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.

Carbon Isotope Disturbances Across the Smithian/Spathian Triassic Boundary in Vietnam

Carbon isotopic excursions and detailed ammonoid and conodont biostratigraphies around Smithian–Spathian boundary in the Bac Thuy Formation, Vietnam

Authors:

Komatsu et al

Abstract:

The Smithian–Spathian boundary is indicated by the first occurrence of the ammonoid Tirolites cf. cassianus in the Olenekian Bac Thuy Formation, northeastern Vietnam. The boundary is intercalated within organic-rich dark gray mudstone that accumulated under anoxic to dysoxic conditions in the An Chau and Nanpanjiang Basins on the South China Block. In Lang Son area, three conodont zones, Novispathodus ex gr. waageni, Novispathodus ex gr. pingdingshanensis, and Icriospathodus collinsoni, are recognized in the formation. The Smithian–Spathian boundary is intercalated within N. ex gr. pingdingshanensis conodont Zone. The positive excursion inδ13C with values increasing from around − 2.3‰ to + 5.7‰ was recorded in the uppermost Smithian Xenoceltites variocostatus ammonoid beds and N. ex gr. pingdingshanensis conodont Zone. The δ13C values decrease across the Smithian–Spathian boundary. These δ13C isotopic patterns are correlated with well-known positive excursions around the Smithian–Spathian boundary globally.

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.

Mercury Anomalies Associated With Three Mass Extinction Events

Mercury anomalies associated with three extinction events (Capitanian Crisis, Latest Permian Extinction and the Smithian/Spathian Extinction) in NW Pangea

Authors:

Grasby et al

Abstract:

Strata of Permian – Early Triassic age that include a record of three major extinction events (Capitanian Crisis, Latest Permian Extinction and the Smithian/Spathian Extinction) were examined at the Festningen section, Spitsbergen. Over the c. 12 Ma record examined, mercury in the sediments shows relatively constant background values of 0.005–0.010 μg g–1. However, there are notable spikes in Hg concentration over an order of magnitude above background associated with the three extinctions. The Hg/total organic carbon (TOC) ratio shows similar large spikes, indicating that they represent a true increase in Hg loading to the environment. We argue that these represent Hg loading events associated with enhanced Hg emissions from large igneous province (LIP) events that are synchronous with the extinctions. The Hg anomalies are consistent across the NW margin of Pangea, indicating that widespread mercury loading occurred. While this provides utility as a chemostratigraphic marker the Hg spikes may also indicate loading of toxic metals to the environment, a contributing cause to the mass extinction events.

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.

Panthalassa Ocean was Suboxic/Hypoxic, not Anoxic Across the Spathian Olenekian/Anisian Triassic

Redox conditions in the end-Early Triassic Panthalassa

Authors:

Takahashi et al

Abstract:

This study focuses on an upper Lower Triassic (Spathian) to lowermost Middle Triassic (Anisian) section representing the central Panthalassic deep sea. Analysed organic carbon isotope ratio (δ13Corg) records from the section demonstrate that lower values in the Spathian increase by up to 6‰ at the Spathian–Anisian transition. This trend accords with the carbonate carbon isotope (δ13Ccarb) record from shallow-water carbonate sections. Most horizons during late Spathian–early Anisian show features of redox conditions of not fully oxic but dysoxic conditions, inferred from low Mn, U, V, Mo and euhedral pyrite-dominated occurrences. Conversely, in the end-Spathian black-coloured beds and underlying siliceous claystone beds, relatively higher concentrations of redox-sensitive elements such as U, V, Mo and abundant pyrite framboids are detected. As enrichment factors of redox-sensitive elements are not much higher than the typical anoxic–sulphidic trend and large pyrite framboids are found, these trends suggest suboxic rather than strong anoxic conditions. These oxygen-poor conditions coincide with carbon isotope minimum values at the late Spathian. At the same time, reducing seawater conditions have been also reported in from continental sections. These coincidences imply global environmental perturbations that may have been related to the delayed recovery of life after the end-Permian mass extinction.

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.

Evidence of the Smithian/Spathian Triassic Extinction From South China

High amplitude redox changes in the late Early Triassic of South China and the Smithian–Spathian extinction

Authors:

Sun et al

Abstract:

The Early Triassic was a time of remarkably high temperatures, large carbon cycle perturbations and episodes of widespread ocean anoxia. The sediments in the Nanpanjiang Basin of South China provide superb opportunities to examine the sedimentary response to these extreme conditions especially during the crisis interval at the Smithian–Spathian (S-S) boundary. We have investigated a deep water section at Jiarong and a shallower water section at Mingtang. These contain a range of facies including black shales, micritic limestone units and rudaceous carbonate event beds that include flat pebble conglomerates and breccia debrites that bear similarities to the hybrid event beds seen in clastic turbidite successions.

Redox proxies (pyrite framboids and trace metals) reveal that widespread anoxia in the late Smithian persisted into the Novispathodus pingdingshanensis Zone of the early Spathian before a sharp transition to highly oxygenated “griotte facies” (red marine strata) in the Icriospathodus collinsoni Zone that records an “oxic rebound”. Benthic faunas are locally common but of low diversity and dominated by thin-shelled bivalves and ostracodes with small foraminifers and exceptionally rare fish remains. Bioturbation was intense only in the early–middle Spathian (I. collinsoni conodont zone) Griotte facies. Anoxia and extremely high temperatures probably played a role in severely restricting the abundance of fish and the small sizes of marine invertebrates at this time. The presence of ooids and seafloor fan cements in our study sections indicates highly saturated conditions rather than acidification at the end of the Smithian.

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.

Chaohusaurus is Oldest Known Ichthyopterygian

Ammonoid age control of the Early Triassic marine reptiles from Chaohu (South China)

Authors:

Ji et al

Abstract:

Here we described a series of ammonoid specimens from the Early Triassic of Chaohu, South China and recognized the occurrence of Procolumbites for the first time in this area. The Procolumbites layer is about one meter above the first appearance of Chaohusaurus, indicating that the oldest Chaohusaurus is within the Procolumbites Zone of middle Spathian age. This new age constrain is significantly older than the previously suggested Subcolumbites Zone assignment (early late Spathian). To date, Chaohusaurus is the oldest known ichthyopterygian.

Eohupehsuchus brevicollis: a new Hupehsuchian Marine Reptile From Spathian Olenekian Triassic China

A Small Short-Necked Hupehsuchian from the Lower Triassic of Hubei Province, China

Authors:

Chen et al

Abstract:

Hupehsuchia is a group of enigmatic Triassic marine reptiles that is known exclusively from two counties in Hubei Province, China. One of the common features of the group was a modestly long neck with nine to ten cervical vertebrae. We report a new species of Hupehsuchia, Eohupehsuchus brevicollis gen. et sp. nov., which for the first time shows a short neck in this group, with six cervicals. The configuration of the skull roof in Eohupehsuchus is also unique among Hupehsuchia, with narrow frontals and posteriorly shifted parietals, warranting recognition of a new species. The taxon superficially resembles Nanchangosaurus in retaining hupehsuchian plesiomorphies, such as low neural spines and small body size. However, its limbs are well-developed, unlike in Nanchangosaurus, although the latter genus is marginally larger in body length. Thus, the individual is unlikely to be immature. Also, Eohupehsuchus shares a suite of synapomorphies with Hupehsuchus, including the second and third layers of dermal ossicles above the dorsal neural spines. A phylogenetic analysis suggests that the new species is not the most basal hupehsuchian despite its short neck, and instead forms the sister taxon of Hupehsuchidae. Until recently, Hupehsuchia contained only two monotypic genera. Now there are at least four genera among Hupehsuchia, and the undescribed diversity is even higher. The left forelimb of the only specimen is incomplete, ending with broken phalanges distally. The breakage could only have occurred pre-burial. The individual may have been attacked by a predator and escaped, given that scavenging is unlikely.

Basal, Amphibious Ichthyosaur Relative Found in Spathian Olenekian Triassic China

A basal ichthyosauriform with a short snout from the Lower Triassic of China

Authors:

Motani et al

Abstract:

The incompleteness of the fossil record obscures the origin of many of the more derived clades of vertebrates. One such group is the Ichthyopterygia, a clade of obligatory marine reptiles that appeared in the Early Triassic epoch, without any known intermediates. Here we describe a basal ichthyosauriform from the upper Lower Triassic (about 248 million years ago) of China, whose primitive skeleton indicates possible amphibious habits. It is smaller than ichthyopterygians and had unusually large flippers that probably allowed limited terrestrial locomotion. It also retained characteristics of terrestrial diapsid reptiles, including a short snout and body trunk. Unlike more-derived ichthyosauriforms, it was probably a suction feeder. The new species supports the sister-group relationships between ichthyosauriforms and Hupehsuchia, the two forming the Ichthyosauromorpha. Basal ichthyosauromorphs are known exclusively from south China, suggesting that the clade originated in the region, which formed a warm and humid tropical archipelago in the Early Triassic. The oldest unequivocal record of a sauropterygian is also from the same stratigraphic unit of the region.

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.

Majiashanosaurus discocoracoidis: An new Eosauropterygian From Olenekian (Spathian) Triassic China

The Early Triassic eosauropterygian Majiashanosaurus discocoracoidis, gen. et sp. nov. (Reptilia, Sauropterygia), from Chaohu, Anhui Province, People’s Republic of China

Authors:

Jiang et al

Abstract:

Records of Early Triassic marine reptiles, when they first emerged after the end Permian mass extinction, are rare. During an excavation at Majiashan, Chaohu, Anhui Province, a new sauropterygian specimen was found co-occurring with the ichthyopterygian Chaohusaurus from the Upper Member of the Nanlinghu Formation, of Olenekian (Spathian, Early Triassic) age, for which a new taxon, Majiashanosaurus discocoracoidis, gen. et sp. nov., is erected. This skeleton is exposed in ventral view, with the last three cervical vertebrae together with 19 dorsal, three sacral, and more than 18 caudal vertebrae preserved. The cervical centra are keeled ventrally, and cervical ribs are double-headed, carrying a free anterior process. The transverse processes of the dorsal vertebrae are not distinctively elongated. The dorsal ribs are single-headed, and the clavicles articulate on the anteromedial aspect of the scapula. The humerus is curved. These features allow assignment to a new sauropterygian taxon. The interclavicle has no posterior process, and the scapula is of typical eosauropterygian shape, with a broad and ventrally expanded glenoidal portion that is separated from a narrow posterodorsal blade by a distinct constriction. The coracoid is round and plate-like without a waist. This feature is different from that of all other known eosauropterygians, but resembles that of placodonts.

Sinusoidal Oxygenation Levels in the Early Triassic Chinese PaleoOcean

Reconstruction of Early Triassic ocean redox conditions based on framboidal pyrite from the Nanpanjiang Basin, South China

Authors:

Tian et al

Abstract:

Widespread oceanic anoxia has been implicated as an important factor in the PTB (Permian Triassic boundary) mass extinction and the delayed recovery of Early Triassic marine ecosystems. An investigation of framboidal pyrite in the Bianyang section (Nanpanjiang Basin, South China) suggests that euxinia/dysoxia peaked during the Induan, late Smithian to earliest Spathian and late Spathian. These anoxic episodes show a relationship, albeit imperfect, to major episodes of climatic warming during the Early Triassic that were associated with intensified oceanic stratification, reduced marine productivity and organic carbon sinking fluxes, as well as diminished burial fluxes of organic carbon and reduced sulfur. In contrast, intervals of better-oxygenated marine conditions were associated with episodes of relative climatic cooling during the early to middle Smithian and mid-Spathian. The degree of ventilation of the thermocline region, in particular, had a profound effect on marine biotas, with intervals of improved ventilation resulting in increased global diversity among ammonoids and conodonts and increased local abundance of foraminifera in the Nanpanjiang Basin. These observations suggest that oceanic redox fluctuations played an important role in the delayed recovery of Early Triassic marine ecosystems, and, specifically, that episodic expansion of oceanic oxygen-minimum zones (OMZs) resulted in repeated setbacks to the recovery process, a pattern that persisted until the late Spathian.

 

Parahupehsuchus longus: a Turtle Convergent, "Tube" Carapaced Marine Reptile From Spathian Triassic China

A Carapace-Like Bony ‘Body Tube’ in an Early Triassic Marine Reptile and the Onset of Marine Tetrapod Predation

Authors:

Chen et al

Abstract:

Parahupehsuchus longus is a new species of marine reptile from the Lower Triassic of Yuan’an County, Hubei Province, China. It is unique among vertebrates for having a body wall that is completely surrounded by a bony tube, about 50 cm long and 6.5 cm deep, comprising overlapping ribs and gastralia. This tube and bony ossicles on the back are best interpreted as anti-predatory features, suggesting that there was predation pressure upon marine tetrapods in the Early Triassic. There is at least one sauropterygian that is sufficiently large to feed on Parahupehsuchus in the Nanzhang-Yuan’an fauna, together with six more species of potential prey marine reptiles with various degrees of body protection. Modern predators of marine tetrapods belong to the highest trophic levels in the marine ecosystem but such predators did not always exist through geologic time. The indication of marine-tetrapod feeding in the Nanzhang-Yuan’an fauna suggests that such a trophic level emerged for the first time in the Early Triassic. The recovery from the end-Permian extinction probably proceeded faster than traditionally thought for marine predators. Parahupehsuchus has superficially turtle-like features, namely expanded ribs without intercostal space, very short transverse processes, and a dorsal outgrowth from the neural spine. However, these features are structurally different from their turtle counterparts. Phylogeny suggests that they are convergent with the condition in turtles, which has a fundamentally different body plan that involves the folding of the body wall. Expanded ribs without intercostal space evolved at least twice and probably even more among reptiles.

This is what happens when you leave hupehsuchines unsupervised!  They converge with turtles AND ichthyosaurs at the same time.  Silly hupehsuchines!

Anoxia, High Temperatures Effected Benthic Biotic Recovery During Scythian Triassic

High temperature and low oxygen perturbations drive contrasting benthic recovery dynamics following the end-Permian mass extinction

Authors:

Pietsch et al

Abstract:

The end-Permian mass extinction event was the greatest loss of biodiversity ever experienced on the planet. The event is thought to have been triggered by the initiation of the volcanic eruptions of the Siberian Traps. The five million year recovery interval that followed the extinction event was strongly influenced by the environmental effects of sustained volcanic eruptions including extreme temperature events and persistent global and regional oxygen minimum zones. The effects of these environmental perturbations on the paleoecological recovery of the benthic marine fauna were studied in two depositional units from the Southwestern United States representing two substages during the Early Triassic recovery. The Smithian Sinbad Limestone was influenced by high sea surface temperatures and contains a relatively high diversity fauna that exhibits extremely small body size. Gastropods that lived in this environment were size-limited, a possible result of metabolic stress due to extreme temperatures. These microgastropods were able to become dominate components of the benthic fauna by occupying niche space vacated by other taxa that were excluded by high temperatures. The Spathian Virgin Limestone shows evidence for low oxygen conditions. The resulting low diversity benthic fauna had a more ecologically complex community structure than the Smithian Sinbad Limestone including the occupation of epifaunal tiering space by crinoids. As the prevalence of aerobic facies increased through time, diversity, body size, and the complexity of faunal interactions also increased suggesting that low oxygen conditions were the limiting factor for the benthic recovery in that region. The differences in diversity and community structure between the two units highlight the importance of environmental and temporal differences in driving the recovery patterns of the benthic fauna following the extinction event. High temperature events and low oxygen conditions restricted the benthic fauna in different ways but both contributed to the delay in recovery from the end-Permian mass extinction.

Utatsusaurus: Full Description Makes Into Ichthyosaurian Hockey Puck

Reinterpretation of the cranial morphology of Utatsusaurus hataii (Ichthyopterygia) (Osawa Formation, Lower Triassic, Miyagi, Japan) and its systematic implications

Authors:

1. Robin S. Cuthbertson (a)
2. Anthony P. Russell (a)
3. Jason S. Anderson (b)

Affiliations:
a. Department of Biological Sciences , University of Calgary , 2500 University Drive, Calgary , Alberta , Canada , T2N 1N4

b. Department of Comparative Biology and Experimental Medicine , University of Calgary, 3330 Hospital Drive , Calgary , Alberta , Canada , T2N 4N1

Abstract:

Utatsusaurus hataii is an early member of Ichthyopterygia from the Osawa Formation (Lower Triassic) of Miyagi Prefecture, Japan. Although the holotype of the species lacks a well-preserved cranium, UHR 30691 preserves a near-complete skull and may be referred to Utatsusaurus based on a similar geologic occurrence and, most importantly, the following shared features with the holotype: subthecodont tooth implantation; the presence of distomesially compressed tooth crowns; a humerus that is longer than wide; and an ulnar facet on the humerus that is as wide as the radial facet. The first complete description of the skull of UHR 30691 and the incorporation of data derived from it into a phylogenetic analysis retrieves a monophyletic Ichthyopterygia that is supported by 18 unambiguous synapomorphies. The updated analysis recovers Utatsusaurus in a basal clade with Parvinatator (united by one unambiguous feature), which collectively form the sister group to all other ichthyopterygians.

No Anoxia During the Spathian (Early Triassic) of Nevada?

Paleoecology and geochemistry of Early Triassic (Spathian) microbial mounds and implications for anoxia following the end-Permian mass extinction

Authors:

1. Pedro J. Marenco (a)
2. Julie M. Griffin (a)
3. Margaret L. Fraiser (b)
4. Matthew E. Clapham (c)

Affiliations:

a. Department of Geology, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010, USA

b. Department of Geosciences, University of Wisconsin–Milwaukee, Milwaukee, Wisconsin 53201, USA

c. Department of Earth and Planetary Sciences, University of California–Santa Cruz, Santa Cruz, California 95064, USA

Abstract:

Large microbialite mounds (1–2 m in height) have previously been reported from two units within the Spathian section of the Virgin Limestone Member of the Moenkopi Formation at Lost Cabin Spring, Nevada (United States). Previous investigations led to the interpretation that the mounds were formed under anoxic and alkaline conditions that suppressed metazoan grazers and delayed the biotic recovery from the end-Permian mass extinction. Here we report low organic carbon and total sulfur abundances throughout the section that suggest that anoxia was not prevalent during deposition. We also report that the upper mound-bearing unit contains stromatolite-sponge patch reefs in which mutual encrustation between stromatolites and sponges contributed to the building of a reef framework. The stromatolite-sponge patch reefs contain discrete burrows within stromatolitic laminations, suggesting that there was sufficient oxygen for grazing during the formation of the upper unit mounds. The enhanced ecological complexity of the upper unit mounds leads us to conclude that the mounds represent the transition to biotic recovery following the end-Permian mass extinction.

Paper link. Pop sci write up.

Mulling here still.