are required, particularly to clarify the context of shell spearing. The ichnogenus Belichnus is proposed to accommodate these unique traces of pointed impacts, with ichnospecies B. monos (single punctures) and B. dusos (combined punctures) to accommodate the main morphological varieties observed.

87Sr/86Sr chronostratigraphy is an important tool for dating and correlating vertebrate and invertebrate faunas preserved in marginal marine sequences. Freshwater flux in marginal marine environments can influence the 87Sr/86Sr of mollusks and, consequently, Sr-chronostratigraphic interpretations based upon them. To appraise the potential problem we have used a two-component mixing equation to evaluate levels of 'measurable effects' (defined as [+ or -]5 x 10-5 departure from the marine 87Sr/86Sr ratio) in marginal marine environments. A measurable effect occurs at 12 parts per thousand salinity for a weighted world average river, but can occur at salinity [greater than] 34 ppt for rivers draining basins with ancient granitic rocks. Predictions were tested with analyses of mollusks from estuaries in the Mississippi Sound and coastal Florida. Analyses document the largely regular variation in 87Sr/86Sr predicted, but also show that a simple two-component model cannot account for all of the variation. Carbonates formed in restricted marine settings may not record a marine 87Sr/86Sr signal, emphasizing the need to consider freshwater flux for 87Sr/86Sr chronostratigraphy.

An early species of the genus Gryphaea showed the evidence of nacreous formation on the insides of its shell. The inner shell is described to be covered with definite prismatic layers formed in a mosaic structure and composed of calcitic material. A cross-section of the shell shows the depositional structure of the nacreous layers as well as the interlaminar matrices occurring between the surfaces.

This paper describes new species of Ostracoda from Late Cretaceous (late Santonian) oyster reefs of the Eutaw Formation of eastern Alabama. The reefs are composed almost exclusively of Ostrea cretacea Morton, with rarer occurrences of the oysters Exogyra upatoiensis Stephenson and Lopha ucheensis (Stephenson) and the bivalve Anomia preolmstedi Stephenson. Total thickness of the reefs is about 30 m, and the reefs are a major topographic feature across most of Macon and Russell Counties, Alabama, a distance of about 60 km. The reefs are interpreted to have been backbarrier sediments deposited under brackish conditions. Eight species of ostracodes are identified, including five new species described herein. The fauna is typically well preserved, and includes males, females, and juveniles. New species include Haplocytheridea? eutawensis, Antibythocypris dimorphicus, A. nephotrema, Brachycythere asymmetrica, and Eocytheropteron mutafoveata. Also discussed and illustrated are Cytherella tuberculifera Alexander, Haplocytheridea renfroensis renfroensis Crane, and Fissocarinocythere gapensis (Alexander).

Description of two new specimens of Macroscenella superba (Billings) provides additional data on this rare, poorly known Paleozoic genus. Macroscenella was considered first to be a gastropod, then a monoplacophoran, and finally a coelenterate. Chondrophorine affinities for this form cannot be totally ruled out, but the new specimens increase the probability that it is a mollusk. If so, Macroscenella is more likely a patellacean gastropod than a member of any other group of the Mollusca, though evidence for placement within the Mollusca is equivocal; the interior of the specimens is not exposed and musculature is unknown. If the integument was a shell, it was thin.

The use of Delta13C values of L and D enantiomers for stable isotopic analysis of amino acid contaminants in quaternary mollusk shells shows that clean samples in 7000 to more than 100,000 yr B.P. age range have similar Delta13C values, proving the indigeneity of the amino acids to the shells. Samples that are partially clean exhibit different isotopic values of L and D enantiomers due to the amino acid contaminants, indicating that proper cleaning of shells is vital. The isotopic method is reliable for the measurement of amino acid indigeneity in fossils.

Speocarcinus berglundi n. sp. is described from the Imperial Formation in Riverside County, California. Although the Imperial Formation spans late Miocene through late Pliocene time, the part of the unit that bears crabs has been radiometrically dated as late Miocene. The identification of a new species was based upon comparison with four extant species and represents the first documented fossil occurrence for the genus. The occurrence of this new species suggests that the genus may have originated in the Pacific and, during the Miocene, dispersed through the Isthmus of Panama to the Caribbean. Two of the specimens exhibit parasitism by Bopyridae (Isopoda).

Kheraiceras Spath, 1924, is known mainly from macroconchs. Matching of dimorphic pairs at species level is difficult due to the rarity of microconchs and consequent difficulty in establishing contemporaneity. The present study reveals dimorphism within Kheraiceras cosmopolitum (Parona and Bonarelli, 1895) from the lower part of the Callovian Chari Formation, Kutch, India, where microconch closely resembles macroconch except for the size, being about three times smaller and having an aperture characterized by terminal construction. The evolution of Kheraiceras from Bullatimorphites Buckman is based on macroconchs only. The discovery of coeval microconch specimens and study of known microconchs within the lineage indicate 'parallel' evolution in macro- and microconchs and improves the understanding of evolutionary trends that involve complex heterochronic processes.

Reticuloceras (Swintoceras) n. subgen. unites an early group of the mid-Carboniferous goniatite family Reticulocertidae, in which reticulate sculpture is weakly developed or lacking and the typically reticuloceratid suture has slightly expanded ventral prongs. The type species, Reticuloceras (S.) spiraloides (Bisat and Hudson, 1943), is a rare, poorly known species from the British Namurian. Two additional species, R. (S.) wainwrighti (Quinn, 1966) and R. (S.) tiro (Gordon, 1969), are common in the basal type Morrowan Series, Lower Pennsylvanian, of Arkansas. Swintoceras occurs with two distinctive, late forms of the ammonoid, Hudsonoceras: Hd. ornatum (Foord and Crick, 1897) in Britain and Hd. moorei Quinn and Saunders, 1968, in Arkansas. The co-occurrence of these taxa correlates the basal Morrowan in its type region with the Namurian Reticuloceras nodosum (R(sub 1b)) Zone of Britain and thereby also dates the close of the Mid-Carboniferous Eustatic Event in the North American Midcontinent.

The aquatic molluscan fauna of the late Oligocene-early Miocene Cabbage Patch beds of western Montana includes eight taxa, six of which are new at specific or subspecific level, Sphaerium bakeri, Valvata paula, Planorbula powelli, Biomphalaria haydeni, Lymnaea tumere, and Lymnaea vetusta ambigua. Two are referred to previously known taxa, Viviparus nanus and Lymnaea shumardi. The genera Biomphalaria, Planorbula, and Viviparus no longer occur in western Montana, nor in the Columbia River drainage. Planorbula powelli is the earliest unequivocal Planorbula from North America. Of the 18 supraspecific taxa of this molluscan fauna, eight (44%) are now displaced, all but one to the east and/or south. Climatic interpretations derived from modern habitats of the genera Biomphalaria and Polygyroidea suggest a late Oligocene-early Miocene Mean Annual Temperature of 10 degrees C, with January means not less than 5 degrees C, and July means about 15 degrees C. Environmental analysis suggests a subhumid to subarid shrub and grassland vegetation similar to modern environments with >50 cm Mean Annual Precipitation, surrounding marshy shallow lakes subject to seasonal desiccation. Effective moisture varied from slightly greater than the present for the late Oligocene to a latest Oligocene pluvial interval followed by subarid conditions for the early Miocene. Geographically, the drainage of this area was into a closed and isolated basin during the late Oligocene-early Miocene. Molluscan assemblages are found to support the tripartite division of the Cabbage Patch beds that has been based on mammals and should be useful in correlation between basins.

Cretaceous and early Tertiary Pholadidae (Mollusca: Bivalvia) from the Pacific Slope of North America are rare and only poorly known. Three new species, each the earliest known Pacific Slope representative of its respective genus, are described: Barnea (Anchomasa) saulae n. sp. (Pholadinae) from the Upper Cretaceous (Coniacian and Santonian) Redding Formation near Redding, uppermost Sacramento Valley, Shasta County, northern California; Chaceia fulcherae n. sp. (Martesiinae) from three widely separated areas of outcrop represented by 1) the middle Miocene ('Temblor') Temblor Formation near Oil City and in Jasper Canyon, western Fresno County, central California, 2) the middle Miocene ('Temblor') Topanga(?) Group in the northern Santa Ana Mountains, Orange County, southern California, and 3) the upper Miocene (Wishkahan) Montesano Formation on the Middle Fork of the Satsop River, Mason County, western Washington; and Netastoma squiresi n. sp. (Jouannetiinae) from the lowest Eocene (uppermost 'Meganos') part of the Santa Susana Formation north of Simi Valley in the Santa Susana Mountains, Ventura County, southern California.

New Mollusca from the shallow marine, highly fossiliferous Wangaloa Formation of southeastern Otago, South Island, New Zealand, are described. This paper reports three new species and one new genus: Leionucula palaioanaxea n. sp. of the Nuculidae, Pyropsis zinsmeisteri n. sp. of the Tudiclidae, and Wangacteon grebneffi n. gen. and sp. of the Acteonidae. These taxa represent new records in New Zealand of apparently endemic taxa. The molluscan fauna of the Wangaloa Formation is important in the understanding of Paleogene biogeography of the Southern Hemisphere and changes in faunal composition of the Cretaceous-Tertiary Gondwana Realm. Genus- and species-level endemism of the 'Wangaloan' fauna is marked and is probably a reflection of 'greater New Zealand' 's geographic and genetic isolation during the Paleocene. Although deposits containing early Paleogene Mollusca are generally rare in the Southern Hemisphere, comparisons of known Gondwana molluscan taxa and those of similar age in the Northern Hemisphere indicate that the Mollusca of the Wangaloa Formation have Early Paleocene affinities. Microfossil evidence, in addition, supports an Early Paleocene age for the fauna. However, an uppermost Cretaceous age is indicated for the basal part of the Wangaloa Formation stratigraphically below the shell beds, but the K-T boundary has yet to be located.

Evaluation of previously undescribed collections of Late Triassic Gryphaea from the North American Cordillera increases the temporal range and geographic distribution ofthe genus. Gryphaea (Gryphaea) arcuataeformis Kiparisova, G. cf. G. Gryphaea) keilhaui Bohm, and a new species, G. (Gryphaea) nevadensis, occur in lower Camian to upper Norian strata from Alaska, British Columbia, Oregon, and Nevada. The distribution is mostly primary with respect to the Upper Triassic North American Craton, and requires long-distance larval dispersal along the latitude of far-eastern Panthalassa. Unlike most modern oysters, the distribution of these Triassic gryphaeids may have been restricted to cool and deeper water environments. An early Carnian age of Gryphaea (Gryphaea) arcuataeformis places this species as the oldest known Gryphaea. When combined with late Carnian and Norian occurrences from the North and South American Cordillera, these data indicate that a low-latitude origin for the genus cannot be overlooked. Gryphaeids survived the end-Triassic extinction event presumably by living in refugia.

A large, diverse, and well-preserved fauna of nonmarine mollusks has been recovered from the late Oligocene to early Miocene (Arikareean) fluviatile and lacustrine sediments that accumulated in four intermontane structural basins of western Montana. The Pupillidae are represented by 10 species, with nine new species and one new subgenus among three extant genera. The Gastrocopta are very diverse, with one new subgenus Ameralbinula represented by three new species, G. obesa, G. russelli, and G. oviforma, while three new species, G. tavennerensis, G. leonardi, and G. Conica are referred to the extant subgenus Vertigopsis Sterki, 1893. Gastrocopta miniscula cannot be referred to a subgenus with certainty. The remaining new species, Vertigo whitei and Pupoides montana, are referred confidently to extant subgenera. Vertigo arenula (White, 1876) is the only previously described species and its description is emended based on new material. The mammalian biostratigraphy of the Cabbage Patch beds is presented.

Two orthothecid genera, Bolitheca n. gen. (type species Orthotheca steinmanni Knod, 1908) and Neobactrotheca n. gen. (type species Neobactrotheca pharetra n. sp.) are described from Bolivian rocks of Emsian and Eifelian age. Two incomplete and poorly preserved hyolithids are also described, one tentatively assigned to the family Pauxillitidae. Because so few specimens are known, it is not possible to compare Bolivian Devonian hyoliths with faunas from other regions, which are also poorly known.

Assume that a catastrophe caused the sudden extinction of the molluscan biota of a Holocene tidal flat. Would this event be recorded accurately in the stratigraphic record? How accurately would the extinction of rare species be recorded? How would sudden, gradual, and stepwise patterns of extinction compare? Bivalve and gastropod species occurences were recorded from eight tidal channel sediment cores (up to 70 cm long) from Bahia la Choya, northern Gulf of California. The distribution of last occurrences of 45 species suggests that a sudden extinction would appear to be gradual in the stratigraphic record, due to error in biostratigraphic range end-points (Signor-Lipps effect). Extinction is typically not accurately recorded for species with less than 15% stratigraphic abundance (i.e., occurring in less than 15% of the sample intervals; 71% of the species). The data were subjected to stipulation of stepwise and gradual extinction. Differences between the sudden, stepwise, and gradual scenarios are apparent in (1) frequency distributions of biostratigraphic last occurrences, (2) graphic relations between stratigraphic abundance and last occurrence, and (3) patterns of apparent diversity decline below the extinction boundary. Extinction studies in outcrops and cores could utilize last occurrence and stratigraphic abundance date (readily available in the fossil recort) to distinguish among sudden, stepwise, and gradual patterns of extinction.

Small, silicified rostroconchs are present in the late Wolfcampian Bird Spring Formation in Nevada. Hadropipetta nevadaensis new species, Minycardita sectilis new genus and species, and Baiosoma sp. are described.

The first opening of the Bering Strait was a significant paleo-geographical and biogeographical event, and an important oceanographic event. The event has not been accurately dated, but the discovery of a bivalve mollusc Astarte in southern Alaska indicates that the strait last opened by at least the Late Miocene or earliest Pliocene epochs. A minimum age range of between 4.8 and 7.3-7.4 Myr ago is suggested, contrasting with previous suggestions of 3.1-4.1 Myr for the initial opening.

Analyses of recent data show that Floridian molluscan diversity declined markedly during the Pliocene-Pleistocene mass extinction. This decline in diversity was seen at all trophic levels, indicating a complete collapse of the ecosystem. These findings contradict the notion that there was a species diversity stasis throughout the Pliocene-Pleistocene and that the diversity of Pliocene Florida was equivalent to that of Recent Florida. The mass extinction was a two-staged, sequential event. A similar two-staged mass extinction occurred in the Miocene, indicating that two ecological catastrophes in quick geological succession may have produced this mass extinction as well., Studies of tropical western Atlantic Pliocene (Plio)-Pleistocene molluscan mass extinctions (1-8) have resulted in two conflicting conclusions. The main data soure used to arrive at these antitheses was the rich [...]

Ongoing controversies surrounding the end-Triassic extinction highlight the need for identifying a causal mechanism leading to extinction. Bivalve data from Lombardia (Italy), Northern Calcareous Alps (Austria and Germany), and northwest Europe (England and Wales) provide the biologic signal of selective extinction to compare two competing extinction hypotheses: (1) sea-level change and associated anoxia and (2) reduced primary productivity. The end-Triassic extinction eliminated 71% of Lombardian species, 85% of northern alpine species, and 90% of northwest European species. The extinction was independent of body size and geographic distribution. With respect to living habits, species from the three regions show a significantly greater proportion of infaunal bivalve extinction. The greater survival of epifaunal bivalves is correlated to their more efficient feeding and suggests that the infaunal bivalves may not have been able to meet their nutritional requirements. This pattern of selective extinction is inconsistent with anoxia and/or sea-level change as a causal factor in which higher survival of infaunal detritus and filter feeders would be predicted. Instead, the pattern is consistent with a reduction of primary productivity. Several regional and global mechanisms, including bolide impact, would have been capable of altering primary productivity levels to affect the food sources for Late Triassic bivalves, thus leading to extinction.

Two ammonite type specimens described in 1850 by Alcide D'Orbigny were given the names Ammonites silimani and Ammonites danae. The species names have been changed, but identification of these two types is valid for referring to either the old names or the new species names, Hoploscaphites nicoletti and Discoscaphites gulosus. The new descriptions are also based on the type specimens described by D'Orbigny.

Questions on the validity of Alteceras originate from a lack of completely preserved material. However, a Queensland Museum specimen of the type species Myloceras (Alteceras) has helped to dispel this doubt. Fossil analysis suggests a mudstone Allaru Formation origin although other fragmented specimens suggest Toolebuc origins. It is generally accepted that Myloceras (Aleteceras) includes three species: M. (A.) andinus, M. (A.) nautiloides and M. (A.) plectoides.

Amino acid geochronology provides important chronostratigraphic insight in the regional correlation and paleoclimatic evaluation of loess-paleosol sequences in the midwestern US, throughout western, central, and eastern Europe, and in China. In general, loess of the last four glacial cycles, corresponding to marine oxygen-isotope stages (OIS) 2-4, 6, 8, and 10, respectively, can be distinguished on the basis of alloisoleucine/isoleucine (A/I) ratios measured in fossil gastropod shells preserved in the loess. The racemization reaction is much slower in older samples, resulting in decreased temporal resolution. In the midwestern US and Europe, it is not possible to confidently subdivide the last glacial cycle on the basis of aminostratigraphic data. However, in China, where effective temperatures were higher during the Late Pleistocene, loess above and below L1SS1, the OIS-3 interstadial paleosol, can be distinguished using amino acid racemization data. With improvements in analytical methods, multiple amino acid D/L-enantiomers are now being measured using reverse-phase liquid chromatography. Aspartic acid racemizes at a higher rate than the traditionally measured alloisoleucine/isoleucine diastereomers and can be measured more rapidly. This development offers hope for better temporal resolution and enhanced stratigraphic subdivision of loess units than has been achieved previously. Keywords: Amino acid geochronology; Pleistocene; Loess; Stratigraphy; Mollusks

Since the beginning of the 20th century, loess biostratigraphy has been strongly influenced by investigations of mollusks, these shells constituting the major fossil remains found in loess sequences. The earlier studies mostly involved identifying species and determining biozones or assemblages with regard to the presence or absence of key species, using the classic concept of biozones. Although this provided accurate elements with which to define an indicative biostratigraphy, the time resolution was not always sufficiently precise to connect those studies with the more recent and high resolution analyses that are now routine in Quaternary investigations. This paper reviews mollusk studies carried out in Northern Hemisphere loess sequences and shows that a consideration of them, as both biostratigraphic and palaeoclimatic indices, enhances their potential and opens up particularly interesting areas of research. The first example demonstrates that the last glacial mollusk assemblages in North America show compositional similarities to those in Europe. The climatic interpretation, however, appears more restricted by local conditions. The second example shows that climatic conditions can be used to infer variations in the composition of biozones and, thus, address the significance of the distributional pattern of key species. The third example demonstrates the value of high-resolution studies and the potential of comparing the results of mollusk analyses with other proxies as an underpinning of the biological interpretation. Finally, the need for more high-resolution investigations in both North America and Asia is stressed. Keywords: Mollusk; Loess; Mollusk assemblages; Biostratigraphy; Paleoclimatology; Northern Hemisphere

Some 425 million years ago, a heavily armored, wormlike mollusk died on the deep sea floor and was buried in volcanic ash. Now, using a novel technique, a team of [...]

In the Silurian carbonate platform succession of Gotland, Sweden, interreef limestone and marl sequences have shallow-marine shelly assemblages dominated by brachiopods, typical of many Paleozoic benthic faunas. Locally, from similar facies, where early skeletal silicification occurred associated with bentonites, there are rich and diverse assemblages of originally aragonitic molluscs. Quantitative faunal analysis suggests that massive depletion of skeletal aragonite, chiefly molluscs, took place, and the entire molluscan fauna may generally be underrepresented by at least 100-fold. Previous workers on the Gotland succession have already shown that abundant diagenetic limestones were sourced by early aragonitic remobilization. Our findings indicate molluscs as the probable source of this diagenetic calcite, not aragonite mud as was previously thought. The taphonomic window represented by the silicified faunas illustrates the importance of aragonitic shells among the original Silurian shelf benthos, and raises the possibility that the paucity of such shells among many fossil faunas may be largely an early taphonomic effect. Keywords: molluscs, aragonite dissolution, Silurian, Gotland.

The biological relationship between the agmatan sclerite Vorbothella from the early Cambrian and the Dimorphoconus granulatus from the Lower Ordovician is explored. The morphology of Vorbothella is remarkably similar to that of Dimorphoconicus and suggests a close biological link. However, speculation based on morphological similarities may be premature since the synamorphities could also be attributed to convergent evolution between the two groups.