Broken pieces: can variable ecological interactions be deduced from the remains of crab attacks on bivalve shells?

Shell fragmentation patterns that result from attacks by durophagous predators on hard‐shelled marine invertebrates are a rich source of indirect evidence that have proved useful in interpreting predation pressure in the fossil record and recent ecology. The behaviour and effectiveness of predators are known to be variable with respect to prey size. It is less well understood if variable predator–prey interactions are reflected in shell fragmentation patterns. Therefore, we conducted experimental trials to test the behavioural response of a living crab, Carcinus maenas, during successful predatory attacks on the blue mussel Mytilus edulis on two prey size categories. Further, we examined resultant shell fragments to determine whether specific attack behaviours by C. maenas could be successfully deduced from remaining mussel shells. In contrast to previous studies, we observed no significant differences in attack behaviour by the predators attributable to prey size. In most experimental predation events, crabs employed an ad hoc combination of five mechanisms of predation previously described for this species. We identified seven categories of shell breakage in predated mussels, but none of these were unambiguously correlated with specific attack behaviour. Combined attack behaviours may produce shell breakage patterns that have previously been assumed to be attributable to a single behaviour. While specific patterns of shell breakage are clearly attributable to durophagy, the results of this study provide important insights into the limitations of indirect evidence to interpret ecological interactions.     

Recognizing biotic breakage of the hard clam, Mercenaria mercenaria caused by the stone crab, Menippe mercenaria: An experimental taphonomic approach

The ability to assign lethal traces left on prey to particular durophagous predators enhances our understanding of predation pressure in the fossil record. To determine whether stone crabs (Menippe mercenaria Say 1818) leave diagnostic traces in the act of feeding on hard clams (Mercenaria mercenaria Linnaeus 1758), live clams were offered to crabs in laboratory aquaria over several months and the fragments produced during predation were examined for diagnostic breakage patterns. These fragments were then compared both macroscopically and using scanning electron microscopy to the fracture patterns produced by tumbling clams in a rock tumbler which simulated breakage during transport in the surf zone, and crushing clams using an Instron which simulated breakage resulting from sediment compaction. Fossil specimens of Mercenaria mercenaria were also examined to determine whether the criteria for recognizing predation traces generated experimentally could be recognized. While not all acts of predation produce diagnostic traces, when larger fragments (greater than 50% shell remaining) are produced during feeding, predatory-diagnostic breakage ranges from 70 to 80%. Macroscopic breakage patterns generated during the predation experiments were also present in fossil specimens. Damage caused by abiotic mechanisms (tumbling and crushing) is highly unlikely to be confused with damage produced by this predator.     

MORPHOLOGY AND BEHAVIOR OF CRABS AND GASTROPODS FROM LAKE TANGANYIKA,AFRICA: IMPLICATIONS FOR LACUSTRINE PREDATOR-PREY COEVOLUTION

The shells of most lacustrine gastropods are typically small, weakly calcified, and modestly ornamented to unornamented. Similarly, most lacustrine crabs are usually small detritivores with weak chelae. A number of invertebrate taxa in Lake Tanganyika, however, deviate from these generalities. This study explores a predator-prey coevolution model as an explanation for the large, heavily calcified, and ornate gastropods and the robust, durophagous crabs of Lake Tanganyika. The endemic thiarid and viviparid gastropods from Lake Tanganyika have significantly thicker shells and higher frequencies of terminal apertural lip thickening than closely related cosmopolitan taxa from outside the lake. Tanganyikan gastropods also display considerably higher incidence of shell repair, following nonlethal shell damage, than cosmopolitan taxa of the same families. There is a strong positive correlation between gastropod apertural lip thickness and shell repair frequency among all the gastropod species analyzed. The endemic Tanganyikan potamonautid crab Platytelphusa armata (a molluscivore) possesses larger, more robust crushing chelae than other African potamonautid or potamonid crabs. In contrast with the cosmopolitan African crabs, the Tanganyikan crabs display molariform, rather than serrate dentition on their crushing chelipeds. In shell-crushing experiments, the Tanganyikan gastropod shells were an order of magnitude stronger than typical lacustrine gastropod shells, many well within the range of tropical marine gastropod shell strengths. Predation experiments with the endemic gastropods Spekia, Neothauma, Lavigeria spp., Paramelania spp. and the crab Platytelphusa armata showed that increased size, apertural lip thickness or shell sculpture reduced the successful predation rate of P. armata. Crabs with large chelae have a greater ratio of successful: unsuccessful attacks than crabs with small chelae. Among cases of successful predation, crabs with large chelae employed predation methods that required less time and energy (such as crushing the shell in the cheliped) than the methods employed by crabs with small chelae (such as peeling the shell from the aperture or the spire). The morphological, shell-crushing, and aquarium experiment data, considered in concert, provide strong support for the idea that the endemic gastropods and crabs of Lake Tanganyika have coevolved over the past 7 million years.     

Paleobiological implications of shell repair in recent marine gastropods from the northern Gulf of California

Shell repair frequencies in eleven species of Recent gastropods from the northern Gulf of California vary with habitat, shell morphology and intensity of durophagous predation. Squat shells with large apertures tend to have high repair frequencies (0.25–0.50). Shell thickness at the aperture and shell size are not correlated with frequency of repair. Significant intraspecific variation in repair frequency exists between habitats. Samples from rocky habitats have statistically higher repair frequencies than samples of the same species from sandy habitats. However, habitat‐related variation between species is not apparent.

Trends in co‐evolution of gastropods and their durophagous predators are based on the indirect evidence of shell repair frequencies through time. Variation in repair frequency due to environmental and morphological factors may obscure predator‐related temporal trends in repair frequency.     

Reappraising the early evidence of durophagy and drilling predation in the fossil record: implications for escalation and the Cambrian Explosion

The Cambrian Explosion is arguably the most extreme example of a biological radiation preserved in the fossil record, and studies of Cambrian Lagerstätten have facilitated the exploration of many facets of this key evolutionary event. As predation was a major ecological driver behind the Explosion – particularly the radiation of biomineralising metazoans – the evidence for shell crushing (durophagy), drilling and puncturing predation in the Cambrian (and possibly the Ediacaran) is considered. Examples of durophagous predation on biomineralised taxa other than trilobites are apparently rare, reflecting predator preference, taphonomic and sampling biases, or simply lack of documentation. The oldest known example of durophagy is shell damage on the problematic taxon Mobergella holsti from the early Cambrian (possibly Terreneuvian) of Sweden. Using functional morphology to identify (or perhaps misidentify) durophagous predators is discussed, with emphasis on the toolkit used by Cambrian arthropods, specifically the radiodontan oral cone and the frontal and gnathobasic appendages of various taxa. Records of drill holes and possible puncture holes in Cambrian shells are mostly on brachiopods, but the lack of prey diversity may represent either a true biological signal or a result of various biases. The oldest drilled Cambrian shells occur in a variety of Terreneuvian‐aged taxa, but specimens of the ubiquitous Ediacaran shelly fossil Cloudina also show putative drilling traces. Knowledge on Cambrian shell drillers is sorely lacking and there is little evidence or consensus concerning the taxonomic groups that made the holes, which often leads to the suggestion of an unknown ‘soft bodied driller’. Useful methodologies for deciphering the identities and capabilities of shell drillers are outlined. Evidence for puncture holes in Cambrian shelly taxa is rare. Such holes are more jagged than drill holes and possibly made by a Cambrian ‘puncher’. The Cambrian arthropod Yohoia may have used its frontal appendages in a jack‐knifing manner, similar to Recent stomatopod crustaceans, to strike and puncture shells rapidly. Finally, Cambrian durophagous and shell‐drilling predation is considered in the context of escalation – an evolutionary process that, amongst other scenarios, involves predators (and other ‘enemies’) as the predominant agents of natural selection. The rapid increase in diversity and abundance of biomineralised shells during the early Cambrian is often attributed to escalation: enemies placed selective pressure on prey, forcing phenotypic responses in prey and, by extension, in predator groups over time. Unfortunately, few case studies illustrate long‐term patterns in shelly fossil morphologies that may reflect the influence of predation throughout the Cambrian. More studies on phenotypic change in hard‐shelled lineages are needed to convincingly illustrate escalation and the responses of prey during the Cambrian.     

Optimal growth pattern of defensive organs: the diversity of shell growth among mollusks

Mollusks show a diversity of shell growth patterns. We develop a model for the dynamic resource allocation to defense organs and analyze it with the Pontryagin maximum principle. A typical optimal growth schedule is composed of the initial phase of soft-body growth without shell followed by a simultaneous growth of shell and soft body and finally the reproductive phase without growth (simultaneous shell growth). If the defensible predation risk is low or if the cost of defense is high, the optimal strategy is to have no shell (shell-less growth). If defensible predation pressure or general mortality differs before and after maturation, an additional three strategies, characteristic of the exclusive growth of shell or soft body, can be optimal (sequential shell growth, additional body-expansion growth, and additional callus-building growth). These optimal strategies are in accord with the patterns observed for mollusks. In particular, the growth strategies with exclusive growth phase of external shells are preferred when durophagous predation pressure after maturation is higher than that before maturation. This result explains the observation that many tropical gastropods with thickened shell lips spend their vulnerable juvenile phase in sheltered habitats.     

DUROPHAGOUS PREDATION ON MIDDLE JURASSIC MOLLUSCS, AS EVIDENCED FROM SHELL FRAGMENTATION

Abstract:  Durophagous (shell-crushing) predation is known from the beginning of the Phanerozoic, but it has been suggested that modern intensity was not reached until the Late Cretaceous and Early Cenozoic, when specialized marine durophagous taxa increased in diversity. In this paper, evidence of durophagous predation on Middle Jurassic communities of molluscan prey is presented on the basis of distinct accumulations of fossil remains in the Polish Jura (south-central Poland) that contain characteristic, angular shell fragments with sharp, non-abraded margins. The diverse fossil content of the accumulations studied, consisting of either benthic or nektic/nekto-benthic taxa, indicates that the potential predatory taxon was an opportunistic generalist, most probably fish. On the basis of taphonomic observations, the faunal accumulations are interpreted to represent regurgitated remains (pellets). The common occurrence of such accumulations in the Middle Jurassic clays of the Polish Jura indicates that durophagous predation has been intense since the mid-Mesozoic, at least locally.     

Poachers and Forest Fragmentation Alter Seed Dispersal,Seed Survival,and Seedling Recruitment in the Palm Attalea butyraceae,with Implications for Tropical Tree Diversity1

We examined the interaction between a palm and two bruchid beetles along with several mammal species to explore how poachers and habitat fragmentation may indirectly alter the spatial pattern of seed dispersal, seed predation, and seedling recruitment in central Panama. The large, stony endocarps of Attalea butyraceae decay slowly and bear distinctive scars when opened by rodents or beetles. We determined the final distance between endocarps and reproductive trees (which we call an ecologically effective dispersal distance), the predation status of each endocarp, and the distance between seedlings and reproductive trees. The 68 focal trees were divided among 14 sites and four levels of anthropogenic disturbance. Levels of disturbance included full protection from poachers, light and heavy pressure from poachers, and small island habitat fragments. Ecologically effective seed dispersal distances were greatest for protected sites, intermediate for lightly poached sites, and shortest for heavily poached sites and habitat fragments. Seed predation by rodents increased with distance to the nearest reproductive Attalea and was greatest for fully protected sites, intermediate for lightly poached sites, and least for heavily poached sites and habitat fragments. Seed predation by beetles reversed the patterns described for seed predation by rodents. Total seed predation by beetles and rodents combined was independent of distance, greatest for fully protected sites, and lower for poached sites and habitat fragments. Seedling densities were always greatest close to reproductive trees; however, the increase in seedling densities close to reproductive trees was minimal for fully protected sites, clearly evident for poached sites, and pronounced for habitat fragments. Increased seedling recruitment near conspecific trees may in time reduce tree diversity where humans disrupt mammal communities.     

Anatomy of a cline: dissecting anti‐predatory adaptations in a marine gastropod along the U.S. Atlantic coast

The scope of anti‐predatory adaptation is expected to be greater in warm than in cold environments. High temperatures lower the costs associated with the production and maintenance of energetically expensive traits and enable ecological interactions to intensify. We tested this hypothesis by characterizing the expression of anti‐predatory morphology within a marine gastropod species (the knobbed whelk Busycon carica) over a large (> 1400 km) geographic area that spans more than 10°C annual temperature variation. We also conducted experimental predation studies with a powerful durophagous predator, the stone crab Menippe, to verify the anti‐predatory advantages of a heavily ornamented shell morphology (e.g. increased thickness, pronounced spines), and we used repair scar data to assess clinal variation in selective pressure from predators. We predicted that repair scar rates would be greatest in warm southernmost latitudes, and that expression of energetically costly anti‐predatory morphology would peak in concert with elevated predation pressures. Experiments confirmed that whelks with energetically costly, heavily ornamented shells had higher survivorship rates than those with weakly ornamented shells. As predicted, we also found that the expression of anti‐predatory traits was greatest in the southern part of B. carica's range. After standardizing shells for size, shape, and exposure time to enemies, repair scar rates also peaked to the south. Taken together, these results suggest that the expression of anti‐predatory traits along the geographic cline is governed by the interaction of two selective factors: temperature and predation, with the former acting as the ultimate control on the scope of adaptation both by escalating predation pressure in the southern part of B. carica's range and by physically limiting (to the north) and facilitating (to the south) the production of anti‐predatory traits. Feedbacks between temperature and predation thus causally interact to enable and drive, respectively, the observed geographic cline in energy‐intensive anti‐predatory shell traits.     

Observations of predation by corvids at a Marbled Murrelet nest

ABSTRACT.   Unlike other alcids, Marbled Murrelets ( Brachyramphus marmoratus ) typically nest solitarily on large platforms in the upper canopy of old-growth coniferous trees. Although Marbled Murrelets exhibit characteristics that minimize the risk of predation, habitat fragmentation has likely increased the risk of nest predation by corvids. Using a video camera at a nest in northern California, we observed nest fates for 4 yr (2002–2005). These recordings revealed two cases of egg predation by a Steller's Jay ( Cyanocitta stelleri ) and a Common Raven ( Corvus corax ), respectively. In both instances, the egg was carried from the nest site, leaving no evidence that nesting had occurred. Our observations revealed (1) the need to be conservative in estimates of nesting attempts and nesting success of Marbled Murrelets based only on the presence or absence of eggshell fragments or feces, (2) that not all predation attempts were successful, and (3) that murrelets may be more susceptible to predation early in the incubation period when adults may be less attentive to eggs and, after hatching, when young are less than 14 d old. We encourage efforts to minimize anthropogenic activities that may increase local corvid densities or disturb murrelets during the early incubation period.     

Increased Productivity and Reduced Seed Predation Favor a Large‐seeded Palm in Small Atlantic Forest Fragments

Large‐seeded plants are especially vulnerable to the loss of seed dispersers in small forest fragments. The palm Attalea humilis goes against this trend by reaching high abundances in small remnants. Productivity, seed dispersal and seed predation of A. humilis were investigated in two large (2400 and 3500 ha) and three small (19, 26 and 57 ha) Atlantic Forest fragments in southeastern Brazil. Palms in the small fragments produced more female inflorescences, resulting in a higher fruit production in these places. Seed dispersal rates were higher in the large fragments, where scatter hoarding was more frequent. Scolytine beetles were the main seed predators and damaged a larger number of seeds in small fragments, but predation by rodents and bruchine beetles was low irrespective of fragment size. As scolytines do not necessarily kill the seeds, low predation by bruchines and rodents, together with its own high productivity, allow A. humilis to be more abundant in small fragments despite the scarcity of its main dispersers. This increased abundance, by its turn, can increase competitive interactions between A. humilis and other plants in small fragments. Thus, abundance patterns of A. humilis are a good example of fragmentation affecting the balance of ecological interactions in a complex way, emphasizing the role of preserving ecological processes for conserving biodiversity in fragmented tropical landscapes. Abstract in Portuguese is available at http://www.blackwell‐synergy.com/loi/btp .     

Early Cambrian record of failed durophagy and shell repair in an epibenthic mollusc

Predation is arguably one of the main driving forces of early metazoan evolution, yet the fossil record of predation during the Ediacaran-Early Cambrian transition is relatively poor. Here, we present direct evidence of failed durophagous (shell-breaking) predation and subsequent shell repair in the Early Cambrian (Botoman) epibenthic mollusc Marocella from the Mernmerna Formation and Oraparinna Shale in the Flinders Ranges, South Australia. This record pushes back the first appearance of durophagy on molluscs by approximately 40Myr.     

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.     

Oral shelling within an adaptive radiation of pupfishes: Testing the adaptive function of a novel nasal protrusion and behavioural preference

Dietary specialization on hard prey items, such as mollusks and crustaceans, is commonly observed in a diverse array of fish species. Many fish consume these types of prey by crushing the shell to consume the soft tissue within, but a few fishes extricate the soft tissue without breaking the shell using a method known as oral shelling. Oral shelling involves pulling a mollusc from its shell and it may be a way to subvert an otherwise insurmountable shell defence. However, the biomechanical requirements and potential adaptations for oral shelling are unknown. Here, we test the hypothesis that a novel nasal protrusion is an adaptation for oral shelling in the durophagous pupfish (Cyprinodon brontotheroides). We first demonstrate oral shelling in this species and then predict that a larger nasal protrusion would allow pupfish to consume larger snails. Durophagous pupfish are found within an endemic radiation of pupfish on San Salvador Island, Bahamas. We took advantage of closely related sympatric species and outgroups to test: (a) whether durophagous pupfish shell and consume more snails than other species, (b) if F1 and F2 durophagous hybrids consume similar amounts of snails as purebred durophagous pupfish, and (c) if nasal protrusion size in parental and hybrid populations increases the maximum size of consumed snails. We found that durophagous pupfish and their hybrids consumed the most snails, but did not find a strong association between nasal protrusion size and maximum snail size consumed within the parental or F2 hybrid population, suggesting that the size of their novel nasal protrusion does not provide a major benefit in oral shelling. Instead, we suggest that the nasal protrusion may increase feeding efficiency, act as a sensory organ, or is a sexually selected trait, and that a strong feeding preference may be most important for oral shelling.     

Viability of ecological processes in small Afromontane forest patches in South Africa

Abstract The conservation of biodiversity is dependent on protecting ecosystem‐level processes. We investigated the effects of fragment size and habitat edge on the relative functioning of three ecological processes – decomposition, predation and regeneration of trees – in small Afromontane forests in KwaZulu‐Natal, South Africa. Ten sampling stations were placed in each of four forest categories: the interior of three large indigenous forest fragments (100 m from the edge), the edges of these large fragments, 10 small indigenous fragments (<1 ha) and 10 small exotic woodlands (<0.5 ha). Fragment size and edge effects did not affect the abundance of the amphipod Talitriator africana, a litter decomposer, and overall dung beetle abundance and species richness significantly. Bird egg predation was marginally greater at large patch edges compared with the other forest categories, while seed predation did not differ among forest categories. Tree seedling assemblage composition did not differ significantly among large patch interiors and edges, and small indigenous fragments. Sapling and canopy assemblage composition each differed significantly among these three indigenous forest categories. Thus, while tree recruitment was not negatively affected by patch size or distance from the edge, conditions in small fragments and at edges appear to affect the composition of advanced tree regeneration. These ecological processes in Afromontane forests appear to be resilient to fragmentation effects. We speculate that this is because the organisms in these forests have evolved under fragmented conditions. Repeated extreme changes in climate and vegetation over the Pleistocene have acted as significant distribution and ecological extinction filters on these southern hemisphere forest biota, resulting in fauna and flora that are potentially resilient to contemporary fragmentation effects. We argue that because small patches and habitat edges appear to be ecologically viable they should be included in future conservation decisions.     

Forest fragmentation relaxes natural nest predation in an Afromontane forest

Nest predation is widely regarded as a major driver underlying the population dynamics of small forest birds. Following forest fragmentation and the subsequent invasion by species from non-forested landscape matrices, shifts in predator communities may increase nest predation near forest edges. However, effects of human-driven habitat change on nest predation have mainly been inferred from studies with artificial nests, despite being regarded as poor surrogates for natural ones. We studied variation in predation rates, and relationships with timing of breeding and characteristics of microhabitats and fragments, on natural white-starred robin Pogonocichla stellata nests during three consecutive breeding seasons (2004–2007) in a Kenyan fragmented cloud forest. More than 70% of all initiated nests were predated during each breeding season. Predation rates nearly quadrupled between the earliest and the latest nests within a single breeding season, increased with distance to the forest edge, and decreased with the edge-to-area ratio of forest fragments. These spatial relationships oppose the traditional perception of edge and fragmentation effects on nest predation, but are in line with results from artificial nest experiments in other East African forests. In case of inverse edge and fragmentation effects on nest predation, such as shown in this study, species that tolerate edges for breeding may be affected positively, rather than negatively, by forest fragmentation, while the opposite can be expected for species restricted to the forest interior. The possibility of inverse edge effects, and its conservation implications, should therefore be taken into account when drafting habitat restoration plans.     

Predation by blue crabs, Callinectes sapidus, on rapa whelks, Rapana venosa: possible natural controls for an invasive species?

Blue crabs Callinectes sapidus are voracious predators in Chesapeake Bay and other estuarine habitats. The rapa whelk Rapana venosa is native to Asian waters but was discovered in Chesapeake Bay in 1998. This predatory gastropod grows to large terminal sizes (in excess of 150 mm shell length (SL)) and has a thick shell that may contribute to an ontogenetic predation refuge. However, juvenile rapa whelks in Chesapeake Bay may be vulnerable to predation by the blue crab given probable habitat overlap, relative lack of whelk shell architectural defenses, and the relatively large size of potential crab predators. Feeding experiments using three size classes of blue crab predators in relation to a size range of rapa whelks of two different ages (Age 1 and Age 2) were conducted. Blue crabs of all sizes tested consumed Age 1 rapa whelks; 58% of all Age 1 whelks offered were eaten. Age 2 rapa whelks were consumed by medium (67% of whelks offered were eaten) and large (70% of whelks offered were eaten) blue crabs but not by small crabs. The attack methods of medium and large crabs changed with whelk age and related shell weight. Age 1 whelks were typically crushed by blue crabs while Age 2 whelk shells were chipped or left intact by predators removing prey. Rapa whelks less than approximately 35 mm SL are vulnerable to predation by all sizes of blue crabs tested. Rapa whelk critical size may be greater than 55 mm SL in the presence of large blue crabs indicating that a size refugia from crab predation may not be achieved by rapa whelks in Chesapeake Bay until at least Age 2 or Age 3. Predation by blue crabs on young rapa whelks may offer a natural control strategy for rapa whelks in Chesapeake Bay and other estuarine habitats along the North American Atlantic coast.     

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.     

Variation in shell morphology of Calliostoma zizyphinum (Gastropoda: Trochidae)

Differences in shell morphology in the intertidal prosobranchmollusc Calliostoma zizyphinum were studied from a number ofsites within four geographical regions of the British Isleswith varying exposures to wave action and crab predation. Meanvalues of damage scarring were highest in shells sampled fromStrangford Lough, Northern Ireland, and lowest in individualsfrom the Atlantic Coast. Shells collected from the Isle of Manwere smaller than those from either the Atlantic coast of Irelandor Strangford Lough. Shells from Strangford Lough had tallershells (higher aspect ratio) than shells from the County Downand Atlantic Coast and shells from the County Down coast weremore squat (lower aspect ratio) than those from all other areas.Shells from Strangford Lough were significantly thinner thanshells from all other geographical areas. The relationshipsbetween shell damage scarring and shell size and tallness werenot consistent among areas. Shells from Strangford Lough arenotable in showing a steep, positive relationship between shellsize and scarring and a steep, negative relationship betweenscarring and tallness. The unusual shell phenotypes observedin shells from Strangford Lough may be explained by rapid shellgrowth, which would not only allow Calliostoma to attain a sizerefuge from crab predators but also to recover successfullyfrom repeated crab attacks on the shell lip. Such a strategywould result in larger, thinner shells with a high number ofdamage scars. (Received 6 June 2006; accepted 20 December 2006)     

Traces of predation in the Cambrian

Series two marks a revolution in Cambrian predation when new predators and new predation methods appeared, which led to general increase in predation intensities and in the diversity of prey groups. The number of bored taxa and taxa with the predation scars is similar in the Cambrian. Most of the borings are associated with brachiopods and most of the scars with trilobites. Brachiopods, arthropods, molluscs, cnidarians and echinoderms were the most common prey in the Cambrian. The Cambrian record of predation is dominated by damage inflicted on brachiopods and trilobites. The fossils with predation signs are known from a majority of paleocontinents and all the Cambrian series.