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Are aeolian ichnofacies distinctive and useful? An analysis of trace fossil assemblages from Cretaceous aeolian facies in northern Patagonia, Argentina
Abstract
In this paper, Cretaceous trace fossil assemblages are reported from aeolian facies within four units from Patagonia, Argentina, to evaluate the usefulness of the aeolian ichnofacies concept. From oldest to youngest, studied units comprise the Agrio (Valanginian-Hauterivian), Cerro Barcino (Aptian-Cenomanian), Candeleros (Cenomanian), and Allen (Campanian-Maastrichtian) formations. Twenty one ichnotaxa were recorded, including ten of invertebrate origin (Archaeonassa fossulata, Arenicolites tenuis, Beaconites isp., Digitichnus laminatus, Edaphichnium lumbricatum, cf. Octopodichnus isp., Palaeophycus tubularis, Skolithos linearis, Taenidium barretti, and an unidentified arthropod trackway), seven tetrapod footprints and burrows (Avipeda isp., Brasilichnium isp., cf. Chelonipus isp., Reniformichnus katikatii, two types of indeterminate footprints, and burrow fills) and four rhizolith types. Entradichnus meniscus (formerly used as eponym of an aeolian ichnofacies) is considered junior synonym of Taenidium barretti. Common ichnotaxa in aeolian and fluvial sequences like Taenidium barretti, Skolithos linearis and Palaeophycus tubularis are facies-crossing ichnotaxa and should not be used to distinguish ichnofacies. Trace fossil assemblages and ichnofabrics from aeolian dune, dry interdune and wet interdune facies are interpreted in terms of the potential producers and their palaeoecological and palaeoenvironmental constraints. This procedure is more informative than the ichnofacies approach in aeolian deposits. Based on a literature review of 32 examples of trace fossil assemblages from Cretaceous aeolian sequences worldwide, we conclude that the most distinctive ichnotaxa occur in aeolian dunes, including Brasilichnium, Farlowichnus, lacertoid footprints, Octopodichnus and Paleohelcura. It is recommended to abandon the usage of the Chelichnus, Entradichnus and Entradichnus-Octopodichnus ichnofacies, which are poorly defined in terms of recurrence and environmental significance or based on uncharacteristic or unavailable ichnotaxa. We propose a new definition of the Octopodichnus ichnofacies, diagnosed by the presence of subequant tetrapod footprints in quadrupedal trackways and/or selected arachnid /insect trackways. This ichnofacies is a taphofacies recorded from the Permian to the Cretaceous, and probably extends to the Cenozoic.
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The earliest Cretaceous Botucatu Formation (Paraná Basin, Brazil) comprises an erg deposit developed in the central part of Gondwana and is dominated by eolian dune facies. In this paper, we improve understanding of the ichnology of eolian deposits by describing trace fossil assemblages in São Bento Quarry in Araraquara County. The trace fossils occur on paleodune slipface surfaces, and include trackways (Paleohelcura tridactyla and P. araraquarensis) and burrows (Arenicolites isp., Skolithos isp., Taenidium serpentinum, Vagorichnus anyao, and Planolites beverleyensis). The Skolithos isp. and Vagorichnus anyao specimens also occur in clusters in more intensely bioturbated beds. We interpret these assemblages as evidence of episodic wet events, which were unable to generate subaqueous facies, but triggered plant growth and invertebrate proliferation. Based on studies of modern hot deserts, we infer that the overall longstanding water input promoted some primary productivity sustaining striving invertebrates, recorded as low bioturbation levels. Episodic wet events controlled the bioturbation bursts by increasing the primary productivity and inducing consequent invertebrate proliferation. We propose that these bursts of invertebrate bioturbation observed along the stratigraphic section of dry facies can be taken as the main ichnological characteristic of a dry eolian system. We also propose refinements to the Octopodichnus–Entradichnus ichnofacies model, addressing unsolved issues to enhance the interpretation of ancient eolian environments.
Theria represent an extant clade that comprises placental and marsupial mammals. Here we report on the discovery of a new Late Cretaceous mammal from southern Patagonia, Patagomaia chainko gen. et sp. nov., represented by hindlimb and pelvic elements with unambiguous therian features. We estimate Patagomaia chainko attained a body mass of 14 kg, which is considerably greater than the 5 kg maximum body mass of coeval Laurasian therians. This new discovery demonstrates that Gondwanan therian mammals acquired large body size by the Late Cretaceous, preceding their Laurasian relatives, which remained small-bodied until the beginning of the Cenozoic. Patagomaia supports the view that the Southern Hemisphere was a cradle for the evolution of modern mammalian clades, alongside non-therian extinct groups such as meridiolestidans, gondwanatherians and monotremes.
Scarce fossil tetrapod burrows have been recorded in Cretaceous rocks, which is probably linked to the dominant equable climates that existed for most of this period. The occurrence of Cretaceous tetrapod burrows from Patagonia (Chubut Province, Argentina) dated between 118 and 115 million years ago, gives insights into their paleoecology and paleoenvironment. The rocks containing the tetrapod burrows are of pyroclastic origin and represent eolian dunes and ash-fall deposits, some reworked by fluvial currents and others showing soil development. Fossil burrow casts preserved in a paleosol are composed by a ramp with a slightly curved or straight path in plan-view and lacking bifurcation, a rounded termination with no enlargement, showing a reniform cross-section, and are assigned to the ichnospecies Reniformichnus katikatii. The strongly flattened cross-sectional shape of the burrow casts and comparison with modern lizard burrows suggest that the producers were lepidosaurs (body mass = 50–323 g). Among Cretaceous fossorial lepidosaurs from Patagonia, the best candidate is an eilenodontine sphenodontian. Sphenodontians burrowed in the fossil soils where also arthropods, earthworms and shrubby plants thrived. The rare occurrence of tetrapod burrows in Cretaceous rocks is linked to stressing conditions related to frequent arrival of volcanic ash and a semiarid seasonal climate.
Under certain conditions, most commonly abrupt flooding events, entire eolian bedforms can be incorporated into the geological record. Sediment that was essentially ‘in transport’ within these bedforms at the time of preservation has a distinct sedimentary architecture compared to that of sensu stricto accumulated intervals. Despite this, while the preservation of bedforms has been readily documented from outcrop and subsurface eolian successions, stratigraphic intervals corresponding to these bedforms have rarely been identified and separated from accumulated intervals. The impact of capturing and representing bedform intervals in reservoir models has therefore not been explored. The Avilé Member (Neuquén Basin, Argentina) is a prolific oil reservoir of eolian origin in which both bedforms and accumulated intervals are documented. The aim of this study is to use the Avilé Member record at the Puesto Hernández oilfield to develop a workflow to identify, characterize, map and model discrete eolian bedform and accumulated intervals in a subsurface scenario. Characterization of the unit's geometry, sedimentary facies, and petrophysics was carried out from seismic, wireline log and core analysis. The development of a conceptual model of the accumulation system and its evolution allowed the identification of bedform and accumulated intervals. Precise mapping of these intervals required the development of a geometrical method, based on correlating interdune lows and using a datum surface to provide for an approximation to the ancient accumulation surface. A zoning scheme conditioned by the intervals was tested against a simple, ‘one-zone’ model, to determine its effectivity in separating discrete heterogeneity zones. The model was also tested in a dynamic simulator to history match the field production and analyze its impact in dynamic reservoir simulation. This example serves as a valuable reference to illustrate how eolian bedforms and accumulated intervals may be identified, characterized, and modelled in subsurface scenarios around the world.
A trackway and burrows of a small rodent-sized bounding mammal (attributed to the Cape gerbil, Gerbilliscus afra ) and a traceway of a large arachnid (spider) from the Pleistocene Waenhuiskrans Formation represent two biological groups not previously reported from this track-rich dune facies, which is widely distributed along the Cape south coast of South Africa. This may be due to biases against the preservation of small tracks. Trackways of hopping or bounding rodent-sized mammals are rare in the fossil record, occurring at only two known Mesozoic sites and three Cenozoic sites. Where these occur in dune facies, they are commonly associated with arachnid and other arthropod surface trails. The arachnid trace fossils commonly include the spider traceway Octopodichnus , known from the Permian to Recent, which is also the temporal range of the eponymous Octopodichnus ichnofacies. The abundance of small-mammal tracks associated with dune ichnofaunas led to the naming of the late Palaeozoic and Mesozoic Chelichnus ichnofacies, which is largely co-extensive with the Octopodichnus ichnofacies at this time. However, the recognition of similar mammal–arthropod dune facies assemblages in the Cenozoic requires adjusting our understanding of their distribution in space and time, and extends the known distribution of dune ichnofacies.
Several studies have emphasized the complexity of the interaction between fluvial and aeolian processes at erg margin settings, and their importance in the resulting geological record. The Cretaceous Candeleros Formation in the "Cañadón de Las Tortugas" site which is located in "La Buitrera Paleontological Area" (Neuquén Basin, Argentina) provides excellent outcrops where the record of a variety of interactions between the aeolian and fluvial processes can be observed. Therefore, the aim of this project was to reconstruct the accumulation systems and the spatial and temporal relations of their associated sedimentary processes. The methodology included the logging of sedimentary sections, a facies and architectural analysis and the identification of the different hierarchies of unconformities. The different architectural elements identified are related both to aeolian and fluvial genesis as mentioned before. The first ones comprise aeolian dune deposits and wet interdune deposits, whilst the second ones are channelized deposits, non-channelized proximal fluvial deposits and non-channelized distal fluvial deposits. These architectural elements were identified in three different evolutive stages of the depositional model made. Hence, the studied interval has a complex pile of overlapping units that represents the contraction/expansion of an erg-margin system as a result of variations of the water table position to climatic conditions. Therefore, this study enhances current understanding of the stratigraphic record of erg margin systems at different time-space scales. This high-resolution study provides a detailed account of the processes that operated in the Kokorkom paleodesert and relevant information for the reconstruction of the accumulation systems in the southern part of the Neuquén Basin during the Late Cretaceous.
In the last decades, several discoveries have uncovered the complexity of mammalian evolution during the Mesozoic Era, including important Gondwanan lineages: the australosphenidans, gondwanatherians, and meridiolestidans (Dryolestoidea). Most often, their presence and diversity is documented by isolated teeth and jaws. Here, we describe a new meridiolestidan mammal, Orretherium tzen gen. et sp. nov., from the Late Cretaceous of southern Chile, based on a partial jaw with five cheek teeth in locis and an isolated upper premolar. Phylogenetic analysis places Orretherium as the earliest divergence within Mesungulatidae, before other forms such as the Late Cretaceous Mesungulatum and Coloniatherium , and the early Paleocene Peligrotherium . The in loco tooth sequence (last two premolars and three molars) is the first recovered for a Cretaceous taxon in this family and suggests that reconstructed tooth sequences for other Mesozoic mesungulatids may include more than one species. Tooth eruption and replacement show that molar eruption in mesungulatids is heterochronically delayed with regard to basal dryolestoids, with therian-like simultaneous eruption of the last premolar and last molar. Meridiolestidans seem endemic to Patagonia, but given their diversity and abundance, and the similarity of vertebrate faunas in other regions of Gondwana, they may yet be discovered in other continents.
A distinctive burrow form, Reniformichnus australis n. isp., is described from strata immediately overlying and transecting the end-Permian extinction (EPE) horizon in the Sydney Basin, eastern Australia. Although a unique excavator cannot be identified, these burrows were probably produced by small cynodonts based on comparisons with burrows elsewhere that contain body fossils of the tracemakers. The primary host strata are devoid of plant remains apart from wood and charcoal fragments, sparse fungal spores, and rare invertebrate traces indicative of a very simplified terrestrial ecosystem characterizing a 'dead zone' in the aftermath of the EPE. The high-paleolatitude (~65-758S) setting of the Sydney Basin, together with its higher paleoprecipitation levels and less favorable preservational potential, is reflected by a lower diversity of vertebrate fossil burrows and body fossils compared with coeval continental interior deposits of the mid-paleolatitude Karoo Basin, South Africa. Nevertheless, these burrows reveal the survivorship of small tetrapods in considerable numbers in the Sydney Basin immediately following the EPE. A fossorial lifestyle appears to have provided a selective advantage for tetrapods enduring the harsh environmental conditions that arose during the EPE. Moreover, high-paleolatitude and maritime settings may have provided important refugia for terrestrial vertebrates at a time of lethal temperatures at low-latitudes and aridification of continental interiors.
The new ichnospecies Paleohelcura araraquarensis isp. nov. is described from the Upper Jurassic-Lower Cretaceous Botucatu Formation of Brazil. This formation records a gigantic eolian sand sea ( erg ), formed under an arid climate in the south-central part of Gondwana. This trackway is composed of two track rows, whose internal width is less than one-quarter of the external width, with alternating to staggered series, consisting of three elliptical tracks that can vary from slightly elongated to tapered or circular. The trackways were found in yellowish/reddish sandstone in a quarry in the Araraquara municipality, São Paulo State. Comparisons with neoichnological studies and morphological inferences indicate that the producer of Paleohelcura araraquarensis isp. nov. was most likely a pterygote insect, and so could have fulfilled one of the ecological roles that different species of this group are capable of performing in dune deserts. The producer could have had a herbivorous or carnivorous diet or been part of the fauna of omnivores, being able to adopt herbivorous, carnivorous, and saprophagous diets when necessary. In modern dune deserts, some species of pterygote insects are detritivores (like Tenebrionidae), relying on organic matter that accumulated among the sand grains of the dunes during dry periods with no plant growth. The presence of additional burrows suggests that the Botucatu paleodesert would have had a detritivorous fauna like this. Based on the interpretation of the ichnofossil producers, it was possible to reconstruct the food web of this paleodesert. All the omnivorous and herbivorous invertebrates and the herbivorous ornithopod dinosaurs made up the primary consumers. These animals were, in turn, the food source for bigger carnivorous or omnivorous animals unable to feed on detritus, like arachnids, possible predatory insects, mammaliaforms, and theropod dinosaurs. The highest trophic level was occupied by larger theropod dinosaurs and mammaliaforms, which, because of their size, could prey upon a wide range of animals. The producer of Paleohelcura araraquarensis isp. nov. could have been a primary consumer if it were an omnivorous detritivore or a herbivore, or a secondary consumer if it were produced by a predatory insect or an omnivore relying on animal biomass. The description of this new trackway expands the knowledge on the faunal composition of the Botucatu paleodesert and provides insights into the ecological relationships in ancient deserts. The presence of these arthropod trackways in Mesozoic eolian deposits helps to trace a continuity between Paleozoic and post-Paleozoic desert ichnofaunas, further reinforcing a single Octopodichnus—Entradichnus Ichnofacies for eolian deposits.
Grand Canyon National Park (GRCA) contains an extraordinary record of invertebrate trace fossils that provide valuable information on paleoecology throughout the Paleozoic Era. Trace fossils are a reflection of organism behavior (ethology) in relation to the substrate (toponomy) and are classified by their morphology. Ichnodisparity classifies groupings of similar invertebrate trace morphologies into 79 different architectural designs. Since organisms were often transported away from their original habitat prior to fossilization, their trace fossil counterparts can provide biogenic information that those body fossils lack. Trace fossils indicate varying organism responses to changing environmental conditions over time and space and give insight into their paleoenvironments represented by ichnofacies, which are recurrent associations of trace morphologies. This highlights the importance of ichnology in the Grand Canyon, where almost every Paleozoic geological unit contains trace fossils. The majority of reported ichnofossils include worm burrows, arthropod tracks and trails, and dwelling or feeding structures. The Cambrian Tonto Group holds the most extensively reported invertebrate trace fossil record in Grand Canyon, particularly the Bright Angel Shale, where 21 ichnogenera have been reported and classified into 15 architectural designs. Other formations with relatively high ichnodisparity and high diversity of ichnogenera include the Tapeats Sandstone, the Hermit Formation, and the Coconino Sandstone, all of which contain a minimal to non-existent body fossil record. Invertebrate trace fossils are regarded as significant, non-renewable resources that must be protected. New specimens are likely to be discovered in Grand Canyon as scientific research is ongoing.
This field trip focuses on the Late Triassic-Early Jurassic transition in northeastern Utah. This transition records one of the most striking terrestrial environmental transformations in the history of North America, wherein the fluvio-lacustrine Chinle Formation is transgressed by the vast erg system of the Nugget (Wingate+Navajo)/Navajo/Aztec Sandstones. Exposures in northeastern Utah are ideal for studying this transition as they are closely spaced and accessible. The uppermost Chinle Formation beds are lacustrine/fluvial fine-grained sediments which are overlain by increasingly drier, sandy, transitional beds. The non-eolian basal beds of the Nugget Sandstone preserve a Late Triassic ichnofauna, with some sites including Brachychirotherium tracks. Large-scale dune deposits comprise most of the Nugget Sandstone and contain vertebrate (Brasilichnium) tracks and a diverse invertebrate ichnofauna. Interdunal, carbonate, spring mounds, as much as 3 m tall, fed carbonate freshwater lake deposits containing gastropod body fossils and invertebrate ichnofossils. Another lacustrine deposit, located at the Saints & Sinners Quarry, is on the shoreline of a non-carbonate interdunal lake/oasis. Over 11,500 bones have been collected from the site and represent two theropod dinosaur taxa, sphenodonts, sphenosuchians, a pterosaur, and drepanosaurs (with many complete, three-dimensional, articulated skeletons). In addition to bones, dinosaur trackways are also preserved in shoreline and other interdunal beds. The fauna shows that this interdunal area of the Nugget Sandstone was the site of intense biological activity. The drepanosaurs are chronologically significant in that they are restricted globally to the Late Triassic, indicating that at least the lower one-fourth to one-third of the formation is Late Triassic in age.
The fossil record of Tenebrionidae (excluding the Quartenary) is presented. In total, 122 fossil species, clearly belonging to the family, are known; some beetles were determined only to genus; 78 genera are listed in the fossil record, including 29 extinct genera. The great diversity of tenebrionids occurs in the Lower Cretaceous Lagerstätte of China (Yixian Formation), Middle Paleocene of France (Menat), Lower Eocene deposits of Germany (Geiseltal), Upper Eocene Baltic amber (Eastern Europe), Upper Eocene deposits of Florissant Formation (USA) and Miocene (Dominican amber). Tenebrionids of the following major lineages, including seven subfamilies, are currently known in the fossil record. These include the lagrioid branch (Lagriinae, Nilioninae), pimelioid branch (Pimeliinae), and tenebrioid branch (Alleculinae, Tenebrioninae, Diaperinae, Stenochiinae). The importance of the fossil record for evolutionary reconstructions and phylogenetic patterns is discussed. The oldest Jurassic and Early Cretaceous darkling beetles of the tenebrionoid branch consist of humid-adapted groups from the extant tribes Alleculini, Ctenopodiini (Alleculinae), and Alphitobiini (Tenebrioninae). Thus, paleontological evidence suggests that differentiation of the family started at least by the Middle Jurassic but does not indicate that xerophilic darkling beetles differentiated much earlier than mesophilic groups.
Lower Eocene fluvial strata in the Chuckanut Formation preserve abundant bird and mammal tracks. Reptile trace fossils include footprints from a small turtle (ichnogenus Chelonipus), and several Crocodylian trackways that consist of irregularly spaced footprints associated with linear tail drag marks. The latter trackways represent "punting" locomotion, where a submerged Crocodylian used intermittent substrate contacts to provide forward motion of their neutrally buoyant bodies. Two adjacent sandstone blocks preserve Crocodylian trace fossils that are named herein as a new ichnogenus and ichnospecies Anticusuchipes amnis. Two other Crocodylian trackways lack sufficient detail for ichnotaxonomic assignment.
The colonization of deserts by tetrapods occurred for the first time in the late Paleozoic. In spite of amniotes being the most abundant and diverse taxon in such environments, fossil tracks indicate that anamniotes also inhabited late Paleozoic deserts. In this paper, the presence of the tetrapod-footprint ichnotaxa Ichniotherium sphaerodactylum and cf. Ichniotherium is documented in the eolian Coconino Sandstone (early Permian), based on 16 trackways found at several localities in Arizona, USA. Because there is a strong association between Ichniotherium and different species of diadectomorphs, we also discuss some aspects of the ichnotaxonomy of this ichnogenus. Diadectomorpha is considered the sister taxon of Amniota and, as a consequence, the tracks described in this paper represent the oldest evidence of occupation of deserts by non-amniote tetrapods. The presence of Ichniotherium in this environmental context also sheds light on the paleobiology of Diadectomorpha and, as a result, the emergence of features typically related to Amniota. The ichnofauna of the Coconino Sandstone has been used as a model for the Chelichnus ichnofacies, which supposedly indicates a low-diversity desert fauna. On the other hand, the tracks described here demonstrate that diadectomorphs were also important faunal components of such deserts and suggests that the significance of this ichnofacies should be reconsidered.
Pavocosa sp. (Lycosidae) burrows found in an open sparsely vegetated area on the edge of the Gran Salitral saline lake, in central Argentina, are described. Burrows were studied by capturing the occupant and casting them with dental plaster. The hosting sediments and vegetation were also characterized. Inhabited Pavocosa sp. burrows display distinctive features as open, cylindrical, nearly vertical, silk lined shafts about 120 mm long, subcircular entrances, a gradual downward widening, and a particularly distinctive surface ornamentation in the form of sets of two linear parallel marks at a high angle to the burrow axis. Instead, casts of vacated Pavocosa sp. burrows showed some disturbances caused either by the reoccupation by another organism or by predation of the dweller. Two morphologies are related to reoccupation of burrows: those with a structure in form of an “umbrella” and another with smaller excavations at the bottom of the burrow. Predation by small mammals produces funnel-shaped burrows. Both active and abandoned Pavocosa sp. burrow casts are compared with existing ichnogenera and inorganic sedimentary structures, highlighting its distinction. It is argued that key features like the presence of a neck, a downward widening and the described surface texture will allow recognition of wolf spider burrows in the fossil record. However, the putative spider burrows described in the literature either lack the necessary preservational quality or do not show ornamentation similar to the modern wolf spider burrows. Fossil wolf spiders are recorded since the Paleogene (possibly Late Cretaceous), therefore Cenozoic continental rocks can contain wolf spider burrows awaiting recognition. In addition, the particular distribution of Pavocosa sp. in saline lakes may imply that this type of burrow is linked to saline environments.
The Spence Shale of northern Utah is the oldest North American middle Cambrian (~506–505 Ma) Burgess Shale-type (BST) deposit and, unlike previously thought for BST deposits, has a very diverse ichnofauna. Twenty-four ichnogenera and 35 ichnospecies were identified: Archaeonassa (A. fossulata and A. jamisoni isp. nov.), Arenicolites carbonaria, Aulichnites, Bergaueria (B. hemispherica and B. aff. perata), Conichnus conicus, Cruziana (C. barbata and C. problematica), Dimorphichnus, Diplichnites (D. cf. binatus, D. gouldi, and D. cf. govenderi), Gordia marnia, Gyrophyllites kwassizensis, Halopoa aff. imbricata, Lockeia siliquaria, Monomorphichnus (M. bilinearis, M. lineatus, and M. cf. multilineatus), Nereites cf. macleayi, Phycodes curvipalmatum, Phycosiphon incertum, Planolites (P. annularius, P. beverleyensis, and P. montanus), Protovirgularia (P. dichotoma and P. cf. pennatus), Rusophycus (R. carbonarius, R. cf. pudicus, and R. cf. cerecedensis), Sagittichnus lincki, Scolicia, Taenidium cf. satanassi, Teichichnus cf. nodosus, and Treptichnus (T. bifurcus, T. pedum, and T. vagans). The ichnofossils comprise three ichnocoenoses—Rusophycus-Cruziana, Sagittichnus, and Arenicolites-Conichnus—representing dwelling, deposit- and filter-feeding, grazing, locomotion, and predation behaviors of organisms (e.g., annelid worms and trilobites). Two ichnofossil associations are suggestive of predation: (1) Planolites terminating at a Rusophycus; and (2) Archaeonassa crosscutting a Taenidium. The Spence Shale ichnofauna represent a distal Cruziana Ichnofacies and depauperate, distal Skolithos Ichnofacies. A new ichnospecies of Archaeonassa is proposed, A. jamisoni isp. nov., and Ptychoplasma (Protovirgularia) vagans is herein transferred to Treptichnus. This study is the first ichnotaxonomic study of the Spence Shale and North American BST deposits and shows highly diverse ichnofaunas can be present in BST deposits.
The formal ichnotaxonomic assignment of a new ichnogenus and ichnospecies, Reniformichnus katikatii, is presented based on the holotype and several field specimens from the Lower Triassic Katberg Formation in the main Karoo Basin of South Africa. The holotype is an inclined, burrow cast with bilobate base and reniform cross-section. Its width ranges from 12.6 to 14.7 cm, and its height is 5 to 7.4 cm resulting in an aspect ratio of 1.89 to 2.74. The surface preserves 70–180 mm long ridges running parallel to the long axis of the burrow on the upper parts of the walls and lower parts of the dorsum and shorter ridges (average length ∼27 mm) are preserved on the more ventral areas in two opposite orientations, cross-cutting each other in a rhomboid pattern. Burrow fills are passive and consist of slightly bedded, laminated, or massive clastic rocks that are coarser than the host mudstones. The burrow casts are isolated, never occurring in clusters. This simple burrow shows no evidence for branching, spiralling, interconnected tunnels, burrow linings, terminal chambers, or entrances. Preserved in fluvial floodplain mudstone units, the burrows were passively filled by layered, laminated, or massive sand and other coarser clastic sediments. The burrow casts are morphologically similar to unnamed Antarctic ichnotaxa that have been attributed to tetrapods (e.g., therapsids, procolophonids), extending the geographic range of the potential producers of Reniformichnus isp. to continental settings in southern Gondwana. Biostratigraphic evidence on the temporal distribution of Reniformichnus isp. suggests that the trace maker emerged in the aftermath of the Permo-Triassic mass extinction event to successfully burrow throughout the Early Triassic.
The Upper Miocene-Lower Pliocene Río Negro Formation (Río Negro Province, Argentina) contains diverse and abundant continental trace fossils. The purpose of this contribution is to recognise distinctive trace fossil assemblages in interdune lakes as response to lake expansion and contraction. The interdune deposits host twenty-three invertebrate, vertebrate and plant ichnotaxa that are linked to the hydrological dynamics of the lake. During lake expansion a highly diverse subaqueous trace fossil assemblage reflects an infaunal bivalve population living in a littoral zone with swampy vegetation and semiaquatic mammals. The trace fossil assemblage recorded during lake highstand is less diverse and mostly linked to bivalve-generated trace fossils reflecting resting, locomotion, and escape / equilibrium behaviour (comparable to the Mermia ichnofacies). The assemblage during lake contraction exhibits high ichnodiversity and is dominated by vertebrate trace fossils reflecting foraging activities of shorebirds, cursorial birds, and herding semiaquatic mammals and ground sloths frequenting water holes. Flat sandy areas with moist substrates marginal to the interdune lake displayed a moderate ichnodiversity and its distinctive components were armadillo meniscate burrows and footprints in cross-section, as well as subvertical calcareous root casts. Neogene interdune lacustrine deposits reflects a particular zonation of trace fossils in response to changing physical conditions.
The Santa Clara Abajo and Santa Clara Arriba formations host a diverse assemblage of trace fossils that record a wide range of behaviors and a broad array of ecological niches during the Middle Triassic, a critical period in the evolution of continental fauna with the diversification of both synapsids (cynodont and dicynodont) and archosauromorphs (dinosaurs, pterosaurs, and crocodilians) that represent post-Permian faunal recovery. The Santa Clara formations are part of the continental infill of the Cuyana rift Basin in Argentina and represent a lacustrine system with fluvial input and delta development. Sedimentological characteristics of these units as well as their stacking patterns characterize a “fluctuating profundal” facies association typical of a balanced-fill lake basin. The lacustrine and associated terrestrial environments preserve a rich record of invertebrate traces with 26 ichnogenera from ethological classes of fodichnia, domichnia, repichnia, pascichnia, and cubichnia occupying all co ntinental tiers (subaerial and subaqueous, surficial/very shallow, shallow, mid, and deeper) and ecological niches (epiterraphilic, terraphilic, hygrophilic, and hydrophilic). In association with the invertebrate traces, two taphonomic modes of tetrapod footprints have been found: a moderate fidelity mode and a high fidelity mode. Physical sedimentary features, burrows, trails, and tracks, and their stratigraphic positions are integrated to interpret the main factors involved in footprint preservation in these subsettings. The most significant and variable preservational factor found is water-table fluctuations controlled by the paleohydrology of a balanced-fill lake system. These data show that in balanced-fill lake systems, diverse trace assemblages occur in the lake and associated subsettings such as delta plains, and lake-margin settings whereas trace fossils can be totally absent in coeval lake-center strata, particularly if anoxic lake bottom conditions occur, as probably occurred in the meromictic Santa Clara lake system.
The Botucatu Formation (Paraná Basin, Brazil and the southern neighboring countries) comprises one of the richest tetrapod ichnological deposits of the Lower Cretaceous in South America. The ichnofossils are found in reddish sandstones lithofacies -interpreted to be dune and interdune deposits. The sandstones of Botucatu Formation originally covered a surface estimated in at least 1,300,000 km2, the largest known fossil desert in the Earth’s history. The distribution area of the Botucatu paleodesert presents one of the world’s largest megatracksites. The tetrapod ichnofauna from the Botucatu Formation comprises minor
bipedal dinosaur tracks (almost all attributable to theropods, with one exception, a doubt ornithopod trackway) along with many thousands of footprints of early mammals, and a single trackway of a lacertiform reptile. Among the bipedal dinosaur footprints, the most common and typical are considered theropod tracks, with long strides and high step angle and always with an acuminate termination. These trackways are straight and very narrow, with long strides and step angles showing high values. The footprints have a relatively large and very wide III digit and small, short, pointed, bladelike outer digits. The most special characteristic
is that the II digit is longer and more important than the IV digit. Because of this morphology, the general outline of the footprint often reminds that of a waterdrop and, although it is structurally tridactyl, it usually looks like functionally monodactylous. These tracks are herein assigned to small theropods adapted to desert life with a prevalently cursorial gait, probably ancestors of clades such as noasaurs and velocisaurs. Due its unique morphological aspects it is defined a new ichnogenus and ichnospecies.
The earwigs, Dermaptera, are a group of insects which have been present since the Mesozoic. They have a relatively sparse fossil record, yet their life activities on and in soil or sediment leave traces with the potential for long-term preservation. These may include some burrows seen in Quaternary dunes and other sandy substrates. The well-known, cosmopolitan, sand-dwelling species Labidura riparia is examined as a potential model and reference for dermapteran tracemakers there and elsewhere in the geological record, through experimentally produced shelter burrows and trackways from wild-caught, laboratory-raised specimens. Shelter burrows were typically U-shaped with a pair of surface entrances, and these U-shapes could be additionally modified into Y-shapes or linked together to form a network. Trackways of L. riparia generally resembled those of other insects but may show features consistent with dermapteran anatomy such as tail-drag impressions produced by cerci.
From Middle-Late Triassic continental deposits of the Timezgadiouine Formation (Argana Basin, Morocco), 17 lithofacies are identified, with alluvial fan, fluvial, floodplain and lacustrine associations. Invertebrate traces include Archaeonassa fossulata, Arenicolites isp., cf. Arenituba, Beaconites isp., cf. Camborygma, Cruziana problematica, Diplocraterion isp., Fuersichnus isp., Helminthoidichnites tenuis, Lockeia isp., Palaeophycus striatus, Palaeophycus tubularis, Planolites isp., Rusophycus carbonarius, Scoyenia gracilis, Skolithos isp., Spongeliomorpha carlsbergi, Taenidium isp. and Taenidium barretti. Additionally, rhizoliths were observed. Six ichnoassemblages were distinguished: overbank facies with (1) Rhizolith ichnoassemblage in a low-energy floodplain environment and (2) Scoyenia-Palaeophycus ichnoassemblage in crevasse splay deposits. The fluvial ichnoassociation is of moderate ichnodiversity consisting of the following assemblages: (3) Arenicolites, developed under higher flow velocities of active channels, (4) Taenidium-Scoyenia, formed by the colonisation of inactive channels, (5) Arenicolites-horizontal meniscate burrows, reflecting a rapid transition between active and abandoned channels and (6) Lockeia-vertebrate footprint, formed in littoral lakes. The Aglegal and Irohalene members indicate climatic shifts between arid dry, semiarid and subhumid in a dryland river environment. The sudden onset and the high frequency of lacustrine deposits in the lower Irohalene Member point to a rapid climate change from dry to intermittent wet and dry. This change is discussed in terms of the Carnian Pluvial Event.
The 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.
This paper includes a detailed sedimentologic and stratigraphic analysis of the fill of the western part of the Neogene Northern Patagonian extra-Andean foreland basin of Argentina. Using facies analysis, stratigraphic relationships, independent age indicators and physical correlation between sections, the depositional history of the basin is reconstructed and linked to regional climatic and tectonic events. The fill of the basin comprises the El Sauzal, Barranca de los Loros, El Palo, Bayo Mesa and Río Negro formations and it reaches up to 60 m thick in outcrop. On the basis of fourteen detailed sedimentologic logs located in the western side of the basin, a total of nine facies associations are recognized: braided permanent fluvial channel belt, pedogenized floodplain, shallow floodplain lakes, eolian dune field, alkaline lake, saline lake, shallow freshwater lake, and permanent braided gravelly channel belt facies associations. Basin sediments were deposited on an erosive unconformity on Late Cretaceous/Paleocene to early Eocene sedimentary rocks and are divided into five depositional episodes. The first depositional episode is represented by a shallow freshwater lacustrine system of local occurrence, tentatively assigned to the late Miocene. The second depositional episode is represented by permanent braided sandy fluvial system that occurred in the late Miocene-early Pliocene in a depression from the center and south of the study area. The large rivers of this episode flowed toward the east and northeast. The third depositional episode is represented from south to north by ephemeral fluvial, eolian dune and saline-alkaline lacustrine deposits that were recorded in all sections and is tentatively assigned to the Pliocene. Eolian dunes migrated toward the northeast and east. The fourth depositional episode is composed of permanent sandy braided fluvial deposits occurring only in the center of the study area. The fifth depositional episode (early Pleistocene?) is represented by permanent braided gravelly fluvial deposits that rests on a regional erosive unconformity interpreted as a large fluvial fan sourced from the south. These deposits resulted calcretized prior to the middle Pleistocene. The paleoclimatic evolution suggest a wetter period (depositional episodes 1 and 2) tentatively linked to the middle member of the Río Negro Formation and the Paranense transgression, followed by a progressive aridization during the Pliocene and Pleistocene.
Beetles (Coleoptera) are a critical component of terrestrial ecosystems filling numerous ecological roles. Soil-dwelling beetles play an important role in pedogenesis through the production of biogenic structures throughout their life cycle. Given their life habits, beetle trace fossils should be abundant in the fossil record and a number of ichnotaxa have been attributed to beetles, yet there is still much to learn about their trace-making techniques and the variety of morphologies of traces they can produce throughout their life cycle. The Tenebrionidae (darkling beetles) is a common, globally distributed group that includes many soil-dwelling species from a variety of environments. The purpose of this project was to gain a better understanding of biogenic structures produced during each life stage of two species of burrowing darkling beetles, Zophobas morio F. and Tenebrio molitor L. Single to multiple specimens of each species were placed in variably sized enclosures filled with massive and layered sediment with and without layers of food. Biogenic structures produced by the two species were similar, but distinct between each life stage and associated with different behaviors. Observed biogenic structures are comparable to Palaeophycus, Planolites, Fictovichnus, Rebuffoichnus, Pallichnus, Taenidium, Skolithos, and Conichnus depending on the life stage. Neoichnological studies such as this can aid in the understanding of biogenic structures in the fossil record. Being able to effectively link continental traces to trace makers will ultimately improve our understanding of the composition of ancient terrestrial ecosystems.
An assemblage of eubrontid-type theropod tracks, representing terrestrial progression and turtle track swim tracks representing subaqueous progression characterises a newly reported site in the Middle Jurassic Zhiluo Formation in Shaanxi Province China. While eubrontid tracks are common in the Jurassic of China, turtle swim tracks have only comparatively recently been reported from the Mesozoic of China, and the present report appears to represent the oldest occurrence of the latter. The co-occurrence of theropod tracks and turtle swim tracks suggests alternating registration of tracks on emergent and subaqueous substrates as localised water-levels fluctuated. The co-occurrence can be characterised as the intersection of an eubrontid ichnocoenosis with a newly defined Chelonipus ichnocoenosis.
The Silurian was an interval of profound change in terrestrial ecosystems as the earliest non-marine animal communities began to become established on the continents. Whilst much is known about the transition of pioneering animals from shallow marine to coastal and alluvial habitats, evidence for animal activity in contemporaneous aeolian strata is rare. Here, we present trace fossil evidence that closes this knowledge gap, indicating that Silurian desert environments, dominated by aeolian processes, were occupied by resident invertebrate communities. The evidence comes from the Mereenie Sandstone, Northern Territory, Australia, which is demonstrated to have been deposited in a wet inland aeolian system, typified by small crescentic sand dunes and extensive interdune flats. The invertebrate trace fossil associations from the Mereenie Sandstone ( Arenicolites isp., “Burrow entrance with radial feeding traces”, Didymaulichnus lyelli, Diplichnites gouldi, Helminthopsis isp., Laevicyclus isp., Palaeophycus isp., Polarichnus garnierensis , Skolithos isp.) are restricted to damp interdune deposits, whereas dune strata are barren. The ichnofauna are described and compared to those from other Palaeozoic aeolian systems, in order to re-evaluate the timing of the early stages of arthropod terrestrialization.
The ichnogenus Brasilichnium, with its ichnospecies type Brasilichnium elusivum, was established for a very common and abundant kind of tracks from the Brazilian aeolian Botucatu Formation in Paraná Basin. It is nowadays a recognized ichnogenus on several continents. A new occurrence of this ichnogenus (and also of the ichnospecies Brasilichium elusivum) is herein announced from Cretaceous arkose sandstones, at Kinshasa, Democratic Republic of Congo. Three slabs with several mammaloid footprints attributable to this ichnogenus were found in Kinshasa, in red sandstone slabs cladding facades of pre-independence (1960) buildings. These slabs were and are quarried at the NW margins of Kinshasa along the left banks of the Congo River, in the districts of Kimbwala and Mbudi. This material can be attributed to the Loia Formation (Berriasian-Aptian). These are the first tetrapod tracks in the Democratic Republic of Congo, and possibly in all of Central Africa. It is important to keep on surveying for tracks in the quarries and on the facades of buildings in Kinshasa, in order to increase the potential use of ichnology to environmental and palaeogeographic reconstructions.
The ichnogenus Brasilichnium Leonardi, 1981 is an early mammal track, presently recognized in several continents, but originally found in the aeolian deposits of Botucatu Formation in the Paraná Basin, Brazil. The sandstones of the Botucatu Formation are generally fine-grained and well-sorted, containing no pebbles; its color can be white, yellowish or reddish, but more commonly it is pinkish. Nearly always, it is silicified and therefore compact and hard, making it a very suitable building material. These sedimentary rocks are interpreted as a Lower Cretaceous desert regarded as the largest paleodesert in the Earth’s history. Although the aeolian environment is generally considered inadequate for track preservation, taphonomic events linked to moist dunes and microbial mats foster a good geological context for an early diagenization of the sediments. Brasilichnium is associated with a large ichnofauna of other mammal, theropod and ornithopod tracks, in addition to invertebrate traces. It is today a worldwide ichnogenus that allows an overview of the arid terrestrial ecosystems during Mesozoic. The presence of tritylodontids in the world after the end of the Triassic and up to the Late Cretaceous, and the possibility of attributing Brasilichnium and related ichnogenera to them, has been discussed at great length. It seems preferable, however, to suggest that these tracks can only belong to the crown-group Mammalia. Thus, these track-bearing deposits bear witness to small- and medium-size mammaliaform trackmakers; some of them would be remarkably larger than the coeval mammals represented by skeletal remains. This chronological discrepancy between ichnological and bone findings is not a surprising phenomenon: it is also known in other clades. A complete check of these tracks will have to be carried out. It would also be advisable to perform a review of all the tracks recently attributed to Brasilichnium world-wide. The Botucatu and Caiuá ichnofaunas and, globally, the ichnogenus Brasilichnium, should be stressed as an important window into the arid terrestrial ecosystems during the Gondwanic Cretaceous. This study is the result of forty-four years of research in the Botucatu Formation by the first author.
Gregarious behaviour among dinosaurs has been inferred from several lines of evidence (monospecific bonebeds, skeletal morphology, phylogenetic inferences, comparison with modern ecosystems and parallel trackways with particular characteristics), but is relatively poorly documented for non-avian theropods. Here, we report five parallel theropod trackways of large track size (average length of 28 cm) in the Cretaceous (Cenomanian) Candeleros Formation from northwestern Patagonia, Argentina. The tracks are provisionally assigned to aff. Asianopodus pulvinicalx and considering the autopod morphology of the theropod taxa documented in the Candeleros Formation, abelisaurid theropods are suggested as trackmakers. The trackways possess similar stride, speed estimation, direction and preservational features, and track show uniform depth and do not overlap. Physical barriers (i.e., large fluvial channels or perennial lake) that could influence the direction of the theropod trackmaker gaits were not recognized in the section. Taking into account these considerations, a gregarious behaviour for the abelisaurid theropod trackmakers is proposed. The tracks are preserved as shallow undertracks in a medium-grained sandstone bed deposited in a floodplain setting. The tracking surface is interpreted as the overlaying layer of muddy-siltstone. The occurrence of swelling clays and microbial mats in the track-bearing level could have contributed to the substrate stabilization and their role in the preservation is discussed.
The Cretaceous Cerro Barcino Formation (Chubut Group) of Central Patagonia, Argentina has yielded a remarkable fossil vertebrate fauna, which form important components of the South American “mid-Cretaceous” fauna, including titanosauriform sauropod dinosaurs, theropod dinosaurs, crocodyliforms, turtles, and lepidosauromorphs. However, a lack of robust chronostratigraphic framework for its fossil occurrences has so far hampered a full realization of their paleobiologic significance. This contribution presents new stratigraphic, sedimentologic, and U-Pb isotopic age data from 11 localities throughout the Patagonian Somuncurá-Canadón Asfalto Basin and analyzes the evolutionary characteristics of the Cerro Barcino fauna within the biostratigraphic context of the Cretaceous of Gondwana.
Four new high-precision ²⁰⁶Pb/²³⁸U zircon dates by the CA-ID-TIMS method range from 118.497 ± 0.063 Ma to 98.466 ± 0.048 Ma (2σ internal errors) and limits the Puesto La Paloma, Cerro Castaño and Las Plumas members of the Cerro Barcino Formation largely to the Aptian, Albian and Cenomanian stages of the Cretaceous, respectively. Accordingly, the majority of the Cerro Barcino vertebrates fall within a ~118–110 Ma time interval in the latest Early Cretaceous, which makes them the oldest documented component of the “mid-Cretaceous” faunal assemblage of Gondwana. Paleobiologic analyses of the latter assemblage suggests a ~10 m.y. period of faunistic stability characterized by only minor evolutionary novelties or faunal turnovers.
The poor preservation and apparent monospecifity of Permian tetrapod footprints from eolian
paleoenvironments have thus far hampered their reliable interpretation. This study clarifies how this is due to
distinct and repeated ichnotaphonomic effects on trackway pattern and footprint morphology on originally inclined
planes. Once these effects are excluded, the anatomy-consistent ichnotaxobases useful for ichnotaxonomy
can be recognized. Several nomina dubia are identified, among these the ichnogenus Chelichnus, here considered
a taphotaxon. The eolian ichnoassociations from the Lopingian of Scotland and Germany include six different
ichnotaxa: cf. Capitosauroides isp. (?eutheriodont therapsid), Dicynodontipus geinitzi (cynodont therapsid),
Dolomitipes isp. (dicynodont therapsid), Pachypes loxodactylus n. comb. (pareiasaurian parareptile),
Procolophonichnium isp. (small parareptile) and Rhynchosauroides isp. (non-archosauriform neodiapsid). This is
completely different from the interpretations of the last 20 years,which postulated that these paleoenvironments
comprised monospecific associations of synapsid tracks. These ichnoassociations are instead moderately diverse,
similar to low-latitude marginal marine to floodplain ichnoassociations and belong to the Lopingian
Paradoxichnium footprint biochron. The Cornberg Formation of Germany, being constrained between the
Illawarra reversal and the mid-Wuchiapingian Kupferschiefer at the Rotliegend/Zechstein transition, constitutes
the earliest evidence of Lopingian tetrapod faunas at low paleolatitudes and the first evidence of low paleolatitude
faunal turnover related to the end-Guadalupian mass extinction from both the skeleton and the
track record. This suggests a global extension of the dinocephalian extinction event, which occurred at high mid
(South Africa and Russia) and low (Western Europe) paleolatitudes of Pangea about 259–260 Ma and was
probably triggered by the eruption of the Emeishan Large Igneous Province of SW China, which considerably
changed global environmental conditions in both marine and continental settings.
The morphology of fossil footprints is the basis of vertebrate footprint ichnology. However, the processes acting during and after trace fossil registration which are responsible for the final morphology have never been precisely defined, resulting in a dearth of nomenclature. Therefore, we discuss the concepts of ichnotaphonomy, ichnostratinomy, taphonomy, biostratinomy, registration and diagenesis and describe the processes acting on footprint morphology. In order to evaluate the morphological quality of tetrapod footprints, we introduce the concept of morphological preservation, which is related to the morphological quality of footprints (M-preservation, acronym MP), and distinguish it from physical preservation (P-preservation, acronym PP), which characterizes whether or not a track is eliminated by taphonomic and diagenetic processes. M-preservation includes all the morphological features produced during and after track registration prior to its study, and may be divided into substages (ichnostratinomic, registrational, taphonomic, stratinomic, diagenetic). Moreover, we propose an updated numerical preservation scale for M-preservation. It ranges from 0.0 (worst preservation) to 3.0 (best preservation); intermediate values may be used and specific features may be indicated by letters. In vertebrate footprint ichnotaxonomy,
we regard the anatomy-consistent morphology and to a lesser extent the trackway pattern as the only acceptable ichnotaxobases. Only footprints showing a good morphological preservation (grade 2.0–3.0) are useful in ichnotaxonomy, whereas ichnotaxa based on poor morphological preservation (grade 0.0–1.5) are considered ichnotaphotaxa (nomina dubia) characterized by extramorphologies. We applied the preservation scale on examples from the Palaeozoic to the present time, including three ichnotaphotaxa and 18 anatomy-consistent ichnotaxa/morphotypes attributed to several vertebrate footprint producers. Results indicate the utility, feasibility and suitability of this method for the entire vertebrate footprint record in any lithofacies, strongly recommending its
use in future ichnotaxonomic studies.
The Lower Cretaceous (Valanginian) Mulichinco Formation of the Neuquén Basin in western Argentina is host to important hydrocarbon reservoirs, encompassing a wide variety of sedimentary facies, including thick eolian deposits in its lower interval in proximal positions. Ten ichnofabrics are characterized based on the analysis of cores from the El Mangrullo oil field. These ichnofabrics have been grouped in four associations, representing eolian dunes, eolian sand sheets, interdunes, and fluvial sheet floods. In terms of the ichnofacies model, both the Scoyenia and Octopodichnus-Entradichnus ichnofacies are identified. Ichnologic information has been integrated with sedimentologic and sequence-stratigraphic information. The studied succession comprises a 3rd-order depositional sequence that is subdivided into three 4th-order sequences stacked in a backstepping pattern as a result of a rise in the water table. The base of the 3rd-order sequence is represented by the intra-Valanginian unconformity that in this area separates marine deposits below from continental deposits above. Overall the 3rd-order sequence reflects the vertical transition from a dominance of eolian dune deposits to eolian sand sheet and fluvial sheet flood deposits, the latter intercalating with marginal-marine intervals. Application of available conceptual frameworks to understand trace-fossil distribution in desert environments suggests that the eolian Mulichinco ichnofauna indicates a temporal evolution from hyper-arid to arid and semi-arid conditions. The results of the present analysis argue against the common assumption of deserts as barren of life and provide further support to the notion of an archetypal eolian ichnofacies. This study expands the realm of application of ichnology in subsurface to eolian environments by providing a characterization of an ichnofauna from a desert setting based on core analysis.
The tetrapod footprint record of Permian eolian environments has long been underestimated because of overall poor preservation and its apparent monospecifity. The best known and most abundant Cisuralian record of tetrapod footprints is from the Coconino and De Chelly formations of Arizona, which, however, thus far encompassed only the ichnogenera Chelichnus and Dromopus. We revised the locomotion and taphonomy of these footprints and propose a new model, basing it on: 1) trackways changing direction, 2) trackways heading in different directions on the same surface, 3) trackways in situ, and 4) laboratory experiments with common wall lizards, Podarcis muralis. In all cases, the Chelichnus-like appearance of footprints is due to digit tip sliding on inclined depositional surfaces, masking the original footprint shape and orientation. Also, the trackway pattern and body position are largely influenced by the angle of inclination (dip) of the substrate being walked on. Based on an anatomy-consistent ichnotaxonomy, Chelichnus and Laoporus are here considered nomina dubia, and the footprints from the Coconino and De Chelly formations are revised and assigned to: parareptiles/captorhinomorph eureptiles (Erpetopus, Varanopus curvidactylus), bolosaurid parareptiles/ diapsid eureptiles (cf. Dromopus), varanopid synapsid (cf. Tambachichnium) and reptiliomorph amphibians (Amphisauropus, Ichniotherium sphaerodactylum). The ichnoassociation is dominated by parareptile/captorhinomorph tracks, similarly to all the late Cisuralian marginal marine, floodplain, alluvial fan and ephemeral lacustrine tetrapod ichnoassociations of North America, Europe and North Africa. A review of all the available data including the new results suggests a facies-crossing transition between an early-Cisuralian amphibian- and synapsid-dominated ichnofauna (Dromopus track biochron) and a late Cisuralian parareptile/captorhinomorph-dominated ichnofauna (Erpetopus track biochron) at low latitudes of Pangea.
The trace fossil Skolithos, with its simple, vertical to very slightly inclined, tubular form, is widely recognized and globally distributed in early Cambrian to Holocene strata, representing deep-sea to continental paleoenviron-ments. The type species, Skolithos linearis, was first described in 1840 by Samuel S. Haldeman, based on his observations of early Cambrian quartzite at Chickies Rock, a well-known landmark on the east bank of the Susquehanna River, in Pennsylvania. The original description was meager; no illustrations were published, no holotype was established, and no specimens directly associated with Haldeman are known to exist today. A "neoholotype" proposed by Howell (1943) is invalid, as it does not conform to requirements of the International Code of Zoological Nomenclature. As a result, the iconic ichnogenus Skolithos is inadequately characterized and some of the numerous ichnospecies that have subsequently been named are not unequivocally assignable to it. In order to stabilize this important ichnogenus and to provide a basis for the taxonomic revision it urgently requires , we have studied S. linearis at its type locality. Our new material is described and illustrated here, and we have designated a neotype, accessioned by the U.S. National Museum of Natural History (Smithsonian Institution). The stratigraphy and regional geologic setting of Chickies Rock, the sedimentology and environment of deposition of cross-bedded quartzite with abundant S. linearis constituting classic "pipe rock," and the structural deformation of this fabric are reviewed. Given the simple morphology of Skolithos, disparate organisms in several phyla have been proposed as its maker. We concur in the general view that Cambrian trace fossils assigned to S. linearis were most probably made by burrowing phoronids or polychaete annelids. The global abundance of largely monospecific pipe rock in analogous Cambro-Ordovician settings is recognized as a characteristic feature of the ecology of shallow-marine environments of that time. The stage has now been set for a thorough re-evaluation of all existing ichnospecies assigned and related to the ichnogenus Skolithos.
Tetrapod ichnofaunas are reported from desert, playa lake facies in the Lower Cretaceous Luohe Formation at Baodaoshili, Shaanxi Province, China, which represent the first Asian example of an ichnnofauna typical of the Chelichnus Ichnofacies (Brasilichnium sub-ichnofacies) characteristic of desert habitats. The mammaliomorph tracks, assigned to Brasilichnium, represent the first report of this ichnogenus from Asia. The assemblages also contain three different theropod trackway morphotypes: one very wide Magnoavipes-like morphotype, one relatively wide, broad-toed, small Eubrontes-like form with short steps and strides, and wide straddle, and an elongate morphotype (Sarmientichnus) with longer steps and narrower straddle representing a didactyl trackmaker, the latter being the first example of the enigmatic ichnogenus found outside its type area in Argentina. The Sarmientichnus occurrence, the first in Asia, has important implications, demonstrating that the trackmaker was not monodactyl, but didactyl with probable affinities to deinonychosaurians which are ichnologically well-represented in the Lower Cretaceous of Asia. Although morphologically distinctive, Sarmientichnus should be recognized as a “form” ichnotaxon compromised by suboptimal preservation. The combination of Brasilichnium isp., Sarmientichnus isp., and tridactyl theropod tracks, indicates mammaliomoprhs and small theropods, and is comparable to ichnofaunas from similar desert facies on other continents. Thus, Cretaceous desert ichnofaunas from China are consistent with global ichnofacies predictions.
The Kokorkom desert extended over an area of 826 km² in the central-west sector of Neuquén and Río Negro provinces along the area of the backbulge basin within the Andean Foreland basin in the Neuquén Basin. Its deposits constitute the middle-upper section of the Candeleros Formation (Cenomanian) and reach approximately 130 m thick. Tracks are found on wet and dry interdune and within draa slipface deposits. They constitute biogenic deformation structures characterized by folded-up and/or brecciated sandstone levels formed under dry and/or wet substrate conditions with passive filling. The degree of preservation varies, but the identification of digit impression suggests that they were produced by theropods or iguanodontians.
Observations along the Conecuh River, southern Alabama, demonstrate the impact that insect larvae can have on bioerosion of freshwater aquatic bedrock substrates. Eocene siliceous claystones and sandstones exposed along the river are locally densely riddled by modern burrows produced by chironomid (midge) and trichopteran (caddisfly) larvae. Chironomid larvae produce diminutive U-shaped burrows (U width = 2–7 mm, U length = 1–4 cm, burrow diameter = 0.5–2.0 mm) generally oriented normal to bedrock surfaces. Trichopteran larvae generally produce somewhat larger (burrow depth = 2–4 cm, burrow diameter = 4–6 mm), vertical, crudely Y-shaped burrows consisting of an upper U-tube, which is extended above the substrate by agglutinated chimneys, and one or two basal subvertical shafts. Both burrow types exhibit faint scratch traces on exposed burrow margins and silk-and-sediment linings that include a thicker constructed wall or septum in interlimb areas of their U-tubes. Distribution of the two structure types is controlled by bedrock texture and induration, tracemaker propensity to occupy transiently available substrates, and other as yet unidentified factors.
During the Early Cretaceous, a large area in Brazil and other South American countries was covered by an extensive paleoerg field, the Botucatu Desert. The Araraquara County (São Paulo State, Brazil) contains some of the most diverse ichnological assemblages in the Botucatu Formation. Mammaliform trace fossils from the Botucatu Formation are of great interest, as they may represent the only record of Lower Cretaceous Mammaliamorpha from Brazil. These trace fossils can be grouped into two distinct classes, based on the dimensions of the footprints. The larger morphotype is described and classified as a new ichnotaxon, Aracoaraichnium leonardii igen. nov. isp. nov., with a discussion of preservational features and paleoecological aspects. This morphotype can be differentiated from Brasilichnium Leonardi, 1981 by digit morphology, with digits III and IV being larger and sub-equal in size. The tracks are mesaxonic, unlike Brasilichnium, which is ectaxonic, and the stride is proportionally smaller, suggesting a trackmaker with shorter limbs in relation to body length. Another characteristic that reinforces the new ichnotaxon is the larger size of the footprints of Aracoaraichnium igen. nov. Footprints representing intermediate ontogenetic stages between Brasilichnium and the larger morphotype are not observed, suggesting that the two track types were made by different taxa. Compared with others tetrapod ichnotaxa, the new ichnotaxon is characterized by differences in the number and morphology of the digits, track morphology, the degree of heteropody, and locomotor parameters. Tracks with good preservation quality were likely originally produced in the humid subsurface, below the surficial dry sand layer. Tracks with smaller dimensions, and trackways with the presence or absence of the manus, may be due to variable degrees of impression into subsurface layers, and substrate heterogeneity. The Aracoaraichnium igen. nov. trackmakers probably inhabited areas near the desert, making occasional incursions into desert areas, while Brasilichnium trackmakers may have been mostly nocturnal residents of the desert environment.
The Cretaceous Puesto La Paloma (PLPM) and Cerro Castaño (CCM) members (Cerro Barcino Formation, Chubut Group) are pyroclastic-rich, alluvial successions deposited in the Somuncurá-Cañadón Asfalto Basin during sag and endorheic conditions. The PLPM comprises sheet-like tuffaceous sandstone strata, whereas the overlying CCM includes sheet-to ribbon-channel sandstone bodies intercalated within tuffaceous and fine-grained sediments. In this context, the goals of this contribution were: i) to make a detailed documentation of the contrasting sedimentary palaeonvironments; and ii) to infer the allocyclic controls that governed the sedimentation of both units. The study area is located in the western sector of the basin, where six localities, which were studied.
A new ichnospecies, Brasilichnium anaiti, is erected on material from the Botucatu Formation of Brazil. The general morphology supports ichnotaxonomic similarity between the new ichnotaxon and Brasilichnium elusivum Leonardi, 1981, even if a separation at the ichnospecies level is evident, based on differences in shape and arrangement of pes digit marks along with a clear dimensional gap between both ichnotaxa. Similar forms from the Lower Jurassic of the United States are known and should be included under this new ichnotaxonomic label, based on shared morphological features. B. anaiti is constantly associated with B. elusivum in dune foresets of hyperarid paleoenvironments, to which these forms are restricted. This makes B. anaiti a further element of the Brasilichnium ichnocoenosis in the larger framework of the Chelichnus ichnofacies. Re–evaluation of possible trackmakers highlights the difficulties of unequivocal referring this ichnotaxon to a specific producer, but restrains potential trackmakers to early mammaliamorph therapsids.