The Jurassic Belemnite Suborder Belemnotheutina

The Belemnotheutina is a monophyletic group of mostly late Jurassic belemnites that possess largely plesiomorphic characters of ten subequal arms with hooks, a simple, conical, rostrum, a narrow breviconic phragmocone and a spatulate pro-ostracum. Although some of the best-preserved belemnites with soft parts have been described from this group, until recently, its status has been in question. A new genus from the Upper Jurassic of Antarctica, Antarctiteuthis is described which, like Acanthoteuthis (=  Belemnotheutis of authors), possesses unique rostral surface morphology of raised ridges with accompanying grooves unknown in other true belemnites. This is an important apomorphy for the group, which is considered to be a monophyletic suborder of the Belemnitida.     

Embryonic shell structure of Early–Middle Jurassic belemnites,and its significance for belemnite expansion and diversification in the Jurassic

Early Jurassic belemnites are of particular interest to the study of the evolution of skeletal morphology in Lower Carboniferous to the uppermost Cretaceous belemnoids, because they signal the beginning of a global Jurassic–Cretaceous expansion and diversification of belemnitids. We investigated potentially relevant, to this evolutionary pattern, shell features of Sinemurian–Bajocian Nannobelus, Parapassaloteuthis, Holcobelus and Pachybelemnopsis from the Paris Basin. Our analysis of morphological, ultrastructural and chemical traits of the earliest ontogenetic stages of the shell suggests that modified embryonic shell structure of Early–Middle Jurassic belemnites was a factor in their expansion and colonization of the pelagic zone and resulted in remarkable diversification of belemnites. Innovative traits of the embryonic shell of Sinemurian–Bajocian belemnites include: (1) an inorganic–organic primordial rostrum encapsulating the protoconch and the phragmocone, its non‐biomineralized component, possibly chitin, is herein detected for the first time; (2) an organic rich closing membrane which was under formation. It was yet perforated and possessed a foramen; and (3) an organic rich pro‐ostracum earlier documented in an embryonic shell of Pliensbachian Passaloteuthis. The inorganic–organic primordial rostrum tightly coating the protoconch and phragmocone supposedly enhanced protection, without increase in shell weight, of the Early Jurassic belemnites against explosion in deep‐water environment. This may have increased the depth and temperature ranges of hatching eggs, accelerated the adaptation of hatchlings to a nektonic mode of life and promoted increasing diversity of belemnoids. This study supports the hypothesis that belemnite hatchlings were ‘a miniature of the adults’.     

Zur Frage der Schwimmverhältnisse bei Belemniten in Abhängigkeit vom Primärgefüge der Hartteile

The fossilized massive calcitic guard of belemnites — when compared with largest preserved accompanying phragmocone-chambers — appears to have been too heavy to support the swimming animal’s presumable horizontal living posture. Calculations of centers of buoyancy and gravity do not exclude a considerable primary porosity of about 20 vol. per cent of the rostrum. Scanning electron micrographs of etched samples of well preserved rostral material favour the assumption of a primary lamellous rostrum. The original porosity might have been more than 20 vol. per cent, but it became cemented in early stages of diagenesis. This is supported by result of chemical and¹⁸0/¹⁶0-isotope analyses. The cyclic arrangement of the δ¹⁸0-values seems to reflect the proportions of primary and secondary carbonate in the samples and to indicate that “paleotemperatures” obtained from rostral calcite of belemnites are not reliable.     

Zur schwimmfähigkeit von belemniten

The influence of rostrum and phragmocone on the swimming ability of belemnites has been analysed. First, theoretical considerations regarding the most favourable position of the centre of gravity for the position at rest, during the forward and during the backward movement have been undertaken, without taking into account the actual conditions. Then the results of calculations of a reconstructed belemnite are presented. By elimination of unfavourable configurations it is found that the coincidence of the centres of gravity and buoyancy leads to the most favourable swimming conditions. This configuration enables a vertical position of rest, an unproblematical slow movement and a backward movement on a wavelike path, with alternating propulsive phases and glide phases on a ballistic trajectory.     

The capsule: an organic skeletal structure in the Late Cretaceous belemnite Gonioteuthis from north‐west Germany

Abstract: An unusual, bilaterally symmetrical black structure that embraces the protoconch and the phragmocone and is overlain by a rostrum has been studied in the Santonian–early Campanian (Late Cretaceous) belemnite genus Gonioteuthis from Braunschweig, north‐west Germany. The structure is here named the capsule. Energy dispersed spectrometry analyses of the capsule show a co‐occurrence of sulphur with zinc, barium, iron, lead and titanium, suggesting their chemical association. The capsule was originally made of organic material that was diagenetically transformed into sulphur‐containing matter. The material of the capsule differs from the chitin of the connecting rings in the same specimens. The capsule has a complex morphology: (1) ventral and dorsal wing‐like projections that are repeated in a breviconic shape of the alveolus, (2) an aperture with lateral lobes and ventral and dorsal sinuses copied by growth lines and (3) a ventral ridge that fits with the position of the fissure in the rostrum. The alveolus in the most anterior part of the rostrum is crater‐like. It is lined with thin, pyritized, laminated material, which appears to be the outermost portion of the capsule attached to the inner surface of the rostrum. A flare along the periphery of the alveolus marks a region where the rostrum was not yet formed, suggesting that the capsule extended beyond the rostrum. Modification of the skeleton in Gonioteuthis comprises a set of supposedly interrelated changes, such as innovation of the organic capsule, partial elimination of the calcareous rostrum and a diminishing of the pro‐ostracum, resulting in the appearance of a new type of pro‐ostracum that became narrower and shorter and lost the spatula‐like shape and gently curved growth lines of a median field that are typical for the majority of Jurassic and Cretaceous belemnites. The partial replacement of a calcareous rostrum with an organic capsule in belemnitellids may have been an adaptive reaction to an unfavourable environmental condition, perhaps related to difficulties in calcium carbonate secretion during the Late Cretaceous that forced animals to reduce carbonate production and to secret an organic capsule around the protoconch and the phragmocone.     

Probable predatory borings in late Cretaceous bryozoans

Borings are described in zooids of Cenomanian to Campanian melicerititids, an aberrant group of cyclostome bryozoans with calcified opercula. The borings are circular or elliptical, straight-sided and have a diameter of 40–90 μn. Autozooids were drilled in preference to heterozooids and most borings penetrate the operculum. The shape and distribution of boreholes suggests that they were made by a predator attacking one zooid at a time. The predator responsible may have been a gastropod, most probably a nudibranch or a micromorphic muricid. Bryozoa, Gastropoda, predation, borings, Upper Cretaceous.     

Composition and ontogeny ofDictyoconites (aulacocerida,cephalopoda)

Dictyoconites from the middle Triassic Cassian Formation is a characteristic representative of the Aulacocerida. Embryonic development and construction of the phragmocone is like that of Jurassic belemnites. The siphuncular tube is double-walled with a long retrochoanitic mineralized septal neck continuing into an organic tube. The extended decoupling zone resembles that ofSpirula. Characteristic ofDictyoconites are the tubular »living chamber« and two layered deposits of the muscular mantle on the phragmocone. The Triassic coleoid was a slender squid with visceral mass and mantle cavity encapsuled in shell and the whole conch covered by muscular mantle extending in two lateral apical fins attached to the aragonitic rostrum.     

Evidence of Osedax worm borings in Pliocene (∼3 Ma) whale bone from the Mediterranean

Osedax worms subsist entirely on vertebrate skeletons on the seafloor, using root-like tissues to bore into and degrade the bones. Paleontologists have only recently begun to appreciate the possible destructive effect that these worms may have had on the marine vertebrate fossil record and little is known of their evolutionary history. Using microcomputed tomography, we document Osedax-like borings in a fossil whale bone from the Pliocene of Italy and present new data on the borings of extant Osedax worms. The fossil borings are distinguished from those of other known borers and identified as traces of Osedax activity based on diagnostic features. Our results suggest that it is necessary to isolate individual borings for the confident identification of Osedax traces. This is only the second paleogeographic occurrence of Osedax in the fossil record and indicates that by the Pliocene these worms had colonised a large portion of the world's oceans. This is the first evidence for Osedax in the Mediterranean, past or present, and suggests that more species await discovery in this region.     

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.     

The palaeobiology of belemnites – foundation for the interpretation of rostrum geochemistry

Belemnites are an extinct group of Mesozoic coleoid cephalopods with a fossil record ranging from the early Late Triassic [about 240 million years ago (Mya)] to the Cretaceous/Palaeogene boundary (65 Mya). Belemnites were widely distributed, highly abundant and diverse, and an important component of Mesozoic marine food webs. Their internal shells, specifically their low‐Mg calcite rostra, have been used as palaeoenvironmental carbonate archives for the last 70 years. This is primarily due to the assumption that the rostrum calcite formed in equilibrium with the oxygen isotope composition of ambient sea water. Of prime importance for the reliable interpretation of isotope data derived from these biogenic carbonates is a robust reconstruction of the palaeobiology of their producers. Here we provide a critical assessment of published reconstructions of belemnite soft‐body organization and their lifestyle and habitats. Different lines of evidence, including sedimentological, geochemical, morphological, and biomechanical data, point towards an outer shelf habitat of belemnites, for some taxa also including the littoral area. Belemnite habitat temperatures, oxygen content, salinities, and life span are constrained based on observations of the ecology and life history of modern coleoids. Belemnite habitat depth might have been largely controlled by food and temperature, with a temperature optimum between 10°C and 30°C. The distribution of modern coleoids is for most species restricted to well‐oxygenated water masses and a salinity between 27 and 37 psu. The trophic position of belemnites as both predators and prey is documented by unique fossil finds of stomach contents and soft tissue preservation, such as jaws, hooks, and ink sacs. Belemnites were medium‐sized predators in the epipelagic zone (not deeper than ～200 m) hunting for crustaceans, other cephalopods, and fishes. Taxa with elongated rostra probably were fast and highly manoeuvrable swimmers. Forms with conical rostra represent slow but highly manoeuvrable swimmers, and forms with depressed rostra likely had a bottom‐related life habit. Predators of adult belemnites were sharks, bony fishes, and marine reptiles. Belemnites, like most of the modern coleoids, were relatively short lived, most likely living only for 1–2 years. Understanding the biomineralization of belemnite rostra is highly relevant for an improved interpretation of their geochemistry. Here we confirm that belemnite rostra are composed of low Mg‐calcite fibres, but they do not contain distinct types of laminae. These fibres are composed of two distinct calcite phases. One phase is a filigree network of tetrahedral organic‐rich calcite and the second phase is represented by organic‐poor calcite.     

The “rostrum”-problem in coleoid terminology – an attempt to clarify inconsistencies

In the coleoid literature, the terminology of shell elements that are deposited on the external surface of the primary shell wall is inconsistent and confusing. Morpho- and phylogenetic interpretations have been therefore controversial. A strict layer-by-layer comparison of seventeen species from seven coleoid subgroups suggests that the coleoid shell is covered by either one (Diplobelida, Spirulida, Sepiida, Vampyropoda) or two (Aulacocerida, Belemnitida, Belemnoteuthidida) outer shell formations. The confusion has been caused mainly by the often ignored presence of a primordial rostrum in the Aulacocerida, Belemnitida, and Belemnoteuthidida. The primordial rostrum is a secondary shell formation, which covers the entire primary shell and, which is itself enveloped by a tertiary shell formation, the rostrum proper. In the Diplobelida, Spirulida, and Sepiida, the primary shell is invested by a single outer formation, the sheath; a rostrum proper is absent in the latter groups. As a secondary shell formation, the aulacocerid, belemnitid and belemnoteuthidid primordial rostrum on the one hand, and the diplobelid, spirulid and sepiid sheath on the other hand are considered to represent homologues. Accordingly, the rostrum proper of the Aulacocerida, Belemnitida, and Belemnoteuthidida are homologues as tertiary shell formations. Outer shell formations in gladius-bearing vampyropods (and teuthids?) might be represented by a single layer. The clarification of the homology of secondary and tertiary shell formations, however, cannot resolve phylogenetic relationships within the Coleoidea.     

Ecomorphological adaptation of acorn weevils to their oviposition site

Comparisons between closely related species in different habitats provide a window into understanding how biotic factors shape evolutionary pathways. Weevils in the genus Curculio have radiated extensively across the Palearctic, where similar ecomorphs have evolved independently on different hosts. We examined ecological and morphological data for 31 Curculio species using multivariate statistics to determine which morphological traits covary and which correlate with the host seed size. A subset of 15 taxa for which phylogenetic relationships were known were used for comparative analyses and inferring historical patterns of trait evolution. The morphological analyses suggest rostrum size increased proportionately to body size in both males and females and that both rostrum and body size correlate with host seed size but that rostrum shape does not correlate with any of the seed traits used in the analyses. Host shifts from small seeds to considerably larger seeds or vice versa have occurred several times independently and historical trait evolution indicates that these host shifts were accompanied by morphological changes in rostrum size. These patterns suggest that seed size is an important selective agent for changes in rostrum length along with body size and thus may be a key factor promoting morphological differentiation in the genus Curculio.     

Anatomy of the mechanosensory lateral line canal system and electrosensory ampullae of Lorenzini in two species of sawshark (fam. Pristiophoridae)

It has long been assumed that the elongated rostra (the saws) of sawsharks (family: Pristiophoridae) and sawfish (family: Pristidae) serve a similar function. Recent behavioural and anatomical studies have shed light on the dual function of the pristid rostrum in mechanosensory and electrosensory prey detection and prey manipulation. Here, the authors examine the distributions of the mechanosensory lateral line canals and electrosensory ampullae of Lorenzini in the southern sawshark, Pristiophorus nudipinnis and the longnose sawshark, Pristiophorus cirratus. In both species, the receptive fields of the mechano- and electrosensory systems extend the full length of the rostrum indicating that the sawshark rostrum serves a sensory function. Interestingly, despite recent findings suggesting they feed at different trophic levels, minimal interspecific variation between the two species was recorded. Nonetheless, compared to pristids, the pristiophorid rostrum possesses a reduced mechanosensory sampling field but higher electrosensory resolution, which suggests that pristiophorids may not use their rostrums to disable large prey like pristids do.     

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.     

Parasitism on Ordovician Chitinozoa

Borings are common in chitinozoans. They are cylindrical or conical, widening towards the outer surface of the vesicle wall. It is suggested that the cylindrical borings were probably caused by bacteria. Actinomycota and lower Fungi including at least Chytridiomycota, and the conical borings mainly by chytridia. Two types of spore-like bodies, operculate and non-operculate, have been found in situ on two chitinozoan species. The spore-like bodies are of about the same size as the supposed boring organisms in chitinozoans but are never found in association with the borings. They are interpreted as cysts of ectoparasitic nannoorganisms that resemble ciliates and amoebae, and their possible use for determining the biochemical composition of the chitinozoans is briefly discussed.     

The sclerobionts of the Bajocian Oolithe ferrugineuse de Bayeux Formation from Calvados (Paris Basin,Normandy, France)

Silicified fossils collected in ploughed fields at Gavrus (Calvados, France), mainly mollusc shells, are Bajocian in age, and come from the Oolithe ferrugineuse de Bayeux Formation. The entire formation is highly condensed and most fossils are reworked. Their silicification allowed treatment with dilute hydrochloric acid. This treatment brought to light numerous encrusting sclerobionts: Porifera (3 taxa), Bryozoa (n), Polychaeta (9), Brachiopoda (n), Bivalvia (5). The borings and bioerosional traces are described using the “categories of architectural design” as defined by Buatois et al. (2017). Among the 28 ichnotaxa described (corresponding to an ichnodisparity of 14), Planavolites wisshaki isp. nov., Kleithrichnus belemnophilus igen. nov., isp. nov. and Foggara foggara igen. nov., isp. nov. are new. Some Gastrochaenolites dijugus Kelly and Bromley, 1984 borings accommodate the shell of the presumed borer Lithophaga fabella J.-A. Eudes-Deslongchamps, 1838. A group of Nododendrina europaea (Fischer, 1875) on a belemnite rostrum provides a good instance of an ichnogenetic series. Encrusting sclerobionts and macroscopic boring and bioerosional trace-makers are dominantly suspension feeders. The ichnofacies is a peculiar Entobia-ichnofacies, found in deeper, lower-energy environments than the “classical” coastal Entobia-ichnofacies, on deep shell-grounds far from the coast, in the deep euphotic zone.     

Receptive field organization of electrosensory neurons in the paddlefish (Polyodon spathula)

Paddlefish use their electrosense to locate small water fleas (daphnia), their primary prey, in three-dimensional space. High sensitivity and a representation of object location are essential for this task. High sensitivity can be achieved by convergence of information from a large number of receptors and object location is usually represented in the nervous system by topographic maps. However the first electrosensory center in the brain, the dorsal octavolateral nucleus in the hindbrain, is neither topographically organized nor does it show a higher sensitivity than primary afferent fibers. Here, we investigated the response properties of electrosensory neurons in the dorsal octavolateral nucleus (DON), the lateral mesencephalic nucleus (LMN) and the tectum mesencephali (TM). LMN units are characterized by large receptive fields, which suggest a high degree of convergence. TM units have small receptive fields and are topographically arranged, at least in the rostro-caudal axis, the only dimension we could test. Well-defined receptive fields, however, could only be detected in the TM with a moving DC stimulus. The receptive fields of TM units, as determined by slowly scanning the rostrum and head with a 5 Hz stimulus, were very large and frequently two or more receptive fields were present. The receptive fields for LMN units were located in the anterior half of the rostrum whereas TM units had receptive fields predominantly on the head and at the base of the rostrum. A detailed analysis of the prey catching behavior revealed that it consists of two phases that coincide with the location of the receptive fields in LMN and TM, respectively. This suggests that LMN units are responsible for the initial orienting response that occurs when the prey is alongside the anterior first half of the rostrum. TM units, in contrast, had receptive fields at locations where the prey is located when the fish opens its mouth and attempts the final strike.     

First insights into the function of the sawshark rostrum through examination of rostral tooth microwear

Potential roles of the rostrum of sawsharks (Pristiophoridae), including predation and self‐defence, were assessed through a variety of inferential methods. Comparison of microwear on the surface of the rostral teeth of sawsharks and sawfishes (Pristidae) show that microwear patterns are alike and suggest that the elongate rostra in these two elasmobranch families are used for a similar purpose (predation). Raman spectroscopy indicates that the rostral teeth of both sawsharks and sawfishes are composed of hydroxyapatite, but differ in their collagen content. Sawfishes possess collagen throughout their rostral teeth whereas collagen is present only in the centre of the rostral teeth of sawsharks, which may relate to differences in ecological use. The ratio of rostrum length to total length in the common sawshark Pristiophorus cirratus was found to be similar to the largetooth sawfish Pristis pristis but not the knifetooth sawfish Anoxypristis cuspidata. Analysis of the stomach contents of P. cirratus indicates that the diet consists of demersal fishes and crustaceans, with shrimp from the family Pandalidae being the most important dietary component. No prey item showed evidence of wounds inflicted by the rostral teeth. In light of the similarities in microwear patterns, rostral tooth chemistry and diet with sawfishes, it is hypothesised that sawsharks use their rostrum in a similar manner for predation (sensing and capturing prey) and possibly for self‐defence.     

Palaeobiogeography of late cretaceous belemnites of Europe

A North Temperate Realm, characterized by Belemnitellidae Pavlov, and a South Temperate Realm, characterized by Dimitobelidae WHITEHOUSE, existed throughout the Late Cretaceous, while Tethyan belemnites belonging to Belemnopseidae Naef existed only in the Cenomanian and disappeared afterwards. The North Temperate Realm may be subdivided into North European and North American Provinces. The latter province includes Greenland, Canada, the Western Interior Region of North America, and the Atlantic and Gulf coasts of North America. The belemnites from the North American Province, consisting of populations of the generaActinocamax Miller andBelemnitella d’Orbigny, are closely related to the belemnites of the North European Province and appear to have migrated from this province to North America via Greenland and Arctic Canada. The North European Province extends from Ireland to the Ural Mountains. Belemnites from this province belong to the following genera:Neohibolites Stolley,Parahibolites Stolley,Belemnocamax Crick,Actinocamax Miller,Belemnellocamax Naidin,Gonioteuthis Bayle,Belemnitella d’Orbigny,Belemnella Nowak, andFusiteuthis Kongiel. Two subprovinces within the North European Province have been recognized: the Central European and Central Russian Subprovinces. These subprovinces are well-defined in the late Coniacian-Early Campanian and are characterized by theGonioteuthis stock andBelemnitella stock, respectively. The two subprovinces are less distinct in other periods of the Late Cretaceous and may disappear completely.     

Origin and paleoecology of Middle Jurassic hiatus concretions from Poland

Bored and encrusted carbonate concretions, termed hiatus concretions, coming from the Middle Jurassic (Upper Bajocian and Bathonian) siliciclastics of the Polish Jura, south-central Poland, have been subjected to detailed paleoecological investigation for the first time. The concretions possess variable morphology and bear distinct traces of bioerosion and encrustation as a result of exhumation on the sea floor during intervals of low sedimentation and/or erosion. The borings are dominated by Gastrochaenolites and Entobia. Epilithozoans, represented by at least 26 taxa, are dominated by sabellid/serpulid worm tubes and bryozoans, while sponges and corals are minor. No relationship between the concretion size and the number of encrusters has been found, suggesting that concretion size was not the primary factor controlling diversity. Stable isotope analyses and the presence of crustacean scratch marks and Rhizocorallium traces on many of the hiatus concretions indicate that they formed just below the sediment–water interface, within the sulfate reduction zone. Moreover, crustacean activities may have been a prelude to their origin, as shapes of many concretions closely resemble thalassinoidean burrow systems. It is also possible that crustacean activity around the concretions promoted their exhumation by loosening the surrounding soft sediment. The presence of borings and encrusters on different concretion surfaces, as well as truncated borings and a number of abraded epilithozoans, indicate that after the concretions were exhumed they were repeatedly overturned and moved on the sea floor, probably due to episodic storm-related bottom currents in shallow subtidal environment.