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

Small shelly fossils and carbon isotopes from the early Cambrian (Stage 3-4) Mural Formation of western Laurentia

The extraordinary window of phosphatised and phosphatic Small Shelly Fossils (SSFs) during the early and middle Cambrian is an important testament to the radiation of biomineralising metazoans. While SSF are well known from most Cambrian palaeocontinents during this time interval, western Laurentia has relatively few SSF faunas. Here we describe a diverse SSF fauna from the early Cambrian (Stage 3-4) Mural Formation at three localities in Alberta and British Columbia, Canada, complemented by carbon isotope measurements to aid in a potential future bio-chemostratigraphic framework. The fauna expands the recorded SSF assemblage diversity in western Laurentia and includes several brachiopods, four bradoriids, three chancelloriids, two hyoliths, a tommotiid and a helcionellid mollusc as well as echinoderm ossicles and specimens of Microdictyon, Volborthella and Hyolithellus. New taxa include the tommotiid genus Canadiella gen. nov., the new bradoriid species Hipponicharion perforata sp. nov. and Pseudobeyrichona taurata sp. nov. Compared to contemporaneous faunas from western Laurentia, the fauna is relatively diverse, particularly in taxa with originally phosphatic shells, which appear to be associated with archaeocyathid buildups. This suggests that the generally low faunal diversity in western Laurentia may be at least partly a consequence of poor sampling of suitable archaeocyathan reef environments. In addition, the tommotiid Canadiella filigrana appears to be of biostratigraphic significance in Cambrian Stage 3 strata of western Laurentia and the unexpected high diversity of bradoriid arthropods in the fauna also suggests that this group may prove useful for biostratigraphic resolution in the region

The Ordovician ostracodes established by Aurel Krause, Part II

The revision of ostracodes originally established by Aurel Krause is continued and finished with the description of the following species: Primitia distans, P. elongata, P. cincta, P. excavata, P. papillata, P. plicata, P. schmidtii, Strepula limbata, S. simplex, Entomis obliqua, E. plicata, E. sigma, E. sigma ornata, E. simplex, E. trilobata, Beyrichia erratica, B. erratica granulosa, B. erratica acuta, B. harpa, and B. marchica lata. Three of these species are younger primary homonyms. For Beyrichia erratica granulosa Krause, 1891 a respective decision of the ICZN according to art. 23.9.5 is presently unnecessary, because it has an older synonym (Beyrichia grewingkii Bock, 1867), and Primitia excavata Krause, 1892 has a younger synonym (Laccochilina paucigranosa Jaanusson, 1957). The third homonym, Beyrichia marchica lata Krause, 1891, is considered as a nomen protectum. Entomis sigma ornata, and E. plicata are presently considered as nomina dubia. Since the type material of the three species P. distans, E. sigma, and E. simplex is apparently lost, neotypes are designated.doi:10.1002/mmng.20130000

The Ordovician ostracodes established by Aurel Krause, Part I

The lack of a revision of the ostracodes described by Aurel Krause at the end of the 19th century from glacial erratic boulders from Berlin and the Mark Brandenburg (Northern Germany) has led to taxonomic confusion in the corresponding literature of the 20th century. To attain stability in names, some of Krause's ostracode species have been revised based on the types stored in the Museum für Naturkunde Berlin, namely Primitia plana, P. plana tuberculata, P. intermedia, P. globifera, Entomis sigma antiquata, Bollia v-scripta, B. granulosa, B. duplex, Strepula lineata, Isochilina canaliculata, Beyrichia dissecta, B. mamillosa, B. signata, and B. bidens. Most species have up to four younger synonyms among species described later from outcrops or borings in Baltoscandia or glacial erratic boulders of Northern Germany and Sweden. Three of Krause's species, which have been considered as nomina dubia by Jaanusson are in fact valid species. Some of Krause's species or of their synonyms are type species.doi:10.1002/mmng.20100001

Population Structure, Life Strategies and Systematics of Phosphatocope Ostracods from the Middle Cambrian of Bornholm

She Middle Cambrian Borregård Member of Bornholm which is the stratigraphical equivalent to the Baltoscandian Exsulans Limestone yielded a rich and comparatively diverse ostracod fauna in its upper part. It comprises eight species out of four genera. They belong to three known subfamilies that are redefined on the basis of special characters of the contact margin. An ontogenetic character unknown from typical ostracods is documented in several species: during early ontogeny the gestalt (l:h ratio) develops constantly in becoming increasingly longer until the so-called ontogenetical turning point (OTP) from which the direction of growth focusses on carapace height. This phenomenon may be explained by changes in body morphology. The Borregård association represents an ecologic community type differing from other yet recorded Middle Cambrian communities in the Baltoscandic region. Apart from Vestrogothia longispinosa which is a common faunal element in Baltoscandian ostracod faunas, the yet recorded species of Bidimorpha are unknown from other Baltoscandian occurrences. Vice versa, the known species of Bidimorpha described from Swedish occurrences have not been recognized in the rich Borregård community. Similarly, Falites insula and Hesslandona abdominalis may be of local significance, too, but the respective records from contemporaneous Swedish localities are insufficient in this respect, yet. Due to specific morphological adaptations, the four genera are assumed to represent different benthic life strategies. New taxa are: Bidimorpha arator n. sp., Bidimorpha labiator n. sp., Bidimorpha sexspinosa n. sp., Falites insula n. sp., Hesslandona abdominalis n. sp., Vestrogothia herrigi n. sp. and Vestrogothia minilaterospinata n. sp.Aus dem mittelkambrischen Borregård Member von Bornholm, einem zeitlichen Äquivalent des baltoskandischen Exsulanskalkes, wurde eine reiche und vergleichsweise diverse Ostrakodenfauna gewonnen. Sie umfaßt 8 Arten aus vier Gattungen, die drei bereits bekannten Unterfamilien zugeordnet werden können. Basierend auf neuen Erkenntnissen hinsichtlich der Ausbildung des Kontaktrandes werden die drei Unterfamilien neu definiert. Außerdem wird an mehreren Arten eine spezielle Entwicklung während der Ontogenese aufgezeigt, die von "echten" Ostrakoden nicht bekannt ist. In einem frühen Stadium der Ontogenese wachsen die Schalen vor allem in die Länge, bis sich bei einer bestimmten Größe, dem ontogenetischen Umkehrpunkt (OTP), die Wachstumsrichtung ändert und dann vor allem in die Höhe gerichtet ist. Dieses Phänomen ist vermutlich an morphologische Veränderungen der Weichkörperanatomie gekoppelt. Die Borregård-Fauna repräsentiert eine besondere Vergesellschaftung, die sich von anderen mittelkambrischen Ostrakodenassoziationen Baltoskandiens deutlich unterscheidet. Abgesehen von Vestrogothia longispinosa, dem häufigsten baltoskandischen Ostrakodenvertreter, zeichnet sich die Borregård-Gemeinschaft durch zwei Arten von Bidimorpha aus, die von anderen baltoskandischen Lokalitäten nicht bekannt sind. Umgekehrt konnten keine der schwedischen Arten von Bidimorpha im Borregård Member nachgewiesen werden. Auch Falites insula und Hesslandona abdominalis haben möglicherweise lokale ökologische Bedeutung; diesbezüglich sind aber vergleichbare Daten aus dem baltoskandischen Raum noch unbefriedigend. Die spezifischen morphologischen Gehäuseausbildungen bei den untersuchten vier Gattungen deuten darauf hin, daß es sich um Adaptationen für unterschiedliche benthische Lebensweisen handelt.doi:10.1002/mmng.1998001010

Late Ordovician Ostracodes from Sardinia and Perigondwanan Ostracode Palaeobiogeography

A Late Ordovician ostracode fauna from Sardinia comprises more than 45 species of beyrichiocopes and podocopes. There is a total of 13 named new species of the genera Grammolomatella, Pseudulrichia, Antiaechmina, Postceratia, Arpaschmidtella, Bairdiocypridella, Prorectella, Dornbuschia, Velapezoides, Bairdia as well as of the new genus Sardicornina. The podocopes constitute about two thirds of all species, the binodicopes take three fourth of the beyrichiocopes. The fauna shows close relationships to faunas from both Thuringia and Central Iran (Yazd Block). The closest relations exist to Iran and the fauna of the so-called Bairdiocypridella clasts of the Thuringian Lederschiefer. Therefore, Thuringia, Sardinia and Central Iran can be regarded as a palaeobiogeographic ostracode province, here called the Thuringian province. Within Gondwana/Perigondwana two further ostracode provinces, the Armorican and Australian provinces can be distinguished

Late Ordovician Ostracoda from Iran and their significance for palaeogeographical reconstructions

The first record of Late Ordovician ostracods from Iran comes from the lowermost part of the Shirgesht Formation east of Anarak, central Iran. The fauna comprises more than 40 species of beyrichiocopes and podocopes with a total of 17 new species and one new subspecies. Among the beyrichiocopes the Binodicopa are represented with 10 species, the Palaeocopa occur with eight species. The Anarak fauna shows relations to both allochthonous and autochthonous sediments from Thuringia as well as to Baltica with the relations being closest to the fauna of certain calcareous clasts of the glaciomarine Lederschiefer of Thuringia. The clasts have been considered as pebbles or boulders from debris flows (Schallreuter & Hinz-Schallreuter 1998), but their origin remained unclear until now. Investigation of the Anarak ostracods proved to be most significant in terms of clarifying this question. The close relations between both faunas suggest that the Thuringian clasts came from the vicinity of Gondwanian Iran