Locomotion Traces Research Articles

Palaeoecological significance of the trace fossil Circulichnis Vyalov, 1971 from the Carboniferous of the Donets Basin, Ukraine

The ichnogenus Circulichnis Vyalov is a horizontal a ring- or ellipse-shaped burrow and/or locomotion trace of an unknown producer, most likely an annelid or a “worm”, preserved on the bedding plane. This ichnogenus is known over a wide age interval (Ediacaran–Oligocene). Circulichnis demonstrates a wide ecological range and has been found in continental (Mermia ichnofacies), shelf, and relatively deep-water (turbidites) deposits. It is commonly interpreted as a sediment feeding trace, but the peculiarities of its formation remain somewhat mysterious, as it is unclear how the tracemaker reached the sediment surface, as lateral branches of the ring-shaped traces are extremely rare and have only been observed by a few researchers. A rather large specimen of Circulichnis montanus Vyalov, 1971 with a preserved lateral branch was found in the Mospyne Formation (upper Bashkirian, Lower Pennsylvanian) of the Donets Basin. This discovery confirmed the assumption made by Alfred Uchman and Bruno Ratazzi regarding the peculiarities of formation of Circulichnis. According to these authors, a single ring-shaped Circulichnis indicates an attempt to forage at a specific level in the sediment, while the lateral branches of Circulichnis are part of a vertical shaft leading to another level within the sediment. The study of Circulichnis montanus from the Donets Basin has confirmed that at least variant C of the Circulichnis formation scheme proposed by Uchman and Ratazzi is correct, i.e. the lateral branch is a horizontal or subhorizontal part of a generally vertical shaft. However, it is important to note that the correctness of variants A and B of the Uchman and Ratazzi scheme cannot be excluded. To answer this question unequivocally, new finds of well-preserved Circulichnis are necessary.

Unobtrusive Cognitive Assessment in Smart-Homes: Leveraging Visual Encoding and Synthetic Movement Traces Data Mining.

The ubiquity of sensors in smart-homes facilitates the support of independent living for older adults and enables cognitive assessment. Notably, there has been a growing interest in utilizing movement traces for identifying signs of cognitive impairment in recent years. In this study, we introduce an innovative approach to identify abnormal indoor movement patterns that may signal cognitive decline. This is achieved through the non-intrusive integration of smart-home sensors, including passive infrared sensors and sensors embedded in everyday objects. The methodology involves visualizing user locomotion traces and discerning interactions with objects on a floor plan representation of the smart-home, and employing different image descriptor features designed for image analysis tasks and synthetic minority oversampling techniques to enhance the methodology. This approach distinguishes itself by its flexibility in effortlessly incorporating additional features through sensor data. A comprehensive analysis, conducted with a substantial dataset obtained from a real smart-home, involving 99 seniors, including those with cognitive diseases, reveals the effectiveness of the proposed functional prototype of the system architecture. The results validate the system's efficacy in accurately discerning the cognitive status of seniors, achieving a macro-averaged F1-score of 72.22% for the two targeted categories: cognitively healthy and people with dementia. Furthermore, through experimental comparison, our system demonstrates superior performance compared with state-of-the-art methods.

Controls on bioturbation and sediment distribution in carbonate shoreface deposits: insights from heterogeneity in Pleistocene and Recent strata

ABSTRACT Burrowing organisms alter sedimentary textures, influence cement distribution, and affect petrophysical characteristics of carbonate strata. Although many descriptions of carbonate successions reference bioturbation, quantitative data on spatial variability of trace fossils is rare, and fewer studies address trace-fossil influence on postdepositional modification of sedimentary deposits, which can affect petrophysical properties. To address these unknowns and determine the controls on ichnology in carbonate shoreface successions, this study evaluates the along- and across-strike distribution of sediment and bioturbation in recent, Holocene, and Pleistocene shoreface deposits on the leeward margin of Crooked–Acklins Platform (CAP), southern Bahamas. To the north, the extant margin shelf is characterized by poorly to moderately sorted, very fine–fine, skeletal–peloid–ooid sand with an average of 16% mud (< 62.5 µm) that is moderately to intensely bioturbated (ii3–6). Trace assemblages are diverse, and include horizontal tracks and trails, abundant horizontal deposit-feeding and locomotion traces, as well as dwelling and resting burrows attributable to the proximal Cruziana Ichnofacies. In marked contrast, shelf margin deposits to the south are well-sorted, medium ooid–peloid sand with < 1% mud, and display a range of bioturbation, from nonbioturbated to moderately intense bioturbation (ii1–4). Trace-fossil assemblages exhibit low ichnodiversity, dominated by vertical dwelling burrows with reinforced wall lining attributable to the Skolithos Ichnofacies. Holocene and Pleistocene strata show similar proximal-to-distal and along-strike variations in sediment attributes, ichnodiversity, and bioturbation. These trends reflect a progressive, north-to-south increase in energy reflecting the change in margin orientation relative to the direction of dominant wave energy, analogous to the recent system. This study provides data for an integrated sedimentologic–ichnologic conceptual model for processes and patterns of sediment accumulation on carbonate shorefaces, and are distinct from siliciclastic analogs.

Multiple-Rusophycus assemblage from the Parnaíba Basin (NE Brazil) reflects trilobites as tracemakers and molting behavior

Trilobites inhabited all environments of Paleozoic seas, ranging from estuaries to continental slopes, and were globally distributed. Although their functional morphology and phylogenetic relations are established by well-preserved body fossils, the behavior of trilobites has received less attention. Three well-known trace fossils are interpreted to be produced by trilobitomorphs when preserved in Paleozoic rocks, Rusophycus (a resting trace), Cruziana (a furrowing trace), and Diplichnites (a locomotion trace). Those trace fossils unveil some aspects of trilobite behavior, but they were not investigated to test paleoecologic strategies based on morphometric parameters. This study uses Rusophycus to access the paleoecologic strategies of trilobites in storm-dominated shallow marine deposits of the Pimenteira and Cabeças formations (Middle to Upper Devonian, Parnaíba Basin, Brazil). It was conducted a detailed analysis of the Rusophycus specimens in a section that represents the transition between the Pimenteira and Cabeças formations (Parnaíba Basin). The width and length of the Rusophycus were measured, and statistical analyses were performed to understand the population characteristics. Relatively small-sized Rusophycus are dominant in such deposits, suggesting the dominance of young tracemakers and inferred r-strategist populations. The here reported multiple-Rusophycus assemblage reveals paleoecologic strategies of the population, and tiers relationship (cross-cutting epistratal and shallow-tier trace fossils such as Bergaueria, Palaeophycus, and Protopaleodictyon) indicate deep Rusophycus. The main reason for those burrowing activities deep in the substrate might be protection during ecdysis. Thus, the random distribution, lack of hunting evidence, and depth of Rusophycus suggest molting activity as the trigger for their production in storm-influenced beds of the Pimenteira Formation, probably by calmoniids or homalonotids.

Activity Recognition in Smart Homes via Feature-Rich Visual Extraction of Locomotion Traces

The proliferation of sensors in smart homes makes it possible to monitor human activities, routines, and complex behaviors in an unprecedented way. Hence, human activity recognition has gained increasing attention over the last few years as a tool to improve healthcare and well-being in several applications. However, most existing activity recognition systems rely on cameras or wearable sensors, which may be obtrusive and may invade the user’s privacy, especially at home. Moreover, extracting expressive features from a stream of data provided by heterogeneous smart-home sensors is still an open challenge. In this paper, we investigate a novel method to detect activities of daily living by exploiting unobtrusive smart-home sensors (i.e., passive infrared position sensors and sensors attached to everyday objects) and vision-based deep learning algorithms, without the use of cameras or wearable sensors. Our method relies on depicting the locomotion traces of the user and visual clues about their interaction with objects on a floor plan map of the home, and utilizes pre-trained deep convolutional neural networks to extract features for recognizing ongoing activity. One additional advantage of our method is its seamless extendibility with additional features based on the available sensor data. Extensive experiments with a real-world dataset and a comparison with state-of-the-art approaches demonstrate the effectiveness of our method.

AQUARIA-BASED OBSERVATIONS OF THE OPHIUROIDOPHIOLEPIS SUPERBAAND THE TRACKWAYS IT PRODUCES

ABSTRACTAn array of trace fossils have been ascribed to brittle-star behaviors including locomotion traces such as Biformites. Brittle-star locomotion has been well described but little work has been done to link modern brittle-star behavior to the trace fossil record. To draw this connection, a brittle star was kept in an aquarium and isolated in a “walking” tank with a fine glass-bead substrate. The animal was left in the walking tank for 30 minutes then the substrate was examined for traces. A digital camera was used to record the animal's movements and to document the resulting traces. Photographs were processed with photogrammetry software to produce digital models in order to acquire high-resolution images. Walking traces were described in detail and two morphologies were identified, which correspond with the ‘rowing' and ‘reverse-rowing' modes of brittle-star locomotion. Interestingly, traces similar to Biformites were not formed although some Biformites characters are observed. Morphological similarities include elongated lobate depressions and bioglyphs. Trackway dissimilarities include a repeating, paired, symmetrical pattern observed in the lab contrasting with Biformites that is often expressed as a texture of dense and overlapping, or isolated imprints. Another dissimilarity is the expression of bioglyphs in the lab as striae compared to the positive protuberances observed in Biformites. This study illustrates the utility of using actualistic observations to: (1) refine interpretations of locomotory mechanisms, such as rowing and reverse rowing, for a better understanding of walking behavior, and (2) to expand recognition criteria for ophiuroid (and other taxa) tracks in the fossil record.

Youngest Cretaceous dinosaur tracksite from the Middle East (Maastrichtian, Farrokhi Formation, Central Iran)

A late early Maastrichtian dinosaur trampling site is reported from the Farrokhi Formation of the Khur area, Central Iran. The largely indeterminate footprints, some of which may represent undertracks, can be classified as natural moulds (i.e. concave epireliefs) bordered by a raised rim of displaced sediment. They reach diameters of up to 0.5 m and were impressed under very shallow to subaerial conditions in an inter- to supratidal environment. Two generations of traces have been imprinted, initially into a soft, fine-grained carbonate sand and afterwards into a superficially hardened substrate that was still plastic underneath; the change in substrate consistency is supported by a conspicuous cracking pattern around the footprints. As a result, hardly any details of the foot morphology of the trackmakers are recorded. Nevertheless, the occurrence improves our knowledge about dinoturbation and its preservation in different kinds of substrates. Furthermore, it is the youngest record (ca. 70 Ma) of dinosaur locomotion traces from Iran and, in all probability, the entire Middle East.

First report of fish trace fossils ( Undichna ) from the Middle Devonian Achanarras Limestone, Caithness Flagstone Group

Two newly discovered specimens of the fish locomotion trace Undichna ( U. britannica and Undichna isp.) are described from the Middle Devonian Achanarras Limestone Member (Caithness Flagstone Group, NE Scotland). Fish trace fossils have not previously been reported from the Achanarras Limestone Member, despite decades of study of the unit as a key locality for fish body fossils. The traces comprise discontinuous sinusoidal grooves; one showing multiple parallel incisions, created by the fins of an acanthodian fish swimming close to the substrate. The apparent absence of trace fossils attributable to infaunal or epifaunal benthic organisms suggests that the sediment at the bottom of the lake was relatively inhospitable. The low ichnodiversity of the Achanarras Limestone Member is likely due to low oxygen levels in the depositional environment. Thematic collection: This article is part of the SJG Early Career Research available at: https://www.lyellcollection.org/cc/SJG-early-career-research

Extensive vertebrate tracksite from the Upper Red Formation (middle–late Miocene), west Zanjan, northwestern Iran

Abstract. An extensive vertebrate tracksite from the middle–late Miocene Upper Red Formation in western Zanjan Province, northwestern Iran, provides new records of paleobiogeographical significance. These are records of common footprints of felids referred to as Felipeda lynxi Panin and Avram, canids referred to as Canipeda longigriffa Panin and Avram and less common bird footprints referred to as Iranipeda abeli Lambrecht. The Canipeda record establishes the late Miocene presence of canids on the Iranian Plateau as part of the Eurasia-wide “Eucyon event”. The Felipeda footprints are consistent with body fossil and footprint records elsewhere in Eurasia that indicate a widespread distribution of felids by late Miocene time. An unusual trace associated with the footprints is a large, shallow grazing or locomotion trace similar to Megaplanolites in some features but distinctive in various features and its occurrence in nonmarine facies, and it will be the subject of further study.

TraMiner: Vision-Based Analysis of Locomotion Traces for Cognitive Assessment in Smart-Homes

The rapid increase in the senior population is posing serious challenges to national healthcare systems. Hence, innovative tools are needed to early detect health issues, including cognitive decline. Several clinical studies show that it is possible to identify cognitive impairment based on the locomotion patterns of the elderly. In this work, we investigate the use of sensor data and deep learning to recognize those patterns in instrumented smart-homes. In order to get rid of the noise introduced by indoor constraints and activity execution, we introduce novel visual feature extraction methods for locomotion data. Our solution relies on locomotion trace segmentation, image-based extraction of salient features from locomotion segments, and vision-based deep learning. We carried out extensive experiments with a large dataset acquired in a smart-home test bed from 153 seniors, including people with cognitive diseases. Results show that our system can accurately recognize the cognitive status of the senior, reaching a macro-F_1 score of 0.873 for the three categories that we target: cognitive health, mild cognitive impairment, and dementia. Moreover, an experimental comparison shows that our system outperforms state-of-the-art methods.

A trace fossil made by a walking crayfish or crayfish-like arthropod from the Lower Jurassic Moenave Formation of southwestern Utah, USA.

New invertebrate trace fossils from the Lower Jurassic Moenave Formation at the St. George Dinosaur Discovery Site at Johnson Farm (SGDS) continue to expand the ichnofauna at the site. A previously unstudied arthropod locomotory trace, SGDS 1290, comprises two widely spaced, thick, gently undulating paramedial impressions flanked externally by small, tapered to elongate tracks with a staggered to alternating arrangement. The specimen is not a variant of any existing ichnospecies, but bears a striking resemblance to modern, experimentally generated crayfish walking traces, suggesting a crayfish or crayfish-like maker for the fossil. Because of its uniqueness, we place it in a new ichnospecies, Siskemia eurypyge. It is the first fossil crayfish or crayfish-like locomotion trace ever recorded.

First xiphosuran traceway in the middle Muschelkalk facies (Middle Triassic) of the Catalan Basin (NE Iberian Peninsula)

In the last decade, the first ichnoassamblages from the middle Muschelkalk facies (upper Anisian–middle Ladinian) of the Catalan Basin (NE Iberian Peninsula) have been discovered. Herein, the first xiphosuran trace fossils are described from the locality of Penya Rubí, a newly discovered ichnosite from the Catalan Basin. The finding opens a window into peri-Tethys ecosystems with coastal influence. The traceway is referred to the ichnogenus Kouphichnium, a locomotion trace attributed to xiphosurans. The traceway preserves telson grooves and different imprint morphologies from the various appendages. The traceway pattern and arrangement of the different traces suggest a crawling locomotion style. The sedimentology suggests a coastal zone with areas influenced by tides (intertidal flat). The morphological variations of the ichnites are correlated to substrate rheology, the locomotion of the tracemaker and environmental conditions.

Segmentichnus mohri igen. et isp. nov., a giant new trace fossil from the Culm facies (lower Carboniferous) of the Franconian Forest (Saxothuringian Belt, Germany)

A new ichnogenus and ichnospecies, Segmentichnus mohri, is recognized in the lower Carboniferous deep-sea Culm facies deposits in the southern Germany. The trace fossil is an unusually large, horizontal, tubular burrow with primary successive branching and transverse annulation with ring-like, slightly irregular swellings, without wall, preserved in full relief in dark grey slate. Segmentichnus mohri is interpreted to be a locomotion and feeding trace (pascichnion) produced within the mud by unknown ‘worm’-like animal in a turbiditic depositional system. It belongs to the transition between the Paleodictyon and Nereites ichnosubfacies of the Nereites ichnofacies.

Horseshoe crab trace fossils and associated ichnofauna of the Pony Creek Shale Lagerstätte, Upper Pennsylvanian, Kansas, USA

The uppermost Pennsylvanian Pony Creek Shale Lagerstätte (Pony Creek Shale Member, Wood Siding Formation, Wabaunsee Group) near Maple Hill, Wabaunsee County, Kansas, contains exceptionally preserved horseshoe crab (Xiphosura) fossils. Associated with these fossils is an ichnofauna that includes trace fossils assumed to be produced by xiphosurids, as well as coprolites and a few burrows. Of the trace fossils recovered from the Pony Creek Shale Member, 26 specimens represent the ichnogenera Arborichnus, Crescentichnus, Kouphichnium, and Selenichnites, all of which are commonly associated with xiphosurids. The other trace fossils consist of the ichnogenus Rhizocorallium, several unidentified burrows, and coprolites, some preserving animal remains. The xiphosuran locomotion traces from the Pony Creek Shale Member are primarily crawling trails. These trace fossils are distinguished by back and forth scratch imprints, as opposed to the typical xiphosurid tracks that show independent foot marks in the substrate. Other trace fossils include resting traces and feeding traces. Previous paleoenvironmental interpretations and the trace and body fossil record indicate a marginal-marine depositional system for the Pony Creek Shale.

Meanderovaleichnus huenickeni ichnogen. et ichnosp. nov. from the Bajo de Vélez Formation (Upper Carboniferous-Permian), Argentina: a new case of worm-type burrowing

A new ichnofossil, Meanderovaleichnus huenickeni ichnogen. et ichnosp. nov., is described from the fluviolacustrine deposits of the Bajo de Véliz Formation (Upper Carboniferous–Permian). The trace fossil consists of meanders (epichnial) with regular constrictions of variable width along the course. It is interpreted as a locomotion trace (repichnion) due to peristaltic burrowing of a worm, probably an annelid

An integrative physical, mineralogical and ichnological approach to characterize underfilled lake‐basins

AbstractLakes are particularly sensitive to environmental fluctuations, which are recorded in their facies and stratigraphy. Ephemeral lakes reveal their sensitivity to palaeoenvironmental changes in the overprinting of the sedimentary features in every single bed. Tetrapod‐track taphonomic‐modes and ichnological taphonomic‐pathways can be used as sensitive indicators of environmental conditions of the track‐bearing beds during deposition and imprinting. The Middle Triassic Cerro de las Cabras succession (Cuyana Basin, Argentina) provides an excellent opportunity to these environmental indicators in an underfilled palaeolake. A model of ichnological preservation for underfilled lake systems is proposed and the role of the ichnology record in the sequence stratigraphy analysis is evaluated, based on the integration of tetrapod‐track modes, taphonomic‐pathways of playa‐lake ichnofauna, mineralogy and physical data. Soft‐ground suites include those dominated by invertebrate grazing traces and arthropod locomotion traces (Suite 1), and those overprinted by horizontal‐vertical dwelling burrows with tetrapod tracks preserved in taphonomic modes B and C (Suite 2). The firm‐ground suite (Suite 3) comprises tetrapod‐tracks with the best preservation styles (modes A and B) along less abundant invertebrate dwelling and feeding traces as found in Suite 2. Clay mineralogy (dominated by illite with subordinate smectite) suggests low plasticity of the layers, in agreement with low‐relief deformation structures observed in tetrapod‐track taphonomic‐modes. The well‐preserved track tetrapod features documented in the Cerro de las Cabras succession, together with the absence of pedogenic disturbance, trampling obliterating the footprints, and/or evidence of strong disturbance by wind, desiccation and/or precipitation, supports short periods of exposure of the imprinted surface particular to this succession. An integrated multiproxy approach is proposed to evaluate the evolutionary interpretation and identification of autogenic versus allogenic controls in underfilled lake‐basin histories. The observed aggradational‐trend suggests an equilibrium between rates of accommodation change and sediment supply, and that the basin‐centre did not experience prolonged sediment‐starved conditions.

Australia's earliest tetrapod swimming traces from the Hawkesbury Sandstone (Middle Triassic) of the Sydney Basin

AbstractThe Hawkesbury Sandstone (Hawkesbury Series, Sydney Basin) on the southeastern coast of New South Wales, Australia, preserves a depauperate but important vertebrate tetrapod body-fossil record from the Early and Middle Triassic. As with many fossil sites around the world, the ichnological record has helped to shed light on the paleoecology of this interval. Herein, we investigate historical reports of a trackway pertaining to a putative short-tailed reptile found at Berowra Creek in the 1940s. Reinvestigation of the surviving track-bearing slabs augmented by archival photographs of the complete trackway, suggests that these impressions, which consist primarily of didactyl tracks (plus less common monodactyl and tridactyl traces), represent the earliest example of a swimming tetrapod found in Australia. Another isolated specimen (possibly from a nearby locality at Annangrove) appears to represent similar didactyl swim traces of a second, larger individual. Although the identities of the trackmakers are unknown, the Berowra Creek individual had an estimated body length of between ~80 cm (short-coupled) and 1.35 m (long-coupled), and produced the subaqueous trackway while travelling upslope (against the current) on a sandbar within a braided river system of the Hawkesbury Sandstone. These trackways partially resemble amphibian swim traces in the so-called Batrachichnus C Lunichnium continuum, but appear to represent a unique locomotion trace. This reanalysis of the Berowra Creek trackway provides insight into the locomotion of tetrapods of the Triassic Hawkesbury Series, which remains a poorly understood aspect of their life history.

Secular variations of ichnofossils from the terrestrial Late Permian–Middle Triassic succession at the Shichuanhe section in Shaanxi Province, North China

Abstract Ichnological studies are exceptionally important for reconstruction of ecosystems in the aftermath of mass extinctions, but they have only rarely been undertaken from strata deposited in continental settings during the Permian–Triassic transition. This paper systematically documents seventeen ichnogenera and three ichno-types coupled with plant fossils (mainly equisetaceous stems and roots) from the fluvial–lacustrine Late Permian to Middle Triassic Shichuanhe section in North China. These ichnofossils constitute several ichnoassemblages, including resting traces ( Lockeia ), locomotion traces ( Diplichnites , Kouphichnium , Protovirgularia ), dwelling traces ( Arenicolites , Camborygma , Macanopsis , Palaeophycus , Skolithos ), grazing traces ( Gordia , Helminthoidichnites , Monomorphichnus ) and feeding traces ( Planolites , Scoyenia , Spongeliomorpha , Taenidium ) and some of them were scarcely reported in the coeval sediments of North China. The ichnological criteria, such as ichnodiversity, intensity of bioturbation, and burrow size and depth, exhibit a significant reduction in the latest Permian rocks, accompanied by simplification of trace maker ethology. These signals initially rebound in the early Early Triassic, when the behavioral generalists opportunistically occupied the empty niches and constructed simple but deep Skolithos . A full reconstruction of continental ecosystems should take place in the late Early Triassic to Middle Triassic, with high ichnodiversity, intensive bioturbation and behavior complexity of trace producers. The small, simple but deep burrows occurring in the early Early Triassic would be the ecological responses of the animals to the lethal heat in the terrestrial facies.

New evidence of xiphosurids from the Middle Jurassic of Morocco: Palaeoenvironmental, palaeoecological and palaeobiogeographical implications

Horseshoe crabs (Chelicerata, Xiphosura) from Mesozoic deposits are extremely rare in the fossil record of the African continent. Here we report new evidence of the occurrence of xiphosurans in North Africa. These are horseshoe crab traces, including the ichnogenera Kouphichnium (repichnia) and Selenichnites (fodinichnia and/or domichnia), which have been discovered in Middle Jurassic strata of the Imilchil area (Central High Atlas, Morocco). They are preserved on upper and lower bed surfaces of sandy limestones and marls in the upper parts of the Tislit and Imilchil formations (late Bajocian-early Bathonian).The Selenichnites traces, measuring up to 30 cm in width, co-occur with theropod and birdlike tracks. The reported Kouphichnium is the first record from Mesozoic deposits of Morocco, while Selenichnites is the second occurrence in Jurassic strata of Africa. These ichnogenera evidence different behaviour of horseshoe crabs, i.e. Selenichnites is the result of burrowing activity when searching for food in the sediment, and Kouphichnium is a regular locomotion trace left on the sediment surface, occasionally leaving an impression of the telson.The combination of sedimentological data and ichnological analysis indicates a shallow-water subtidal depositional environment preceding the Bathonian regression of the Atlas domain.Palaeobiogeographically, the discoveries indicate the presence of horseshoe crabs at the southern margin of the Tethys. Furthermore, they enhance our knowledge of their previously scarcely documented distribution in Gondwana during the Mesozoic.

BIOGENIC STRUCTURES OF UNIONIFORM BIVALVES IN WET-INTERDUNE DEPOSITS (LATE MIOCENE–EARLY PLIOCENE, ARGENTINA)

Abstract Environmental changes within a Neogene coastal dune system are recorded by endobenthic unioniform bivalves that lived in muddy or sandy interdune pond sediments. These bivalves were suspension-filter feeders that formed dense, almost monospecific communities in the wet-interdune deposits of the continental intervals of the Rio Negro Formation (late Miocene–early Pliocene). Activity of unioniform bivalves appears to be related to sediment type; resting and locomotion traces dominate in the muddy heterolithic facies, whereas equilibrium/escape structures prevail in the sand-dominated heterolithic facies. These traces characterize two scenarios of the wet-interdune development. First, during high and/or relatively stable water levels, bivalves colonized the muddy bottom and produced resting and locomotion traces. When water level dropped due to desiccation, biogenic structures were impacted by the formation of mud cracks and subsequently covered by sand delivered by migrating dunes. Second, in spite...