• Pentaradial eukaryote suggests expansion of suspension feeding in White Sea-aged Ediacaran communities

      Cracknell, Kelsie; García-Bellido, Diego C; Gehling, James G; Ankor, Martin J; Darroch, Simon AF; Rahman, Imran (Springer Science and Business Media LLC, 2021-12)
      Suspension feeding is a key ecological strategy in modern oceans that provides a link between pelagic and benthic systems. Establishing when suspension feeding first became widespread is thus a crucial research area in ecology and evolution, with implications for understanding the origins of the modern marine biosphere. Here, we use three-dimensional modelling and computational fluid dynamics to establish the feeding mode of the enigmatic Ediacaran pentaradial eukaryote Arkarua. Through comparisons with two Cambrian echinoderms,Cambraster and Stromatocystites, we show that flow patterns around Arkarua strongly support its interpretation as a passive suspension feeder.Arkarua is added to the growing number of Ediacaran benthic suspension feeders, suggesting that the energy link between pelagic and benthic ecosystems was likely expanding in the White Sea assemblage (~ 558–550 Ma). The advent of widespread suspension feeding could therefore have played an important role in the subsequent waves of ecological innovation and escalation that culminated with the Cambrian explosion.
    • Vertically migrating Isoxys and the early Cambrian biological pump

      Pates, Stephen; Daley, Allison C; Legg, David A; Rahman, Imran (The Royal Society, 2021-06-30)
      The biological pump is crucial for transporting nutrients fixed by surface-dwelling primary producers to demersal animal communities. Indeed, the establishment of an efficient biological pump was likely a key factor enabling the diversification of animals over 500 Myr ago during the Cambrian explosion. The modern biological pump operates through two main vectors: the passive sinking of aggregates of organic matter, and the active vertical migration of animals. The coevolution of eukaryotes and sinking aggregates is well understood for the Proterozoic and Cambrian; however, little attention has been paid to the establishment of the vertical migration of animals. Here we investigate the morphological variation and hydrodynamic performance of the Cambrian euarthropod Isoxys. We combine elliptical Fourier analysis of carapace shape with computational fluid dynamics simulations to demonstrate that Isoxys species likely occupied a variety of niches in Cambrian oceans, including vertical migrants, providing the first quantitative evidence that some Cambrian animals were adapted for vertical movement in the water column. Vertical migration was one of several early Cambrian metazoan innovations that led to the biological pump taking on a modern-style architecture over 500 Myr ago.
    • Lack of support for Deuterostomia prompts reinterpretation of the first Bilateria

      Kapli, Paschalia; Natsidis, Paschalis; Leite, Daniel J; Fursman, Maximilian; Jeffrie, Nadia; Rahman, Imran; Philippe, Hervé; Copley, Richard R; Telford, Maximilian J (American Association for the Advancement of Science (AAAS), 2021-03)
      The bilaterally symmetric animals (Bilateria) are considered to comprise two monophyletic groups, Protostomia (Ecdysozoa and the Lophotrochozoa) and Deuterostomia (Chordata and the Xenambulacraria). Recent molecular phylogenetic studies have not consistently supported deuterostome monophyly. Here, we compare support for Protostomia and Deuterostomia using multiple, independent phylogenomic datasets. As expected, Protostomia is always strongly supported, especially by longer and higher-quality genes. Support for Deuterostomia, however, is always equivocal and barely higher than support for paraphyletic alternatives. Conditions that cause tree reconstruction errors—inadequate models, short internal branches, faster evolving genes, and unequal branch lengths—coincide with support for monophyletic deuterostomes. Simulation experiments show that support for Deuterostomia could be explained by systematic error. The branch between bilaterian and deuterostome common ancestors is, at best, very short, supporting the idea that the bilaterian ancestor may have been deuterostome-like. Our findings have important implications for the understanding of early animal evolution.
    • The alteration history of the CY chondrites, investigated through analysis of a new member: Dhofar 1988

      Suttle, Martin; Greshake, A; King, A; Schofield, PF; Tomkins, A; Russell, Sara (Elsevier BV, 2021-02)
      We provide the first detailed analysis of the carbonaceous chondrite Dhofar (Dho) 1988. This meteorite find was recovered in 2011 from the Zufar desert region of Oman and initially classified as a C2 ungrouped chondrite. Dho 1988 is a monomict breccia composed of millimetre-sized clasts, between which large (~50-250µm) intermixed sulphide-Ca-carbonate veins formed. It has high sulphide abundances (~14 vol%), medium-sized chondrules (avg. 530µm, N=33), relatively low chondrule/CAI abundances (<20 area%), a heavy bulk O-isotope composition (δ17O=9.12‰, δ18O=19.46‰) and an aqueously altered and then dehydrated alteration history. These characteristics are consistent with the newly defined Yamato-type (CY) carbonaceous chondrite group, suggesting this meteorite should be reclassified as a CY chondrite. Dho 1988 experienced advanced aqueous alteration (petrologic subtype 1.3 in the scheme of Howard et al., [2015]). Alteration style and extent are similar to the CM chondrite group, with the matrix having been replaced by tochilinite-cronstedtite intergrowths and chondrules progressively pseudomorphed by phyllosilicates, sulphides and in one instance Ca-carbonates. However, departures from CM-like alteration include the replacement of chondrule cores with Al-rich, Na-saponite and upon which Cr-spinel and Mg-ilmenite grains precipitated. These late-stage aqueous alteration features are common among the CY chondrites. Fractures in Dho 1988 that are infilled by phyllosilicates, sulphides and carbonates attest to post-brecciation aqueous alteration. However, whether aqueous alteration was also active prior to brecciation remains unclear. Veins are polymineralic with a layered structure, allowing their relative chronology to be reconstructed: intermixed phyllosilicate-sulphide growth transitioned to sulphide-carbonate deposition. We estimate temperatures during aqueous alteration to have been between 110ºC<T<160ºC, based on the co-formation of Na-saponite and tochilinite. Dho 1988 was later overprinted by thermal metamorphism. Peak temperatures are estimated between 700ºC and 770ºC, based on the thermal decomposition of phyllosilicates (both serpentine and saponite) combined with the survival of calcite. As temperatures rose during metamorphism the thermal decomposition of pyrrhotite produced troilite. Sulphur gas was liberated in this reaction and flowed through the chondrite reacting with magnetite (previously formed during aqueous alteration) to form a second generation of troilite grains. The presence of both troilite and Ni-rich metal in Dho 1988 (and other CY chondrites) demonstrate that conditions were constrained at the iron-troilite buffer.
    • Ancient life and moving fluids

      Gibson, Brandt M; Furbish, David J; Rahman, Imran; Schmeeckle, Mark W; Laflamme, Marc; Darroch, Simon AF (Wiley, 2021-02)
      Over 3.7 billion years of Earth history, life has evolved complex adaptations to help navigate and interact with the fluid environment. Consequently, fluid dynamics has become a powerful tool for studying ancient fossils, providing insights into the palaeobiology and palaeoecology of extinct organisms from across the tree of life. In recent years, this approach has been extended to the Ediacara biota, an enigmatic assemblage of Neoproterozoic soft-bodied organisms that represent the first major radiation of macroscopic eukaryotes. Reconstructing the ways in which Ediacaran organisms interacted with the fluids provides new insights into how these organisms fed, moved, and interacted within communities. Here, we provide an in-depth review of fluid physics aimed at palaeobiologists, in which we dispel misconceptions related to the Reynolds number and associated flow conditions, and specify the governing equations of fluid dynamics. We then review recent advances in Ediacaran palaeobiology resulting from the application of computational fluid dynamics (CFD). We provide a worked example and account of best practice in CFD analyses of fossils, including the first large eddy simulation (LES) experiment performed on extinct organisms. Lastly, we identify key questions, barriers, and emerging techniques in fluid dynamics, which will not only allow us to understand the earliest animal ecosystems better, but will also help to develop new palaeobiological tools for studying ancient life.
    • Calathus: A sample-return mission to Ceres

      Gassot, Oriane; Panicucci, Paolo; Acciarini, Giacomo; Bates, HC; Caballero, Manel; Cambianica, Pamela; Dziewiecki, Maciej; Dionnet, Zelia; Enengl, Florine; Gerig, Selina-Barbara; et al. (Elsevier BV, 2021-01-12)
      Ceres, as revealed by NASA's Dawn spacecraft, is an ancient, crater-saturated body dominated by low-albedo clays. Yet, localised sites display a bright, carbonate mineralogy that may be as young as 2 Myr. The largest of these bright regions (faculae) are found in the 92 km Occator Crater, and would have formed by the eruption of alkaline brines from a subsurface reservoir of fluids. The internal structure and surface chemistry suggest that Ceres is an extant host for a number of the known prerequisites for terrestrial biota, and as such, represents an accessible insight into a potentially habitable “ocean world”. In this paper, the case and the means for a return mission to Ceres are outlined, presenting the Calathus mission to return to Earth a sample of the Occator Crater faculae for high-precision laboratory analyses. Calathus consists of an orbiter and a lander with an ascent module: the orbiter is equipped with a high-resolution camera, a thermal imager, and a radar; the lander contains a sampling arm, a camera, and an on-board gas chromatograph mass spectrometer; and the ascent module contains vessels for four cerean samples, collectively amounting to a maximum 40 g. Upon return to Earth, the samples would be characterised via high-precision analyses to understand the salt and organic composition of the Occator faculae, and from there to assess both the habitability and the evolution of a relict ocean world from the dawn of the Solar System.
    • Female aristocrats in the natural history world before the establishment of the Geological Society of London

      Sendino, Consuelo; Porter, Julian (Geological Society of London, 2020-12-07)
      A fascination with natural history does not recognize class, as is shown through the activities of female aristocrats who, during the eighteenth and nineteenth centuries, contributed significantly by increasing the number of collections at natural history museums. These women were not members of the Geological Society of London because, at that time, women were not even allowed to be members, but they still left their impressive legacy in museums. This paper will focus on three women who made extensive collections that are now incorporated into British museums. The first of these, the Duchess of Portland, made one of the finest collections in England and, possibly, the best collection of shells and fossils in Europe of her time, which was later acquired by the Natural History Museum, London. She was followed by the Countess of Aylesford who made one of the most important mineral collections of her time, which is now at the Natural History Museum, London. Finally, Baroness Brassey collected geological samples during her trips that were used to establish the Brassey Institute in Hastings. These three women used their own income and influence to build collections.
    • The Natural History Museum Fossil Porifera Collection

      Sendino, Consuelo (SAGE Publications, 2020-12-02)
      This article provides updated information about the Porifera Collection at The Natural History Museum (NHM), London. With very little information available regarding fossil sponge digitization or any similar initiative, this paper covers the type and figured specimens and drawer label content data of the Porifera Collection and also describes the collection and its research potential. With approximately 71,000 specimens, of which more than 60% are Mesozoic, the NHM holdings offer the best Mesozoic sponge collection in the world and one of the most important due to its breadth and depth. The Porifera Collection covers all stratigraphic periods and all taxonomic groups and includes almost 3000 cited and figured specimens including types. Although most of the specimens come from the British Isles, worldwide samples are also present, with abundant specimens from other Commonwealth countries and from Antarctica.
    • Disparate compound eyes of Cambrian radiodonts reveal their developmental growth mode and diverse visual ecology

      Paterson, John R; Edgecombe, GD; García-Bellido, Diego C (American Association for the Advancement of Science (AAAS), 2020-12)
      Radiodonts are nektonic stem-group euarthropods that played various trophic roles in Paleozoic marine ecosystems, but information on their vision is limited. Optical details exist only in one species from the Cambrian Emu Bay Shale of Australia, here assigned to Anomalocaris aff. canadensis. We identify another type of radiodont compound eye from this deposit, belonging to ‘Anomalocaris’ briggsi. This ≤4-cm sessile eye has &gt;13,000 lenses and a dorsally oriented acute zone. In both taxa, lenses were added marginally and increased in size and number throughout development, as in many crown-group euarthropods. Both species’ eyes conform to their inferred lifestyles: The macrophagous predator A. aff. canadensis has acute stalked eyes (&gt;24,000 lenses each) adapted for hunting in well-lit waters, whereas the suspension-feeding ‘A.’ briggsi could detect plankton in dim down-welling light. Radiodont eyes further demonstrate the group’s anatomical and ecological diversity and reinforce the crucial role of vision in early animal ecosystems.
    • Cooling and exhumation of the Late Paleozoic Tulasu epithermal gold system, Western Tianshan, NW China: implications for preservation of Pre-Mesozoic epithermal deposits

      Zhao, Xiao-Bo; Xue, Chun-Ji; Zhao, Wei-Ce; Seltmann, Reimar; Symons, David T.A.; Dolgopolova, Alla; Zhang, Yong (Geological Society of London, 2020-11-22)
      Epithermal gold deposits are rarely well preserved in pre-Mesozoic terranes because their low-temperature mineralization in shallow crust levels, and easily destroyed by subsequent erosion or depleted by tectonic events. However, several significant late Paleozoic epithermal gold deposits have been found in the Tulasu volcanic basin in NW China, forming one of the largest gold districts in the western Tianshan orogen. Here, we report new 40Ar/39Ar age from a monzonite porphyry enclave hosted in andesite and apatite fission track (AFT) data for 10 volcanic rocks from the Tulasu basin. These data, combined with the previous dataset, are used to perform inverse thermal modelling to quantify the district's cooling and exhumation history. Our modelling indicates a phase of burial reheating during late Paleozoic sedimentation following the mineralization, and subsequent a rapid exhumation in the Jurassic to Early Cretaceous (∼196–128 Ma), and a slow exhumation until to present. The Mesozoic exhumation is likely related to the far-field effects of the Cimmerian orogeny along the southern Eurasian margin. Therefore, we suggest that the quick burial by thick sediments and the slow protracted exhumation after mineralization were crucial for the preservation of the Paleozoic epithermal gold system at Tulasu.
    • The cranial morphology of Tanystropheus hydroides (Tanystropheidae, Archosauromorpha) as revealed by synchrotron microtomography

      Spiekman, Stephan NF; Neenan, James M; Fraser, Nicholas C; Fernandez, Vincent; Rieppel, Olivier; Nosotti, Stefania; Scheyer, Torsten M (PeerJ, 2020-11-20)
      The postcranial morphology of the extremely long-necked Tanystropheus hydroides is well-known, but observations of skull morphology were previously limited due to compression of the known specimens. Here we provide a detailed description of the skull of PIMUZ T 2790, including a partial endocast and endosseous labyrinth, based on synchrotron microtomographic data, and compare its morphology to that of other early Archosauromorpha. In many features, such as the wide and flattened snout and the configuration of the temporal and palatal regions, Tanystropheus hydroides differs strongly from other early archosauromorphs. The braincase possesses a combination of derived archosaur traits, such as the presence of a laterosphenoid and the ossification of the lateral wall of the braincase, but also differs from archosauriforms in the morphology of the ventral ramus of the opisthotic, the horizontal orientation of the parabasisphenoid, and the absence of a clearly defined crista prootica. Tanystropheus hydroides was a ram-feeder that likely caught its prey through a laterally directed snapping bite. Although the cranial morphology of other archosauromorph lineages is relatively well-represented, the skulls of most tanystropheid taxa remain poorly understood due to compressed and often fragmentary specimens. The recent descriptions of the skulls of Macrocnemus bassanii and now Tanystropheus hydroides reveal a large cranial disparity in the clade, reflecting wide ecological diversity, and highlighting the importance of non-archosauriform Archosauromorpha to both terrestrial and aquatic ecosystems during the Triassic.
    • The influence of fractionation of REE-enriched minerals on the zircon partition coefficients

      Zhong, Shihua; Li, Sanzhong; Seltmann, Reimar; Lai, Zhiqing; Zhou, Jie (Elsevier, 2020-11-05)
      Zircon is widely used to simulate melt generation, migration and evolution within the crust and mantle. The achievable performance of melt modelling generally depends on the availability of reliable trace element partition coefficients (D). However, a large range of DREE values for zircon from natural samples and experimental studies has been reported, with values spanning up to 3 orders of magnitude. Unfortunately, a gap of knowledge on this variability is evident. In this study we model the crystallization processes of common REE-bearing minerals from granitic melts and show that the measured zircon DREE would be elevated if there is crystallization of REE-enriched minerals subsequent to zircon. Nevertheless, compared to zircon DREE values measured from experimental studies, this mechanism appears to have a less significant influence on those from natural granite samples since the quantity of crystallized REE-enriched minerals is very low in natural magmatic systems and/or most of them crystallize prior to zircon. Combined with recently published studies, this work supports that analysis of natural zircon/host groundmass pairs provides more robust DREE values applicable to natural systems than those measured from experimental studies, which can be used to constrain the provenance of detrital zircons.
    • Phylogeny of Lithobiidae Newport, 1844, with emphasis on the megadiverse genus Lithobius Leach, 1814 (Myriapoda, Chilopoda)

      Ganske, Anne‐Sarah; Vahtera, Varpu; Dányi, László; Edgecombe, GD; Akkari, Nesrine (Wiley, 2020-11-04)
      Phylogenetic analyses based on molecular and morphological data were conducted to shed light on relationships within the mostly Palaearctic/Oriental centipede family Lithobiidae, with a particular focus on the Palaearctic genus Lithobius Leach, 1814 (Lithobiidae, Lithobiomorpha), which contains >500 species and subspecies. Previous studies based on morphological data resolved Lithobius as nonmonophyletic, but molecular-based phylogenetic analyses have until now sampled few species. To elucidate species inter-relationships of the genus, test the validity of its classification into subgenera, and infer its relationships with other Lithobiidae, we obtained molecular data (nuclear markers: 18S rRNA, 28S rRNA; mitochondrial markers: 16S rRNA, COI) and 61 morphological characters for 44 species of Lithobius representing four of its eight subgenera and nine other representatives of Lithobiidae. The data were analyzed phylogenetically using maximum-likelihood, parsimony and Bayesian inference. This study suggests that (i) a close relationship between L. giganteus and the pterygotergine Disphaerobius loricatus highlighted in recent morphological analyses is also strongly supported by molecular data, and Pterygoterginae is formally synonymized with Lithobiinae; (ii) the Oriental/Australian genus Australobius is consistently resolved as sister group to all other sampled Lithobiidae by the molecular and combined data; (iii) the subfamily Ethopolyinae may be paraphyletic; (iv) the genus Lithobius is nonmonophyletic; (v) the subgenera Lithobius, Sigibius and Monotarsobius are nonmonophyletic and should not be used in future taxonomic studies; and (vi) there are instances of cryptic species and cases in which subspecies should be elevated to full species status, as identified for some European taxa within Lithobius.
    • Flying too close to the Sun – The viability of perihelion-induced aqueous alteration on periodic comets

      Suttle, Martin; Folco, L; Genge, MJ; Russell, SS (Elsevier BV, 2020-11)
      Comets are typically considered to be pristine remnants of the early solar system. However, by definition they evolve significantly over their lifetimes through evaporation, sublimation, degassing and dust release. This occurs once they enter the inner solar system and are heated by the Sun. Some comets (e.g. 1P/Halley, 9P/Tempel and Hale-Bopp) as well as chondritic porous cosmic dust – released from comets – show evidence of minor aqueous alteration resulting in the formation of phyllosilicates, carbonates or other secondary phases (e.g. Cu-sulphides, amphibole and magnetite). These observations suggest that (at least some) comets experienced limited interaction with liquid water under conditions distinct from the alteration histories of hydrated chondritic asteroids (e.g. the CM and CR chondrites). This synthesis paper explores the viability of perihelion-induced heating as a mechanism for the generation of highly localised subsurface liquid water and thus mild aqueous alteration in periodic comets. We draw constraints from experimental laboratory studies, numerical modelling, spacecraft observations and microanalysis studies of cometary micrometeorites. Both temperature and pressure conditions necessary for the generation and short-term (hour-long) survival of liquid water are plausible within the immediate subsurface (<0.5m depth) of periodic comets with small perihelia (<1.5 A.U.), low surface permeabilities and favourable rotational states (e.g. high obliquities and/or slow rotational periods). We estimate that solar radiant heating may generate liquid water and perform aqueous alteration reactions in 3-9% of periodic comets. An example of an ideal candidate is 2P/Encke which has a small perihelion (0.33 A.U.), a high obliquity and a short orbital period. This comet should therefore be considered a high priority candidate in future spectroscopic studies of comet surfaces. Small quantities of phyllosilicate generated by aqueous alteration may be important in cementing together grains in the subsurface of older dormant comets, thereby explaining observations of unexpectedly high tensile strength in some bodies. Most periodic comets which currently pass close to the Sun are dormant, having experienced surface heating, significant cometary activity and dust release in the past. These bodies may be responsible for the partially hydrated cometary micrometeorites we find at the Earth’s surface and their aqueous alteration histories may have been produced by perihelion-induced subsurface heating. This is in contrast to radiogenic and impact heating that operated during the early solar system on asteroids. This study has implications for the alteration history of the active asteroid Phaethon, the target of JAXA’s DESTINY+ mission.
    • Reptile-like physiology in Early Jurassic stem-mammals

      Newham, E; Gill, Pamela; Brewer, Philippa; Benton, MJ; Fernandez, Vincent; Gostling, NJ; Haberthür, D; Jernvall, J; Kankaanpää, T; Kallonen, A; et al. (Springer Science and Business Media LLC, 2020-10-12)
      Despite considerable advances in knowledge of the anatomy, ecology and evolution of early mammals, far less is known about their physiology. Evidence is contradictory concerning the timing and fossil groups in which mammalian endothermy arose. To determine the state of metabolic evolution in two of the earliest stem-mammals, the Early Jurassic Morganucodon and Kuehneotherium, we use separate proxies for basal and maximum metabolic rate. Here we report, using synchrotron X-ray tomographic imaging of incremental tooth cementum, that they had maximum lifespans considerably longer than comparably sized living mammals, but similar to those of reptiles, and so they likely had reptilian-level basal metabolic rates. Measurements of femoral nutrient foramina show Morganucodon had blood flow rates intermediate between living mammals and reptiles, suggesting maximum metabolic rates increased evolutionarily before basal metabolic rates. Stem mammals lacked the elevated endothermic metabolism of living mammals, highlighting the mosaic nature of mammalian physiological evolution.
    • The origin and diversification of pteropods precede past perturbations in the Earth’s carbon cycle

      Peijnenburg, KTCA; Janssen, AW; Wall-Palmer, D; Goetze, E; Maas, AE; Todd, JA; Marlétaz, F (Proceedings of the National Academy of Sciences, 2020-09-24)
      Pteropods are a group of planktonic gastropods that are widely regarded as biological indicators for assessing the impacts of ocean acidification. Their aragonitic shells are highly sensitive to acute changes in ocean chemistry. However, to gain insight into their potential to adapt to current climate change, we need to accurately reconstruct their evolutionary history and assess their responses to past changes in the Earth’s carbon cycle. Here, we resolve the phylogeny and timing of pteropod evolution with a phylogenomic dataset (2,654 genes) incorporating new data for 21 pteropod species and revised fossil evidence. In agreement with traditional taxonomy, we recovered molecular support for a division between “sea butterflies” (Thecosomata; mucus-web feeders) and “sea angels” (Gymnosomata; active predators). Molecular dating demonstrated that these two lineages diverged in the early Cretaceous, and that all main pteropod clades, including shelled, partially-shelled, and unshelled groups, diverged in the mid- to late Cretaceous. Hence, these clades originated prior to and subsequently survived major global change events, including the Paleocene–Eocene Thermal Maximum (PETM), the closest analog to modern-day ocean acidification and warming. Our findings indicate that planktonic aragonitic calcifiers have shown resilience to perturbations in the Earth’s carbon cycle over evolutionary timescales.
    • Late Silurian zircon U–Pb ages from the Ludlow and Downton bone beds, Welsh Basin, UK

      Catlos, EJ; Mark, DF; Suarez, S; Brookfield, ME; Giles Miller, C; Schmitt, AK; Gallagher, V; Kelly, A (Geological Society of London, 2020-09-21)
      The Ludlow Bone Bed (Welsh Basin) is a critical stratigraphic horizon and contains a rich assemblage of fish scales. Units above provide insights into the early evolution of animal and plant life. The bed has not yet been radioisotopically dated. Here, we report 207 secondary ion mass spectrometry (SIMS) ages from 102 zircon (ZrSiO4) grains from the Ludlow (n = 2) and stratigraphically higher Downton (n = 1) bone beds. SIMS ages are middle Ordovician (471.6 ± 20.7 Ma) to late Devonian (375.7 ± 14.6 Ma, 238U–206Pb, ±1σ analytical uncertainty). Cathodoluminescence images show that the youngest ages appear affected by alteration. Chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-ID-TIMS) U–Pb geochronology was utilized to improve precision. Detrital zircon grains from Downton yield 424.91 ± 0.34/0.42/0.63 Ma and from Ludlow 424.85 ± 0.32/0.41/0.62 Ma (n = 5 each, 238U–206Pb, ±2σ analytical, tracer or systematic uncertainty). These ages provide a maximum deposition age. Results overlap the basal Přídolí age (423.0 ± 2.3 Ma) in its stratotype (Požáry Section, Reporyje, Prague, Czech Republic). The Ludlow Bone Bed marks the base of the local Downton Group, which has previously been correlated with the base of the Přídolí Series. The CA-ID-TIMS ages are older than those for other land arthropod-bearing sediments, such as the Cowie Harbour Fish Bed and Rhynie Chert.
    • Isotopic and textural analysis of giant unmelted micrometeorites – identification of new material from intensely altered 16O-poor water-rich asteroids

      Suttle, Martin; Dionnet, Z; Franchi, I; Folco, L; Gibson, J; Greenwood, RC; Rotundi, A; King, A; Russell, Sara (Elsevier BV, 2020-09-15)
      Bulk oxygen isotope data has the potential to match extraterrestrial samples to parent body sourcesbased on distinctive 𝛿 18O and Δ 17 O ratios. We analysed 10 giant (>500µm) micrometeorites using combined µCT and O-isotope analysis to pair internal textures to inferred parent body groups. We identify three ordinary chondrite particles (L and LL groups), four from CR chondrites and the first micrometeorite from the enstatite chondrite (EH4) group. In addition, two micrometeorites are from hydrated carbonaceous chondrite parent bodies with 16 O-poor isotopic compositions above the terrestrial fractionation line. They experienced intense aqueous alteration, contain pseudomorphic chondrules and are petrographically similar to the CM1/CR1 chondrites. These micrometeorites may be members of the newly established CY chondrites and/or derived from the enigmatic “Group 4” micrometeorite population, previously identified by Yada et al., 2005 [GCA, 69:5789-5804], Suavet et al., 2010 [EPSL, 293:313-320] (and others). One of our 16 O-poor micrometeorite plots on the same isotopic trendline as the CO, CM and CY chondrites – “the CM mixing line” (with a slope of ~0.7 and a 𝛿 17 O intercept of -4.23‰), implies a close relationship and potentially a genetic link to these hydrated chondrites. If position along the CM mixing line reflects the amount of 16 O-poor (heavy) water-ice accreted onto the parent body at formation, then the CY chondrites and these 16 O-poor micrometeorites must have accreted at least as much water-ice as CM chondrites but potentially more. In addition, thermal metamorphism could have played a role in further raising the bulk O isotope compositions through the preferential loss of isotopically light water during phyllosilicate dehydration. The study of micrometeorites provides insights into asteroid belt diversity through the discovery of material not currently sampled by larger meteorites, perhaps as a result of atmospheric entry biases preventing the survival of large blocks of friable hydrated material.
    • Adakite-like granitoids of Songkultau: A relic of juvenile Cambrian arc in Kyrgyz Tien Shan

      Konopelko, D; Seltmann, Reimar; Dolgopolova, Alla; Safonova, I; Glorie, S; De Grave, J; Sun, M (Elsevier BV, 2020-09-01)
      The early Paleozoic Terskey Suture zone, located in the southern part of the Northern Tien Shan domain in Kyrgyzstan, comprises tectonic slivers of dismembered ophiolites and associated primitive volcanics and deep-marine sediments. In the Lake Songkul area, early-middle Cambrian pillow basalts are crosscut by the Songkultau intrusion of coarse-grained gneissose quartz diorites and tonalites with geochemical characteristics typical for high-SiO2 adakites (SiO2 ​> ​56 ​wt.%, Al2O3 ​> ​15 ​wt.%, Na2O ​> ​3.5 ​wt.% and high Sr/Y and La/Yb ratios). The Songkultau granitoids have positive initial εNd (+3.8 to +6.4) and εHf (+12.3 to +13.5) values indicating derivation from sources with MORB-like isotopic signature. Volcanic formations, surrounding the Songkultau intrusion, have geochemical affinities varying from ocean floor to island arc series. This rock assemblage is interpreted as a relic of an early-middle Cambrian primitive arc where the adakite-like granitoids were derived from partial melting of young and hot subducted oceanic crust. An age of 505 ​Ma, obtained for the Songkultau intrusion, shows that hot subduction under the Northern Tien Shan continued until middle Cambrian. The primitive arc complexes were obducted onto the Northern Tien Shan domain, where the Andean type continental magmatic arc developed in Cambrian and Ordovician. Formation of the Andean type arc was accompanied by uplift, erosion and deposition of coarse clastic sediments. A depositional age of ca. 470 Ma, obtained for the gravellites in the Lake Songkul area, is in agreement with the timing of deposition for lower Ordovician conglomerates elsewhere in the Northern Tien Shan, and corresponds to the main phase of the Andean type magmatism. The Songkultau adakites in association with surrounding ocean floor and island arc formations constitute a relic of a primitive Cambrian arc and represent a juvenile domain of substantial size identified so far within the predominantly crustal-derived terranes of Tien Shan. On a regional scale this primitive arc can be compared with juvenile Cambrian arcs of Kazakhstan, Gorny Altai and Mongolia.
    • Aquatic Habits and Niche Partitioning in the Extraordinarily Long-Necked Triassic Reptile Tanystropheus

      Spiekman, Stephan NF; Neenan, James M; Fraser, Nicholas C; Fernandez, Vincent; Rieppel, Olivier; Nosotti, Stefania; Scheyer, Torsten M (Elsevier BV, 2020-08-06)
      Tanystropheus longobardicus is one of the most remarkable and iconic Triassic reptiles. Mainly known from the Middle Triassic conservation Lagerstätte of Monte San Giorgio on the Swiss-Italian border, it is characterized by an extraordinarily long and stiffened neck that is almost three times the length of the trunk, despite being composed of only 13 hyper-elongate cervical vertebrae [1-8]. Its paleobiology remains contentious, with both aquatic and terrestrial lifestyles having been proposed [1, 9-12]. Among the Tanystropheus specimens, a small morphotype bearing tricuspid teeth and a large morphotype bearing single-cusped teeth can be recognized, historically considered as juveniles and adults of the same species [4]. Using high-resolution synchrotron radiation microtomography (SRμCT), we three-dimensionally reconstruct a virtually complete but disarticulated skull of the large morphotype, including its endocast and inner ear, to reveal its morphology for the first time. The skull is specialized toward hunting in an aquatic environment, indicated by the placement of the nares on the top of the snout and a "fish-trap"-type dentition. The SRμCT data and limb bone paleohistology reveal that the large morphotype represents a separate species (Tanystropheus hydroides sp. nov.). Skeletochronology of the small morphotype specimens indicates that they are skeletally mature despite their small size, thus representing adult individuals of Tanystropheus longobardicus. The co-occurrence of these two species of disparate size ranges and dentitions provides strong evidence for niche partitioning, highlighting the surprising versatility of the Tanystropheus bauplan and the complexity of Middle Triassic nearshore ecosystems.