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.     

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.     

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.     

Can Naticid Gastropod Predators Be Identified by the Holes They Drill?

We tested the hypothesis that drillholes made by different species of predatory naticid gastropods can be differentiated by variability in the inner (IBD) and outer borehole diameters (OBD) of the holes they drill. We compared two samples of Mya arenaria that were drilled by different predators, Euspira heros and Neverita duplicata, under experimental conditions. Mean IBD:OBD ratio was significantly greater for holes drilled by Euspira compared to Neverita, indicating that Euspira drills a steeper drillhole than Neverita. We also found consistent differences between the two naticids for slopes of regression lines of IBD on OBD after standardization for predator size and prey size and thickness, with slopes for Euspira being steeper, but results were not statistically significant. However, the range of IBD:OBD ratios was wide and overlapped considerably for each species, which decreases confidence in assignment of individual drillholes to a particular predator species. At least in the case of these two naticid species, interspecific differences in variation of the inner and outer diameters of the holes they drill have limited utility in identifying the maker of individual boring traces in the fossil record.     

High frequency of drill holes in brachiopods from the Pliocene of Algeria and its ecological implications

The fossil record holds a wealth of ecological data, including data on biotic interactions. For example, holes in the skeletons of invertebrates produced by drilling activities of their enemies are widely used for exploring the intensity of such interactions through time because they are common and easily distinguished from non-biotic holes or holes produced by other types of interactions. Such drill holes have been described in numerous studies of Palaeozoic brachiopods but rarely in those focusing on brachiopods of the post-Palaeozoic, a striking pattern given that in the late Mesozoic and Cenozoic 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 Cenozoic, suggesting that this phenomenon may be more common than has been previously assumed. Here we report on drilled brachiopods from a Pliocene locality in Algeria where 90 of 261 (34.5%) specimens of Megerlia truncata show evidence of predatory drilling. These data confirm that Cenozoic drilling frequencies of brachiopods may be locally high and, when taken together with other published data, that drilling frequencies are highly heterogeneous in space and time.     

Drilling under threat: An experimental assessment of the drilling behavior of Nucella lamellosa in the presence of a predator

Using the drilling muricid, Nucella lamellosa (Gmelin 1791) and its prey, the mussel Mytilus trossulus (Gould 1850), the impact of a secondary predator, the crab Cancer gracilis, on drilling was investigated experimentally. The frequency of incomplete holes was compared under two conditions: (1) when the gastropod's natural predator, C. gracilis, was present and (2) when it was absent. The results indicate that the presence of a secondary predator can affect drilling activity, leading to a significant increase in the frequency of incomplete drill holes. The introduction of a secondary predator can also decrease the overall drilling frequency. The size distributions of completely and incompletely drilled mussels suggest that in the presence of the secondary predator the decision by the gastropod to either abandon or continue drilling its prey might be influenced by how much time it has already invested into drilling or the size of the prey item. These results are important for the ecological and evolutionary implications of incomplete drill holes frequencies, especially with regard for their use as proxies for evolutionary prey improvement.     

Effects of fire on the structure and diversity of a Spartina argentinensis tall grassland

Question: What are the effects of fire on the structure and the diversity of a Spartina ar gentinensis tall grassland in the short and medium run. S. argentinensis is the dominant species of tall grasslands on inland marshes of the Chaco‐Pampean region (Argentina), where spontaneous or man‐made fires are very frequent. Location: Federico Wildermuth Reserve (31°57′S; 61°23′W), Province of Santa Fe, Argentina, an area never ploughed that supported cattle until its exclusion in 1988. Methods: Vegetation was surveyed in randomly placed permanent plots using the Braun‐Blanquet cover‐abundance scale. The data were analysed by multivariate methods (PCA and MRPP) for synthesizing information and testing hypotheses. Results: Fire did not have a long‐lasting effect on the tall grassland. There was only a temporarily reduction of cover‐abundance of S. argentinensis which allowed an increase in the number of accompanying species such as Heliotropium curassavicum, Pluchea sagittalis, and Verbena litoralis and of some naturalised or weed species, such as Melilotus alba and Cirsium vulgare, respectively. Fire increased diversity, which remained relatively high for two to three years. Three years after the fire there were no significant differences on the amount of litter accumulated on burned and unburned plots. Conclusion: Fire should be considered an intrinsic part of the dynamics of S. argentinensis tall grassland.     

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.     

Drilling predation on the clypeasteroid echinoid Echinocyamus pusillus from the Mediterranean Sea (Giglio,Italy)

Drilling predation of cassid gastropods (tonnacean) on echinoids is common in marine environments but is rarely documented. Tests of the minute clypeasteroid Echinocyamus pusillus OF Müller (1776) were collected from the Mediterranean Sea (Isola del Giglio, Italy). Besides general morphology, features pertaining to the morphology and distribution of predatory boreholes were examined. Furthermore, borehole frequencies among different samples sites were compared. Cassid gastropods are assumed to be the originators of the boreholes. A total of 1061 tests were analysed for drilling rates with 15.3% drilled with predominantly single boreholes. The borehole morphology is strongly affected by the microstructure of the skeleton; the borehole outline is irregular if drilled within areas where ambulacral pores are present. Vertical borehole morphology is influenced by stereom density. The size frequencies of non-drilled and drilled specimens show significant differences. Comparisons of borehole size with test size show only a low correlation between predator and prey size. The distribution of boreholes shows a high site selectivity of the predator for the aboral side of the test and the petalodium.     

Stereotypic and size-selective predation in Polinices pulchellus (Gastropoda: Naticidae) Risso 1826

Polinices pulchellus were size-selective in their choice of Cerastoderma edule. Large predators (12-15.9 mm shell length) selected both larger and a wider size range of cockles than smaller individuals (4-11.9 mm shell length). Considerable overlap occurred in the sizes of cockles frequently drilled by different size classes of snails, indicating that certain sizes of cockles may be most profitable to a wide range of predator sizes. Consumption rates were highest during July and August and were closely related to seawater temperature. Inner and outer drill hole diameters were both correlated with predator size, and the morphology of the drill hole was geometrically similar across a range of predator sizes. Polinices pulchellus showed no preference for either the left or right valve and drilled most cockles in the centre of the shell valve. The relationship between the distance of the drill hole from the umbo and prey size was unaffected by predator size, such that predators of different sizes were not found to drill cockles in different positions. When disturbed during drilling, incomplete drill holes were abandoned and, when drilling resumed, it occurred in new locations on the surface of the shell valve. The findings of this study highlight the stereotyped nature of drilling behaviour seen in the family Naticidae.     

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.     

Pulling or drilling, does size or species matter? An experimental study of prey handling in Octopus dierythraeus ()

The influence of both predator and prey size on the shift from a pulling to a drilling predatory response was examined in the intertidal octopus Octopus dierythraeus, using an experimental program. Additionally, selective drilling, where particular regions of the prey are targeted, was examined for a variety of bivalve and gastropod prey. O. dierythraeus always initially attempted to pull bivalves apart. Shells that were eventually drilled were always subjected to significantly more pulling attempts than those that could be pulled apart, indicating that octopus are willing to expend more energy to access the flesh quickly. There was no defined threshold where bivalve size caused an octopus to switch from a pulling to a drilling response. Instead, there was a broad size range where the octopus could adopt either handling method and it varied for each individual. Octopus may only able to pull open bivalves before the molecular ratchet or ‘catch’ mechanism that many bivalves possess is engaged. This might explain the lack of a relationship between either octopus or bivalve size and the success of pulling, as it is likely that when the bivalves were presented to individual octopus they were either setting the ‘catch’ mechanism, or had already engaged it. O. dierythraeus demonstrated selective drilling on a variety of molluscan prey, with penetration sites differing between prey species. O. dierythraeus targeted the valve periphery, which was the thinnest part of the shell, therefore minimizing handling time. O. dierythraeus always drilled gastropods, but did not target the thinnest regions of the shells, with drill site varying according to the morphology of the prey. Elongate species with pronounced aperture lips were drilled in the apical region, close to the columella on the side of the opercula whereas nonelongate species were drilled immediately above the aperture. The location of drilling sites may represent a trade-off between targeting the most effective places to inject paralyzing secretions and the mechanically simplest places to drill.     

Dynamics of pleustonic ostracod populations in small ponds on the Island of Martín García (Río de la Plata,Argentina)

The biogeography and ecological preferences of Neotropical freshwater ostracods are poorly known, and more so the dynamics of populations and habitat selection of species living in pleustonic environments of temporary ponds. In the present survey we analyze the population changes of ostracods living in pleustonic environments of small freshwater bodies on Martín García Island (Río de la Plata, Argentina). Between June 2005 and June 2007, monthly samples of floating vegetation from eight different ponds on the island were collected, and limnological parameters were measured in situ. The results of multivariate logistic regression showed that the presence of ostracods was significantly related to high dissolved oxygen content and high water temperature. In addition, multivariate regression analysis indicated that, when ostracods were present, their total abundance was negatively related to floating vegetation dry weight. Four ostracod species were found: Strandesia bicuspis, Chlamydotheca incisa, Cypridopsis vidua, and Bradleytriebella trispinosa. The seasonal variation in abundances indicated that populations of the most common species, S. bicuspis and C. incisa, were denser during the summer and autumn months. The results of canonical correspondence analysis showed that individuals of S. bicuspis were more abundant at higher temperatures and lower conductivity than C. incisa. Further research is needed to clarify the observed negative correlation between floating vegetation dry weight and ostracod density and the possible differential thermal preference of the two species studied.     

Attack responses of the southern Australian whelk, Lepsiella vinosa (Lamarck, 1822) (Gastropoda: Muricidae), to novel bivalve prey: an experimental approach

In their native ranges, muricid gastropods feed on similar prey, often bivalves and barnacles, which they usually drill. Throughout its wide southern Australian distribution, the intertidal Lepsiella vinosa feeds on a range of prey from barnacles and littorinid gastropods in the southeast to mussels in the southwest. A number of muricids have been introduced throughout the world, either with oysters or in ship ballast water. In their new environments, they switch to native prey but their feeding responses to them have never been studied in the laboratory. The object of this study was to study the feeding of L. vinosa on a suite of non-native species. Australian Lepsiella vinosa was taken to Hong Kong, offered five different possible prey species and allowed to feed to satiation for many weeks. Replacement of consumed prey items by similar-sized conspecifics was undertaken until trends emerged. Lepsiella vinosa readily attacked thick- and thin-shelled bivalves from Hong Kong’s sandy beaches, Anomalocardia squamosa and Caecella chinensis, respectively, and from rocky shores, Septifer virgatus and Hormomya mutabilis, again respectively. It attacked them all, as it does its major prey item, Xenostrobus inconstans, in its native southwestern Australia, by either drilling or marginal probing with its proboscis. It also preferred intermediate sized prey (10–15 mm shell length), as with its natural prey. It quickly attacked the sandy shore species, and Hormomya mutabilis and Mytilopsis sallei, the latter two being closely similar in shell form and size to its natural prey X. inconstans. Hormomya mutabilis was the most favored prey, and was most similar in shell form and thickness to X. inconstans. This study therefore suggests that if introduced elsewhere, L. vinosa could radically affect intertidal community structure.     

Survival and repair of surgical and natural shell damage in the articulate brachiopod Terebratulina retusa (Linnaeus)

Living specimens of Terebratulina retusa from the Firth of Lorn, Scotland, were surgically damaged by drilling 2 mm diameter holes or narrow slits one cm long in the anterior portion of one valve, by bevelling the anterior margin of both valves, or by amputation of the anterior third of one valve. These injuries to the shell and mantle simulated the type of repaired shell damage seen in Paleozoic species, i.e., scalloped, divoted, cleft, and embayed valves. Less than ten percent of the 200 damaged specimens survived until the 25th week after surgery. Specimens of T. retusa showed the ability to repair drill holes, slits, and bevelled anterior shell regions, but not the most severe damage, i.e., amputations of the anterior third of one valve. Shell‐repair was initiated in the fourth week after surgery by the development of a membrane across the wound. The development of caeca in the new shell layer secreted to plug the drill holes became apparent by the eighth week. The punctate pattern was complete in the new, translucent shell material of bevelled and drilled specimens by the 25th week following surgery. Failure of any specimens to survive amputation of the anterior portion of a valve for more than seven weeks after surgery, and the absence of initiation of the repair process, suggests that terebratulids do not have the tolerance for, nor the ability to repair, the severe injuries (embayed valves) which were sustained and mended by extinct strophomenids.     

Intense drilling in the Carboniferous brachiopod Cardiarina cordata Cooper, 1956

The brachiopod Cardiarina cordata, collected from a Late Pennsylvanian (Virgilian) limestone unit in Grapevine Canyon (Sacramento Mts., New Mexico), reveals frequent drillings: 32.7% (n = 400) of these small, invariably articulated specimens (<2 mm size) display small (<0.2 mm), round often beveled holes that are typically single and penetrate one valve of an articulated shell. The observed drilling frequency is comparable with frequencies observed in the Late Mesozoic and Cenozoic. The drilling organism displayed high valve and site selectivity, although the exact nature of the biotic interaction recorded by drill holes (parasitism vs. predation) cannot be established. In addition, prey/host size may have been an important factor in the selection of prey/host taxa by the predator/parasite. These results suggest that drilling interactions occasionally occurred at high (Cenozoic-like) frequencies in the Paleozoic. However, such anomalously high frequencies may have been restricted to small prey/host with small drill holes. Small drillings in C. cordata, and other Paleozoic brachiopods, may record a different guild of predators/parasites than the larger, but less common, drill holes previously documented for Paleozoic brachiopods, echinoderms, and mollusks.     

Functional significance of Micraspis discolor (F.) (Coccinellidae: Coleoptera) in rice ecosystem

Coccinellids are key predators that are conserved and augmented in agricultural ecosystems, to achieve biological control of pests. Actual quantification of field predation has not been attempted for many of the beneficial coccinellids. Numerous reports show coccinellids as opportunistic, feeding on a variety of food material in addition to their preferred prey. Micraspis discolor is the most abundant species of coccinellid in rice ecosystems and touted as a biocontrol option for brown planthopper (BPH), Nilaparvata lugens (Stal), a key pest of rice. However, it has been reported as both entomophagous and phytophagous. Native polyacrylamide gel electrophoresis (PAGE) was used to separate esterases from whole‐body homogenates of Micraspis and its prey viz., green leafhopper (GLH) Nephotettix virescens (Distant), BPH N. lugens, whitebacked planthopper (WBPH) Sogatella furcifera (Horvath), aphid Rhopalosiphum padi L., thrips, Haplothrips sp., and pollen. Field‐collected beetles showed a range of bands, some corresponding with pollen and GLH, while others were different from prey offered, indicating a wider range of prey spectrum than envisaged. Feeding preference studies confirmed a preference for pollen and GLH in no‐choice (H = 20.724; P = 0.001) and multiple‐choice tests (H = 20.52; P < 0.001) and a significant preference for pollen over all insects offered in the paired‐choice test (t = 5.099; P = 0.007). The abundance of adult M. discolor in rice at flowering phase does not correspond to prey abundance in the field but rather reflects an inclination to pollen feeding more than entomophagy.     

Traces of predation/parasitism recorded in Eocene brachiopods from the Castle Hayne Limestone,North Carolina,USA

Schimmel, M., Kowalewski, M. & Coffey, BP. 2011: Traces of predation/parasitism recorded in Eocene brachiopods from the Castle Hayne Limestone, North Carolina, USA. Lethaia, Vol. 45, pp. 274–289. The Castle Hayne Limestone (Middle Eocene, North Carolina), noted for its diverse macro‐invertebrate fossils, was sampled to assess if Early Cenozoic brachiopods from eastern North America record any traces of biotic interactions. Systematic surveys of two North Carolina quarries yielded 494 brachiopods dominated by one species: Plicatoria wilmingtonensis (Lyell and Sowerby, 1845). Despite subtle variations in taphonomy, taxonomy and drilling patterns, the two sampled quarries are remarkably similar in terms of quantitative and qualitative palaeoecological and taphonomic patterns. In both quarries, brachiopods contain frequent drillholes (24.5% specimens drilled). The majority of drillholes were singular, perpendicular to shell surface and drilled from the outside. Ventral valves were drilled slightly more frequently than dorsal ones, but site‐selectivity in drilhole location was not evident. Larger brachiopods were drilled significantly more frequently than smaller ones. However, drillhole diameter did not correlate with brachiopod size. The drillholes are interpreted as records of ‘live‐live’ biotic interactions, representing either predatory attacks or parasitic infestations or a combination of those two types of interactions. A notable fraction of specimens bear multiple drillholes, which is consistent with either parasitic nature of interactions or frequent failed predatory events. The high drilling frequency reported here reinforces other reports (from other continents and other epochs of the Cenozoic), which suggest that brachiopods may be an important prey or host of drilling organisms in some settings. The number of case studies reporting high frequencies of drilling in brachiopods is still limited and thus insufficient to draw reliable generalizations regarding the causes and consequences of these occasionally intense ecological interactions. □Brachiopods, drilling parasitism, drilling predation, Eocene, North Carolina, taphonomy.     

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.     

Opposing deer and caterpillar foraging preferences may prevent reductions in songbird prey biomass in historically overbrowsed forests

Overbrowsing by ungulates decimates plant populations and reduces diversity in a variety of ecosystems, but the mechanisms by which changes to plant community composition influence other trophic levels are poorly understood. In addition to removal of avian nesting habitat, browsing is hypothesized to reduce bird density and diversity through reduction of insect prey on browse‐tolerant hosts left behind by deer. In this study, we excluded birds from branches of six tree species to quantify differences in songbird prey removal across trees that vary in deer browse preference. Early in the breeding season, birds preyed on caterpillars at levels proportional to their abundance on each host. Combining these data with tree species composition data from stands exposed to experimentally controlled deer densities over 30 years ago, we tested whether overbrowsing by white‐tailed deer reduces prey biomass long after deer densities are reduced. Our analysis predicts total prey availability in the canopy of regenerating forests is fairly robust to historic exposure to high deer densities, though distribution of prey available from host species changes dramatically. This predicted compensatory effect was unexpected and is driven by high prey abundance on a single host tree species avoided by browsing deer, Prunus serotina. Thus, while we confirm that prey abundance on host trees can act as a reliable predictor for relative prey availability, this study shows that quantifying prey abundance across host trees is essential to understanding how changes in tree species composition interact with ungulate browse preference to determine prey availability for songbirds.