Oxygen as a Driver of Early Arthropod Micro-Benthos Evolution

BACKGROUND: We examine the physiological and lifestyle adaptations which facilitated the emergence of ostracods as the numerically dominant Phanerozoic bivalve arthropod micro-benthos. METHODOLOGY/PRINCIPAL FINDINGS: The PO(2) of modern normoxic seawater is 21 kPa (air-equilibrated water), a level that would cause cellular damage if found in the tissues of ostracods and much other marine fauna. The PO(2) of most aquatic breathers at the cellular level is much lower, between 1 and 3 kPa. Ostracods avoid oxygen toxicity by migrating to waters which are hypoxic, or by developing metabolisms which generate high consumption of O(2). Interrogation of the Cambrian record of bivalve arthropod micro-benthos suggests a strong control on ecosystem evolution exerted by changing seawater O(2) levels. The PO(2) of air-equilibrated Cambrian-seawater is predicted to have varied between 10 and 30 kPa. Three groups of marine shelf-dwelling bivalve arthropods adopted different responses to Cambrian seawater O(2). Bradoriida evolved cardiovascular systems that favoured colonization of oxygenated marine waters. Their biodiversity declined during intervals associated with black shale deposition and marine shelf anoxia and their diversity may also have been curtailed by elevated late Cambrian (Furongian) oxygen-levels that increased the PO(2) gradient between seawater and bradoriid tissues. Phosphatocopida responded to Cambrian anoxia differently, reaching their peak during widespread seabed dysoxia of the SPICE event. They lacked a cardiovascular system and appear to have been adapted to seawater hypoxia. As latest Cambrian marine shelf waters became well oxygenated, phosphatocopids went extinct. Changing seawater oxygen-levels and the demise of much of the seabed bradoriid micro-benthos favoured a third group of arthropod micro-benthos, the ostracods. These animals adopted lifestyles that made them tolerant of changes in seawater O(2). Ostracods became the numerically dominant arthropod micro-benthos of the Phanerozoic. CONCLUSIONS/SIGNIFICANCE: Our work has implications from an evolutionary context for understanding how oxygen-level in marine ecosystems drives behaviour

An enigmatic early ? palaeocope ostracode from the Arenig of NW Russia

The ostracode Lavachilina evae gen. et sp. nov. is described from the Arenig of Western Russia. Its carapace possesses a unique discontinuous velum, developed at both ends as a narrow spinose ridge. The systematic position of L. evae is uncertain. Its character set shows mostly palaeocope affinities but also some features of leiocopes. L. evae is tentatively assigned to the palaeocope family Oepikellidae, possibly representing an early member of that family. Although L. evae existed contemporaneously with palaeocopes such as Laccochilina, it does not appear to be closely related to these early eurychilinoids

Carbon isotope chemostratigraphy and conodonts of the Middle-Upper Ordovician succession in the Tungus Basin, Siberian Craton

© 2015 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. Stable carbon isotope chemostratigraphy has been applied for correlation of Ordovician marine sedimentary successions of many continents, but not yet for those located on the Siberian Craton. In this study we present the first δ13C data from the Middle and Upper Ordovician successions of the Tungus Basin, the extensive Palaeozoic intracratonic basin on the Palaeocontinent Siberia. Carbon isotope curves from two separate areas of the craton, from the Kulyumbe River and Podkamennaya Tunguska River regions, demonstrate a great similarity. Three global carbon isotope events can be recognized in the Tungus Basin: the Mid-Darriwilian Excursion (MDICE), the Upper Kukruse Low, and the lower rising interval of the Guttenberg Excursion (GICE). These data partly support the previous inter-continental stratigraphic correlations but also suggest that the base of the Upper Ordovician in the Siberian succession lies at a lower level than previously thought. Although the conodont fauna in Siberia differs almost completely from that in Baltoscandia, the distribution of selected Upper Ordovician conodont taxa do not contradict the isotope chemostratographic conclusions

Carbon isotope chemostratigraphy and conodonts of the Middle-Upper Ordovician succession in the Tungus Basin, Siberian Craton

© 2015 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. Stable carbon isotope chemostratigraphy has been applied for correlation of Ordovician marine sedimentary successions of many continents, but not yet for those located on the Siberian Craton. In this study we present the first δ13C data from the Middle and Upper Ordovician successions of the Tungus Basin, the extensive Palaeozoic intracratonic basin on the Palaeocontinent Siberia. Carbon isotope curves from two separate areas of the craton, from the Kulyumbe River and Podkamennaya Tunguska River regions, demonstrate a great similarity. Three global carbon isotope events can be recognized in the Tungus Basin: the Mid-Darriwilian Excursion (MDICE), the Upper Kukruse Low, and the lower rising interval of the Guttenberg Excursion (GICE). These data partly support the previous inter-continental stratigraphic correlations but also suggest that the base of the Upper Ordovician in the Siberian succession lies at a lower level than previously thought. Although the conodont fauna in Siberia differs almost completely from that in Baltoscandia, the distribution of selected Upper Ordovician conodont taxa do not contradict the isotope chemostratographic conclusions

Carbon isotope chemostratigraphy and conodonts of the Middle-Upper Ordovician succession in the Tungus Basin, Siberian Craton

© 2015 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. Stable carbon isotope chemostratigraphy has been applied for correlation of Ordovician marine sedimentary successions of many continents, but not yet for those located on the Siberian Craton. In this study we present the first δ13C data from the Middle and Upper Ordovician successions of the Tungus Basin, the extensive Palaeozoic intracratonic basin on the Palaeocontinent Siberia. Carbon isotope curves from two separate areas of the craton, from the Kulyumbe River and Podkamennaya Tunguska River regions, demonstrate a great similarity. Three global carbon isotope events can be recognized in the Tungus Basin: the Mid-Darriwilian Excursion (MDICE), the Upper Kukruse Low, and the lower rising interval of the Guttenberg Excursion (GICE). These data partly support the previous inter-continental stratigraphic correlations but also suggest that the base of the Upper Ordovician in the Siberian succession lies at a lower level than previously thought. Although the conodont fauna in Siberia differs almost completely from that in Baltoscandia, the distribution of selected Upper Ordovician conodont taxa do not contradict the isotope chemostratographic conclusions

Stratigraphy and facies differences of the middle darriwilian isotopic carbon excursion (Mdice) in baltoscandia

© 2020 Authors. The Middle Darriwilian Isotopic Carbon Excursion (MDICE) is a global isotopic event described in sections from different palaeocontinents. Here we present new stable carbon isotopic data from carbonates of ten sections in different parts of the Baltoscandian Palaeobasin (Estonia, Latvia, Lithuania, Sweden, NW Russia). The definition of the MDICE as a chemostratigraphic unit is discussed, as well as the subdivision of its peak into two distinct peaks. The MDICE is one of the longest carbon isotopic events in the Palaeozoic. It was preceded by the L­chondritic cosmic dust flow event, which may have been responsible for cooling through the Darriwilian and the initiation of the Great Ordovician Biodiversification Event. High­resolution chemostratigraphic analyses show that the time interval between these environmental events and the base of the MDICE is up to one million years. Due to the long duration of the MDICE the modelling of this excursion should address more complex scenarios than a simple response of the carbon cycle to rapid climatic perturbations

Biogeographical patterns of Ordovician ostracods

The biogeography of marine shelf ostracod genera is analysed for two Ordovician time slabs, the earliest Late Ordovician and the terminal Ordovician, that have been considered to reflect comparatively warmer and cooler global climate states, respectively. The earlier time slab is equivalent to the Nemagraptus gracilis graptolite interval (centred about 460 Ma), and defined as the total range of the eponymous species. The Hirnantian time slab comprises the Normalograptus extraordinarius and Normalograptus persculptus graptolite biozones (445.6–443.7 Ma). The ostracod dataset consists of 160 taxa from 24 early Late Ordovician localities and 86 taxa from 10 Hirnantian localities. Ordination and variation partitioning analyses show that patterns in ostracod distribution in the gracilis time slab are largely related to palaeocontinental affinity of the samples and to a lesser degree to palaeolatitude. Some decrease of provincialism can be suggested for the Hirnantian, although the ostracod dataset is limited for this interval