Modern and fossil traces in terrestrial lithic substrates

A number of biogenic processes leads to the formation of distinctive traces in terrestrial lithic substrates. These include: burrowing by vertebrates in moderately lithified rocks; scraping by mammals; smoothing and polishing of limestone surfaces by the locomotion of mammals; excavation by bees, wasps, and ants producing nesting and dwelling tunnels; dissolution of limestone surfaces by terrestrial snails; endolithic activity of fungi, algae, and lichens on subaerial rock surfaces; root corrosion; etc. Processes of biochemical weathering, biophysical erosion, and enlargement of cracks and fissures by the pressure of plant roots do not leave distinctive traces and therefore lie outside the ichnological realm. The fossil preservation of terrestrial bioerosional traces is expected to be uncommon. Nevertheless, various possible means of preservation must be considered, such as by rapid burial by volcanic material, by fluvial sediments, by travertine or tufa, by loess, “conservation”; in caves, case hardening of surfaces of porous rocks, and preservation of subsoil traces below fossil soils.     

Lichen Bioerosion on Fossil Vertebrates from the Cenozoic of Patagonia and Antarctica

Different traces occur on fossil bones and teeth coming from the Early Miocene Gaiman Formation (Patagonia, Argentina). Most traces were attributed to the action of terrestrial and marine predators and scavengers. However, other traces on bones and teeth from this unit and one tooth from the Eocene La Meseta Formation (Antarctica) are attributed to chemical corrosion by lichens in recent times, that is, in a very late diagenetic time. The living lichens and calcium oxalate deposits occurring on the traces and their particular pattern indicates that they were not produced by vegetal roots. The lichens include reproductive structures which allowed a proper determination. A kind of corrosion pattern (Type 1) on bones and teeth from Patagonia is associated to Sarcogyne orbicularis Körber, Verrucaria sp. Schrad, and Buellia aff. punctiformis (Hoff.) Massal. The lichen Aspicilia aff. aquatica produced rounded holes on an Antarctic tooth (Type 2). On the same tooth, the epilithic lichen Caloplaca sp. Th. Fries did not leave any kind of mark on the enameloid.     

Phylogeny, speciation and species turnover. The case of the Mediterranean gastropods of genus Cyclope Risso, 1826

The genus Cyclope Risso, 1826 (family Nassariidae) has appeared in the fossil record since the Pliocene. Although it is still found today, the teleoconch morphology has never undergone modification, despite the fact that the protoconch morphologies of fossils (multispiral) and living forms (paucispiral) are different. They vary in their embryological and larval development and, hence, are two different species: C. migliorinii (Bevilacqua, 1928), the fossil species, and C. neritea (Linnaeus, 1758), the living species. We discuss the morphologic modifications in the evolution of this genus: the speciation that leads to its appearance and the speciation driving the Pliocene species to the living one. The order and the direction of these changes are based on phylogenetic analysis. No intermediate forms have been found showing a gradual morphological change that could have been worked by natural selection. Our analysis takes as the origin of the morphological novelties the genetic modifications in the ontogenetic processes which resulted in rapid and important phenotypic changes. Both speciation processes are sympatric cladogenetic. The changes that determine the appearance of the genus affect only the teleoconch, not the larval development. The modifications that lead from one species to the other, within the genus Cycope, affect the larval development exclusively. This points to a certain disconnection between the development of the embryo-larval phase and the young-adult formation, such that evolutionary processes could have occurred independently in different ontogenetic stages. The influence of larval ecology in relation to extinction of the ancestor and persistence of the derived species is also analysed. We hypothesize that climatic fluctuations may have affected the planktonic larvae of the fossil species, driving it to extinction. The living species, developing without the planktonic phase, would have resisted these climatic changes. We consider that the mechanisms described as drivers of the evolution of this genus can be of more general validity in prosobranch gastropods.     

Sponge borehole size as a relative measure of bioerosion and paleoproductivity

Bioerosion intensity has been proposed as a measure of paleoproductivity in fossil reefs, but it is difficult to measure directly because fossil corals are often incomplete and because it is difticult to infer the length of time a given coral was exposed to bioeroding organisms. Both nutrient availability and taphonomic factors can affect bioerosion intensity as measured in dead corals. Here, we examine these two effects separately using data from previous studies on bioerosion in modern and fossil corals. Size of individual sponge borings accurately reflects total bioerosion in modern massive and branching corals on the Great Barrier Reef. Total bioerosion in both massive and branching corals decreases outward across the continental shelf, paralleling trends in nutrient availability. Size of individual Cliothosa hancocki borings decreases across the shelf in branching Acropora but not in massive Porites. Fossil sponge borings Entobia convoluta and Uniglobites glomerata in massive corals from Oligocene and Miocene reefs in Puerto Rico are smallest in Oligocene shelf-edge reefs, intermediate in Oligocene patch reefs, and largest in Miocene patch reefs. Both facies-related influence, represented by Oligocene shelf-edge reefs vs. Oligocene patch reefs, and nutrient-related influence, represented by Oligocene vs. Miocene patch reefs, were reflected in the size of sponge boreholes. Size of sponge borings also varies among species of host corals, apparently in relation to skeletal architecture. Borehole size is inversely correlated with skeletal density as measured by the relative proportion of skeleton and pore space in transverse thin section. There is a weak positive correlation between borehole size and corallite diameter. These findings contradict reported positive correlations between total bioerosion and bulk density in modern corals. Borehole size appears accurately to reflect intensity of total internal bioerosion in fossil corals. Facies-controlled taphonomic overprints and influence of skeletal differences between coral species limit the use of sponge borehole size to a rough indicator of paleoproductivity in fossil coral reef environments.     

性畸变对腹足类生殖和种群的影响

具有内分泌干扰效应的三丁基锡能引起腹足类产生性畸变现象。在性畸变过程中 ,雌性个体会由于生殖孔口被前列腺取代或被输精管阻塞、贮精囊或卵囊腺开裂、卵囊腺内部被阻塞以及卵巢转化为精巢等多种原因而丧失生殖能力 ,甚至死亡。并由此引起雌、雄性比和幼、成年个体比的降低 ,导致种群衰退。有浮游幼体的种类可以通过外来种群的成功迁入使种群得以维持 ,而无浮游幼体的种类 ,由于幼体迁移能力差而最终导致种群的区域性灭绝。性畸变这种典型的功能效应对其他内分泌干扰物质的生态效应研究有启示作用。     

The palaeobiology of nerineacean gastropods

Amongst nerineacean gastropods which have been preserved in fine grained carbonate sediments, remnants of a calcite rod system contained within the helically coiled body chamber can frequently be found. The position of these rods, their petrography and the presence of side branches suggest that they represent the original duct system within the digestive gland/gonad complex of the gastropod. The characteristic internal spiral folds secreted by the nerineids were emplaced between the major lobes of the digestive gland/gonad complex, possibly at the expense of the nutrient storage capacity. The absence of folds at the aperture and apex, together with the origin of the superfamily in the Lias, indicates that folding was not developed as a protective adaptation against durophagous molluscivores. Instead, the deposition of calcium carbonate internally enabled these gastropods to exploit the food resources of carbonate substrates, initially infaunally and subsequently epifaunally. Most of this ecological diversification was attained during the Bathonian and from this time, the Nerineacea became prominent members of shallow water Mesozoic carbonate communities.     

Regulation of spiral growth in planorbid gastropods

Extensive experimentation has been performed on the planorbid Planorbarius metidjensis in order to determine which mechanism allows the snail to coil its shell regularly. Individuals of this species, like all Planorbidae, are permanently active and secrete their shells while crawling on the substrate. Experiments consisted of attaching weights to either side of the shell (which is carried almost vertically) in an umbilical position; these weights cause the shell to fall towards the substrate on the loaded side. It can be demonstrated, qualitatively and quantitatively, that during further growth the shell tube deviated initially (i.e. within the first half whorl after loading) towards the loaded side. In a later stage, when the animal is able to re-balance the shell-load complex by muscular activity, the shell tube gradually deviates away from the loaded side. This behaviour is to be expected if, after loading, secretion of the shell continued with the aperture parallel to the substrate and forming a constant angle with the direction of growth. The main implication is that in normal conditions the living posture largely controls the correct coiling of the shell. Minor experiments made with another planorbid species, Gyraulus laevis , confirm these conclusions. The growth pattern of planorbids requires that the snail has constant information on the orientation of the shell with respect to the substrate. This is permitted by the particular physiological ecology of this group, members of which, unlike terrestrial gastropods, are permanently active.     

Recolonization of a burned Mediterranean area by terrestrial gastropods

Wildfires are common natural perturbations in Mediterranean ecosystems. Their frequency and extent have changed in recent decades to become one of the main ecological problems for wildlife. The response of fauna to wildfires depends greatly on the life histories and biological traits of each species. Terrestrial gastropods have limited mobility, and their presence is restricted by the vegetal and abiotic characteristics of habitats. For this reason, they are expected to have a low ability to recolonize burned areas. We have explored their survivorship and recolonization patterns according to the cryptic-refuge and fire-edge models in a Mediterranean protected area affected by a large fire in August 2003. The low number of species recorded at burned sites demonstrates the negative effects of a wildfire on the richness of gastropod assemblages 4 years after the perturbation. However, the total number of living individuals did not vary between burned and unburned areas, suggesting an after-fire shift in dominant species from woodland to open-space species. Forest species with wide European distributions dominated in unburned sites, whereas open-space species and xerophytic Mediterranean species were present at burned sites. These differences were evident even at the burned sites closest to the unburned forest, suggesting low recolonization rates from the fire edge. By contrast, the abundance of xerophilous species as well as isolated records of mesophilous species in the burned areas suggests the survival of small populations and further recuperation after fire following the cryptic-refuge model.     

Bioerosion caused by foraging of the tropical chiton Acanthopleura gemmata at One Tree Reef, southern Great Barrier Reef

The bioerosive potential of the intertidal chiton Acanthopleura gemmata on One Tree Reef was determined by quantification of CaCO₃ in daily faecal pellet production of individuals transplanted into mesocosms after nocturnal-feeding forays. Mean bioerosive potential was estimated at 0.16 kg CaCO₃ chiton⁻¹ yr⁻¹. Bioerosion rates were estimated for populations on two distinct chiton habitats, reef margin (0.013 kg CaCO₃ m⁻² yr⁻¹) and beachrock platform (0.25 kg CaCO₃ m⁻² yr⁻¹). Chiton density on the platform was orders of magnitude greater than on the reef margin. The surface-lowering rate (0.16 mm m⁻² yr) due to bioerosion by the beachrock population is a substantial contribution to the total surface-lowering rate of 2 mm m⁻² yr⁻¹ previously reported for One Tree Reef across all erosive agents. At high densities, the contribution of A. gemmata to coral reef bioerosion budgets may be comparable to other important bioeroders such as echinoids and fish.     

A mineralogical method to determine cyclicity in the taphonomic and diagenetic history of fossilized bones

The study of authigenic minerals within the voids of a fossilized bone can reveal its diagenetic history. When the order of precipitation of minerals is plotted on an Eh/pH diagram any cyclicity in the diagenetic history is revealed. If one cycle is displayed then it can be assumed that the bone has been found in its original bed of deposition; if two cycles or more are revealed then reworking or environmental change may have taken place. This is demonstrated in a case study of two bones from the Wealden Group (Lower Cretaceous) from the Isle of Wight, UK.     

Large-scale terrestrial gastropod community composition patterns in the Great Lakes region of North America

Abstract: Previous ordination studies of land snail community composition have been limited to four or fewer habitat types from sites separated by no more than 300 km. To investigate the nature of large-scale patterns, North American land snail assemblages at 421 sites, representing 26 habitat types and covering a 1400 × 800 km area, were ordinated using global, nonmetric multi-dimensional scaling (NMDS). These data were then subjected to model-based cluster analysis and kmeans clustering to identify the main compositional groups and most important environmental covariables. Six primary compositional groups were identified. Three of these largely represent upland forest and rock outcrop sites, while the remaining largely represent either lowland forest, lowland grassland or upland grassland habitats. The geographical location and moisture level of sites also influences community composition. A strong compositional difference exists between sites having duff vs. turf soil surface layers. Only 8% of sites were improperly classified when soil surface architecture was used as the sole predictor variable. Fully 43% of taxa exhibited significant preferences towards one of these surface types, while only 15% of relatively common (10 + occurrence) taxa showed no preferences. Twelve groups of closely related taxa within the same genus had members that favoured different surface types, indicating that differential selection pressures have existed over evolutionary time scales. While turf faunas appeared unaffected by anthropogenic disturbance, duff faunas were strongly impacted, suggesting that their conservation will require protection of soil surface architecture.     

Bioerosion versus colonisation on Bivalvia: A case study from the Upper Miocene of Cacela (southeast Portugal)

A study of the bioerosion structures and the skeletobionts associated with the most common bivalves (infauna and epifauna) from the classic Upper Tortonian site of Cacela, Algarve region, SE Portugal, revealed 24 different ichnotaxa and five systematic groups of encrusters (Foraminifera, Annelida, Bryozoa, Balanomorpha and Bivalvia).Despite a relatively high ichnodiversity, the percentage of bioerosion in the specimens analysed is quite low (10-12%). This is explained by rapid sedimentation with only short periods of exposure on the sea-floor.The dominant bioerosion structures were linked to the boring activity of nonpredatory organisms. Algal microborings are the most common, followed by annelid borings (Caulostrepsis-Maeandropolydora), sponge borings (Entobia) and ctenostome bryozoans (Pinaceocladichnus).Spatial distribution of bioerosion structures and encrusters allow the reconstruction of three successive stages. The first was restricted to the biosubstrate lifetime, with structures showing a preferred orientation and situated exclusively on the outside of the shells. The second comprises the period immediately after death, with structures that extend outwards and start with the colonization of the interior of the valves, losing their initial orientation. The third stage relates to later postmortem colonisation, with structures on both sides of the valves and without a preferential orientation.     

Turritelline mass accumulations from the Lower Miocene of southern Germany: implications for tidal currents and nutrient transport within the North Alpine Foreland Basin

The mass occurrence of turritelline gastropod shells from the Lower Miocene of southern Germany allows for detailed studies of their palaeoecology, transport mechanisms, preservation potentials and the reconstruction of nutrient regimes. Changes in the fabric of the gastropod-dominated beds are used to reconstruct a generally deepening environment corresponding to the Lower Miocene transgression within the Upper Molasse Sea of the North Alpine Foreland Basin. The sedimentary succession ranges from chaotically arranged, densely packed and near-shore transported; wave-influenced deposits showing bimodal shell orientations; more widely dispersed shells showing a uni-directional orientation; and dispersed shells showing diverse orientations. The shells often show damage to the apex and aperture though it is not clear whether this is due to predation events, pagurisation or abrasion due to transport. An outstanding feature is the replacement of aragonite shells by calcite leading to internal vugs as well as modulating the outer shell surface morphology. The high density of turritelline gastropods indicates a nutrient-rich palaeoenvironment at the northern edge of the Molasse Sea.     

A review of the effects of temperature on the oxygen consumption of intertidal gastropods

A multiple regression analysis has been used to relate oxygen consumption, body weight, and temperature, for 8 species of gill-bearing intertidal gastropods. Using a standard sized animal, the oxygen consumption of the snails in sea water at each temperature is very similar and the analysis gives a Q₁₀ of 2.1. In air the mid and high shore species have similar rates of oxygen consumption to those in water and a Q₁₀ of 2.2. The low shore species show lower values for both aerial oxygen consumption and Q₁₀. Similar patterns have been found in a further 20 species.     

Bioerosion of oyster shells in brackish modern mangrove swamps,Nigeria

Studies on shells of the intertidal oyster Crassostrea tulipa cemented to aerial prop roots and stems of the mangroves Rhizo‐phora racemosa, R. harrisonii, and R. mangle from the Cross River and Qua Iboe River estuaries show that photosynthetic en‐dolithic cyanobacteria (blue‐greens) are the major bioerosional agent, affecting about 94% of the shells examined. Pblychaetes attacked less than 10% of these materials and thus have low bioerosional impact.

Herbivorous gastropods play a secondary role because, by grazing, they clear the shell surface of encrusting cyanobacteria and thus enhance the activity of boring forms. Where epilithic cyanobacteria have been removed, the gastropods sometimes leave faint grazing traces of low fossilization potential.

Microfloral boring activity is high at all stations, but the assemblage is of markedly low diversity compared with those of littoral and shallow sublittoral marine communities and may thus be useful as a paleoenvironmental tool. Bioerosional agents are directly or indirectly responsible for the disintegration of oyster shells, whose fragments are incorporated in muddy intertidal sediments.     

Structural features and taphonomic pathways of a high-biomass epifauna in the northern Gulf of Trieste, Adriatic Sea

Benthic ecologists and palaeoecologists usually associate soft bottoms with infaunal species. On the sublittoral muddy soft bottoms in the inner Gulf of Trieste, however, a complex epifauna is developed, whose biomass, structural features and taphonomy is investigated here. The total biomass amounted to an average of 556 g wet weight/m² and is strongly dominated by suspension feeders, followed by predators and deposit feeders. The biomass can be divided into two major groups: biomass on benthic islands (isolated and small-sized rockgrounds and shellgrounds which are embedded in or lie on the sediment) and sediment dwellers. The former category includes so-called multi-species clumps, which make up 92.5% of the total biomass. The latter category encompasses organisms that inhabit the sediment surface itself. The epigrowth on benthic islands makes up 84.6% of total epifaunal biomass and is exclusively represented by suspension feeders. Serpulids are strongly dominant, followed by ascidians, sponges, anemones and bivalves. The vagile organisms associated with multi-species clumps represent 7.9% of the total epifauna and are also mostly suspension feeders. The echino-derms Ophiothrix quinquetnaculata and Cucumaria planci are the two dominant forms, followed by crustaceans and echinoids. Soft-bottom dwellers represent only 7.5% of total epifaunal biomass and consist mainly of deposit feeders and predators. Three different post-mortem pathways can be recognized for the studied epifauna. Taphonomic loss due to selective preservation is the most important taphonomic process shaping the death assemblage and affects especially the soft-bodied epigrowth on benthic islands. Mineralized epigrowth and shelled soft-bottom dwellers are the main source of benthic islands. Vagile faunas on such islands, in contrast, are strongly affected by disarticulation / fragmentation and their body parts contribute considerably to the sediment composition. The death assemblage does not reflect the trend of low biomass near the shallow stations off the mouth of the Isonzo River and higher biomass at most stations positioned further away from the river and in deeper water (> 10 m), but acccurately reflects the borders of the epifauna, which coincide with the sedimentary facies and the preponderance of the suspension-feeding life habit.     

Anthropogenic impacts and historical decline in body size of rocky intertidal gastropods in southern California

Abstract The diverse fauna and flora of rocky intertidal ecosystems are being impacted by the activities of rapidly increasing coastal populations in many regions of the world. Human harvesting of intertidal species can lead to significant changes in body sizes of these taxa. However, little is known about the temporal trajectories of such size declines and more importantly, the long‐term effects of chronic human impacts. Furthermore, it is unclear whether sizes of species not directly targeted for harvesting are also declining through indirect effects. Here we use historical (extending back to 1869) and field survey data covering 200 km of mainland southern California coast to show that human activities have led to significant and widespread declines in body sizes of rocky intertidal gastropod species over the last century. These declines, initiated several decades ago, are continuing and contrary to expectation, they are not restricted to species harvested for human consumption. Data from the only national park in this area, where conservation laws are strictly imposed, demonstrate that negative ecological impacts can be ameliorated if existing laws are enforced.     

Infaunal or semi-infaunal bellerophont gastropods: analysis of Euphemites and functionally related taxa

Burrowing and plowing gastropods may have existed prior to the Mesozoic, contrary to the conservative tendency of categorizing Paleozoic archaeogastropods as herbivorous hardground dwellers. We propose that Euphemites and other bellerophontiform molluscs such as Praematuratroph and Beyrichidiscus make functional and paleoecological sense only if reconstructed with an internal shell adapted to an infaunal mode of life. Attributes diagnostic of a probable infaunal mode of life in fossil bellerophontiform molluscs include: (1) lack of apertural flare; (2) restricted aperture; (3) low rate of whorl expansion; (4) semi-radial aperture; (5) extensive secondary shell deposits; (6) absence of extensive collabral ornament; (7) dorsolateral or umbilical furrows; (8) color patterns indicative of mantle extension and retraction capabilities; (9) absence of shell breakage and repair; and (10) associated lithologies indicative of penetrable substrates such as mudstones. Niche diversity in the bellerophontacean molluscs was probably much greater than previously suspected. This is entirely consistent with their long geologic range. Most bellerophontaceans, particularly the Late Paleozoic forms, were probably either 'nestling' or semi-infaunal with the apertural margins enwrapped by mantle or mantle and foot. As such they may have been particularly susceptible to predation during the postulated Mesozoic increase in number of infaunal predators- a factor which may have been contributory to the bellerophontacean demise.