Early Triassic

Tetrapod swim tracks attributed to reptiles occur abundantly throughout Lower to Middle Triassic deposits across the western United States. In central and southern Utah these swim track localities are stratigraphically restricted to the upper portion of the Torrey Member of the Moenkopi Formation. Here they show detailed features such as longitudinal striae and disc-shaped claw impressions that must have required specific substrate conditions in order to be produced and preserved. A suite of sedimentologic and ichnologic observations at several swim track localities demonstrates the widespread development and persistence of subaqueous firmground substrates buried by crevasse splay deposits in the interdistributary areas of a large lower delta plain. The heterolithic stratigraphy is typical of interdistributary bays and channels and generally consists of decimeter-scale fining-upward cycles of mud- and siltstone beds below the track-bearing horizons and thicker, massive or cross-bedded sandstones above. Siltstone and sandstone beds show low angle accretion sets, vary laterally in thickness, and commonly pinch out so that they cannot be correlated regionally. Common sedimentary structures indicate predominately quiet subaqueous conditions with periodic higher energy events. These include trough cross stratification, climbing ripples, rip-up clasts, and soft sediment deformation. Track surfaces often exhibit localized dewatering structures and load casts in addition to flute casts and current crescents indicating unidirectional current flow. Mudcracks are rare. The low diversity invertebrate ichnoassemblage is comprised of locally high densities of relatively diminutive traces and reflects stressed brackish water faunas. These characteristics are almost certainly augmented by delayed biotic recovery following the end-Permian mass extinction and resulted in extremely low degrees of bioturbation. This lack of biogenic mixing promoted semi-consolidation of dewatered mud substrates resulting in the widespread production and persistence of firmgrounds capable of recording and maintaining detailed swim tracks. The subsequent burial of these firmground surfaces under coarser-grained crevasse splay deposits resulted in sharp heterolithic contacts further facilitating the preservation of detailed track features.

The Permian and Triassic were key time intervals in the history of life on Earth. Both periods are marked by a series of biotic crises including the most catastrophic of such events, the end-Permian mass extinction, which eventually led to a major turnover from typical Palaeozoic faunas and floras to those that are emblematic for the Mesozoic and Cenozoic. Here we review patterns in Permian-Triassic bony fishes, a group whose evolutionary dynamics are understudied. Based on data from primary literature, we analyse changes in their taxonomic diversity and body size (as a proxy for trophic position) and explore their response to Permian-Triassic events. Diversity and body size are investigated separately for different groups of Osteichthyes (Dipnoi, Actinistia, 'Palaeopterygii', 'Subholostei', Holostei, Teleosteomorpha), within the marine and freshwater realms and on a global scale (total diversity) as well as across palaeolatitudinal belts. Diversity is also measured ...

Terrestrial floras underwent important changes during the Lopingian (late Permian), Early Triassic, and Middle Triassic, i.e., before, during, and after the end-Permian mass extinction. An accurate account of these developments requires reliable correlation. Macrofossils of land plants can only provide a low-resolution biostratigraphy, while detailed zonation schemes based on palynomorphs are available for many regions. Their applicability is still limited due to several factors, such as (micro-)floral provincialism, a lack of suitable marker taxa commonly occurring at important boundaries, and in many cases a lack of independent age control. Nevertheless, these palynostratigraphic schemes are regularly used for dating and correlation of successions between different regions. To support such efforts, the biozonation schemes based on palynomorphs from the Lopingian up to and including the Middle Triassic from across the world are summarized and revised. Thus, a consistent correlation of palynozones with the currently recognized international stages is established.

Reports of vertebrate body fossils from the Moenkopi Formation in Utah, Arizona, and New Mexico are dominated by occurrences of temnospondyl amphibians whereas reptiles are rare.  No vertebrate body fossils have been reported from the Red Peak Formation in Wyoming.  In contrast, a medium-high diversity vertebrate ichnofossil assemblage dominated by reptile tracks and trackways is known from both formations, and a common component of these assemblages is scratch marks commonly interpreted as swim tracks.  Swim tracks, including those from the Moenkopi and Red Peak formations, can be distinguished from other types of tracks by a unique combination of characteristics such as highly variable trace lengths, variable or unexpected trackway configurations, kick-off scours, digit reflectures, and posterior overhangs.  These characteristics reflect the aquatic behavior of animals that are fully or partially buoyant, and therefore contact with the substrate is not required to support their full weight.  Any contact with the substrate which may occur and leave a trace is a result of the animal’s swimming behavior as opposed to walking, running, etc.  Swim tracks from the Moenkopi and Red Peak formations may be categorized into four morphotypes distinguished by size, shape, and individual trace characteristics.  Each morphotype has different interpretations regarding possible trackmakers and aquatic behaviors.  Previously published swim track localities are reviewed and new swim track localities are described which add considerably to our body of knowledge about this unique type of vertebrate ichnofossil.  When considered in context with other associated ichnofossils (both vertebrate and invertebrate) swim tracks from the Moenkopi and Red Peak formations provide important information about the paleoenvironments, paleoecology, and aquatic behaviors of Early-Middle Triassic reptiles from western North America.

Although skeletal remains attributed to reptiles are rare in the Lower-Middle Triassic Moenkopi Formation of western North America, this formation does preserve a medium- to high-diversity assemblage of reptile tracks. This assemblage commonly includes swipe marks made by buoyant or partially buoyant tetrapods interpreted as reptile swim tracks. In south-central Utah swim tracks occur exclusively within the Torrey Member and are more abundant and better preserved there than in other areas throughout Utah. The Torrey Member is interpreted as representing deposition within a large delta complex, and the stratigraphic and ichnologic observations reported here support that interpretation. Stratigraphic sections measured at two swim track sites in Glen Canyon National Recreation Area show evidence of deposition within interdistributary channels and bays filled by crevasse splay deposits. These environments most likely provided ideal conditions for the development of firmground substrates that greatly increased the preservation potential of swim tracks. Due to the paucity of skeletal remains from units of this age in western North America, these tracks and the paleoenvironmental controls on their preservation provide valuable insights into the paleoecology of Early-Middle Triassic reptiles.

The Permian Chert Event (PCE) was a 30 Ma long episode of unusual chert accumulation along the northwest margin of Pangea, and possibly worldwide. The onset of the PCE occurred at about the Sakmarian-Artinskian boundary in the Sverdrup Basin, Canadian Arctic, where it coincides with a maximum flooding event, the ending of high-frequency/high-amplitude shelf cyclicity, the onset of massive biogenic chert deposition in deep-water distal areas, and a long-term shift from warm- to cool-water carbonate sedimentation in shallow-water proximal areas. A similar and coeval shift is observed from the Barents Sea to the northwestern USA. A landward and southward expansion of silica factories occurred during the Middle and Late Permian at which time warm-water carbonate producers disappeared completely from the northwest margin of Pangea. Biotically impoverished and increasingly narrow cold-water carbonate factories (characterised by non-cemented bioclasts of sponges, bryozoans, echinoderms and brachiopods) were then progressively replaced by silica factories. By Late Permian time, little carbonate sediments accumulated in the Barents Sea and in the Sverdrup Basin. where the deep- to shallow-water sedimentary spectrum was occupied by siliceous sponge spicules. By that time, biogenic silica sedimentation was common throughout the world. Silica factories collapsed in the Late Permian, abruptly bringing the PCE to an end. In northwest Pangea, the end- Permian collapse of the PCE was associated with a major transgression and with a return to much warmer oceanic and continental climatic conditions. Chert deposition resumed in the distal oceanic areas during the early Middle Triassic (Anisian) after a 8-10 Ma interruption (Early Triassic Chert Gap). The conditions necessary for the onset, expansion and zenith of the PCE were provided by the thermohaline circulation of nutrient-rich cold waters along the northwestern and western margin of Pangea, and possibly throughout the world oceans. These conditions provided an efficient transportation mechanism that constantly replenished the supply of silica in the area, created a nutrient- and oxygen-rich environment favouring siliceous biogenic productivity. established cold sea-floor conditions, hindering silica dissolution, while increasing calcium carbonate solubility, and provided conditions adverse to organic and inorganic carbonate production, The northwest margin of Pangea was, for nearly 30 Ma. bathed by cold waters presumably derived from the seasonal melting of northern sea ice, the assumed engine for thermohaline circulation. This process started near the Sakmarian-Artinskian boundary. intensified throughout Middle and Late Permian time and ceased suddenly in latest Permian time, It led to oceanic conditions much colder than normally expected from the palaeolatitudes. and the influence of cold northerly-derived water was felt as far south southern Nevada. The demise of silica factories was caused by the rapid breakdown of these conditions and the establishment of a much warmer marine environment accompanied by sluggish circulation and perhaps a reduced input of dissolved silica to the ocean. Complete thawing of northern sea ice would have ended thermohaline circulation and led to warm and sluggish oceanic conditions inimical to the production. accumulation and preservation of biogenic silica.

Molybdenum isotopes are considered to be a promising paleoredox proxy in reducing facies for evaluating either global-ocean redox conditions (given quantitative Mo uptake) or local redox conditions (given non-quantitative Mo uptake). Here, we examine the Mo-isotopic composition of black to gray shales from the Permian-Triassic boundary (PTB) section at Chaohu, eastern China, in order to assess the utility of this proxy under a range of paleoredox conditions. We evaluated local redox conditions using a combination of redox-sensitive trace-element concentrations (Mo, U) and Fe T /Al ratios, recognizing six intervals of more reducing conditions at the PTB and Induan-Olenekian boundary (IOB), in the mid-Smithian, at the Smithian-Spathian boundary (SSB), and in the mid-and upper Spathian. These six intervals are associated with variably weak to moderate enrichments of Mo, and they show variable shifts away from background δ 98 Mo values of ca. −0.4 to +0.1‰ (recording detrital Mo-isotopic compositions) toward δ 98 Mo values as high as +2.3 ± 0.2‰. Based on an analysis of local redox proxies versus δ 98 Mo as well as of sample-to-sample variance in δ 98 Mo values, we conclude that only one of the six reducing intervals in the study section is likely to record contemporaneous seawater δ 98 Mo (as a result of quasi-quantitative Mo uptake), i.e., the interval from the Hindeodus typicalis conodont Zone close to the PTB, for which δ 98 Mo values of +2.3 ± 0.2‰ suggest average global-ocean redox conditions similar to those of the modern ocean. For the remaining five reducing intervals, non-quantitative Mo uptake led to Mo-isotope signatures reflecting local, mostly suboxic redox conditions. The highest Mo concentrations (17–23 ppm) were yielded by the mid-and upper Spathian intervals, and the lack of concurrent U enrichment in the mid-Spathian interval suggests the local operation of a Mn-Fe particulate shuttle, an inference that is consistent with its relatively low δ 98 Mo values (0 ± 0.3‰). The lack of evidence for strong oceanic anoxia in the South China Craton following the PTB crisis may have been a factor in the relatively rapid recovery of marine ecosystems in this region during the Early Triassic. The present contribution serves as a case study of the application of Mo-isotopes as a paleoredox proxy in low-[Mo] sediments, which requires a careful assessment of the relative importance of global versus local redox influences based on additional proxies and evaluation criteria.

This note discusses the lithostratigraphic nomenclature used to characterise the Permian–Triassic transition at outcrop in the Oman Mountains, with emphasis on the position of the boundary between the Saiq and Mahil formations. Two inconsistent criteria for picking the Saiq/Mahil Boundary (SMB) prevail in the literature causing confusion regarding the correct position of the Permian/Triassic Boundary (PTB). The position of the PTB plays a central role in the correlation of these two formations from outcrop to the subsurface Khuff and overlying Sudair formations.
The Khuff Formation contains one of the world’s greatest reserves of non-associated gas, and its outcrop equivalent in the Oman Mountains is increasingly being studied for the purposes of regional correlations, reservoir characterisation and exploration. Therefore an agreement on the position of the SMB is a pre-requisite for precise communication among geoscientists. In this note we review the historical source of the confusion and recommend applying stratigraphic rules to resolve the position of the Saiq/Mahil Boundary (SMB).

This study describes the megaspore assemblages from the Ryabinsk Member of the Vokhma Formation of the Moscow Syneclise. The genus Otynisporites is emended, three new species, Maexisporites meditectatus, M. rugulaeferus and Otynisporites maculosus, are erected, and one new combination, Maexisporites grosstriletus, is proposed. Megaspore descriptions relate the gross morphology and fine structure of the exine surface of thirteen taxa. From the appearance of the exine surface and ornamentation processes, it appears that some forms currently included in certain genera according to their morphological features do not belong to them. The assemblage from Sholga is evidently of low diversity at the generic level, possibly reflecting the end-Permian biotic crisis. The composition of the megaspore assemblages indicates their Induan age.

The rate of developmental changes in ornamentation of the dermal skull observed at the submature stages of the trematosauroid Benthosuchus (Amphibia, Temnospondyli) shows a wide range of individual variation divided into two dominant modes. The analysis of this variation based on comparisons within samples of two dermal bones (supratemporal and squamosal) displays that such a bimodality is distinctly expressed at the earliest known growth stage and tends to disappear with age.

The vertebrate recovery after the end-Permian mass extinction can be approached through the ichnological record, which is much more abundant than body fossils. The late Olenekian (Early Triassic) tetrapod ichnoassemblage of the Catalan Pyrenean Basin is the most complete and diverse of this age from Western Tethys. This extensional basin, composed of several depocenters, was formed in the latest phases of the Variscan orogeny (Pangea breakup) and was infilled by braided and meandering fluvial systems of the red-beds Buntsandstein facies. Abundant and diverse tetrapod ichnites are recorded in these facies, including Prorotodactylus mesaxonichnus isp. nov. (tracks possibly produced by euparkeriids), cf. Rotodactylus, at least two large chirotheriid morphotypes (archosauriform trackmakers), Rhynchosauroides cf. schochardti, two other undetermined Rhynchosauroides forms, an undetermined Morphotype A (archosauromorph trackmakers) and two types of Characichnos isp. (swimming traces, here ...

Along with anatomy and kinematics, substrate conditions constitute a third major contributing factor to overall trace fossil morphology. Therefore, trace fossil suites (ichnofacies) provide insights into paleoenvironmental conditions not readily apparent from sedimentary structures alone. Here we report preliminary details on a collection of 25 trace fossil specimens from the Lower Triassic Moenkopi Formation housed at the Raymond M. Alf Museum of Paleontology (RAM). These specimens are important for interpreting terrestrial biodiversity and paleoenvironmental conditions during the ecological recovery period after the end-Permian mass extinction. The specimens were collected near Cameron, Arizona (RAM V94005), between 1950–1970. The specimens exhibit vertebrate traces (tracks, slip traces, and swim tracks), desiccation cracks, and invertebrate traces, with bioturbation indices ranging from 1–3. Vertebrate ichnotaxa include Chirotherium barthii, Chirotherium rex, Isochirotherium marshalli, and Rhynchosauroides, with C. barthii being most common. Invertebrate ichnotaxa include Arenicolites, Planolites, and Skolithos. This trace fossil assemblage, comprising vertical domiciles and locomotion traces with locally high abundances, represents the Scoyenia ichnofacies that is associated with terrestrial floodplain paleoenvironments, such as abandoned channels and desiccated overbank deposits. Crosscutting relationships and the disparate preservation of detail among traces are a product of changing substrate conditions. Some vertebrate tracks exhibit scale impressions, indicating that they were produced in a soft, but firm, fine-grained substrate that subsequently dried and produced mudcracks. After being cast by the overlying siltstone, the substrate was rehydrated and organisms continued to bioturbate the track surface, as evidenced by traces crosscutting the mudcracks and the tracks. Vertical burrows are preserved in both convex and concave hyporelief, indicating that they were produced within the substrate by organisms moving in both directions across the track surface. Future relocation of and collection at this locality will further elucidate details about paleoenvironmental conditions and paleoecology in this region during the Early Triassic.

The Lower-Middle Triassic Moenkopi Formation in central Utah is devoid of body fossils. However, tracks attributed to reptiles have long been known from the Torrey Member which was deposited by a large, prograding delta during the Early Triassic. Recently discovered vertebrate track sites from this unit and the invertebrate trace fossils associated with them are beginning to reveal the "hidden" biodiversity of this ancient deltaic ecosystem. Track sites are dominated by fish swimming traces (ichnogenus Undichna) and larger elongate traces interpreted as swim tracks produced by reptiles. Occurrences of reptile footprints (Rhynchosauroides and ?Protochirotherium) are rare. Recently, a commonly occurring track morphotype has been recognized which represents a new ichnotaxon characterized by four triangular digits of equal length arranged in a crescentic pattern with a total track width of about 2 cm. Invertebrate trace fossils associated with the vertebrate tracks represent a range of possible tracemakers and include ichnogenera commonly attributed to polychaete worms (Arenicolites and Skolithos), horseshoe crabs (Kouphichnium), crustaceans (Thalassinoides), and bivalves (Lockeia). These trace fossils also demonstrate a range of behaviors (ethologies) and can be grouped into several different ethological classes which include feeding traces (Rhizocorallium), locomotion traces (Planolites), permanent dwellings (Diplocraterion), and predation activities (rusophycid traces). Although ichnotaxonomic diversity is relatively high and trace fossils can be locally dense, an overwhelming majority of the beds within the Torrey Member completely lack bioturbation. This is most likely a result of the protracted ecologic recovery following the end-Permian mass extinction and reflects the activity of opportunistic organisms under stressed, brackish conditions. As a whole trace fossils from the Torrey Member provide evidence for the presence of fish, at least three types of reptiles, several arthropods, bivalves, and multiple other invertebrates as well as insights into the life habits for many of them. These trace fossils reveal the previously unknown biodiversity and ecology of Early Triassic organisms which would have remained hidden were it not for the traces they left behind.

The Dinwoody Formation of the western United States represents an important archive of Early Triassic ecosystems in the immediate aftermath of the end-Permian mass extinction. We present a systematic description and a quantitative paleoecological analysis of its benthic faunas in order to reconstruct benthic associations and to explore the temporal and spatial variations of diversity, ecological structure and taxonomic composition throughout the earliest Triassic of the western United States. A total of 15 bivalve species, two gastropod species, and two brachiopod species are recognized in the study area. The paleoecological analysis shows that the oldest Dinwoody communities are characterized by low diversity, low ecological complexity and high dominance of few species. We suggest that this low diversity most likely reflects the consequences of the mass extinction in the first place and not necessarily the persistence of environmental stress. Whereas this diversity pattern persists into younger strata of the Dinwoody Formation in outer shelf environments, an increase in richness, evenness and guild diversity occurred around the Griesbachian–Dienerian boundary in more shallow marine habitats. This incipient recovery towards the end of the Griesbachian is in accordance with observations from other regions and thus probably represents an interregional signal. In contrast to increasing richness within communities (alpha-diversity), beta-diversity remained low during the Griesbachian and Dienerian in the study area. This low beta-diversity reflects a wide environmental and geographical range of taxa during the earliest Triassic, indicating that the increase of within-habitat diversity has not yet led to significant competitive exclusion. We hypothesize that the well-known prevalence of generalized taxa in post-extinction faunas is primarily an effect of reduced competition that allows species to exist through the full range of their fundamental niches, rather than being caused by unusual and uniform environmental stress.

Sixteen specimens of the Early Triassic cynodont Galesaurus planiceps (including eight that were scanned using micro-computed tomography) representing different ontogenetic stages were assembled to study the dental replacement in the species. The growth series shows that the incisors and postcanines continue to develop and replace, even in the largest (presumably oldest) specimen. In contrast, replacement of the canines ceased with the attainment of skeletal maturity, at a basal skull length of ~90 mm, suggesting that Galesaurus had a finite number of canine replacement cycles. Additionally, the functional canine root morphology of these larger specimens showed a tendency to be open-rooted, a condition not previously reported in Mesozoic theriodonts. An alternating pattern of tooth replacement was documented in the maxillary and mandibular postcanine series. Both postcanine series increased in tooth number as the skull lengthened, with the mandibular postcanine series containing mor...

Abstract Molybdenum isotopes are considered to be a promising paleoredox proxy in reducing facies for evaluating either global-ocean redox conditions (given quantitative Mo uptake) or local redox conditions (given non-quantitative Mo uptake). Here, we examine the Mo-isotopic composition of black to gray shales from the Permian-Triassic boundary (PTB) section at Chaohu, eastern China, in order to assess the utility of this proxy under a range of paleoredox conditions. We evaluated local redox conditions using a combination of redox-sensitive trace-element concentrations (Mo, U) and FeT/Al ratios, recognizing six intervals of more reducing conditions at the PTB and Induan-Olenekian boundary (IOB), in the mid-Smithian, at the Smithian-Spathian boundary (SSB), and in the mid- and upper Spathian. These six intervals are associated with variably weak to moderate enrichments of Mo, and they show variable shifts away from background δ98Mo values of ca. −0.4 to +0.1‰ (recording detrital Mo-isotopic compositions) toward δ98Mo values as high as +2.3 ± 0.2‰. Based on an analysis of local redox proxies versus δ98Mo as well as of sample-to-sample variance in δ98Mo values, we conclude that only one of the six reducing intervals in the study section is likely to record contemporaneous seawater δ98Mo (as a result of quasi-quantitative Mo uptake), i.e., the interval from the Hindeodus typicalis conodont Zone close to the PTB, for which δ98Mo values of +2.3 ± 0.2‰ suggest average global-ocean redox conditions similar to those of the modern ocean. For the remaining five reducing intervals, non-quantitative Mo uptake led to Mo-isotope signatures reflecting local, mostly suboxic redox conditions. The highest Mo concentrations (17–23 ppm) were yielded by the mid- and upper Spathian intervals, and the lack of concurrent U enrichment in the mid-Spathian interval suggests the local operation of a Mn-Fe particulate shuttle, an inference that is consistent with its relatively low δ98Mo values (0 ± 0.3‰). The lack of evidence for strong oceanic anoxia in the South China Craton following the PTB crisis may have been a factor in the relatively rapid recovery of marine ecosystems in this region during the Early Triassic. The present contribution serves as a case study of the application of Mo-isotopes as a paleoredox proxy in low-[Mo] sediments, which requires a careful assessment of the relative importance of global versus local redox influences based on additional proxies and evaluation criteria.

The Griesbachian part of the Marmarasar Formation (Kara Baglyar) [1] in the Zangakatun (Sovetachen) section (Armenia) is characterized by microbial build-ups, spaced from 5 to 20m and surrounded by thin-bedded platy lime mudstone in a deep ramp environment. Above a basal carbonate fan crust follows a succession of thrombolitic domal forms, some of them up to 1.5m thick. The synoptic relief of the thrombolite head is estimated at 40-60cm above the muddy sea bottom. The overturned cone-shaped build-up geometry has a top head diameter up to 8m width consisting of numerous thrombolite domes, and an usual height of up to 15m. The water depth is interpreted below storm wave base and the asymmetrical build-up growth hints to a steady bottom current. Changes in the paleo-environment at the top of the kummeli conodont zone end the thrombolite growth. The overall duration of these post-extinction microbial build-ups is estimated at 700'000 years. Comparable Late Proterozoic Conophyton-Jac...

Systematic study of microfossil associations on the Krivi Potok section (Gučevo Mt. area, NW Serbia) has been carried out to document and to refine the Lower Triassic stratigraphic correlations within Alpine-Mediterranean domain. Field investigation and laboratory process have enabled the identification of lowermost Olenekian (lower Smithian) conodonts, ostracodes and pyrite framboids. Two conodont zones are established in this region, in ascending order they are: Pachycladina obliqua-Foliella gardenae Assemblage Zone and Neospathodus planus Zone. A new ostracode species Paracypris ? krivipotokensis FOREL n. sp. has been described, it co-occurs with conodont Neospathodus planus within the Zone of the same name. The pyrite framboids were formed within the ostracode carapaces after their death. The size distribution of pyrite framboids supports the former suggestion that large size (>6 µm in diameter) is not suitable for the reconstruction of seawater redox conditions. Апстракт. Систематско изучавање микрофосила профила Криви поток у области планине Гучево спроведено је ради документовања асоцијација и утврђивања детаљнијих доњотријаских стратиграфских односа у северозападној Србији, а у циљу корелација у оквиру Алпско-медитеранског региона. Након детаљног теренског рада и лабораторијских обрада узоркованог материјала, омогућена је идентификација старости конодоната, остракода и пиритских фрамбоида и добијен је најнижи олењок (доњи смит). У испитиваној области утврђене су две конодонтске зоне, Pachycladina obliqua-Foliella gardenae Assemblage Zone и Neospathodus planus Zone. Такође је описана нова остракодска врста Paracypris ? krivipotokensis FOREL n. sp., која се појављује удружена са врстом Neospathodus planus у истоименој конодонтској зони. Присутни пиритски фрамбоиди су настали унутар остракодских љуштура после њиховог изумирања, а како су пречника већег од 6 µm потврђена је ранија сугестија да због тога нису били погодни за реконструкцију оксидо-редукционих услова у морској води. Кључне речи: доњи тријас, олењок, конодонти, остракоди, пиритски фрамбоиди, Јадарски блок, северозападна Србија. GEOLO[KI ANALI BALKANSKOGA POLUOSTRVA ANNALES GÉOLOGIQUES DE LA PÉNINSULE BALKANIQUE 75 1-15 BEOGRAD, decembar 2014 BELGRADE,

Systematic study of microfossil associations on the Krivi Potok section (Gučevo Mt. area, NW Serbia) has been carried out to document and to refine the Lower Triassic stratigraphic correlations within Alpine-Mediterranean domain. Field investigation and laboratory process have enabled the identification of lowermost Olenekian (lower Smithian) conodonts, ostracodes and pyrite framboids. Two conodont zones are established in this region, in ascending order they are: Pachycladina obliqua-Foliella gardenae Assemblage Zone and Neospathodus planus Zone. A new ostracode species Paracypris ? krivipotokensis FOREL n. sp. has been described, it co-occurs with conodont Neospathodus planus within the Zone of the same name. The pyrite framboids were formed within the ostracode carapaces after their death. The size distribution of pyrite framboids supports the former suggestion that large size (>6 µm in diameter) is not suitable for the reconstruction of seawater redox conditions.

Examining the geological past of our planet allows us to study periods of severe climatic and biological crises and recoveries, biotic and abiotic ecosystem fluctuations, and faunal and floral turnovers through time. Furthermore, the recovery dynamics of large predators provide a key for evaluation of the pattern and tempo of ecosystem recovery because predators are interpreted to react most sensitively to environmental turbulences. The end-Permian mass extinction was the most severe crisis experienced by life on Earth, and the common paradigm persists that the biotic recovery from the extinction event was unusually slow and occurred in a step-wise manner, lasting up to eight to nine million years well into the early Middle Triassic (Anisian) in the oceans, and even longer in the terrestrial realm. Here we survey the global distribution and size spectra of Early Triassic and Anisian marine predatory vertebrates (fishes, amphibians and reptiles) to elucidate the height of trophic pyramids in the aftermath of the end-Permian event. The survey of body size was done by compiling maximum standard lengths for the bony fishes and some cartilaginous fishes, and total size (estimates) for the tetrapods. The distribution and size spectra of the latter are difficult to assess because of preservation artifacts and are thus mostly discussed qualitatively. The data nevertheless demonstrate that no significant size increase of predators is observable from the Early Triassic to the Anisian, as would be expected from the prolonged and stepwise trophic recovery model. The data further indicate that marine ecosystems characterized by multiple trophic levels existed from the earliest Early Triassic onwards. However, a major change in the taxonomic composition of predatory guilds occurred less than two million years after the end-Permian extinction event, in which a transition from fish/amphibian to fish/reptile-dominated higher trophic levels within ecosystems became apparent.

Occurrences of Paleozoic Rusophycus have been interpreted as predatory traces produced by trilobite arthropods which went extinct during the end-Permian extinction. Traces with a rusophyciform morphology from the younger Lower Triassic Moenkopi Formation in Utah are also interpreted as predatory traces based on evidence for a change in digging strategy during trace production and their close association with other traces (Rhizocorallium). The traces range from 3 to 8 cm wide and 0.8 to 5 cm deep, penetrate the substrate at an angle, and are preserved in convex hyporelief on the base of siltstone beds originally deposited in a low-relief, tidally-influenced delta. They are characterized by an overall bilobate morphology with a median furrow separating bilaterally symmetrical, primary lobes sculpted by millimeter-scale bioglyphs. A distinct pair of secondary lobes representing the deepest portions of the trace are superimposed on the primary lobes. These may be smooth or sparsely sculpted by bioglyphs. Bioglyphs on the primary lobes are subparallel whereas those on the secondary lobes lack a shared orientation. This distinct primary and secondary lobe morphology and the bioglyph patterning of these lobes suggest that the tracemakers systematically changed their digging strategies during trace production. Rhizocorallium occur at the same bedding horizon with individual burrow tubes sometimes preserved protruding from the median furrow of the rusophycid traces. Close association with other traces and changes in digging strategy support a hunting interpretation where there was an active prey item and the rusophycid trace recorded the initial attack and subsequent adjustments made by the predator. Characteristics of the Moenkopi rusophycid assemblage include randomly oriented traces of varying size that do not overlap indicating a single, uncoordinated gathering of arthropod tracemakers for feeding purposes. Based on their age, their unusually large size and the appendage dexterity required to produce the trace and its bioglyphs, a decapod crustacean is considered the most likely tracemaker. These rusophycid traces are an example of behavioral convergence in the evolution of predatory feeding strategies and associated functional morphologies of Paleozoic trilobites and early Mesozoic arthropods.

Fossil tetrapod swim tracks have been reported from deposits throughout the world, ranging
in age from the Carboniferous (Mississippian) to the Neogene (Pleistocene). A normalized
analysis of these occurrences demonstrates that lower Triassic strata contain an anomalously
high number of occurrences. Lower Triassic swim tracks also tend to be better preserved,
showing exceptionally detailed features such as scale striae and crescent-shaped claw margins.
Preservation of these features required a firm and semicohesive substrate in order to maintain
track detail before and after burial. Swim-track localities from the lower Triassic Moenkopi
Formation in Utah (USA) are characterized by sedimentary and trace fossil features that
demonstrate the widespread development and persistence of firmground substrates in a large
delta plain complex. Within this delta, complex low-diversity invertebrate trace fossil assemblages
consist of locally high densities of diminutive, millimeter-scale traces characteristic of
stressed brackish-water faunas. We suggest that the depauperate infauna characteristic of
such environments was repressed due to delayed biotic recovery following the end-Permian
mass extinction, resulting in extremely low intensities of bioturbation. Lack of biogenic mixing
promoted semiconsolidation of dewatered mud substrates and the widespread production and
persistence of firmgrounds capable of recording and maintaining swim tracks. Thus a combination
of factors, unique to the Early Triassic, increased the preservation potential of detailed
swim tracks: (1) depositional environments that promoted the production of firmground substrates,
(2) delayed ecologic recovery resulting in the lack of well-bioturbated sediment, and
(3) the swimming behavior of various Early Triassic tetrapods.

This note discusses the lithostratigraphic nomenclature used to characterise the Permian–Triassic transition at outcrop in the Oman Mountains, with emphasis on the position of the boundary between the Saiq and Mahil formations. Two inconsistent criteria for picking the Saiq/Mahil Boundary (SMB) prevail in the literature causing confusion regarding the correct position of the Permian/Triassic Boundary (PTB). The position of the PTB plays a central role in the correlation of these two formations from outcrop to the subsurface Khuff and overlying Sudair formations. The Khuff Formation contains one of the world’s greatest reserves of non-associated gas, and its outcrop equivalent in the Oman Mountains is increasingly being studied for the purposes of regional correlations, reservoir characterisation and exploration. Therefore an agreement on the position of the SMB is a pre-requisite for precise communication among geoscientists. In this note we review the historical source of the confu...

The Lower-Middle Triassic Moenkopi Formation in central Utah almost completely devoid of body fossils. However, tracks attributed to reptiles have long been known from the Torrey Member which was deposited by a large, prograding delta during the Early Triassic. Recently discovered vertebrate track sites from this unit and the invertebrate trace fossils associated with them are beginning to reveal the " hidden " biodiversity of this ancient deltaic ecosystem. Track sites are dominated by fish swimming traces (ichnogenus Undichna) and larger elongate traces interpreted as swim tracks produced by reptiles. Occurrences of reptile footprints (Rhynchosauroides and ?Protochirotherium) are rare. Recently, a commonly occurring track morphotype has been recognized which represents a new ichnotaxon characterized by four triangular digits of equal length arranged in a crescentic pattern with a total track width of about 2 cm. Invertebrate trace fossils associated with the vertebrate tracks represent a range of possible tracemakers and include ichnogenera commonly attributed to polychaete worms (Arenicolites and Skolithos), horseshoe crabs (Kouphichnium), crustaceans (Thalassinoides), and conchostracans (Lockeia). These trace fossils also record a range of behaviors (ethologies) and can be grouped into several different ethological classes which include feeding traces (Rhizocorallium), locomotion traces (Planolites), permanent dwellings (Diplocraterion), and predation activities (rusophycid traces). Although ichnotaxonomic diversity is relatively high and trace fossils can be locally dense, an overwhelming majority of the beds within the Torrey Member completely lack bioturbation. This is most likely a result of the protracted ecologic recovery following the end-Permian mass extinction and reflects the activity of opportunistic organisms under stressed, brackish conditions. As a whole, trace fossils from the Torrey Member provide evidence for the presence of fish, at least three types of reptiles, several arthropods, conchostracans, and multiple other invertebrates as well as insights into the life habits for many of them. They reveal a previously unknown biodiversity and ecology of Early Triassic organisms which would have remained hidden were it not for the traces they left behind.

A new fossiliferous locality, Granja Palmeiras, is described for the Sanga do Cabral Formation (Lower Triassic of Southern Brazil, Rosário do Sul Group, Paraná Basin). It consists on orange and reddish fine sandstones, with sandy and calcareous concretions and intercalated fossiliferous intraformational conglomerates. Its fossils are fragmentary and badly preserved. Nevertheless, among the 46 specimens collected so far, putative actinopterygians, temnospondyls, procolophonoids, archosauromorphs, and non-mammalian cynodonts were identified. Besides, several non-diagnostic appendicular elements are ascribed to Tetrapoda indet. The fossiliferous content found in Granja Palmeiras can provide a valuable new framework for future correlation with other Lower Triassic South American units as well as other continental tetrapod-bearing deposits from Gondwana.