Drilling predation on scaphopods and other molluscs from the Upper Cretaceous of Manitoba, Canada

Abundant information on drilling predation upon fossil bivalves, gastropods, and brachiopods has been accumulated during the past several decades, but very little is known about the predation on marine, infaunal carnivorous scaphopods. A survey of over 440 specimens of the scaphopod Dentalium gracile collected from the Upper Cretaceous Millwood Member (Campanian) of the Pierre Shale at a site near Russell, Manitoba displays a drilling percentage of approximately 35%. This figure is higher than previously reported for the scaphopods of similar age elsewhere, but is comparable to or lower than that of the sub-Holocene (34–61%). The difference in drilling percentage among different collections may be taxon-related or affected by the composition and structure of the fossil community. Morphologically, the drill-holes, produced by predatory drilling, are beveled with a countersunk profile of clean sharp edges. The drill-hole inner margin is ovate whereas the outer margin is nearly circular. Among the Manitoba specimens, drill-holes seem to be more common on the lateral side. Presumably due to the lack of effective defense strategy, the prey effectiveness is low (∼3.2%). There is no correlation between drill-hole dimension and scaphopod prey size, indicating that predator size does not correlate with the prey size. Nearly 480 specimens of cephalopods, pelecypods, and gastropods were also collected from the same community. There were only a total of 16 drill-holes on this additional material. Over 400 specimens of the only naticid Euspira obliquata were recovered from the same site and are believed to be the predators of the scaphopods and other molluscs. The low percentage (∼2.5%) of drilling on the abundant gastropod E. obliquata may indicate mistaken or opportunistic attacks by the predator, or that the cannibalism is not common in this community.     

Drilling and crushing predation on scaphopods from the Miocene of the Netherlands

Klompmaker, A.A. 2011: Drilling and crushing predation on scaphopods from the Miocene of the Netherlands. Lethaia, Vol. 44, pp. 429–439. Reports on the predators of scaphopods are rare. This study records two types of predation traces on the Miocene dentaliid scaphopod Fissidentalium sp. from Langenboom in the Netherlands. The first type is demonstrated by naticid drillholes, located primarily on the middle (and thickest) part of the shell. Based on the examination of more than 700 specimens, the percentage of completely drilled scaphopods is low, at 1%. This is in line with the first graphical overview of drilling percentages on scaphopods through time. The second type of predation is found as jagged, arcuate margins at the functionally anterior end of a significant part of the scaphopod population. These breakages were not caused by pressure due to overburden, as experimental results indicate that such breakages form at right angles to the longitudinal axis of the shell. Reworking was also ruled out, mainly because the breakages were formed at the anterior end of the shell only. Rather, the damage is attributed to carnivorous decapods chipping/peeling with their claws or mandibles. The predation traces suggest that Fissidentalium sp. was a shallow burrower. □Scaphopoda, drillholes, predators, Miocene, the Netherlands, Langenboom     

A note on exceptionally high confamilial naticid drilling frequency on Natica gualteriana from the Indian subcontinent

Although common, confamilial naticid predation intensity was not very high in the geological record. Here, we gathered modern confamilial predation data from the Indian coasts and showed that confamilial naticid predation on a naticid species, Natica gualteriana, is exceptionally high at Chandipur, one of our studied areas. We studied the different aspects of confamilial predation from the Indian coasts and showed that the predators in Chandipur were highly efficient as evident from high drilling frequency (DF), site stereotypy and low prey effectiveness. Unusually high DF on N. gualteriana may be attributed to its new arrival in Chandipur where it faced competitive elimination through predation by sympatric naticid predators. Reports of failed invasion are rare. Natica gualteriana is a small invader and therefore its invasion success is threatened by resident populations of large species that extensively drill on young individuals of N. gualteriana just to break the bottleneck of their own offspring from competition.     

Drilling predation on serpulid polychaetes (Ditrupa arietina) from the pliocene of the Cope Basin, Murcia Region, Southeastern Spain

We report quantitative analyses of drilling predation on the free-living, tube-dwelling serpulid polychaete Ditrupa arietina from the Cope Cabo marine succession (Pliocene, Spain). Tubes of D. arietina are abundant in the sampled units: 9 bulk samples from 5 horizons yielded ~5925 specimens of D. arietina. Except for fragmentation, tubes were well preserved. Complete specimens ranged from 3.1 to 13.4 mm in length and displayed allometric growth patterns, with larger specimens being relatively slimmer. Drilled Ditrupa tubes were observed in all samples. Drillholes, identified as Oichnus paraboloides, were characterized by circular to elliptical outline (drillhole eccentricity increased with its diameter), parabolic vertical profile, outer diameter larger than inner diameter, penetration of one tube wall only, narrow range of drill-hole sizes, and non-random (anterior) distribution of drillholes. A total of 233 drilled specimens were identified, with drilling frequencies varying across horizons from 2.7% to 21% (3.9% for pooled data). Many tube fragments were broken across a drillhole suggesting that the reported frequencies are conservative and that biologically-facilitated (drill-hole induced) fragmentation hampers fossil preservation of complete serpulid tubes. No failed or repaired holes were observed. Multiple complete drillholes were present (3.9%). Drilled specimens were significantly smaller than undrilled specimens and tube length and drill-hole diameter were weakly correlated. The results suggest that drillholes were produced by a size-selective, site-stereotypic predatory organism of unknown affinity. The qualitative and quantitative patterns reported here are mostly consistent with previous reports on recent and fossil Ditrupa and reveal parallels with drilling patterns documented for scaphopod mollusks, a group that is ecologically and morphologically similar to Ditrupa. Consistent with previous studies, the results suggest that free-dwelling serpulid polychaetes are preyed upon by drilling predators and may provide a viable source of data on biotic interactions in the fossil record.     

The scaphopod foot is ventral: more evidence from the anatomy of Rhabdus rectius (Carpenter, 1864) (Dentaliida: Rhabdidae)

Scaphopods comprise about 900 described species of elongate infaunal molluscs, separated into two orders. The phylogenetic position of this class is contentious, having been proposed as a sister-group to bivalves or alternatively cephalopods, all groups that notably represent dramatic modifications of the molluscan body plan and historical confusion over the fundamental body axes. The digging scaphopod foot was previously considered to be anterior. Here we use a three-dimensional tomographic reconstruction of digestive anatomy and partial dorso-ventral musculature, to test the hypothesis that the scaphopod foot is ventral. Similar to cephalopods, the body orientation is confounded by ano-pedal flexion, but rationalising scaphopods is perhaps further undermined by their infaunal lifestyle, which confounds comparison of ecological life position. Some scaphopods are locally abundant, providing good quality material for anatomical study. In our focal species, Rhabdus rectius (Carpenter, 1864), sexes can reliably be differentiated in vivo by differential colour of the gonad (yellow in females; white in males). The gut is composed of three complete loops. Based on the orientation of the digestive tract and the dorso-ventral muscles, we find further evidence to support the interpretation that the concave side of the scaphopod shell is anterior (the site of the mouth) and the foot is ventral.     

Comparing predatory drillholes to taphonomic damage from simulated wave action on a modern gastropod

Marine drilling predation, in which the predator bores a hole through shelled invertebrate prey, plays a role in the structure of benthic communities. As drilling often leaves the prey shell otherwise undamaged, the resulting holes are also an excellent proxy for drilling predation pressure in the fossil record. Considering that a large number of predation studies focus on drilling predation in the fossil record, it is crucial that we are able to distinguish true drilling predation from taphonomy. The purpose of this study is to determine damage on Olivella biplicata shells, drilled by naticid gastropods, is distinguishable from taphonomically produced damage to these shells. In addition, the potential for preferential breakage due to either the presence or whether absence of a drillhole was investigated. Drilled and non-drilled O. biplicata shells were tumbled to simulate wave action and were checked at intervals to record accumulated damage. Drilled and non-drilled shells do not show a significant difference in damage accumulated while undergoing simulated wave action. Taphonomic damage is unlikely to be mistaken for drilling damage, due to the jagged, irregular appearance of taphonomically produced holes.     

Invasion of Laguncula pulchella (Gastropoda: Naticidae) and predator–prey interactions with bivalves on the Tona coast, Miyagi prefecture, northern Japan

On the Tona coast, Miyagi prefecture, northern Japan, interactions between the alien predator Laguncula pulchella and its bivalve prey were explored using annually collected quadrat samples over a 10 year period, from 2001 to 2010. A single L. pulchella individual was first recorded in 2002, and the density increased 12-fold from 2002 to 2004. In contrast, population densities of Ruditapes philippinarum and Macoma incongrua rapidly decreased during this interval. Based on frequency of predatory drill holes on the dead shells, more than 35 % of Ruditapes philippinarum and 20 % of Macoma incongrua died because of naticid predation after 2004, while Pillucina pisidium was less vulnerable to naticid predation. L. pulchella focused attacks on P. pisidium in 2004, when R. philippinarum and M. incongrua had became scarce due to naticid predation. This species-selective predation affected bivalve community structure, and caused disagreements in taxonomic composition and species’ rank-order abundance between the living bivalve community and the assemblage of dead shells. This approach (live–dead analysis), frequently used in paleoecological research, is a conservative tool to identify impacts of an alien predator on community structure. When sample size is sufficient, frequency of predatory drill holes in preferred prey species is likely to reflect predation intensity.     

Naticid gastropod predation in the Gatun Formation (late Middle Miocene), Panama: preliminary assessment

Understanding predator-prey interactions is an important component of community studies, both present and past. Patterns of naticid predation in a fossil molluscan assemblage were studied by examination of drilling frequencies in a series of samples collected at three sites of the Gatun Formation (late Middle Miocene), Panama. Overall drilling intensities were relatively low (18 %) and were not correlated with abundance. Turritellids, turrids, and terebrids (making up to 11 % of the studied fauna) were the most consumed, representing almost 29 % of the total prey. Especially important were turritellids representing over 20 % of the total consumed prey. Albeit abundant (54 % of the studied fauna), columbellids, cerithiids, and marginellids showed low drilling intensities (8.2–10.4 %). Naticids were the major predators. Con-familial drilling among naticids is high and did not seem to be related to absence of preferred prey. Consistent with other studies, these data indicate that predators demonstrate high prey selectivity.     

EVIDENCE FROM THE FOSSIL RECORD OF AN ANTIPREDATORY EXAPTATION: CONCHIOLIN LAYERS IN CORBULID BIVALVES

Conchiolin layers, organic-rich laminae, are characteristic of the shells of corbulid bivalves. The retention of these layers, despite their high metabolic cost, throughout the evolutionary history of Corbulidae has prompted the proposal of several adaptive scenarios to explain the origin and maintenance of these layers. The most widely held hypothesis contends that conchiolin layers are an adaptation for inhibiting drilling by predatory naticid gastropods. However, others suggest that the layers are adaptations to retard shell dissolution in waters undersaturated with calcium carbonate or to increase shell strength in the face of durophagous (shell crushing) predators. In this paper, experiments using recent Corbula (Varicorbula) gibba (Olivi) and observations of corbulids' present natural habitat demonstrate the current utility of conchiolin layers for all three functions: retardation of shell dissolution in waters undersaturated in calcium carbonate, increase of mechanical shell strength, and inhibition of drilling by predatory naticid gastropods. Earlier analyses of the extensive history of naticid predator-corbulid prey interactions suggested that conchiolin layers were an adaptation, a feature that promotes fitness and was built by selection for its current role, for deterring naticid predators. Not only are naticid drillholes widespread in fossil and recent corbulid shells, but an unusually large number of incomplete drillholes terminate unsuccessfully at conchiolin layers. In addition, a phylogenetic analysis of the origin of conchiolin layers and its function to deter naticid predators is consistent with a hypothesis of adaptation for this function. However, this hypothesis is rejected by an examination of fossil Jurassic Corbulomima. These oldest corbulids contained conchiolin layers before the evolution of naticid drilling during the Early Cretaceous. Therefore, conchiolin layers appear to be an exaptation, characters evolved for other usages and later “coopted” for their current role, for defense against drilling predators. The layers may in fact be an adaptation to resist durophagous predation.     

Body size variation in the sexually dimorphic scaphopod Rhabdus rectius (Carpenter, 1864) (Dentaliida: Rhabdidae)

ABSTRACT

Male-biased sexual size dimorphism typically evolves via sexual selection for larger males that are favoured by choosy females or are more successful in mate competition with other males. Among marine invertebrates that broadcast their gametes into the ocean for fertilisation, this form of sexual size dimorphism is rare because such species lack direct interactions among males or between the sexes. However, the broadcast-spawning tusk shell Rhabdus rectius was recently reported to show strong male-biased sexual size dimorphism. That pattern might imply interesting and undiscovered sexual selection in this species. We found instead that the distribution of body size variation (weight, shell length) was similar between males and females of R. rectius, and mean sizes were not different between the sexes. However, we noted a male-biased sex ratio (～1:1.3) in our large sample of individuals. Many live scaphopods (and several dead shells) showed partial or complete boreholes drilled by predatory gastropods. Boreholes were observed on males and females in similar proportions. We collected scaphopods along with multiple individuals of one likely scaphopod predator, the small moon snail Euspira pallida, and in the lab we observed successful attacks by moon snails on tusk shells.     

Traces of Naticid Predation on the Gryphaeid Oyster Pycnodonte dissimilaris: Epifaunal Drilling of Prey in the Paleocene

Traces of drilling predation by naticid gastropods were observed on 51 valves of the free-lying, semi-infaunal oyster Pycnodonte dissimilaris (Gryphaeidae) from the Paleocene Hornerstown Formation, in New Jersey. Stereotypic behavior of the predator is indicated by the highly constrained placement of drill holes, 94% of which are centrally located on the oyster shells. Predator—prey mismatches in size, involving small predators that drilled through the upper valves of relatively large oysters, are documented by comparison of outer borehole diameter, as an index of predator size, with the sizes of the oyster shells. Results of this analysis suggest that at least some prey were drilled epifaunally, as they were too large to be manipulated and buried by the predator. This indicates, together with reports of epifaunal drilling by living naticids, that such behavior is geographically and stratigraphically more widespread in the Naticidae than has previously been acknowledged. This in turn suggests that epifaunal drilling of prey is a plesiomorphic, opportunistic mode of behavior, conserved in the evolution of the Naticidae, that has permitted subsequent escalation or expansion in range of naticid foraging from a more narrowly defined infaunal paradigm into exposed intertidal refugia.     

Evolutionary trends within bivalve prey of chesapeake group naticid gastropods

Five genera of Miocene bivalves evolved antipredatory adaptations in response to predation by drilling naticid gastropods. I examined the evolution of two traits affecting predator‐prey interaction, prey shell thickness (TH) and internal volume (IV). Thickness controls predation costs by determining drilling time, and internal volume influences the benefit derived by the predator.

Internal volume showed no consistent pattern of temporal change among the taxa studied. IV fluctuated nondirectionally during the history of most genera, though both increasing and decreasing trends occurred within species ofAstarte. In contrast, all five genera exhibited significant thickness increases (from 8–157%) during the three‐million‐year interval. Both gradual intraspecific and interspecific directional changes occurred. Taxa with the greatest predation intensities displayed the most change, suggesting that predation selected for the thickness increases. Increased thickness apparently reduced predation; a significant negative correlation between TH and predation intensity occurred within four of the bivalve genera. Improvement of predator capabilities apparently did not keep pace with increased antipredatory morphologic adaptations over the interval studied.     

Diversity,palaeoecology and systematics of a marine fossil assemblage from the Late Triassic Cassian Formation at Settsass Scharte,N Italy

A marine fossil assemblage from the Late Triassic (Early Carnian) Cassian Formation is reported. It was retrieved by bulk sampling, including wet sieving and quantitative picking, and by quantitative surface collection. The collection consists of c. 460 specimens (foraminiferans not included) representing 54 species. In terms of abundance and species richness, it is strongly dominated by molluscs, especially gastropods. 97 % of the individuals are molluscs. The most abundant species are the gastropods Goniospira armata, Schartia carinata and Helenostylina convexa, followed by the scaphopod Plagioglypta undulata and the bivalve Palaeonucula strigilata. Disarticulated echinoderm ossicles (mostly echinoids, crinoids, few holothurians) comprise almost all of the rest of the assemblage. The studied assemblage shows moderate diversity, similar to those of previously reported assemblages or associations from basinal settings. However, it differs considerably in taxonomic composition from previously described associations of the Cassian Formation. The abundance of small gastropods is a result of their primary abundance in these ancient living communities and of the sampling method (sieving at 0.5 mm), because most of the previous associations were obtained by performing surface collections, in which small gastropods are easily overlooked. The fauna is interpreted as an autochthonous soft bottom assemblage dominated by species that lived in low epifaunal to shallow infaunal habitats. Detritivory, deposit feeding and microcarnivory represent the main feeding types. Most of the species were fully motile but slow, and either infaunal (scaphopods, nuculids, the gastropod Domerionina) or epifaunal (most other gastropods, echinoids). The present assemblage underlines the pronounced heterogeneity of the Cassian biota. The low grade of lithification and diagenetic alteration facilitates bulk sampling and the investigation of small species. This minimizes possible sampling and preservation biases, so the studied assemblage reflects the alpha diversity of this ancient living community to an unusually high degree. The following gastropod taxa are new: Helenostylina convexa n. sp., Schartia carinata n. gen. n. sp., Schartiinae n. subfam.; Cassianastraea Bandel non Volz is replaced with Bandelastraea nom. nov.     

Invasion of a naticid predator and associated changes in death assemblages of bivalve prey in northern Japan: implications for palaeoecological studies

The recent invasion of a naticid predator (Laguncula pulchella) and associated changes in the death assemblages of bivalve prey (Ruditapes philippinarum) provide a baseline for interpreting predator–prey interactions in the fossil record. This article presents quantitative data on size‐frequency distributions (SFDs) of living and death assemblages, prey size selectivity and drillhole site selectivity from the Tona Coast, northern Japan. Before the appearance of the predator, the SFD of the death assemblage exhibited a right‐skewed platykurtic distribution, and there were very few predatory drillholes. Once the predator appeared, frequencies of predatory drillholes increased, particularly in the smallest size class (2–10 mm shell length). Furthermore, juvenile peaks in the SFDs of death assemblages sharpened, and thus, SFDs exhibited strongly right‐skewed leptokurtic distributions. These changes suggest that intense naticid predation precluded juvenile clams from growing to adulthood, and thus, many dead shells of juvenile clams were introduced into the sediment. The changes in SFDs may also indicate intensification of predation pressure in the fossil record. No temporal shifts in prey size selectivity and drillhole site selectivity were noted, despite substantial changes in the demographics of Ruditapes philippinarum. This suggests that lack of specific size classes of preferred prey species is unlikely to be a primary factor accounting for size mismatches between predator and prey, because, in such situations, naticid predators probably attack other prey species. Therefore, such a factor is unlikely to primarily explain the less stereotypical predatory behaviour (i.e. low prey size selectivity and low drillhole site selectivity), which has been frequently recognized in fossil assemblages. Such less stereotypical predatory behaviour in fossil assemblages is likely to be explained by other factors, such as the existence of multiple predator taxa and lack of specific size classes of all available prey.     

On the systematic position of Baltimartyria Skalski, 1995 and description of a new species from Baltic amber (Lepidoptera, Micropterigidae)

This paper describes a rare case of a male moth in Baltic amber in an excellent position for establishing a species. The moth represents the second species of the genus Baltimartyria Skalski, 1995, described herein as Baltimartyria rasnitsynisp. n. The detection of this new species prompts research on the systematic position of the genus within the family Micropterigidae. The genus was found to provide none of the apomorphic characters that would allow placement in one of the monophyletic lineages within the family. The genus is provisionally assigned to the "southern sabatincoid group", a weakly supported assemblage of Southern Hemisphere genera. The sister genus has still to be determined. Baltimartyria is the first North Hemisphere representative in this group. Some general aspects of historical biogeography relevant for the group are briefly discussed.     

Drill holes in Australian Cainozoic brachiopods

The fossil record of drill holes in marine invertebrates has received a considerable amount of interest from paleontologists, primarily due to its importance for reconstructing the history of interactions between drilling predators and their prey. Such drill holes have been described in numerous studies of Paleozoic brachiopods but rarely in those focusing on brachiopods of the post-Paleozoic, a striking pattern given that in the late Mesozoic and Cainozoic drilling gastropods diversified and frequencies of drilled molluscs increased dramatically. During the past several years, however, drilled brachiopods were reported in several studies of the Mesozoic and Cainozoic, suggesting that this phenomenon may be more common than has been previously assumed. Here we report on 10 genera of brachiopods from four Cainozoic basins in Australia of which 7 shows evidence of having been drilled by predators. Of 298 specimens examined, 38 contain a single complete hole. Drilled specimens were identified in all 4 basins and in all stratigraphic units. When considered in the context of recent reports of drilled Cainozoic brachiopods, these Australian brachiopods further imply that drilling predation on these invertebrates was geographically, taxonomically and temporally widespread.     

Retracted: Tusk shells in trouble? Physiology and behavior in response to changing temperature in a scaphopod (Mollusca: Scaphopoda: Dentaliida)

Scaphopods (tusk shells) are infaunal marine predators that occur at locally high densities in coastal and deep‐sea mud habitats, and as consumers of foraminifera they are important in carbon cycling. We investigated oxygen metabolism and burying behavior of the scaphopod Rhabdus rectius and its responses to altered temperatures. These are the first measurements of oxygen uptake rates for any member of this taxonomic class. In response to elevated temperatures, oxygen uptake rates increased, but the ability of animals to bury themselves in sediment was compromised. Female scaphopods were significantly larger than males and, when corrected for body mass, oxygen uptake rates were consistently higher for female individuals than for males. This is consistent with previous anecdotal observations of females in other scaphopod species being larger and potentially more active. In conditions of declining oxygen availability, individuals of Rhabdus rectius showed strong oxyregulatory ability by maintaining the same oxygen uptake rate displayed in normoxic conditions. The ability to maintain normal metabolic functioning even in conditions of oxygen limitation would benefit a species living in a benthic environment that may be prone to temporary or transient anoxic events. Yet the decrease in normal escape response in moderately elevated temperatures indicates these animals may be at risk from rising sea temperatures.     

Do predatory drill holes influence the transport and deposition of gastropod shells?

Predatory gastropod drill holes are an abundant and easily identifiable signal of predation in ancient and modern molluscan shell assemblages. Many workers have used drill holes to interpret patterns of predation intensity and success in fossil assemblages. These studies are predicated on the assumption that the relative abundances of drilled and undrilled shells in an assemblage accurately reflect those of the community from which the shells were originally derived. The underlying assumption is that drilled and undrilled shells are transported into shell accumulations in the same manner. If this assumption is false, shell accumulations do not represent taphonomically unbiased samples, but rather preferentially sorted deposits from which conclusions about drilling predation cannot be made. To test the hypothesis that drilled and undrilled gastropod shells transport at different flow velocities, multiple transport trials were conducted on two morphologically distinct taxa, Olivella biplicata and Euspira lewisii. Individual specimens were placed in a recirculating flume tank and observed from rest (in stable orientation) until they were transported downstream. During each trial, flow velocity was slowly and incrementally increased, so as to avoid pulses of acceleration, until shells began to move downstream. Drilled and undrilled specimens of both taxa demonstrate statistically significant correlations between shell mass and average transport velocity. Similarly sized drilled and undrilled specimens of both taxa do not exhibit significant differences in transport velocity. These results indicate that predatory drill holes do not change the hydrodynamic properties of gastropod shells. Therefore, gastropod shell assemblages are not likely to be affected by differential transport and sorting of drilled and undrilled shells.     

Facies of two important Early Triassic gastropod lagerstätten: implications for diversity patterns in the aftermath of the end-Permian mass extinction

Two important lagerstätten of Early Triassic gastropods, the Sinbad Limestone (Utah, USA) and the Gastropod Oolite (North Italy) yield about 40% of all described Early Triassic species. This great contribution to the global diversity and the exceptional good preservation render high information content, which characterizes fossil lagerstätten. The Smithian Sinbad Limestone contains the most diverse Early Triassic gastropod fauna. At the type locality, it occurs in single, probably storm-induced shell bed within a series of high energy deposits underlain by intertidal microbial mats and subtidal oolite/peloid shoals. The main shell bed contains about 40 invertebrate taxa. Gastropods, scaphopods, and bivalves are most abundant and form an assemblage, which is dominated by small neritaemorphs, the opisthobranch Cylindrobullina convexa and the scaphopod Plagioglypta (annulated tubes). This assemblage lived on shallow, subtidal soft-bottoms based on sedimentological and ecological characteristics. The Dienerian (to Smithian?) Gastropod Oolite Member (North Italy) has extremely abundant, probably salinity-controlled gastropod faunas with low species richness. Almost monospecific assemblages of Pseudomurchisonia kokeni as well as assemblages with about four species are present in the Gastropod Oolite. Modern hydrobiid mudsnail faunas which are adapted to strongly fluctuating salinity in intertidal to shallow subtidal coastal areas form probably a suitable model for the Gastropod Oolite biota. Gastropods from the Werfen- and Moenkopi-Formation lagerstätten are well preserved compared to other Early Triassic deposits. The high contribution to the global diversity of just two sites suggests very incomplete sampling and preservational bias. However, the low richness of the major faunas reflects depauperate Early Triassic faunas and slow recovery from the Permian/Triassic crisis.