Trace Makers Research Articles

Sedimentology and neoichnology of a muddy translating point bar in the fluvio-tidal transition, Serpentine River, BC, Canada

Point bars are common in the fluvio-tidal transition of rivers, yet detailed characterization of their sedimentology and neoichnology is rarely reported. Herein, we present sedimentological and ichnological descriptions for a seaward translating point bar located in the fluvio-tidal transition of the Serpentine River, BC, Canada. This bar accumulates in mainly polyhaline water, and channel flow is tide-dominated. The landward bar has steep channel banks and grain size fines from medium sand in the thalweg to mud in the upper intertidal zone. The seaward side of the bar forms a bench-like morphology that is steeply inclined in the intertidal zone, has a wide, gently dipping platform in the lower intertidal/uppermost subtidal zone, and a steep lower subtidal channel bank. Sediment sizes fine from coarse- to medium-grained sand in the thalweg, to mud in the lower intertidal zone. Medium-grained sand is deposited on the middle- and upper-intertidal zone of the seaward-side of the bar as a result of flow reversal and impingement of the flood tidal current against the seaward side of the translating point bar.The neoichnological assemblage of the intertidal part of the translating point bar is characteristic of brackish-water environments, and comprises low diversities of diminutive structures that occur locally in high densities (Bioturbation Indices 3–4). The neoichnological distribution correlates closely with the macrobenthos distribution, which in turn indicates marine-nutrient distribution. Marine nutrient supply is likely controlled by the bar's morphology. Biogenic structures attributable to Arenicolites, Skolithos, Polykladichnus and Siphonichnus mark the middle and upper intertidal zones, as well as the lower intertidal zone along the landward side of the bar. The trace makers that produce this trace assemblage are resilient to prolonged subaerial exposure and employ diverse feeding strategies. The lower intertidal zone along the seaward side of the bar is affected by decreasing current velocities across the wide bench-like morphology, which permits regular deposition of marine nutrients. Here, population counts are high and trace makers specialize in surface deposit- and filter-feeding. Traces include Gyrolithes-like structures and Siphonichnus. The Gyrolithes and Gyrolithes-like burrows that are produced by S. kowalevskii at the study site are hypothesized to potentially reflect the trace maker's anatomical predisposition, and not represent some spatial or anchoring advantage.This work represents the first published study on the neoichnology of a tide-dominated, translating point bar in the fluvio-tidal transition. The model we present is intended as an analog to show the variability in fluvio-tidal point bars and how they might be manifested in the sedimentary record.

A twig-like insect stuck in the Permian mud indicates early origin of an ecological strategy in Hexapoda evolution

Full body impressions and resting traces of Hexapoda can be of extreme importance because they bring crucial information on behavior and locomotion of the trace makers, and help to better define trophic relationships with other organisms (predators or preys). However, these ichnofossils are much rarer than trackways, especially for winged insects. Here we describe a new full-body impression of a winged insect from the Middle Permian of Gonfaron (Var, France) whose preservation is exceptional. The elongate body with short prothorax and legs and long wings overlapping the body might suggests a plant mimicry as for some extant stick insects. These innovations are probably in relation with an increasing predation pressure by terrestrial vertebrates, whose trackways are abundant in the same layers. This discovery would possibly support the recent age estimates for the appearance of phasmatodean-like stick insects, nearly 30 million years older than the previous putative records. The new exquisite specimen is fossilized on a slab with weak ripple-marks, suggesting the action of microbial mats favoring the preservation of its delicate structures. Further prospections in sites with this type of preservation could enrich our understanding of early evolutionary history of insects.

PALEOENVIRONMENTAL IMPLICATIONS OF INVERTEBRATE FECAL PELLETS (EDAPHICHNIUMISP.) AT AN ICHNOFOSSIL-RICH DINOSAUR NESTING LOCALITY, UPPER CRETACEOUS TWO MEDICINE FORMATION, MONTANA, USA

ABSTRACTThe terrestrial feeding trace Edaphichnium lumbricatum is known from the Triassic to the Pleistocene and is characterized by tubular burrows with ellipsoidal fecal pellets, indicating substrate feeding by earthworms or other invertebrates. We describe 11 specimens attributable to Edaphichnium isp. from Egg Mountain, a terrestrial locality with a diverse fossil assemblage from the Upper Cretaceous Two Medicine Formation in Montana, USA, and assess their paleoenvironmental and paleoecological implications. These ichnofossils were recovered from a 1.5 meter stratigraphic succession comprised of calcareous siltstones and limestones with abundant fossil insect pupal cases, representing well-drained paleosols. Although burrows are not always present, three recurring arrangements of Edaphichnium isp. fecal pellets are identified: linearly arranged pellets, horizon-confined pellets, and pellets in clusters dispersed vertically and horizontally throughout the matrix. Two color patterns (light and dark pellets) are also distinguished. Pellets are fine-grained and have a consistently ellipsoidal shape (length:diameter of 1.57), with maximum lengths ranging from 1.9–6.7 mm (mean 4.1 mm) and maximum diameters ranging from 1.0–4.1 mm (mean 2.6 mm). Geochemical analyses indicate pellets are comprised of varying proportions of calcite, plagioclase, and quartz, and are enriched in phosphorus relative to the sedimentary host matrix. Possible trace makers include chafer or other coleopteran larvae, millipedes, and earthworms, suggesting a range of capable trace makers of Edaphichnium-like fecal pellets. Edaphichnium isp. at specific stratigraphic horizons suggests increased organic content in the subsurface, potentially connected to depositional hiatuses. Edaphichnium isp. adds a secondary component to the Celliforma ichnofacies known from Egg Mountain and surrounding strata, and to the array of nesting, feeding, and dwelling traces of wasps, beetles, other invertebrates, mammals, and dinosaurs from the locality.

Trace fossils from the Permian Lopingian Talung Formation at the northern Penglaitan section of Laibin area, South China: Ichnology, palaeoenvironment, and palaeoecology

The end‐Permian mass extinction was the largest biotic crisis in the Phanerozoic. Previous studies of this catastrophe have mainly concentrated on geochemistry or body fossil records. The Changhsingian Talung Formation strata exposed in the Penglaitan section, the Global Stratotype Section and Point for the Guadalupian−Lopingian boundary in Laibin, South China, yield abundant trace fossils that have not been systematically described yet. Herein, we report abundant ichnotaxa from the Talung Formation, including 12 ichnospecies in 10 ichnogenera: Didymaulichnus isp., Helicorhaphe tortilis, Nereites isp., Palaeophycus isp., Planolites beverleyensis, Planolites montanus, Protovirgularia dichotoma, Protovirgularia longespicata, Rusophycus isp., Skolithos linearis, Thalassinoides isp., and Treptichnus isp. They can be assigned to two ichnoassemblages: the Nereites−Planolites (beds 18–45) and Protovirgularia−Skolithos (beds 46–59) ichnoassemblages. Ichnological and sedimentological features indicate that the former ichnoassemblage was probably developed in a deep‐marine turbidite setting, while the latter ichnoassemblage represents an ichnofossil record from a shallow marine environment, that is, subtidal to supratidal zones. In addition, the continuous ichnological records spanning from the Wuchiapingian to Changhsingian, together with facies features show a distinct regression, and they also indicate that diverse trace makers, such as arthropods, bivalves, and worms may have inhabited the Lopingian ocean, with no sign of the long‐term environmental deterioration in the studied area.

The trace fossil record of the Toarcian Oceanic Anoxic Event in the Iberian Massif

Trace fossil (ichnological) analysis of the Toarcian Oceanic Anoxic Event (T‐OAE) in several sections from the Iberian Massif reveals a comparatively minor incidence of this global anoxic event in the macrobenthic trace maker community. A variable trace fossil record can be recognized, involving changes in ichnodiversity, abundance and size of structures, evidencing not extinctions, but the effects of the event on the behaviour, palaeoecology and palaeobiology of trace makers. However, the influence of anoxia is only partially identified, with other palaeoenvironmental conditions—nutrient availability and substrate features, among others—being the major parameters influencing the trace maker community during the T‐OAE.

The earliest occurrence of the ichnogenus Psilonichnus: a new record from the Mississippian of the West of Ireland

The ichnogenus Psilonichnus Fürsich, 1981 is recorded for the first time from the Mississippian (Brigantian regional substage) limestones of the Slievenaglasha Formation from the west coast of County Clare, Ireland. This record extends the known range of Psilonichnus which has previously been recorded from rocks of Jurassic or younger age. The trace maker of the burrows described herein has not been preserved and remains unknown; however, the ichnogenus Psilonichnus is generally ascribed to the burrowing activities of decapod crustaceans such as crabs or shrimp. Decapods from the Paleozoic are poorly known and assigning the traces to a maker must be treated with caution. However, this record indicates that burrowing organisms using a similar life strategy to modern decapods were established by Brigantian times. These examples are assigned to the Glossifungites ichnofacies, as they occur on an omission surface in a shallow marine carbonate firmground. The burrows were subsequently infilled with deposits of possible storm origin. Glacioeustatic sea-level fluctuation related to the onset of the Late Paleozoic Ice Age is a common feature of Carboniferous sedimentary successions at this level, and the Irish (Mississippian) Psilonichnus horizon occurs just below a significant regional sequence boundary at the top of the Slievenaglasha Formation.

MERCURY INTRUSION POROSIMETRY TO EVALUATE THE INCIDENCE OF BIOTURBATION ON POROSITY OF CONTOURITES

The effect of bioturbation on rocks’ flow-media properties (e.g., porosity and permeability) and its impact on reservoir quality has been previously documented. However, the occurrence of ichnological features and their impact on rock properties in contourite deposits, a facies of economic interest, is poorly known. The study evaluates the effects of bioturbation on different types of contourite facies, particularly dominantly calcareous contourites and sandy clastic contourites, using mercury intrusion porosimetry. Porosity (total, intraparticle and interparticle) is characterized in selected samples, comparing the host rock with the infills of the trace fossils; Macaronichnus, Parahaentzschelinia and Scolicia from El Adergha and Kirmta sections in Morocco, and Chondrites, Planolites and Thalassinoides from Petra Tou Romiou, Agios Konstantinos, and Kalavassos outcrops in Cyprus. The obtained data reveal variance between porosities according to different types of contourite facies and trace fossils. Total porosity shows similar values for the host sediment in clastic and calcarenitic contourites, but interparticle porosity is nearly absent in calcarenitic contourites, where intraparticle porosity is almost exclusive. This is owing to the abundance of foraminifera chambers that increase intraparticle primary porosity. Regarding the ichnotaxa, higher total porosity values were obtained from the infilling material of Parahaentzschelinia, Scolicia and Macaronichnus, which could be related with the redistribution of grains by trace makers during feeding activity. Considering the impact of bioturbation on reservoir quality, there are significant differences between clastic and calcareous contourites. In the clastic contourites, bioturbation increases in the total porosity, particularly interparticle porosity, suggesting a positive impact for the reservoir properties of the studied units. However, in calcarenitic and muddy chalk contouritic facies, bioturbation has a minor effect on porosity and no predictable influence on the flow-media characteristics.

An assemblage of large-sized insect traces in paleosols from the middle Miocene of northern Patagonia related to the climatic optimum

A new assemblage of large insect trace fossils is recognized in paleosols of the middle Miocene pyroclastic deposits from extra-Andean north Patagonia. This assemblage includes Racemusichnus jacobacciensis igen. isp. nov., the largest trace fossil in paleosols attributed to solitary insects. R. jacobacciensis is represented by clusters of two to seven thickly walled cylinders horizontally orientated in the paleosol. The cluster arrangement, its orientation, the large size and wall of the cylinders suggest a dung beetle, probably a representative of the Geotrupidae as the possible trace maker. The new ichnoassemblage, also comprising large-sized specimens of Coprinisphaera ispp., Teisseirei barattinia and Feoichnus challa, belongs to the Rosellichnus assemblage-SAPIA of the Coprinisphaera Ichnofacies. Mollic paleosols along with the trace fossils, mammal remains and previous data for this unit suggest an open grassy habitat compatible with high productive grass savannas, under a temperate-warm and seasonal subhumid climate. This assemblage of large-sized trace fossils is attributed to highly productive ecosystems related to the rise of temperature occurred during the Middle Miocene Climatic Optimum.

The Late Miocene Rifian corridor as a natural laboratory to explore a case of ichnofacies distribution in ancient gateways

Oceanic gateways have modulated ocean circulation and have influenced climatic variations throughout the Earth´s history. During the late Miocene (7.8–7.35 Ma), the Atlantic Ocean and the Mediterranean Sea were connected through the Rifian Corridor (Morocco). This gateway is one of the few examples of deep ancient seaways with a semi-continuous sedimentary record. Deposits comprise turbidites intercalated between deep-sea mudstone (i.e., hemipelagites and drift deposits), channelized sandstone contourite facies, and shallow marine sandstone. Herein an ichnological analysis was conducted in these upper Miocene sediments to improve characterisation of palaeoenvironmental conditions. In addition, ichnofacies were analysed to elucidate how bottom currents control ichnofacies distribution and can modify their attributes. Turbidite deposits are typified by vertical trace fossils (i.e., Ophiomorpha), conforming the Ophiomorpha rudis ichnosubfacies. Contouritic sandstone exhibits high density and low diversity trace-fossil assemblage, with predominant Macaronichnus and Scolicia, resembling a proximal expression of the Cruziana ichnofacies. Shallow marine environments are dominated by vertical trace fossils (e.g., Conichnus, Ophiomorpha, Skolithos), allowing an assignation to the Skolithos ichnofacies. This study reveals for the first time a variability in ichnofacies attributes and distribution at the Rifian Corridor, associated with turbidites, contourite and shallow marine sediments. Hydrodynamic energy reveals as the major factor controlling trace maker communities in the studied seaway. Highly energetic conditions typical of shallower settings are present in deeper-water environments (i.e., slope), contributing to ichnodiversity impoverishment in ichnofacies.

The Halimedides record in the Asturian Basin (northern Spain): supporting the Toarcian Oceanic Anoxic Event relationship

Abstract Recent ichnological analysis conducted in two sections (Rodiles and Lastres) of the Asturian Basin revealed the presence of Halimedides Lorenz von Liburnau 1902, which occurs just above the black shales related to the end of the Toarcian Oceanic Anoxic Event (T-OAE). Halimedides is associated with recovery of the trace-maker community after the re-establishment of favourable, oxic, conditions. The appearance of Halimedides after the T-OAE event, previously not registered, supports the close relationship of the trace maker with oxygen conditions, as occurs in other anoxic events including the Cretaceous OAE-1a and OAE-2. Also, a relationship between morphometric and palaeoenvironmental parameters is observed: occurring larger and densely chambered specimens in darker, weakly oxygenated facies, while smaller and sparsely chambered forms are registered in lighter, better oxygenated sediments.

Trace fossil analysis of sandy clastic contouritic deposits in the late Miocene Rifian Corridor (Morocco): Ichnotaxonomical and palaeoenvironmental insights

Ichnological analysis was conducted in the late Miocene sandy clastic contouritic deposits from the Rifian Corridor (Morocco). The Rifian Corridor was a main gateway between the Mediterranean Sea and the Atlantic Ocean during the late Miocene. An initial detailed ichnological analysis of clastic contourite facies revealed trace fossil assemblages of high abundance (similar to that of calcareous contourites) and low ichnodiversity. Parahaentzschelinia and Rosselia were registered for the first time in contouritic facies. Scolicia and Macaronichnus were found to be the dominant ichnogenera in the studied sandy clastic contourites. Abundant Macaronichnus, Parahaentzschelinia and Scolicia evidence the adaptation of trace makers to “unfavourable” energetic conditions, food availability being a major parameter that favoured opportunistic colonization of the supposedly “un-inhabitable” high-energy contourite depositional setting. Similar ichnological studies conducted in selected outcrops will allow us to address the representative ichnoassemblage of coarser (silty/sandy) clastic contourites.

The youngest known Dictyodora from the Late Permian(Lopingian) deep sea in West Qinling, central China

Dictyodora has been generally considered an ichnogenus with a restricted temporal range from the Cambrian to the Mississippian. Until now, there have been no reports of Dictyodora after the Mississippian. Here we report on well-preserved and abundant Dictyodora from deep-sea sediments of the Lopingian Maomaolong Formation in West Qinling, central China, which is hitherto the youngest occurrence of Dictyodora and extends the stratigraphic range of Dictyodora to the Late Permian. Two ichnospecies of Dictyodora are distinguished: D. zimmermanni and D. cf. scotica. Unlike the small-sized Dictyodora in the pre-Pennsylvanian, the three-dimensional morphology of Dictyodora studied here shows larger amplitudes and longer limbs with clearly inclined walls and basal burrows, which are interpreted to have been made by a soft-bodied worm-like organism with a snorkel-like organ as similarly documented in previous studies. Detailed systematic ichnological features and SEM and EDS results indicate that Dictyodora here is not simply a respiration structure made during the locomotion of the trace maker, but resulted from active filling by the trace maker. Dictyodora is probably not a good indicator of the deep-marine environment in the Paleozoic. From our dataset, Dictyodora originated from the shallow-marine environment in the early Cambrian, then migrated into the deep sea in the Ordovician and the marginal-marine setting in the Wenlock, and was finally restricted to the deep-marine environment in the Carboniferous and Permian. Both Psammichnites and Dictyodora are structures made by organisms with snorkel-like organs, and both were eliminated during the end-Permian mass extinction.

Decomposition of dinosaurian remains inferred by invertebrate traces on vertebrate bone reveal new insights into Late Jurassic ecology, decay, and climate in western Colorado.

A survey of 2,368 vertebrate fossils from the Upper Jurassic Mygatt-Moore Quarry (MMQ) (Morrison Formation, Brushy Basin Member) in western Colorado revealed 2,161 bone surface modifications on 884 specimens. This is the largest, site-wide bone surface modification survey of any Jurassic locality. Traces made by invertebrate actors were common in the assemblage, second in observed frequency after vertebrate bite marks. Invertebrate traces are found on 16.174% of the total surveyed material and comprise 20.148% of all identified traces. Six distinct invertebrate trace types were identified, including pits and furrows, rosettes, two types of bioglyph scrapes, bore holes and chambers. A minimum of four trace makers are indicated by the types, sizes and morphologies of the traces. Potential trace makers are inferred to be dermestid or clerid beetles, gastropods, an unknown necrophagous insect, and an unknown osteophagus insect. Of these, only gastropods are preserved at the site as body fossils. The remaining potential trace makers are part of the hidden paleodiversity from the North American Late Jurassic Period, revealed only through this ichnologic and taphonomic analysis. Site taphonomy suggests variable, but generally slow burial rates that range from months up to 6 years, while invertebrate traces on exposed elements indicate a minimum residence time of five months for carcasses with even few preserved invertebrate traces. These traces provide insight into the paleoecology, paleoclimate, and site formation of the MMQ, especially with regards to residence times of the skeletal remains on the paleolandscape. Comprehensive taphonomic studies, like this survey, are useful in exploring patterns of paleoecology and site formation, but they are also rare in Mesozoic assemblages. Additional work is required to determine if 16.174% is typical of bulk-collected fossils from Jurassic ecosystems in North America, or if the MMQ represents an unusual locality.

Elipsoideichnus meyeri Roselli 1987 revisited: A helicoidal fossil bee nest from the Paleogene of Uruguay

The rare helicoidal trace fossil Elipsoideichnus meyeri Roselli 1987 was known only from its holotype. New materials were collected and revised, confirming the validity and interpretation of this ichnotaxon. Its previously inferred internal structure, composed of two pair of internal, opposite cells per whorl, was checked and completed with these new materials. Sections of specimens show that cells have a thick lining. The finding of a spiral cap in cells finally confirms that unknown bees are the trace makers of E. meyeri, possibly related with Oxaeinae or Halictinae

High frequencies of theropod bite marks provide evidence for feeding, scavenging, and possible cannibalism in a stressed Late Jurassic ecosystem.

Bite marks provide direct evidence for trophic interactions and competition in the fossil record. However, variations in paleoecological dynamics, such as trophic relationships, feeding behavior, and food availability, govern the frequency of these traces. Theropod bite marks are particularly rare, suggesting that members of this clade might not often focus on bone as a resource, instead preferentially targeting softer tissues. Here, we present an unusually large sample of theropod bite marks from the Upper Jurassic Mygatt-Moore Quarry (MMQ). We surveyed 2,368 vertebrate fossils from MMQ in this analysis, with 684 specimens (28.885% of the sample) preserving at least one theropod bite mark. This is substantially higher than in other dinosaur-dominated assemblages, including contemporaneous localities from the Morrison Formation. Observed bite marks include punctures, scores, furrows, pits, and striations. Striated marks are particularly useful, diagnostic traces generated by the denticles of ziphodont teeth, because the spacing of these features can be used to provide minimum estimates of trace maker size. In the MMQ assemblage, most of the striations are consistent with denticles of the two largest predators known from the site: Allosaurus and Ceratosaurus. One of the bite marks suggests that a substantially larger theropod was possibly present at the site and are consistent with large theropods known from other Morrison Formation assemblages (either an unusually large Allosaurus or a separate, large-bodied taxon such as Saurophaganax or Torvosaurus). The distribution of the bite marks on skeletal elements, particularly those found on other theropods, suggest that they potentially preserve evidence of scavenging, rather than active predation. Given the relative abundances of the MMQ carnivores, partnered with the size-estimates based on the striated bite marks, the feeding trace assemblage likely preserves the first evidence of cannibalism in Allosaurus.

CHARACTERIZATION OF TRACES OF PREDATION AND PARASITISM ON FOSSIL ECHINOIDS

ABSTRACTInteractions with predators and parasites can result in traces found on Recent and fossil echinoids. However, identifying specific trace makers, particularly on fossil echinoids, remains contentious. To document the range of trace morphologies present on echinoids and improve our ability to identify and quantify biotic interactions affecting echinoids, we characterized traces found on fossil echinoids using museum collections and field sampling spanning the Jurassic to Recent worldwide. Using light microscopy, 8,564 individual echinoid specimens were examined including 130 species, and 516 traces of potential biotic interactions identified. Morphological characteristics were recorded for each trace, including the shape of the trace outline, maximum diameter and cross-section profile. Based on shared morphological characteristics, it was possible to classify all traces into eight categories: circular, subcircular, elongated, irregular, rectangular, figure-eight, notched, and linear. Cross-section characteristics provided additional insights into the identity of potential trace makers. To further evaluate the proposed biotic origins of these traces, trace diversity was examined through time and compared with anticipated ecological trends associated with the diversification of echinoids, and their predators and parasites. Trace diversity increased over time, starting in the late Eocene, coincident with the proliferation of echinoid-drilling gastropods, an indication that biotic interactions intensified through evolutionary time, as predicted by several macroevolutionary hypotheses previously tested using mollusks. The morphological descriptions provided here enhance our understanding of biotic traces on fossil echinoids, and the potential to identify temporal trends in the intensity and diversity of biotic interactions that have affected echinoids throughout their evolutionary history.

A new terrestrial trace fossil Feoichnus martini n. isp. from the Upper Cretaceous Two Medicine Formation (USA)

AbstractA new trace fossil, Feoichnus martini new ichnospecies, from the Two Medicine Formation is here described. This ichnotaxon is reported from the upper Campanian deposits of the Egg Mountain locality (Montana) and consists of a hemispherical to hemiellipsoidal structure with a truncated upper edge, and a regular, rounded lower edge marked by a lined border composed of stained layers. The trace maker likely impregnated the border using organic fluids. The simple lined wall observed in F. martini n. isp. suggests that the structure was produced by an invertebrate soil-dwelling organism, likely an insect. Specimens are preserved as casts in calcitic Inseptisols alongside an abundant vertebrate fossil record composed by dinosaurian and nondinosaurian fossil remains, dinosaur eggs and nest structures, and pervasive insect bioturbation. Feoichnus martini n. isp. represents an additional, minor component of the impoverished Celliforma ichnofacies reported at Egg Mountain and expands the paleogeographical distribution of the ichnogenus Feoichnus Krause et al., 2008 to the Upper Cretaceous deposits of Montana, USA.UUID: http://zoobank.org/7c1a5026-7f27-4f12-a9fb-1eb8daa93baf

Behavioural responses of Rhizocorallium to storm events: Evidence from the Middle Triassic of SW China

Large numbers of densely distributed Rhizocorallium provide a window to understanding the behavioural and functional changes of the trace maker after extreme environmental events. This study focuses on the analysis of Rhizocorallium from the Middle Triassic (Anisian) limestones in the Boyun section, Yunnan Province, Southwest China to investigate the ecological strategies and ethological signatures of its producers before and after storm events. Based on its morphological features, the studied Rhizocorallium is attributed to two ichnospecies Rhizocorallium jenense and R. commune, the latter showing two varieties R. commune var. auriforme and R. commune var. irregulare. In addition to Rhizocorallium, the trace fossil assemblage consists of Arenicolites, Palaeophycus, Planolites and Thalassinoides, which allows assignation to the Cruziana ichnofacies associated with the shallow marine environment. The studied ichnofossil-bearing intervals in the Boyun section are usually high bioturbated, with BPBI (bedding plane bioturbation index) around 5. The ichnoassemblage has a relatively low ichnodiversity and shows high density of Rhizocorallium, which is interpreted as the result of the opportunist strategy when the Rhizocorallium trace makers exploited the quiet, nutrient-rich substrates after storm events. Crosscutting relationships between multiple levels of Rhizocorallium indicate that earlier burrows were reworked by later ones due to successive storm events and erosion of the shallow-tier burrows. Orientation of the marginal tubes of Rhizocorallium jenense shows a bidirectional pattern at 295°NW and 160°SE, which may record the changes of the main flow direction. Diameter measurements support the total recovery of the macrobenthic trace makers during the Middle Triassic (Anisian).

Macaronichnus and contourite depositional settings: Bottom currents and nutrients as coupling factors

The trace fossil Macaronichnus segregatis degiberti (7–15 mm in diameter) is recorded for the first time in deep-marine contourites which were deposited in a Late Miocene outer-shelf to upper slope of the Rifian Corridor (Morocco). Macaronichnus is typical of shallow-marine, mainly foreshore environments. It is produced by deposit feeding opheliid polychaetes in high to intermediate latitudes. This record supports the significance of bottom current processes on environmental conditions as a major limiting factor affecting the macrobenthic trace maker community. Mediterranean overflow water during the Late Miocene enabled a high nutrient supply to the seafloor, favouring colonization by Macaronichnus producers. Thus, M. s. degiberti should be used as an indicator for nutrient availability instead of mainly a palaeodepth indicator. This finding provides significant information for oceanographic and environmental reconstructions related to contouritic processes, as well as to contourite characterization.

The earliest burst of necrophagous dung beetles in South America revealed by the Cenozoic record of Coprinisphaera

New ichnological, sedimentological and palaeobotanical information from a Miocene palaeosol succession from Patagonia bearing abundant fossil brood balls of dung beetles (Coprinisphaera) allow inferring novel aspects of the evolutionary history, biology and feeding habits of Scarabaeinae, along with the palaeoenvironmental and palaeoclimatic conditions in which they nested. Coprinisphaera tonnii and Coprinisphaera akatanka, both attributed to necrophagous dung beetles, represent 40.2% of the specimens. Considering their scarce or null record in older Cenozoic units from South America, these high values reveal that the first burst of necrophagous Scarabaeinae took place during the Miocene. Some Coprinisphaera preserve characters that indicate the developmental stage of the ball occupant and the adult emergence success. Both ichnospecies show the egg chamber isolated from the provision chamber, which was associated with a higher preference of cleptoparasites for necrophagous balls. The comparison among the abundance of traces of nest intruders in Coprinisphaera attributed both to necrophagous and to coprophagous beetles from different units of South America indicates that the presence of such intruders would be independent of the nature of the organic matter contained within the balls. Phytolith analyses performed in Coprinisphaera and extant necrophagous and coprophagous balls indicate that the comparison between the relative abundance of phytoliths in the wall of the brood ball, their infilling and the bearing palaeosol is a useful tool for inferring the feeding behaviour of the trace makers and support the attribution of Coprinisphaera tonnii and Coprinisphaera akatanka to necrophagous Scarabaeinae. Sedimentary and palaeosol analyses indicate that the beetles would have nested in well-drained soils showing mollic-like features, in grass-dominated habitats, under a seasonal sub-humid, temperate–warm climate.