Trace Makers Research Articles

Infaunal holothurian distributions and their traces in the Fraser River delta front and prodelta, British Columbia, Canada

Holothurians (sea cucumbers) constitute one of the largest and most abundant infaunal groups inhabiting the Fraser River delta front (0 to 150m water depth) and prodelta (greater than 150m water depth). The spatial distribution and density of animals reveal their preferred substrate grain sizes, and their tolerance or sensitivity to various stress factors, including salinity fluctuations, available food resources, sedimentation rate, and pollution. In the delta front, below 25m water depth (below storm-wave base), holothurians are asymmetrically distributed with respect to the main distributary channel. Population densities primarily reflect asymmetry in grain-size distributions across the delta front. Holothurians are absent or occur in low density in the sand-dominated southern delta front (SDF) whereas the mud-dominated northern delta front (NDF) is more heavily colonized. Sedimentation rate and nutrient content are equally important in holothurian distribution. Population densities of certain holothurians show significant increase where there are moderate sedimentation rates (2–4cmyr−1), and river-derived nutrient supply.Several subsurface traces and their surface expressions are attributed to holothurians. Subsurface traces include diminutive- and robust-Artichnus, Thalassinoides, and U-shaped bio-deformation structures. On the sediment surface, bio-topographic structures such as mounds and funnel-shaped depressions are produced by the activity of sea cucumbers. Of the holothurian-generated traces, only Artichnus can conclusively be attributed to sea cucumbers. Based on the distributions of the trace makers of Artichnus, we hypothesize that in the rock record this trace fossil can be used as evidence of stable euhaline salinity conditions, and sediment deposition and colonization below storm-wave base. Artichnus occurs mainly in mud-dominated (>55% mud) substrates.

Review of Dinosaur Tail Traces

Since 1858, when Hitchcock first recorded dinosaur tail traces from the Jurassic of Massachusetts, USA, a number of dinosaur tail traces have been reported. Although considered rare, at least 38 records of dinosaur tail traces have previously been reported in the literature. These occurrences are herein reviewed in order to understand their geographic and stratigraphic distribution, types of tail trace makers, and characteristics of dinosaur tail traces. Several terms for dinosaur tail traces have been employed and they are divided into tail impressions (TIs) for resting traces, and tail drag impressions (TDIs) for locomotion traces. Possible criteria for distinguishing, measuring and comparing TIs and TDIs are suggested. In addition, herringbone structures, one of the characteristic features of tail traces associated with ornithopod and theropod tracks, are discussed. Estimated speeds of tail trace makers are shown to be rather low. Finally, the abundance of tail traces associated with bipedal, rather than quadrupedal, dinosaurs is considered a reflection of behavior.

EuflabellaN. Igen.: Complex Horizontal Spreite Burrows in Upper Cretaceous–Paleogene Shallow-Marine Sandstones of Antarctica and Tierra del Fuego

Fine-grained sandstones and siltstones of Late Cretaceous to Eocene age in Antarctica and Tierra del Fuego yield an association of well-known shallow-marine trace fossils. Among them stick out complex spreite burrows, which are formally described asEuflabellan. igen. and subdivided into five ichnospecies with different burrowing programs and occurrences. As shown by concentrations of diatoms, radiolarians, foraminifers, and calcispheres in particular backfill lamellae, the unknown trace makers lived on fresh detritus from the surface as well as the burrowed sediment. In some ichnospecies, vertical sections show that the spreite is three-dimensionally meandering in upward direction and that upper laminae tend to rework the upper backfill of the folds underneath. This could mean a second harvest, after cultivated bacteria had time to ferment refractory sediment components, which the metazoan trace maker had been unable to digest before.

Balanoglossites ichnofabrics from the Middle Ordovician Volkhov formation (St. Petersburg Region, Russia)

The limestone succession of the Middle Ordovician Volkhov Formation in the St. Petersburg region (Russia) exposes numerous horizons with firm- and hardgrounds below omission surfaces, which contain trace fossils attributable to the ichnogenus Balanoglossites Magdefrau, 1932. Although known from the literature since 75 years, such trace fossils were previously only informally described as “Korrosionsgruben”, “Karandashi”, or ascribed to different ichnotaxa such as Trypanites, Arenicolites and Pseudopolydorites. Owing to their complexity and often high bioturbation density, the morphology of these trace fossils is difficult to capture. Ichnofabrics containing Balanoglossites triadicus were studied in detail from sawn rock faces, broken rock blocks and sectioned slabs, including those from historical buildings in St. Petersburg. Accordingly, different trace-fossil elements can be revealed in dependence on the original substrate consistency, reflecting various stages of lithification: Mineral-stained and Trypanites-perforated hardground surfaces are bioeroded with long elongated grooves which are assigned to the ichnogenus Sulcichnus. Subtle openings lead into the partly lithified limestone where they branch into complex galleries of B. triadicus. They are characterized by J-, U- and Y-shaped shafts and multiply branched tunnels, which gradually continue into the underlying firmground. Other portions of the ichnofabric only exhibit biodeformational structures or the strongly compacted and branched burrow networks Labyrintichnus, which is due to the original soft sediment consistency. Balanoglossites ichnofabrics demarcate certain omission surfaces within the Dikari Limestone and can be traced for more than 300 km, supporting the regional lithostratigraphical correlation. The trace maker of B. triadicus and related trace fossils is interpreted to be a eunicid polychate with the ability to bioerode and burrow the sediment. The studied material from the Ordovician is similar to the Balanoglossites from the type area, the Triassic of Germany, in many respects. B. triadicus is a very common trace fossil in Ordovician and other Palaeozoic rocks of Baltoscandia and North America but so far has been seldom identified as such but instead is commonly confused with Thalassinoides, from which, however, it differs in several aspects.

REPLY TO “COMMENT ON MARDEN (2013) REGARDING THE INTERPRETATION OF THE EARLIEST TRACE FOSSIL OF A WINGED INSECT”

Benner, Knecht, and Engel have replied to my critique of their interpretation of a Carboniferous trace fossil produced by an insect at the edge of water. Here I respond by pointing out that their reiterated scenario still requires mutually exclusive paths of motion and I show that their assertions of methodological shortcomings are tangential and lack merit. Overall, this discussion provides an opportunity to examine in greater detail competing hypothesis about behaviors and taxonomic identity of the trace maker, and relevance thereof to competing theories regarding early events in the evolution of pterygote insects.

Variations in population structure of Diplocraterion parallelum: Hydrodynamic influence, food availability, or nursery settlement?

In the Triassic of the Betic Cordillera, the U-shaped trace fossil Diplocraterion parallelum exhibits pronounced spatial variations in its abundance, size, and orientation. Higher density populations are found in small patches on bedding planes that were topographic lows on the palaeo-seafloor. These patches consist mainly of small specimens, separated into two size-groups: group A with larger specimens, and a similar preferred orientation, and group B of smaller individuals, densely distributed, and with a more variable orientation.Between the patches, isolated large individuals occur sparsely. Comparison with populations of crustaceans (which are among the potential trace makers of Diplocraterion parallelum) allows possible population dynamics of D. parallelum trace makers in this setting to be considered. Important factors determining changes in the abundance and distribution of crustacean populations are protection of small individuals against predators and/or comparatively high-energy conditions, nursery settlement, and/or temporal, typically seasonal, variations in environmental parameters. Depressions of the seafloor appear to have represented hospitable habitats in which juveniles of the producer of D. parallelum developed, reflecting either a deliberate reproductive strategy or the consequence of accumulation of eggs deposited elsewhere. In these depressions energy conditions may have been lower and food availability higher. During early ontogeny, defenseless young individuals used these areas as an ecological refuge against predators and high energy conditions. When the juveniles of the D. parallelum trace makers grew, they presumably spread from the nursery to settle in the surrounding area.

Asthenopodichnium in fossil wood: Different trace makers as indicators of different terrestrial palaeoenvironments

The ichnospecies Asthenopodichnium xylobiontum comprises U-shaped traces in wood, usually attributed to the activity of mayfly nymphs (Insecta, Ephemeroptera), which indicate the presence of freshwater palaeoenvironments. The record of a new ichnospecies in wood, Asthenopodichnium lignorum, in the Miocene of New Caledonia, strongly indicates that it may correspond to other trace makers because the potential producing Ephemeroptera are absent around these Miocene oceanic islands and in a wide area comprising New Zealand and Australia. We present herein the evidence for wood rotting fungi as potential trace maker of the new ichnospecies that has been previously recorded from Argentina, Egypt, Czech Republic, USA, and Lithuania. The new ichnospecies A. lignorum, in contrast with A. xylobiontum, is an indicator of terrestrial, humid to subhumid, palaeonvironments.

REANALYSIS AND EXPERIMENTAL EVIDENCE INDICATE THAT THE EARLIEST TRACE FOSSIL OF A WINGED INSECT WAS A SURFACE-SKIMMING NEOPTERAN

A recent description and analysis of an imprint fossil from the Carboniferous concluded that it was made by a mayfly landing in sediment at the edge of water. Here, I reanalyze that trace fossil and supply experimental evidence regarding wing traces and behavior. The thorax of the trace maker lacked structures characteristic of mayflies, but closely matches a modern neopteran insect family (Taeniopterygidae, Plecoptera) little changed from Early Permian fossils. Edges of the folded wings of live Taeniopteryx leave marks on sediment closely matching marks in the trace fossil. Faint marks lateral to and beyond the reach of meso- and metathoracic legs match the location where wings of surface-skimming Taeniopteryx stoneflies lightly touch the sediment when these insects skim onto wet ground at shorelines. Dimensions of the thorax of the trace indicate relatively weak flight ability compared to fossils from the Early Permian, making doubtful the hypothesis that the trace maker was flight capable. Ultimately, this fossil best fits a scenario in which a neopteran insect skimmed across the surface of water, then folded its wings. Surface skimming as a precursor to the evolution of flight in insects is supported by this fossil evidence of skimming behavior in a Carboniferous insect.

A Long Mortichnial Trackway of Mesolimulus walchi from the Upper Jurassic Solnhofen Lithographic Limestone near Wintershof, Germany

A 9.7 m long trackway was discovered in a plattenkalk quarry near the village of Wintershof, Bavaria, Germany, in 2002. The huge ichnofossil derives from the Lower Tithonian, Upper Jurassic Solnhofen Lithographic Limestone. The trackway is complete from beginning to end and consists of footprints, telson drag impressions, prosoma imprints and is identified as the ichnotaxon Kouphichnium isp. Preserved at the very end of the trackway is a complete specimen of Mesolimulus walchi confirming the trackway as a mortichnia (death march). Trackways and trace makers preserved together in the fossil record are rare and such specimens allow unique insights into behavior and ecology. The events that led to M. walchi preserved in this sediment are unknown; however, a most likely scenario is that the limulid was washed into the lagoonal environment during a harsh storm.

Early Permian Xiphosurid Trackways from India

Abstract Present work is the first report of Early Permian xiphosurid trackways from India. Surface trackways and undertracks, preserved within ice-marginal storm-affected, shoreface sediments of the Talchir Formation, Jayanti coalbasin closely resemble Kouphichnium Nopsca 1923. Trackways reveal distinct heteropody with foliate pusher impressions, paired series of semi-circular, oval, V- or Y-shaped chilate (walking) leg impressions. Varied ventral impressions also include telson drag marks and telson dents; spine drag marks, book -gills impression, genal gouges as well as symmetric, paired lateral genal furrows, partial cubichnial impressions of prosoma and spinose opisthosoma. A tentative early Permian age (Asselian/Sakmarian) and marginal marine facies association points towards a paleolimuloidae affinity for the trace makers, which is in conformity with their inferred widths of exoskeleton, sub-rounded prosoma and subtriangular spinose opisthosoma with predictable movable spines. Flexed pusher impressions and co-dominant pincer impressions as well as, other ventral impressions in abundance, confirm crawling as their dominant mode of locomotion. Inferred presence of juvenile crawlers in the community suggests a probable shoreline or marginal marine ecospace.

Late Silurian and Early Devonian terrestrialisation: Ichnological insights from the Lower Old Red Sandstone of the Anglo-Welsh Basin, U.K.

Late Silurian to Early Devonian deposits from the Lower Old Red Sandstone Anglo-Welsh Basin preserve a diverse assemblage of trace fossils that collectively comprise an important record of early terrestrialisation. Five main palaeoenvironmental categories are represented: (1) perennial rivers, (2) ephemeral rivers, (3) floodplain lakes, (4) alluvial fan, and (5) marginal marine. Ichnocoenoses mainly reflect the activity of aquatic and/or semi-aquatic animals. Fluvial deposits preserve evidence for colonisation by eurypterids, fish and myriapods. Ephemeral river channel margins/splays preserve the most diverse ichnofauna composed of deposit feeders' burrows and trackways produced by arthropods feeding and foraging in channel-margin soft grounds that were colonised after fluvial flood events. High densities of deposit-feeding structures may indicate of explosive population growth in response to periodic, acyclical replenishment of nutrients in these aquatic settings. Ichnotaxa common to both perennial and ephemeral fluvial environments suggest that there might have been only one aquatic ecosystem. The degree to which the channel-margin ichnofaunas record a truly subaerial terrestrial arthropod signature is difficult to ascertain and most trace makers were probably semi-aquatic. Some terrestrial animals invaded channel-margin areas to feed and were also capable of inhabiting high-energy, alluvial fan environments. However the fans contain low diversity ichnological assemblages and were likely to have been inhabited by an opportunistic fauna. Possibly the only truly subaerial terrestrial ichnocoenosis is that of pedogenically modified mudrock with Scoyenia, which represents an early soil ichnofauna. The majority of ichnocoenoses described from continental palaeoenvironments could be classified under the Scoyenia ichnofacies. Marginal marine deposits contain an impoverished Skolithos–Cruziana ichnofacies typical of Silurian–Devonian brackish water assemblages.

FEEDING TRACES AND PALEOBIOLOGY OF A CRETACEOUS (CENOMANIAN) CROCODYLIFORM: EXAMPLE FROM THE WOODBINE FORMATION OF TEXAS

Direct evidence of behavior in extinct tetrapods is rare. However, these traces can inform a variety of research questions touching on paleoecology, taphonomy, and functional morphology. Here we present fossil specimens from the Upper Cretaceous (Cenomanian) Woodbine Formation that exhibit tooth marks consistent with predation by a new taxon of large crocodyliform currently under study. Collected from the recently discovered Arlington Archosaur Site, the marked bones were largely found in a single peat horizon and in close association with the new crocodyliform. The feeding traces themselves consist of pits, scores, and punctures that occur on multiple turtle shell fragments and two dinosaur limb bones. The pattern of marks and the breakage on turtle carapaces and plastra suggest that they were crushed, whereas the marks on dinosaur bones indicate possible dismemberment. These interpretations and the association with a crocodyliform trace maker are based on observations of feeding behaviors and accompanying, diagnostic bite mark patterns made by extant crocodylians. The morphology of the new crocodyliform taxon and the distribution of bite marks indicates it was likely a generalist: an opportunistic predator that fed on a variety of prey, including turtles and dinosaurs. Given this evidence and the paleoenvironmental setting, the ecology of the large crocodyliform from the Woodbine Formation was likely most similar to that of fossil and living crocodylians inhabiting delta-plain environments. Not only were these crocodyliforms likely significant predators in the Woodbine paleoecosystem, they also played an important taphonomic role in the assembly of vertebrate remains from the surrounding community.

Palaeonvironmental and palaeoecological significance of flamingo-like footprints in shallow-lacustrine rocks: An example from the Oligocene–Miocene Vinchina Formation, Argentina

This article describes the lacustrine trace-fossil assemblage of the Late Oligocene–Early Miocene Vinchina Formation of northwest Argentina. The thick (> 5000 m) continental succession of the formation is essentially fluvial with thin aeolian and lacustrine intervals. The trace-fossil assemblage from the lacustrine facies is dominated by bird footprints, notably flamingo-like palmate bird footprints, and also contains invertebrate traces. The assemblage is of contrasting composition with those of the ubiquitous fluvial facies of the Vinchina Formation. We identify the possible trace maker of the web-footed bird footprints and infer the palaeoenvironmental and palaeoecological meaning of the lacustrine trace-fossil assemblage of the Vinchina Formation. The lacustrine succession is mainly composed of wave-rippled fine-grained sandstones and siltstones and wave-rippled heterolithic facies, with subordinate laminated mudstone and medium-grained sandstone with parallel lamination or cross-bedding. Metre-scale shallowing-upward cycles are typical and desiccation cracks were observed in a single bedding plane. The analysed interval was deposited in a wave-dominated littoral zone of a shallow permanent lake basin. Ichnofossils were found mostly in three trampled horizons of the upper part of the analysed succession. The trace-fossil assemblage is dominated by Phoenicopterichnum isp. (flamingo-like footprints), slender bird tracks without web traces, and triangular and fusiform hypichnial ridges (interpreted as bird undertracks). The remaining trace fossils are Lockeia siliquaria (bivalve resting trace), Rusophycus isp. (shallow arthropod burrow), Taenidium barretti (endostratal meniscate burrow) and small hypichnial double knobs (possible beak probing marks). Neoichnological observations on modern Chilean flamingo footprints ( Phoenicopterus chilensis) suggest that Phoenicopterichnum isp. is morphologically akin to modern flamingo footprints, although its average size is slightly smaller. The likely producers of the fossil footprints are members of the Palaelodidae and Phoenicopteridae, which are recorded in South America since the Late Oligocene. Phoenicopterichnum isp. appears in cuasi-parallel trackways with short pace length and forming a low angle with ripple crests. By comparison with observations of modern flamingo behaviour during this study and of shorebird studies from the literature, these tracks and trackways likely reflect flock-feeding behaviour (probably filter feeding) in a subaqueous belt parallel to the waterline. Invertebrate ichnofossils that appear on the same slabs from trampled horizons are mainly triangular and fusiform hypichnial ridges, while Phoenicopterichnum isp. and sparse small hypichnial double knobs also occur. In consequence, it is possible that these birds were foraging on small invertebrates (represented by Lockeia siliquaria, Rusophycus isp. and probably Taenidium barretti) in the coast of the Vinchina lake. The only fossil evidence for these invertebrates is the impression of articulated valves probably belonging to a small mollusc (potential producer of Lockeia). Trace-fossil assemblages dominated by flamingo-like footprints (including ichnogenera Phoenicopterichnum, Culcitapeda and similar unnamed tracks) are indicative of alkaline and/or saline waters, as suggested by the specialised filter-feeding mechanism of Late Oligocene to modern Phoenicopteriformes. These particular assemblages are distinguished as a subset within the “shorebird ichnofacies” with a definite palaeoenvironmental and palaeoecological meaning: the Phoenicopterichnum ichnosubfacies.

Evidence of microbial activity from a shallow water whale fall (Voghera, northern Italy)

The fossil bones, associated carbonate cements and enclosing concretion of a Miocene mysticete from inner shelf deposits (Monte Vallassa Formation, northern Italy) were analyzed for evidence of microbial activity. Optical and scanning electron microscopy, Raman spectroscopy, and stable C and O isotope geochemistry were used for high spatial resolution microfacies and biosedimentological analyses. Whale cancellous bones were filled by different carbonate cements including microcrystalline dolomite, rhombohedral dolomite and sparry calcite. Biofabric and biominerals such as microbial peloids, clotted textures and pyrite framboids were associated with the dolomite cements. Dolomite inside cancellous bones and in the enclosing concretion showed similar isotopic values (avg δ13C: −7.12‰; avg δ18O: +3.81‰), depleted with respect to the (late) sparry calcite cement (avg δ13C: −0.55‰; avg δ18O: −0.98‰). Microcrystalline barite (BaSO4) was observed on the external surface of the bones. In addition, two different types of microborings were recognized, distinguished by their size and morphology and were ascribed respectively to prokaryote and fungal trace makers. Our results testify for the development of a diverse microbial ecosystem during the decay of a shallow water whale carcass, which could be detected in the fossil record. However, none of the observed biosignatures (e.g., microbial peloids, clotted textures) can be used alone as a positive fossil evidence of the general development of a sulfophilic stage of whale fall ecological succession. The occurrence of the hard parts of chemosynthetic invertebrates associated with fossil whale bones is still the more convincing proof of the development of a sulfide-base chemoautotrophic ecosystem.

The trace fossil Nummipera eocenica from the Tatra Mountains, Poland: morphology and palaeoenvironmental implications

Jach, R., Machaniec, E. & Uchman, A. 2011: The trace fossil Nummipera eocenica from the Tatra Mountains, Poland: morphology and palaeoenvironmental implications. Lethaia, Vol. 45, pp. 342–355. The tubular trace fossil Nummipera eocenicaHölder 1989 occurs in a single stratigraphical horizon in Eocene nummulitic limestones of the Tatra Mountains, Poland. The wall of N. eocenica is built of Discocyclina and Nummulities (larger foraminifera) tests, very rarely of the Ditrupa (Polychaeta) tube fragments, bivalve shell fragments, echinoid spines and coralline algae. Morphotype are distinguished on the basis of wall composition and structure. Morphotype A is dominated by fusiform Discocyclina tests, which were preferentially selected by the trace makers for construction of a well-constructed and resistant wall. Morphotype B contains more robust tests of Nummulites, while morphotype C is dominated by saddle-shaped tests of Discocyclina. Nummipera eocenica was produced during a period of seafloor stabilization caused by a deepening. The succession of the morphotypes B, A reflects diminishing energy and increasing water depth. Probably morphotype C represents even lower energy environment than morphotype A. The trace fossil is interpreted as a domichnion, which wall was constructed for protection. The trace maker can be considered between polychaetes and crustaceans; however, comparisons to the closest recent analogues, the polychaete Diopatra cuprea or alpheid shrimps, are not satisfactory. □Bartonian, burrow, Carpathians, large foraminifera, trace fossils.

Late Carboniferous paleoichnology reveals the oldest full-body impression of a flying insect

Insects were the first animals to evolve powered flight and did so perhaps 90 million years before the first flight among vertebrates. However, the earliest fossil record of flying insect lineages (Pterygota) is poor, with scant indirect evidence from the Devonian and a nearly complete dearth of material from the Early Carboniferous. By the Late Carboniferous a diversity of flying lineages is known, mostly from isolated wings but without true insights into the paleoethology of these taxa. Here, we report evidence of a full-body impression of a flying insect from the Late Carboniferous Wamsutta Formation of Massachusetts, representing the oldest trace fossil of Pterygota. Through ethological and morphological analysis, the trace fossil provides evidence that its maker was a flying insect and probably was representative of a stem-group lineage of mayflies. The nature of this current full-body impression somewhat blurs distinctions between the systematics of traces and trace makers, thus adding to the debate surrounding ichnotaxonomy for traces with well-associated trace makers.

AN AGRICHNIAL FEEDING STRATEGY FOR DEEP-MARINE PALEOGENE OPHIOMORPHA GROUP TRACE FOSSILS

Abstract Ophiomorpha group trace fossils occur abundantly in a range of Eocene-aged deep-marine environments of deposition in the Basque basin, northern Spain. The morphology and dimensions of these trace fossils, observed in off-axis submarine lobe deposits, are discussed. The reported specimens display a highly organized and systematic burrowing behavior preserved on turbidite bed bases that display interconnecting Y-shaped (hexagonal-polygonal) morphologies. This observation, together with the cross-cutting relationship with tool marks, suggests construction of postdepositional agrichnial burrow networks. The networks probably harvested microbes that broke down cellulose-based organic matter providing an exploitable nutrient source for crustacean trace makers of Ophiomorpha. Therefore, the Ophiomorpha group–related traces discussed herein are postulated to represent an ethological response to changes in deep marine environmental conditions driven by global climate change during the early Paleogene, inc...

Zoophycos cyclicity during the last 425 ka in the northeastern South China Sea: Evidence for monsoon fluctuation at the Milankovitch scale

In a deep-sea piston core, covering the last 425 ka from the northeastern South China Sea, power spectrum analysis of several core data from sediment parameters has been conducted and compared with that obtained from time-series analysis of the distribution of the trace fossil Zoophycos through the core. Power spectra show a more or less well developed cyclical pattern, with similar cyclostratigraphic patterns for sand and carbonate content, oxygen isotopes and Zoophycos distribution, but different for carbon isotopes and total organic carbon content (TOC). Temporal calibration allows the recognition of Milankovitch orbital–scale cycles, with a duration of 111–100 ka for short-term eccentricity, 63–55 ka for the combined effect of both precession and obliquity, 42–40 ka for the obliquity cycle, and 28–21 ka for the precessional cycle band. The variable Milankovitch-scale cyclicity suggests the influence of a complex interaction of variable processes. East Asian monsoon variability at the Milankovitch orbital–scale cycles could determine variations in environmental conditions, including changes in the organic material reaching the sea floor, and in turn influencing the cyclical occurrence of the Zoophycos trace makers. The cyclicity of Zoophycos is of special interest to basin analysis, where Zoophycos has the potential of being used as a proxy for cyclical monsoon fluctuations at the Milankovitch scale.

Two episodic changes of trace fossils through the Permian-Triassic transition in the Meishan cores, Zhejiang Province

Six ichnogenera, Chondrites, Palaeophycus, Planolites, Rhizocorallium, Skolithos, and Thalassinoides, were identified from the drilling cores near the Global Stratotype Section and Point (GSSP) of Permian-Triassic boundary at Meishan, Zhejiang Province. The ichnological indices, including abundance, bioturbation index, and disturbed depth of trace fossils, show two episodes of intense changes near the Permian-Triassic Boundary (PTB). Episode I occurred in Beds 25–27b when the ecologically complicate forms such as Chondrites, Skolithos, Rhizocorallium, and Thalassinoides disappeared hereafter, the bioturbation index reduced from 1–5 to 1–3, and the disturbed depth declined from 5–66 to 2–5 cm. Episode II took place at the base of Bed 33 with the disappearance of Palaeophycus and Planolites, and subsequent absence of trace fossils and bioturbation till the middle-upper part of Bed 41 when the disturbed structures reoccurred, but they are only tiny Planolites and the bioturbation index was never higher than 3 and the disturbed depth less than 4 mm. Episode I shows an intense change, corresponding to the main stage of the end-Permian mass extinction, whereas Episode II is relatively weak, corresponding to the epilogue of the mass extinction of trace makers in the Early Triassic. Subsequently, ichnofossils were dominated by surface tracks in simple ecological habit and structures. This phenomenon indicates that the Early Triassic benthonic fauna is changed from sessile benthic system to mobile benthic system after the end-Permian mass extinction. In other words, the evolution of the trace fossils across the Permian-Triassic transition had an episodic process similar to the body fossils. In addition, the change of ichnofabrics is well coincided with the negative excursion of carbon isotopes and the expansion of cyanobacteria. As the results of physical and biogenic processes, trace fossils provided unique materials for the study of the biotic and environmental events, as well as their coupling evolution through the great Permian-Triassic transition.

Attributes of the wood-boring trace fossil Asthenopodichnium in the Late Cretaceous Wahweap Formation, Utah, USA

A common, macroscopic, wood-boring trace fossil occurs in the Upper Cretaceous braided- and meandering-stream deposits of the upper and capping sandstone members of the Wahweap Formation in Grand Staircase-Escalante National Monument, Utah. Upon detailed examination, this trace warrants assignment to Asthenopodichnium (Thenius, 1979). Asthenopodichnium is a scoop-shaped, pouch-like trace that is preserved as iron hydroxide rind casts of wood fragments and logs. The long axes of the scoops are typically aligned parallel or sub-parallel to the long axis of the preserved wood. In the upper and capping sandstone members, Asthenopodichnium characteristically occur in dense clusters in which pouches overlie one another, although they are found as isolated, individual traces and tight clusters of multiple individuals as well. The Asthenopodichnium trace maker has been purported to be the possible product of mayfly nymphs developed in moving fresh water. As a fresh water trace Asthenopodichnium may be used in conjunction with Teredolites, a marine or brackish indicator, to delimit the brackish-fresh water limit in estuarine deposits.