Determination of a Late Miocene rocky palaeoshore by bioerosion trace fossils from the Bozcaada Island, Çanakkale,Turkey

Bioerosion is a common process in hard substrates. This study introduces an example from the rocky palaeoshore cropping out at a sea cliff on the Bozcaada Island. It includes bioerosion trace fossils preserved in limestone boulders of the shallow marine and lacustrine Alcitepe Formation of Late Miocene age. The ichnotaxa include borings produced by duraphagous drillers (Oichnus isp.), phonorids (cf. Conchotrema isp.), clionid sponges (Entobia cf. goniodes, Entobia geometrica, Entobia laquea, Entobia ovula, E. cf. solaris, Entobia isp.), endolithic bivalves (Gastrochaenolites torpedo, Gastrochaenolites lapidicus, Gastrochaenolites isp., Phrixichnus isp.), polychaete annelids (Maeandropolydora isp., Maeandropolydora sulcans, Maeandropolydora decipiens, Caulostrepsis taeniola, Caulostrepsis isp.), echinoids (cf. Circolites isp.) and spinculid worms (cf. Trypanites isp.). Barnacles are also common as encrusters. The borings can be ascribed to the Gastrochaenolites-Entobia assemblage, which is typical of Neogene rocky-shores. They belong to the Entobia ichnofacies indicating various conditions of light, energy, and depth. Therefore they can reveal environmental changes and play an important role in forming palaeo-rocky shores and wave-cut platforms during marine trangressive events.     

Ichnofacies and microbial build-ups on Late Miocene rocky shores from Menorca (Balearic Islands), Spain

Angular unconformites between Jurassic and Miocene strata are exposed in the sea cliffs of Cala Cigonya on the northwest coast of Menorca in the Balearic Islands of Spain. The geological discontinuities represent rocky shores on opposite sides of a former headland with 15 m of topographic relief. On the east flank, Jurassic dolomite is overlain by Upper Miocene (Tortonian to Messinian) breccia and laminated limestone. Here, a partially exhumed dolomite surface records Miocene bivalve borings of the ichnospecies Gastrochaenolites torpedo and G. lapidicus that achieved a density of >1,000 borings/m². Other associated traces include sponge borings (Entobia isp.) and polychaete borings (Caulostrepsis isp.). A breccia deposit 0.8 m thick was derived from the underlying dolomite and angular clasts still retain evidence of bivalve borings. Above follows a succession of laminated limestone beds more than 5 m thick, including some levels with dome-shaped stromatolites and other horizons with reworked dolomite clasts. Thin-section analysis of the laminated limestone reveals dark and light couplets 0.2 mm thick consistent with microbial origins. In contrast, the west flank was buried by coarse sandstone and laminated sediments. Here, dwelling structures of regular echinoids (Circolites kotoncensis) are the dominant traces preserved on the dolomite surface, reaching a maximum density of 66 borings/m². Associated borings include Entobia geometrica as well as rare traces of Gastrochaenolites isp. and Trypanites isp. Notable for the absence of a basal Miocene breccia, the west flank is interpreted as a sheltered rocky shore coeval with an exposed rocky shore on the east flank. Today, heavy surf on the north coast of Menorca is related to the Tramontana winds that blow out of Spain during winter months. Similar atmospheric circulation patterns must have prevailed during the Late Miocene, but the replacement of ichnofacies by microbial build-ups resulted from increased salinity during the Messinian crisis.     

Miocene intertidal zonation on a volcanically active shoreline: Porto Santo in the Madeira Archipelago,Portugal

Santos, A., Mayoral, E.J., da Silva, C.M., Cachão, M., Johnson, M.E. & Baarli, B.G. Miocene intertidal zonation on a volcanically active shoreline: Porto Santo in the Madeira Archipelago, Portugal. Lethaia, Vol. 44, pp. 26–32. Short‐term biological colonization of rockgrounds on the basaltic shorelines of oceanic islands has, as yet, been poorly explored. A Miocene sea cliff on Ilhéu de Cima off Porto Santo in the Madeira Archipelago of Portugal provides a case study showing intertidal zonation with two types of barnacles, serpulid worm tubes, two coral species, epifaunal bivalves and the trace fossils of endolithic bivalves. Large barnacles (Balanus sp.) and serpulids are limited to the upper 400 mm of a basalt cliff of 1.6 m in height. Small barnacles, possibly of the same species, extend to the base. The upper half includes the corals Isophyllastrea orbignyana and Tarbellastraea reussiana, to which many small, coral‐inhabiting, barnacles (Ceratoconcha costata) are fixed. Borings identified as Gastrochaenolites torpedo appear through the bottom two‐thirds of the cliff face. Rarely, Gastrochaenolites lapidicus is exposed in longitudinal section with borings up to 45 mm deep in solid basalt. Epifaunal bivalves, such as Spondylus sp., are limited to a middle zone. Associated with the sea cliff is an outer platform on which a multitude of T. reussiana colonies occur in growth position. The corals exhibit planar erosion over180 m². The shelf was faulted and cut by a basalt dike prior to the brief recolonization of I. orbignyana, found attached to low fault scarps. Habitation of the sea cliff was facilitated by rising sea level, but abruptly terminated by burial under volcanoclastic ejecta. □Basalt bioerosion, coastal dynamics, Ilhéu de Cima (Porto Santo), Miocene intertidal zonation, volcanogenic perturbations.     

Entobia exogyrarum (Frič, 1883) from the Upper Cretaceous of the Bohemian Cretaceous Basin

The validity of the little-known ichnospecies Entobia exogyrarum (Fri?) is verified. Shells of an oyster, Rhynchostreon suborbiculatum (Lam.), represent the substrate for the sponge borings. The borings occur in many Upper Cenomanian to Middle Turonian localities of the Bohemian Cretaceous Basin. This study revealed that the sponges attacked shells of living oysters. Entobia exogyrarum (Fri?) also represents one of the shallowest occurrences of Entobia borings in the Upper Cretaceous rocks.     

Borings in mobile clasts from Eocene conglomerates of Northern Dalmatia (Coastal Dinarides, Croatia)

Summary Bored clasts occur in Eocene conglomerates deposited in the upper shoreface and beachface settings of the Dinaric foreland basin. The trace fossil assemblage consists ofGastrochaenolites, Trypanites, and possibly some other ichnotaxa and may be compared to theTrypanites Ichnofacies. The preservation characteristics of the borings reflect many stages of colonisation/boring and abrasion. The removal of shells of the boring bivalves, the different depths of the abrasional truncation of borings, and the predominant preservation of the largest excavations (Gastrochaenolites) in the ichnocoenosis are related to repeated phases of abrasion, caused by the mobility of clasts. Coastal gravel is a specific variant of hard substrates, whose mobility controls the colonisation of borers, the type of assemblage and its preservation potential.     

Rocky-shore unconformities marking the base of Badenian (Middle Miocene) transgressions on Mt. Medvednica basement (North Croatian Basin,Central Paratethys)

Badenian (Middle Miocene) transgressive deepening-upward successions located in the NE part of Mt. Medvednica (North Croatian Basin, Pannonian Basin System) unconformably overlie Mesozoic basement. Triassic and Upper Cretaceous limestone pebbles, cobbles, and boulders of the Badenian basal conglomerates display abundant in situ bivalve borings of Gastrochaenolites and sponge borings of Entobia. This Gastrochaenolites-Entobia ichnoassemblage is related to the Entobia subichnofacies of the Trypanites ichnofacies, characterizing littoral rocky-shore environments (wave-cut platforms and marine transgressive surfaces with a low or null rate of sedimentation). Gastrochaenolites torpedo, Gastrochaenolites lapidicus, and Entobia recorded in Badenian basal conglomerates (compared with modern Northern Adriatic rocky-shore environments), enabled more precise palaeoenvironmental interpretations. The occurrence of G. torpedo (produced by lithophaginid bivalves) on all sides of individual limestone lithoclasts in the Gornje Ore?je basal conglomerate, coupled with truncation of the formation (possibly indicating multiphase colonization), reflect gravel transport, roll-over, overturning and erosion by wave action in high-energy rocky-shore settings. Gornje Psarjevo-2 basal conglomerate boulders were probably not subjected to significant movement and abrasion, as suggested by good preservation of both G. lapidicus (potentially produced by gastrochaenid bivalves), associated G. torpedo, as well as abundant shallow Entobia borings. The Badenian Gastrochaenolites-Entobia ichnoassemblage also could be the result of a composite development. However, direct cross-cutting relationships between G. torpedo and G. lapidicus and/or Entobia were rarely observed. In addition, Badenian boring tracemakers might have coexisted at the same water depth. Northeast Mt. Medvednica Badenian successions probably formed during different Central Paratethys transgressive pulses (NN5 and NN6 Zones). However, exact timing of Badenian transgressions, stratigraphic correlations and tectono-eustatic implications are unresolved, due to sparsely integrated biostratigraphic and high-precision geochronological studies of Early–Middle Miocene North Croatian Basin deposits and due to the absence of a uniform biostratigraphic zonation and regional chronostratigraphic division of Central Paratethys.     

A New Ichnospecies of Gastrochaenolites Leymerie from the Pleistocene Port Morant Formation of Southeast Jamaica and the Taphonomy of Calcareous Linings in Clavate Borings

The ichnospecies Gastrochaenolites pickerilli isp. nov. is based on ten borings found in a shell of the gastropod Strombus gigas Linné from the Pleistocene (Sangamonian) Port Morant Formation of southeast Jamaica. These borings bear morphological similarities to Gastrochaenolites torpedo Kelly and Bromley but differ from all other Gastrochaenolites ispp. in having prominent and numerous calcareous meniscate structures arrayed adjacent to one side of the boring. These menisci are concave towards the center of the boring and are the remnants of calcareous tubes that lined earlier boreholes, that the boring bivalve treated as part of the lithified substrate when relocating. They are thus evidence of the former positions of borings that, unusually, were breached as the bivalve migrated sideways. Although this was a common behavior for Gastrochaenolites-producing bivalves within this substrate, the reason for it occurring is uncertain.     

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.     

Borings in Quartzite Surf Boulders from the Upper Cambrian Basal Deadwood Formation,Black Hills of South Dakota

Shallow, semi-spherical borings occur in clusters with densities of 1–3.5/cm² in quartzite boulders and in vein quartz from the localized basal conglomerate of the Cambrian-Ordovician Deadwood Formation in the east-central Black Hills of South Dakota. Some borings are superimposed on primary but enigmatic semi-circular structures, 2.5–5 cm in diameter, which are soft-sediment trace fossils formed prior to lithification. The macroborings are the first to be recorded from quartzite and vein quartz. Host boulders were eroded from near vertically dipping Paleoproterozoic quartzites from several different stratigraphic units. The thin boulder conglomerate grades were abruptly changed to sandstone through a layer ≤2 m thick in the Marjuman transgression (regionally correlated to the Cedarina dakotaensis trilobite zone). This transgression occurred prior to the start of the globally recognized Upper Cambrian Paibian Stage. Physically similar rocky-shore settings are widely known from quartzite islands of Cambrian age in Wisconsin, Middle Ordovician age on Ontario's Manitoulin Island, Ordovician-Silurian age in Manitoba, and Devonian age in western Australia. Erosion of quartzite surf boulders of equal or larger size occurred in all those regions, but the Black Hills of South Dakota is the only region where borings in quartzite are documented.     

Paleontological evidence of a brief global sea-level event during the last interglacial

A gently undulating to flat erosion surface with shallow-water borings and burrows is present in the midst of a Sangamonian (Eemian; marine oxygen isotope substage 5e) reefal facies on the islands of San Salvador and Great Inagua, Bahamas. Precise U/Th dating of corals above and below this surface show that it formed around 125-124 ka, and that the sea-level regressive-transgressive cycle which produced it lasted for 1500 years or less. The surface occurs on entirely carbonate rocks and has a low relief punctuated by erosional channels and karstic caves formed during the sea-level lowstand. A terra rossa paleosol, developed during that lowstand, partially fills a set of large lithophagid bivalve borings ( Gastrochaenolites torpedo ), showing that they were excavated during the regression. Rhizomorphs formed by plant roots occur on the erosion surface at Great Inagua. Extensive boring of the upward-facing surfaces occurred during the ensuing transgression, including a smaller G. torpedo and a clionid sponge boring ( Entobia ovula ). The bored surface is encrusted by a variety of shallow-water corals and, eventually, the re-established bank-barrier coral reefs. A sparse assemblage of serpulid worm and vermicularid gastropod tubes encrusted the channel and cave walls. Robust Ophiomorpha burrow systems occur within pockets of sediment in the coral facies both below and above the erosion surface. The channels and caves are filled with transgressive calcarenitic sediments in which occur numerous Ophiomorpha and Skolithos burrows. The ichnofossils on, below, and above this erosion surface are prominent indicators of a short-lived but significant global sea-level event.     

Clypeasteroid echinoid tests as benthic islands for gastrochaenid bivalve colonization: evidence from the Middle Miocene of Tarragona,north‐east Spain

Abstract: Middle Miocene tests of Clypeaster from L’Arrabassada (Tarragona, north‐east Spain) show evidence of intense endoskeletozoan colonization, preserved as borings and associated carbonate secretions that allow gastrochaenid bivalves to be identified as the colonizers. Two modes of occurrence have been recognized for these bivalve dwelling cavities; ‘intrastereom clavate borings’ which are restricted to the echinoid stereom, and ‘semi‐endoskeletal dwellings’, which penetrate across the test wall and extend as carbonate crypts into the sediment fill of the internal test cavity. Their size, density and position rule out a syn‐vivo relationship with the echinoids and demonstrate that colonization was post mortem. Because of the endurance of clypeasteroid skeleton and the pronounced bell‐shaped morphology of Clypeaster, the tests of these echinoids provided the most suitable substrates for hard‐bottom colonizers on an otherwise sandy seafloor. The scenario described from Tarragona can be extended to other Neogene and Quaternary strata elsewhere; there is ample evidence for the long‐term utilization of tests of Clypeaster by gastrochaenid bivalves in shoreface palaeoenvironments.     

Epi- and endobiontic organisms on Late Jurassic crinoid columns from the Negev Desert, Israel: Implications for co-evolution

Columns of the articulate crinoids Millericrinus and Apiocrinites from the Upper Jurassic (Upper Callovian) Zohar and Matmor formations of the Negev Desert of Israel display abundant encrusting organisms of about ten species, as well as diverse trace fossils produced by endobionts. Pluricolumnals were colonized by epi- and endobiontic organisms both during life and post-mortem. Skeletonized encrusting organisms include abundant ostreid bivalves (which evidently colonized both live and dead crinoid columnals), two types of serpulid worms, encrusting foraminifera, three species of bryozoans, and small encrusting sclerosponges. Several types of borings are present: Trypanites (possibly produced by sipunculids), Gastrochaenolites (crypts of boring lithophagid bivalves), elliptical barnacle? borings, and channel-like annelid? borings. In addition, approximately 16% of the pluricolumnals display circular parabolic embedment pits assignable to the ichnogenus Tremichnus. They are associated with substantial deformation of the containing columnals and were probably the work of host-specific ectoparasitic organisms. Discovery of Tremichnus on Jurassic crinoids extends the range of this trace by almost 100 million years, providing evidence for one of the longest-ranging host-parasite interactions documented thus far (over 200 million years). The relationship of epibionts to the Jurassic crinoids thus ranged from simple utilization of dead hard substrate to probable opportunistic commensalism in forms that colonized the live upright stems, as in some oysters, through host-specific parasitism in the case of Tremichnus.     

Bioerosion in the Miocene Reefs of the northwest Red Sea,Egypt

Macroborings provide detailed information on the bioerosion, accretion and palaeoenvironment of both modern and fossil reefs. Dolomitized reefal carbonates in the Um Mahara Formation exhibit an outstanding example of spatially distributed, well‐preserved bioerosion structures in tropical to subtropical syn‐rift Miocene reefs. Ten ichnospecies belonging to five ichnogenera are identified; three belonging to the bivalve‐boring ichnogenus Gastrochaenolites, three attributed to the sponge‐boring ichnogenus Entobia, and four ichnospecies assigned to three worm‐boring ichnogenera Trypanites, Maeandropolydora and Caulostrepsis. The distribution of the reported borings is strongly linked to the palaeo‐reef zones. Two distinctive ichnological boring assemblages are recognized. The Gastrochaenolites‐dominated assemblage reflects shallower‐marine conditions, under water depths of a few metres, mostly in back‐reef to patch‐reef zones of a back‐reef lagoon. The Entobia‐dominated assemblage signifies relatively deeper marine conditions, mostly in reef core of the fringing Miocene reefs. These ichnological assemblages are attributed herein to the Entobia sub‐ichnofacies of the Trypanites ichnofacies. This ichnofacies indicates boring in hard carbonate substrates (such as corals, rhodoliths, carbonate cements and hardgrounds) during periods of non‐sedimentation or reduced sediment input.     

Taphonomy and ichnology of cephalopod shells in a Maastrichtian chalk from Western Australia

The post-mortem history of a prolific Maastrichtian ammonite and nautiloid fauna preserved as phosphatic steinkerns in chalk of the upper Miria Formation of Western Australia is described. Sediment infilling of phragmocones, required for their fossilisation, was accomplished by means of perforations in the shell wall induced by the activity of abundant endoliths. These include borings ascribed to clionid sponges (Entobia), thallophytes, polychaete worms (including Caulostrepis and probable Maeandropolydora), phoronids (Talpina and Gnathichnus) and others of conjectural origin. Sediment infilling by this mechanism is considered to be more applicable to the taphonomy of phragmocones in general than sediment entry through the siphuncle and to be indicative of low sedimentation rates for the hosting strata. Nonheteromorph ammonites, and the nautiloid Cimomia, are preserved almost exclusively as phragmocones in the upper Miria Formation, and are numerically subordinate to the heteromorph Eubaculites which, together with Glyptoxoceras, is preserved predominantly as body chambers. This phragmocone/body chamber preservational contrast is attributed to the influence of shell shape on pre-burial mechanical abrasion. The apparent dominance of Eubaculites is considered to be largely a preservational artifact and ascribed to the ease with which body chambers were infilled, and thereby favoured for steinkern formation, relative to phragmocones. Phragmocones, or parts thereof. not filled with sediment were eliminated from the fossil record by diagenetic aragonite dissolution. Many ammonites with open umbilici have the early whorls missing. This we attribute to the trapping of sediment in the umbilicus prior to burial, preventing endolith attack whereby the early whorls avoided a sediment infilling. However, the protected inner whorls of involute ammonites and Cimomia, which have closed umbilici, and the inner whorls of evolute ammonites where a cemented umbilical plug supported the mouldic cavity left by shell dissolution, were preserved and were commonly infilled with calcite spar later in diagenesis. The dearth of cephalopod fossils in chalk underlying the upper Miria Formation is ascribed to diagenesis in which aragonite dissolution was not preceded by cementation.     

Bivalve borings in Lower Jurassic Lithiotis fauna from northeastern Italy and its palaeoecological interpretation

Random shell sections of the Pliensbachian (Early Jurassic) larger bivalve Opisoma from columns within the Main Post Office building of Ferrara, northern Italy, have been discovered to bear neat clavate-shape boreholes. These boreholes belong to the ichnogenus Gastrochaenolites Leymerie and represent bivalve borings. Opisoma is a subordinate component of the Lithiotis fauna characterised by aberrant shells thriving in tropical lagoonal settings which were widespread throughout the Tethyan and Panthalassa coasts. Although the Lithiotis fauna is well known in the palaeontological literature, no bivalve boring have been so far been formally described. The uniqueness of the morphology, size and substrate of these borings merits the designation of the new species Gastrochaenolites messisbugi ichnosp. nov. which thereby represents the first ichnospecies described from this fauna. The morphology of the boreholes and the included bivalves allows the boring activity to be ascribed to a mytilid bivalve. Palaeoecological and taphonomic analyses allowed the presence of the boreholes to be correlated to the Opisoma mode of life (epifaunal, free-living form) as well as to generally low sedimentation rates and seasonal mesotrophic conditions during an overall oligotrophic regime.

http://zoobank.org/urn:lsid:zoobank.org:act:CCF77B32-D459-4305-BC86-93F228852E50     

New Miocene scarabeid and hymenopterous nests and early miocene (santacrucian) paleoenvironments,patagonian Argentina

Three new trace fossils are described from Miocene paleosols of southern Argentina. Celliforma pinturensis, n. ichnosp. and Celliforma rosellii, n. ichnosp. are interpreted as cells of digging bees, possibly Anthophoridae, and Coprinisphaerafrenguellii, n. ichnosp. are brood balls of dung‐beetles. Both burrowing bees and dung‐beetles are common nesters in relatively open areas, confirming previous reconstructions of the paleoenvironment of the Pinturas Formation. A brief review of scarabeid and bee fossil nests from South America is presented, and we propose that constructed nests have a higher preservation potential than excavated nests. This fact explains their more common occurrences as trace fossils in paleosols. A new ethological category, calichnia, is proposed for hymenopterous and coleopterous traces, in which adult individuals make nests exclusively for larvae.     

Architectural complexity of marine crustacean burrows: unusual helical trace fossils from the Miocene of Mallorca,Spain

Gibert, J.M. de, Mas, G. & Ekdale, A.A. 2012: Architectural complexity of marine crustacean burrows: unusual helical trace fossils from the Miocene of Mallorca, Spain. Lethaia, Vol. 45, pp. 574–585. Unusual helical trace fossils occur in Tortonian shelfal calcarenites in the island of Mallorca. Their morphology may be either simple (ichnogenus Gyrolithes) or, more commonly, consist of two concentric helical burrows (ichnogenus Lapispira). They bear a very characteristic pelleted lining and are associated and probably connected to Thalassinoides and Ophiomorpha burrow systems very abundant in the same unit. These features allow the interpretation that the tracemaker was a thalassinidean shrimp. The complex and compound nature of these trace fossils is comparable to that seen in other modern and fossil crustacean burrow systems, and it reflects the behavioural plasticity of the architects. □Trace fossils, ichnology, ichnofabrics, crustacean burrows, Miocene, shallow marine, Lapispira.     

Paleoecology of epizoans and borings on some Upper Cretaceous chalk oysters from the Gulf Coast

Analysis was made of a hard substrate fauna found on right valve interiors and exteriors of the epifaunal reclining oyster Pycnodonte mutabilis from the Maastrichtian (Navarroan) Saratoga Formation (southwestern Arkansas). Comparison of boring and encrustation patterns on both sides of valves indicates that a major portion of colonization on valve exteriors occurred while host oysters were alive. Paleoautecologic information derived from such valve exterior patterns includes evidence of rheotropic orientation by encrusting juvenile P. mutabilis and preferential location of Trypanites sp. borings in surficial shell grooves. Valve exteriors supported a hard substrate paleocommunity which had the following non-interactive progressive colonization sequence: (1) Trypanites sp. and P. mutabilis juveniles; (2) Entobia sp., serpulid worm tubes, and Bullopora sp.; and (3) cheilostome bryozoans. This sequence could have been caused by low seasonality and ranked success of colonizing encrusters and borers. Colonization of valve interiors generally differed from exteriors only in that many interiors were first colonized by the clionid sponge that created Entobia sp., which had already occupied the exterior, and which quickly bored through the valve to occupy the interior upon the host's death. □ Trace fossils, epizoans, borings, Gryphaeidae, palaeoecology, communities, colonization sequence, Late Cretaceous, Maastrichtian, Navarroan, Arkansas.