Coprolites Give Evidence of Early Triassic Polar Predators

An Early Triassic polar predator ecosystem revealed by vertebrate coprolites from the Bulgo Sandstone (Sydney Basin) of southeastern Australia

Authors:

Niedźwiedzki et al

Abstract:

Vertebrate trace fossils often provide a measure of cryptic biodiversity, and are especially pertinent when skeletal remnants are exceptionally rare. The Lower Triassic (lower Olenekian) Bulgo Sandstone at Long Reef in the Sydney Basin of southeastern Australia constitutes just such a deposit, having yielded isolated bones of giant capitosaurian temnospondyls and proterosuchid archosauriforms, together with abundant coprolites that are geochemically rich in elemental phosphate and carbon denoting vertebrate predators. Microstructural analysis of these preserved droppings reveals occasional bone fragments, fish scales, insect cuticles, plant material and bacterial traces (pseudomorph voids), as well as silicate mineral particles. REE concentrations indicate that burial and early diagenesis occurred explicitly within fluvial sediments. Furthermore, external morphological characterization permits attribution of spiral coprolites to chondrichthyan or osteichthyan fishes, polygonal, ovoid–spherical and typically flattened feces to temnospondyls, and conspicuously large cylindrical droppings to archosauriforms or other amniote apex predators. Collectively, the Bulgo Sandstone coprolite assemblage thus offers new insights into ecosystem structure and palaeoenvironment in what was an earliest Triassic near polar setting. Such data compliments the documented skeletal record, but indicates a greater range of aquatic and possibly terrestrial carnivores — the latter being enigmatically sparse in the Australian Triassic and yet detected here via the hitherto underexplored trace fossil evidence of their ecological presence.

How the Skulls of Early Triassic Basal Cynodont Galesaurus Grew

Cranial Ontogeny of the Early Triassic Basal Cynodont Galesaurus planiceps

Authors:

Jasinoski et al

Abstract:

Ontogenetic changes in the skull and mandible of thirty-one specimens of Galesaurus planiceps, a basal non-mammaliaform cynodont from the Early Triassic of South Africa, are documented. The qualitative survey indicated eight changes in the craniomandibular apparatus occurred during growth, dividing the sample into three ontogenetic stages: juvenile, subadult, and adult. Changes in the temporal region, zygomatic arch, occiput, and mandible occurred during the transition from the subadult to adult stage at a basal skull length of 90 mm. At least four morphological and allometric differences divided the adult specimens into two morphs, indicating the presence of sexual dimorphism in Galesaurus. Differences include extensive lateral flaring of the zygomatic arches in the ‘male' morph resulting in a more anterior orientation of the orbits, and a narrower snout in the ‘female'. This is the first record of sexual dimorphism in a basal cynodont, and the first time it is quantitatively documented in a non-mammaliaform cynodont. An ontogenetic comparison between Galesaurus and the more derived basal cynodont Thrinaxodon revealed differences in the timing and extent of sagittal crest development. In Galesaurus, the posterior sagittal crest, located behind the parietal foramen, developed relatively later in ontogeny, and the anterior sagittal crest rarely formed suggesting the anterior fibres of the temporalis were less developed than in Thrinaxodon. In contrast, craniomandibular features related to the masseters became more developed during the ontogeny of Galesaurus. The development of the adductor musculature appears to be one of the main factors influencing skull growth in these basal non-mammaliaform cynodonts.

Recovery From the Permian Extinction Delayed by Productivity Crises During Early Triassic

Early Triassic productivity crises delayed recovery from world's worst mass extinction

Authors:

Grasby et al

Abstract:

The recovery of life after the latest Permian extinction was protracted over Early Triassic time. Detailed geochemistry of marine sections along northwest Pangea indicates that upwelling ceased at the extinction event. Nitrogen stable isotope data suggest that this was associated with progressive increase in nutrient stress throughout the Early Triassic, coincident with a significant decrease in organic carbon content despite pervasive anoxic to euxinic conditions. We argue that the Early Triassic hothouse both reduced marine productivity and deepened the nutricline, reducing the overall rate of nutrient delivery to the photic zone, creating an Early Triassic nutrient gap. When oceans finally cooled by Middle Triassic time, renewed nutrient upwelling and onset of organic-rich shale deposition occurred across northwest Pangea, marking the final return of global marine productivity.

Sclerocormus: a new Ichthyosauriform from Spathian Triassic China

A large aberrant stem ichthyosauriform indicating early rise and demise of ichthyosauromorphs in the wake of the end-Permian extinction

Authors:

Jiang et al

Abstract:

Contrary to the fast radiation of most metazoans after the end-Permian mass extinction, it is believed that early marine reptiles evolved slowly during the same time interval. However, emerging discoveries of Early Triassic marine reptiles are questioning this traditional view. Here we present an aberrant basal ichthyosauriform with a hitherto unknown body design that suggests a fast radiation of early marine reptiles. The new species is larger than coeval marine reptiles and has an extremely small head and a long tail without a fluke. Its heavily-built body bears flattened and overlapping gastral elements reminiscent of hupehsuchians. A phylogenetic analysis places the new species at the base of ichthyosauriforms, as the sister taxon of Cartorhynchus with which it shares a short snout with rostrally extended nasals. It now appears that ichthyosauriforms evolved rapidly within the first one million years of their evolution, in the Spathian (Early Triassic), and their true diversity has yet to be fully uncovered. Early ichthyosauromorphs quickly became extinct near the Early-Middle Triassic boundary, during the last large environmental perturbation after the end-Permian extinction involving redox fluctuations, sea level changes and volcanism. Marine reptile faunas shifted from ichthyosauromorph-dominated to sauropterygian-dominated composition after the perturbation.

The Implications of a Stromatolite From the Olenekian (Spathian) Triassic of China

Upper Lower Triassic stromatolite from Anhui, South China: Geobiologic features and paleoenvironmental implications

Authors:

Luo et al

Abstract:

Widespread stromatolites and other microbialite deposits characterize Lower Triassic marine successions worldwide. This study documents a stromatolite deposit, 1.1 m thick, from the upper Spathian (Lower Triassic) of the Susong area, South China. The stromatolite comprises distinct laminated domes in the basal part and columns at the upper part. Dark laminae are loosely spaced and interlayered with thicker light colored laminae. Diffusive dark colored laminae are composed of peloidal micrite that grade locally into microclotted structures, and yield copies of bacteria clump-like and coccoid-like spheroid aggregates. The former are characterized by cloudy, micrite nuclei rimmed by coarse-grained, euhedral sparry calcite crystals, while the latter are comprised of solid calcite crystal nuclei coated with rather thin micrite envelopes. The cloudy, micrite nuclei resemble bacteria clump-like structures observed in present-day travertine. Both the coccoid-like spheroids and bacteria clump-like structures are surrounded by coarse-grained euhedral calcite crystals, suggesting a similar accretion mechanism. Both spherical structures therefore could be crucial in the accretion of the Susong stromatolite. The laminated/microclotted structures are interpreted as the result of variation in timing of lithification relative to the timing of the decay of microbes. Micro-analysis also unravels the common occurrence of authigenic micro-quartz crystals in association with Fe-bearing illite clay minerals in the stromatolite columns. Their coalescing nature with each other, together with the associated pyrite grains, strongly support the formation of micro-quartz crystals from microbial reduction of an Fe-bearing smectite precursor by sulfate reducing bacteria. A comparison of the Susong stromatolite with its counterparts from the upper Lower Triassic strata in Dajiang, South China reveals many similarities in stromatolite microstructures, suggesting that a harsh, euxinic–anoxic environment resulting in the bloom of sulfate reducing bacteria most likely extended into the latest Spathian in South China.

Teyujagua paradoxa: a new sister Taxon to Archosauriformes From Olenekian Triassic Brazil

An exceptional fossil skull from South America and the origins of the archosauriform radiation

Authors:

Pinheiro et al

Abstract:

Birds, dinosaurs, crocodilians, pterosaurs and their close relatives form the highly diverse clade Archosauriformes. Archosauriforms have a deep evolutionary history, originating in the late Permian, prior to the end-Permian mass extinction, and radiating in the Triassic to dominate Mesozoic ecosystems. However, the origins of this clade and its extraordinarily successful body plan remain obscure. Here, we describe an exceptionally preserved fossil skull from the Lower Triassic of Brazil, representing a new species, Teyujagua paradoxa, transitional in morphology between archosauriforms and more primitive reptiles. This skull reveals for the first time the mosaic assembly of key features of the archosauriform skull, including the antorbital and mandibular fenestrae, serrated teeth, and closed lower temporal bar. Phylogenetic analysis recovers Teyujagua as the sister taxon to Archosauriformes, and is congruent with a two-phase model of early archosauriform evolution, in response to two mass extinctions occurring at the end of the Guadalupian and the Permian.

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Climates Changes During the Early to Middle Triassic

Climate changes during the Early–Middle Triassic transition in the E. Iberian plate and their palaeogeographic significance in the western Tethys continental domain

Authors:

Borruel-Abadía et al

Abstract:

Until recently the climate of the Early–Middle Triassic at low latitudes was broadly considered as generally temperate-warm with no major climate oscillations. This work examines the climate of this period through a detailed study of the sedimentary, plant, soil and mineral records of continental rocks (Buntsandstein facies) in eastern Iberian basins. Our findings indicate temporal climate variations for these near equator (10°–14°N) regions and unveil the significance of such variations in the southern Laurasian domain.

The climate of Iberia's Early Triassic was mainly dominated by alternating brief (< 0.4 ma) arid and semi-arid climate periods, with two main arid periods documented at the end of the Smithian and middle Spathian. However, an initial short subhumid to semi-arid period was also observed in the late Spathian. Remarkably, this latter period appears just after an unconformity related to the tectonically induced Hardegsen Event in western Europe. It is also of interest that this short subhumid climate period is concurrent with the beginning of faunal and floral recovery in the basins examined. The Early Triassic ended again with a short very arid period. Although the beginning of the Anisian (Aegean) was represented by alternating arid and semi-arid to subhumid intervals, during the Bithynian and Pelsonian clearly wetter climates are recorded by the succession consisting of alternating semi–arid to semi-humid intervals. This general tendency was interrupted by three short but marked intervals, two humid intervals in the late Bithynian, and one arid period near the Bithynian/Pelsonian boundary. Iberia was crossed by prominent irregular highs separating marked corridors or isolated areas. This palaeogeography, prevailing since Variscan tectonics, clearly conditioned dominant climates and their geographical distribution. No clear climate belts developed in these conditions. However, isolated internal climate zones separated by elevated areas are identified. This palaeogeographic configuration and the low latitudinal position of Iberia determined central Iberia highs in the southernmost border of Laurasia, beyond which more humid conditions clearly extended towards the equator reaching the present-day Moroccan Meseta and Argana Basin.

The Survivors of the Permian Mass Extinction Delayed Benthic Marine Recovery

Competition in slow motion: the unusual case of benthic marine communities in the wake of the end-Permian mass extinction

Authors:

Hautmann et al

Abstract:

Changes of community structure in response to competition usually take place on timescales that are much too short to be visible in the geological record. Here we report the notable exception of a benthic marine community in the wake of the end-Permian mass extinction, which is associated with the microbial limestone facies of the earliest Triassic of South China. The newly reported fauna is well preserved and extraordinarily rich (30 benthic macroinvertebrate species, including the new species Astartella? stefaniae (Bivalvia) and Eucochlis obliquecostata (Gastropoda)) and stems from an environmentally stable setting providing favourable conditions for benthic organisms. Whereas changes in the taxonomic composition are negligible over the observed time interval of 10–100 ka, three ecological stages are identified, in which relative abundances of initially rare species continuously increased at the cost of previously dominant species. Concomitant with the changes of dominant species is an increase in faunal evenness and heterogeneity. In the absence of both environmental and taxonomic changes, we attribute this pattern to the long-term effects of interspecific competition, which acted at an unusually slow pace because the number of competing species and potential immigrants was dramatically reduced by the end-Permian mass extinction. We suggest that these non-actualistic conditions led to decreased rates of niche differentiation and hence to the delayed rediversification of benthos that characterizes the aftermath of the greatest Phanerozoic mass extinction event. A hyperbolic diversification model is proposed, which accounts for the positive relationship between the intensity of interspecific competition and the rate of niche differentiation and resolves the conundrum of delayed rediversification at a time when niche space was largely vacated.

Mesozoic Marine Revolution Started Very Quickly After Permian Triassic Extinction

Coprolites of marine vertebrate predators from the Lower Triassic of southern Poland

Authors:

Brachaniec et al

Abstract:

Numerous coprolites are described for the first time herein from the Lower Triassic (Olenekian) shallow marine sedimentary rocks in southern Poland. X-ray Diffraction and geochemical analyses show that they are preserved as calcium phosphate with small admixtures of quartz and calcite. Additionally, SEM and thin section studies revealed that they contain highly fragmented faunal remains (crinoids, molluscs and vertebrates). The size, shape, geochemistry, biostratigraphic distribution and co-occurrence with vertebrate skeletal remains imply that the coprolites at hand were likely produced by nothosaurids, the durophagous sauropterygian reptiles and actinopterygian (ray-finned) fish. The large number of recorded coprolites implies that durophagous predation has been intense during the Early Triassic and suggests that the so-called Mesozoic Marine Revolution probably started soon after the end-Permian extinction. Furthermore, discovery of sinusoidal trails attributable to nematodes in some coprolites implies that the intestinal parasitic associations with these predators had already evolved by at least the Early Triassic.

Eretmorhipis carrolldongi: an Excellent Fossil of a Mysterious Spathian Olenekian Triassic Hupehsuchian

A New Specimen of Carroll’s Mystery Hupehsuchian from the Lower Triassic of China

Authors:

Chen et al

Abstract:

A new specimen of an enigmatic hupehsuchian genus is reported. The genus was first recognized by Robert L. Carroll and Zhi-ming Dong in 1991, who refrained from naming it because of the poor quality of the only specimen known at the time. After more than two decades, we finally report a second specimen of this genus, which remained unprepared until recently. The new specimen preserves most of the skeleton except the skull, allowing us to erect a new genus and species, Eretmorhipis carrolldongi. The new species shares many characters with Parahupehsuchus longus, including the strange axial skeleton that forms a bony body tube. However, the body tube is short in the new species, being limited to the pectoral region. The vertebral count and limb morphology considerably differ between the new species and P. longus. The forelimb of E. carrolldongi is markedly larger than its hind limb as in Hupehsuchus nanchangensis but unlike in P. longus. The new species is unique among hupehsuchians in a list of features. It has manual and pedal digits that spread radially, forming manus and pes that are almost as wide as long. The third-layer elements of the dermal armor are unusually large, spanning four vertebral segments, yet there are substantial gaps among them. With the addition of the unique paddle, it is now clear that Hupehsuchia had diverse forelimb morphologies spanning from paddles to flippers, unlike ichthyopterygians that were taxonomically more diverse yet only had flippers.

Trace Fossils From Smithian/Spathian Triassic South China Suggest Gradual Biotic Recovery From PT Extinction

Early Triassic trace fossils from the Three Gorges area of South China: Implications for the recovery of benthic ecosystems following the Permian–Triassic extinction

Authors:

Zhao et al

Abstract:

The Lower Triassic Daye and Jialingjiang formations of the Three Gorges area (South China) record the recovery interval of benthic tracemaking invertebrates following the P–Tr mass extinction. A total of 17 ichnospecies in 14 ichnogenera are documented from Smithian and Spathian strata. Our trace fossil data, in combination with previously published studies, show that ichnodiversity in the Middle Yangtze region increased markedly in the early Spathian. Trace fossils in the Smithian are dominated by simple, small, horizontal burrows, including Didymaulichnus and Planolites, whereas Spathian trace fossils are diverse and abundant with moderate–high bioturbation levels and complex burrow networks, such as Thalassinoides. Both burrow sizes and penetration depths increased gradually from the early Spathian to the middle–late Spathian, implying a gradual recovery pattern for benthic ecosystems. Early Triassic ichnofossils are characterised by aspects of opportunistic behaviour (e.g., low-to-moderate ichnodiversity, low-to-moderate bioturbation, small burrow widths, and shallow tiering), suggesting stressed environmental conditions. The recovery tempo and pattern of ichnocoenoses in South China is likely structured by temporal and spatial changes of the refuge zone in the Early Triassic.

The Kids Were Scarier: Cranial Ornamentation DECREASE With age in Early Triassic Trematosauroid Temnospondyl Benthosuchus?

On the development of surface ornamentation of skull bones in the ontogeny of Early Triassic benthosuchids (Amphibia, Temnospondyli)

Author:

Morkovin

Abstract:

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.

Early Triassic Tetrapod Swimming Trace Fossils Left due to PT Extinction Aftershocks?

Swimming reptiles make their mark in the Early Triassic: Delayed ecologic recovery increased the preservation potential of vertebrate swim tracks

Authors:

Thomson et al

Abstract:

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.

Cranial Ontogeny of the Early Triassic Cynodont Thrinaxodon liorhinus

Ontogeny of the Early Triassic Cynodont Thrinaxodon liorhinus (Therapsida): Cranial Morphology

Authors:

Jasinoski et al

Abstract:

The cranial morphology of 68 Thrinaxodon liorhinus specimens, ranging in size from 30 – 96mm in basal skull length, is investigated using both qualitative and quantitative analyses. From this comprehensive survey, we determined that nine cranial features, including five in the temporal region, separated the sample into four ontogenetic stages. A bivariate analysis of 60 specimens indicated that the skull generally increased in size isometrically, with the exception of four regions. The orbit had negative allometry, a result consistent with other ontogenetic studies of tetrapods, whereas the length of the snout, palate, and temporal region showed positive allometry. The last trend had strong positive allometry indicating that during ontogeny the length of the sagittal crest increased at a much faster rate than the rest of the skull. The large number of changes in the temporal region of the skull of Thrinaxodon may indicate a greater development of the posterior fibres of the temporalis musculature from an early ontogenetic stage. For example, the posterior sagittal crest developed much earlier in ontogeny than the anterior crest that formed in adults, and bone was deposited dorsally creating a unified posterior sagittal crest rather than having a suture that spanned the entire depth of the skull roof. In combination with the isometric height of the zygomatic arch and the almost complete absence of the zygomatic arch angulation, these ontogenetic changes suggest that there was greater development of the temporalis relative to the masseter muscles, indicating a strong posterodorsal movement of the mandible in Thrinaxodon.

Spathian Triassic ichthyopterygian Chaohusaurus chaoxianensis is a Valid Taxon

Status of Chaohusaurus chaoxianensis (Chen, 1985)

Authors:

Motani et al

Abstract:

The Early Triassic ichthyopterygian Chaohusaurus chaoxianensis was previously known from juvenile specimens only. It was considered to represent immature forms of C. geishanensis, which was based on a single adult specimen, because allometric regression lines of the forelimb skeletons suggested that the two name groups fitted along a single growth trajectory. The sample size for the analysis, however, was small (n = 5). We collected new specimens of Chaohusaurus from Majiashan, Chaohu City, Anhui Province, China, through field excavations that started in 2010. New specimens included an immature individual whose forelimb resembled that of mature C. geishanensis, as well as a large adult individual whose forelimb retained the characteristics of immature C. chaoxianensis. Therefore, C. chaoxianensis is not the juvenile of C. geishanensis. With the addition of the new specimens, two growth trajectories are now clearly detected on allometric regression plots (n = 15). The two species are unambiguously distinguished from each other based on a suite of discrete characters that are diagnostic to each species, as well as statistical analyses of forelimb measurements. It is unlikely that the two forms represent the genders of a single species given that C. geishanensis is vastly outnumbered by C. chaoxianensis and completely lacking in major fossiliferous rock layers. Therefore, C. chaoxianensis should be resurrected as a valid species.

Early Triassic Chaohusaurus Fauna's Paleoenvironment

Microfacies characteristics of the Lower Triassic containing Chaohusaurus fauna in Chaohu area, Anhui Province and its palaeoenvironment.

Authors:

Zhang et al

Abstract:

The Early Triassic Chaohusaurus fauna was found at No.598-630 layers at the top of the Middle Member-the bottom of the Upper Member of the Nanlinghu Formation in Majiashan section of Chaohu area,Anhui Province. Based on the microfacies characteristics and the carbon and oxygen isotope analysis,the sedimentary environment of the fossil beds where the Chaohusaurus fauna had occurred was studied. 4microfacies types were recognized from the studied layers,which contained the red-grey thick nodular limestone with spicules-bivalves,the gray bioclastic-argillaceous micrite limestone,the gray laminated argillaceous micrite limestone,and the light gray micrite limestone, respectively. It was indicated that the sedimentary environment of the fossil beds was from the foot of the outer ramp-abyssal basin to the outer ramp. The values of the δ13C and δ18O are generally low in the whole of fossil beds. Combined with the above characteristics,it might be inferred that the Chaohusaurus fauna was living in the outer ramp zone with low-energy,less numbers and types of the biocoenose,and high seawater temperature.

Environmental Impacts During Biotic Recovery After the Permian/Triassic Mass Extinction

Environmental controls on marine ecosystem recovery following mass extinctions, with an example from the Early Triassic

Authors:

Wei et al

Abstract:

The recovery of marine ecosystems following a mass extinction event involves an extended interval of increasing biotic diversity and ecosystem complexity. The pace of recovery may be controlled by intrinsic ecosystem or extrinsic environmental factors. Here, we present an analysis of changes in marine conditions following the end-Permian mass extinction with the objective of evaluating the role of environmental factors in the protracted (~ 5-Myr-long) recovery of marine ecosystems during the Early Triassic. Specifically, our study examines changes in weathering, productivity, and redox proxies in three sections in South China (Chaohu, Daxiakou, and Zuodeng) and one in northern India (Mud). Our results reveal: 1) recurrent environmental perturbations during the Early Triassic; 2) a general pattern of high terrestrial weathering rates and more intensely reducing marine redox conditions during the early Griesbachian, late Griesbachian, mid-Smithian, and (more weakly) the mid-Spathian; 3) increases in marine productivity during the aforementioned intervals except for the early Griesbachian; and 4) stronger and more temporally discrete intervals of environmental change in deepwater sections (Chaohu and Daxiakou) relative to shallow and intermediate sections (Zuodeng and Mud). Our analysis reveals a close relationship between episodes of marine environmental deterioration and a slowing or reversal of ecosystem recovery based on metrics of biodiversity, within-community (alpha) diversity, infaunal burrowing, and ecosystem tiering. We infer that the pattern and pace of marine ecosystem recovery was strongly modulated by recurrent environmental perturbations during the Early Triassic. These perturbations were associated with elevated weathering and productivity fluxes, implying that nutrient and energy flows were key influences on recovery. More regular secular variation in deepwater relative to shallow-water environmental conditions implies that perturbations originated at depth (i.e., within the oceanic thermocline) and influenced the ocean-surface layer irregularly. Finally, we compared patterns of environmental disturbance and ecosystem recovery following the other four “Big Five” Phanerozoic mass extinctions to evaluate whether commonalities exist. In general, the pace of ecosystem recovery depends on the degree of stability of the post-crisis marine environment.

Marine–terrestrial Kockatea Biota From Smithian Olenekian Triassic Australia

Early Triassic (early Olenekian) life in the interior of East Gondwana: mixed marine–terrestrial biota from the Kockatea Shale, Western Australia

Authors:

Haig et al

Abstract:

A new terrestrial–marine assemblage from the lower beds of a thin outcrop section of the Kockatea Shale in the northern Perth Basin, Western Australia, contains a range of fossil groups, most of which are rare or poorly known from the Lower Triassic of the region. To date, the collection includes spinose acritarchs, organic-cemented agglutinated foraminifera, lingulids, minute bivalves and gastropods, ammonoids, spinicaudatans, insects, austriocaridid crustaceans, actinopterygians, a temnospondyl-like mandible, plant remains, and spores and pollen. Of these groups, the insects, crustaceans and macroplant remains are recorded for the first time from this unit.

Palynomorphs permit correlation to nearby sections where conodonts indicate an early Olenekian (Smithian) age. The locality likely represents the margin of an Early Triassic shallow interior sea with variable estuarine-like water conditions, at the southwestern end of an elongate embayment within the East Gondwana interior rift–sag system preserved along the Western Australian margin. Monospecific spinose acritarch assemblages intertwined with amorphous organic matter may represent phytoplankton blooms that accumulated as mats, and suggest potentially eutrophic surface waters. The assemblage represents a mixure of marine and terrestrial taxa, suggesting variations in water conditions or that fresh/brackish-water and terrestrial organisms were transported from adjacent biotopes. Some of the lower dark shaly beds are dominated by spinicaudatans, likely indicating periods when the depositional water body was ephemeral, isolated, or subjected to other difficult environmental conditions.

The biota of the Kockatea Shale is insufficiently known to estimate biotic diversity and relationships of individual taxa to their Permian progenitors and Triassic successors, but provides a glimpse into a coastal-zone from the interior of eastern Gondwana. Specialist collecting is needed to clarify the taxonomy of many groups, and comparisons to other Lower Triassic sites are required to provide insights into the pattern of biotic decline and recovery at the end-Permian crisis.

Five Million Years After Permian Extinction Marine Ecosystem More Complex Than Anticipated

Coprolites from the upper Osawa Formation (upper Spathian), northeastern Japan: Evidence for predation in a marine ecosystem 5 Myr after the end-Permian mass extinction

Authors:

Nakajima et al

Abstract:

Lower Triassic marine deposits, which can potentially provide important information on the diversity and trophic structure of marine ecosystems following the end-Permian mass extinction, are rarely exposed in the world. Given the sparse body fossil record from the Lower Triassic, non-body fossil evidences, such as trace fossils for example, may provide additional windows on fossil ecosystems. Herein, the authors recently found dark, amorphous lumps of various sizes, ranging from a few millimetres to approximately 7 cm in maximum dimension, from the offshore marine deposit of upper Osawa Formation (Spathian, Lower Triassic) in the South Kitakami Terrane of northeast Japan. Compared with the surrounding siliciclastic sediments, the lumps are rich in phosphate and organic carbon, and poor in silicates. Shape, mode of occurrence, bone inclusion and geochemical signatures of these lumps confirm that these are coprolites, produced not by benthic sediment feeders, but most likely by nektonic animals. Bone inclusion also suggests that carnivorous fish and/or marine reptiles, constituting the higher part of the food chain, produced at least a part of the specimens. Despite the low diversity of the known fossil vertebrates from the Osawa formation, coprolites first shed light on the predator–prey interactions in the marine ecosystem in South Kitakami Terrane 5 Myr after the end-Permian mass extinction.

An Early Triassic Ichthyopterygian From Japan

An Early Triassic ichthyopterygian fossil from the Osawa Formation in Minamisanriku Town, Miyagi Prefecture, Japan

Authors:

TAKAHASHI et al

Abstract:

The Ichthyopterygia Owen 1840 is a remarkable group of Mesozoic marine reptiles with distinctive fish-shaped bodies. There are conflicting views on the taxonomic nomenclature of ichthyopterygians (e.g., Motani and McGowan, 2003; Maisch, 2010). In this study, we employed the phylogeny and nomenclature of McGowan and Motani (2003) in which the term Ichthyosauria refers to a derived clade within the Ichthyopterygia; according to this system, Utatsusaurus is a basal ichthyopterygian and not an ichthyosaurian. The phylogenetic relationships and systematics within the group have been analyzed in recent synthetic studies (e.g., Motani, 1999; Sander, 2000; McGowan and Motani, 2003; Maisch 2010), but a consensus is yet to be reached regarding the phylogenetic relationship with other reptiles (e.g., McGowan and Motani, 2003). More information on early ichthyopterygians is crucial to understand their origin. Ichthyopterygian fossil record extends from the Early Triassic Olenekian to the Late Cretaceous Cenomanian (Motani and McGowan, 2003). Early Triassic taxa have been reported from Europe, North America, and Asia (Table 1). Note that some species are represented by fragmentary specimens, whereas the ichthyopterygian affinity of a few taxa have been debated (e.g., Omphalosaurus and “Pessopteryx nisseri”; Motani, 2000, Sander and Faber 2003; McGowan and Motani, 2003; Dalla Vecchia, 2004; Maisch, 2010).

Permian–Triassic mass extinction affected the marine ecosystem seriously (Raup, 1979; Sepkoski, 1984), and the Paleozoic fauna was largely replaced by the modern fauna (Sepkoski, 1984). The occurrence of marine reptiles added a new trophic level of top predators in the Mesozoic marine ecosystem, and their radiation started in the Olenekian (Chen and Benton, 2012; Fröbisch et al., 2013). However, only a limited number of Early Triassic reptilian faunas actually document this process (e.g., Sulphur Mountain Formation in Canada, Vikinghøgda Formation in Norway, Nanlinghu Formation in China: see Table 1). The Osawa reptilian fauna is important in this regard as well.

In 2007, a partial skeleton of a reptile was discovered from the Lower Triassic Osawa Formation (Spathian or late Olenekian: Bando and Shimoyama, 1974; Bando and Ehiro, 1982), Inai Group, in Miyagi Prefecture, northeastern Japan (Fig. 1). This formation has yielded a number of articulated skeletons of the primitive ichthyopterygian Utatsusaurus hataii Shikama et al. 1978, which is one of the oldest animals secondarily adapted to life in open (Nakajima et al., in press). Apart from U. hataii, only two other vertebrate taxa, i.e., hybodontoid shark (Kato et al., 1995) and “Metanothosaurus nipponicus” Yabe and Shikama 1948, have been reported from the formation to science. The holotype and only specimen of the latter taxon has been missing, and the existing information is not sufficient to determine its taxonomic status (e.g., sauropterygian in Mazin [1986]; ichthyosaur and not sauropterygian in Rieppel [2000: 109]); hence this taxon is regarded as nomen dubium.

The new specimen was discovered at the base of the dark gray shale exposed along the coast in Minamisanriku Town in the northeastern corner of the Miyagi Prefecture. It was collected as a float but retained fresh surface. The locality is within 1 km from the holotype locality of Utatsusaurus hataii, and the horizon of the new specimen is correlated to the middle part of the formation and is within the stratigraphic range of Utatsusaurus (Shikama et al., 1978).