Evolution of Lamayuru palaeolake in the Trans Himalaya: Palaeoecological implications

Vor etwa 35 000-40 000 Jahren schuf eine Episode neotektonischer Aktivität an der Indus-Sutur bei Lamayuru (Ladakh) einen See, von dem eine über 105 m mächtige Abfolge fluviolakustriner Ablagerungen erhalten ist. Die zwischen Ton/Silt/Sand eingelagerten lakustrinen Horizonte (Kalkschlämme) und karbonatreichen Schichten haben Süßwasser-Ostrakoden, Gastropoden und Charophyten geliefert. Insgesamt wurden 9 Fossilhorizonte angetroffen. Die hauptsächlichen Ostrakodentaxa sind llyocypris (l. gibba und I. bradyi), Eucypris und Candona. Bei den Gastropoden dominieren Lymnaea, Succinea und Gyraulus. Die Charophyten werden durch Chara globularis vertreten. Die paläoökologische Interpretation basiert auf den charakteristischen Faunen- und Florenelementen und auf der Natur der Sedimente. Es wird vermutet, daß der See während seiner ganzen Existenz ziemlich flach war und kaltes, extrem salzarmes, langsam fließendes, pflanzenreiches Wasser führte. Als ein offenes Becken mag er einen kontinuierlichen Abfluß während seiner ganzen Existenz gehabt haben. Die Entleerung des Sees wurde verursacht durch eine strukturelle Zerrüttung des Seebodens und die Ausfüllung durch riesige, durch einen weiteren Impuls tektonischer Aktivität ausgelöste Schuttmassen.researc

Baring it all- undressing Cambrian ´Orsten´phosphatocopine arthropods using synchrotron X-ray tomographic microscopy

Synchrotron radiation X-ray tomographic microscopy (SRXTM) was used to virtually dissect and peel the shields off of the microscopic, bivalved phosphatocopine crustaceans in the Cambrian ‘Orsten’ type of preservation of Sweden. Doing so opened up for an array of concealed internal structures to be observed in a fully enclosed specimen of Hesslandona ventrospinata and a semi-enclosed specimen of Hesslandona angustata. For comparison, also a head-larva stage specimen of H. angustata, with shields in ‘butterfly position’, was analysed. The X-ray tomographic data sets revealed excellently preserved structures, such as labrum, sternum, antennae, mandibular and post-mandibular limbs with their minute setae, all of which were more or less dis-guised by the enclosing shields. This, moreover, allowed assignment to growth stages of the specimens, which is impossible based solely on external morphology and size.Microspherules observed inside the shields of the semi-enclosed H. angustata specimen may represent remains of food particles, and the feeding biology of phosphatocopines is discussed in detail. Our analyses suggest that phosphatocopines were particle feeders. The SRXTM technique offers the ability to three-dimensionally reconstruct the morphology in high resolution, construct virtual serial sections and study concealed structures. The resulting data allow for new structures to be revealed for previously known taxa and for new taxa to be identified, with the added benefit of not destroying the specimens in the process. Hence, we do not longer have to rely on serendipitous finds of broken and/or open phosphatocopine specimens to elucidate their diagnostic ventral morphology

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

Geobiology of a lower Cambrian carbonate platform, Pedroche Formation, Ossa Morena Zone, Spain

The Cambrian Pedroche Formation comprises a mixed siliciclastic-carbonate succession recording subtidal deposition on a marine platform. Carbonate carbon isotope chemostratigraphy confirms previous biostratigraphic assignment of the Pedroche Formation to the Atdabanian regional stage of Siberia, correlative to Cambrian Series 2. At the outcrop scale, thrombolitic facies comprise ~. 60% of carbonate-normalized stratigraphy and coated-grains another ~. 10%. Petrographic point counts reveal that skeletons contribute at most 20% to thrombolitic inter-reef and reef-flank lithologies; on average, archaeocyath clasts make up 68% of skeletal materials. In contrast, petrographic point counts show that skeletons comprise a negligible volume of biohermal and biostromal thrombolite, associated nodular carbonate facies, and ooid, oncoid and peloid grainstone facies. As such, archaeocyathan reefal bioconstructions represent a specific and limited locus of skeletal carbonate production and deposition. Consistent with data from coeval, globally dispersed lower Cambrian successions, our analysis of the Pedroche Formation supports the view that lower Cambrian carbonates have more in common with earlier, Neoproterozoic deposits than with younger carbonates dominated by skeletal production and accumulation. © 2013 Elsevier B.V.Jessica R. Creveling, David Fernández-Remolar, Marta Rodríguez-Martínez, Silvia Menéndez, Kristin D. Bergmann, Benjamin C. Gill, John Abelson, Ricardo Amils, Bethany L. Ehlmann, Diego C. García-Bellido, John P. Grotzinger, Christian Hallmann, Kathryn M. Stack, Andrew H. Knol

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 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

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

Sexual dimorphism and pore systems in Ordovician ostracodes

Open antra, a special form of external brood pouches in Ordovician ostracodes suitable for both egg and brood care, are enabled by the associated pore system. Special kinds of radial pores connected with the adventral sculptures are described for the first time. Relationships exist between antral development and lifestyle in that open antra occur in nektobenthic taxa, while closed antra (false brood pouches) are connected with a benthic lifestyle. Taxa, particularly those with open antra, which are morphologically very similar in being non−lobate or non−sulcate, can be distinguished by the construction of the respective antra and the associated pore systems, as exemplified by Levisulculus, Swantina, and Ampletochitina

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