Silurian Myodocope Research Articles

Ecologically distinct myodocope ostracod faunas from a single horizon in the late Silurian of Spain

Silurian myodocopes have been demonstrated to be the pioneer pelagic ostracods. Their ecological shift into the water column, during the middle Silurian (Wenlock-Ludlow), is now well documented from sites around the world, but the evolution of this fauna during the late Silurian (Pridoli) remains little studied. We recognise, for the first time, two ecologically distinct myodocope ostracod faunas from the same late Pridoli horizon (possibly ?Wolynograptus bouceki - Skalograptus transgrediens biozones) of southern Spain (Alcaracejos, province of Córdoba). One fauna, associated with black shales, comprises five species belonging to three myodocope families (bolbozoids, entomozoids and cypridinids). The other fauna, recovered from large dark-reddish calcareous nodules and associated with the planktonic crinoid Scyphocrinites elegans, comprises seven myodocope species belonging to the same three families and includes one new species, Calocaria callundosa sp. nov. Although the shale and nodule faunas have two species in common, they are clearly different in terms of diversity, abundance and size of the specimens. The discrepancies between these two assemblages could either be explained by sampling or taphonomic bias, or because they represent faunas with different ecologies. In the latter hypothesis, the myodocope association in the shales could represent the “background” planktonic fauna, while the fauna in the nodules could have lived in the water column in the vicinity of the Scyphocrinites “floating islands”, or scavenge around the dead crinoids on the sea floor. These two diverse assemblages also allow discussions on the temporal and palaeogeographical distributions of these late Silurian myodocope ostracods.

Silurian myodocopes display adaptations for a nektobenthic lifestyle: The paleobiological evidence

There is comprehensive, complementary sedimentological, faunal and paleogeographic data to indicate that myodocopid ostracods invaded the water column in the Silurian, in the latest Wenlock and especially the Ludlow Epoch, resulting in the pioneer pelagic ostracod fauna. As detailed herein, there is now also considerable paleobiological evidence, from study of rare, exceptionally preserved fossil myodocopes, particularly the nektobenthic myodocopids of the mid Wenlock Herefordshire Lagerstätte, UK, that anatomical and other features that enabled this ecological transition were already present in early Silurian myodocopes. The oldest known Silurian myodocope, a species of the Herefordshire cylindroleberidid myodocopid genus Pauline, established from shells from Telychian Llandovery Series carbonates of Greenland, would have had similar anatomical features and therefore adaptations for nektonic activity. Evidence from rare Late Ordovician species suggests even earlier nektobenthic activity by myodocopes.

Cosmopolitan myodocope ostracods from the Silurian of Uzbekistan, Central Asia

Four species of myodocope ostracod are documented from the Silurian Ludlow Series of the Aburtkan gorge on the southern slope of Dzhalpak Mountain, Uzbekistan: namely,Parabolbozoe bohemica(Barrande, 1872),Bolbozoe anomalaBarrande, 1872,Silurocypridina calvaPerrier, Vannier and Siveter, 2011 andRichteria migrans(Barrande, 1872). These species have a palaeogeographically widespread trans-oceanic distribution, which supports the notion that Silurian myodocopes signify the earliest zooplanktonic ostracods.Richteria migrans(Barrande, 1872), in particular, provides a precise intercontinental biostratigraphic marker that identifies rocks of the upper Gorstian to upper Ludfordian stages.

British Silurian Myodocope Ostracods

The Silurian myodocope ostracods from Britain comprise six families, 12 genera and 22 species, plus three species in open nomenclature. New material includes representatives of the families Bolbozoidae, Entomozoidae, Cypridinidae and Seminovidae n. fam.; newly described genera and species are Seminova gen. nov., Oculparva moncola gen. et sp. nov., Piscarista sagenata gen. et sp. nov., Nudator inflatus gen. et sp. nov., Nudator angiportatus gen. et sp. nov., Nudator artumatus gen. et sp. nov. and Bolbozoe psittaca sp. nov. Fine biostratigraphic control allows the development of a myodocopid biozonation for the Wenlock and Ludlow series. Seven myodocopid biozones are established, from the early Homerian (Wenlock) to the late Ludfordian (Ludlow) stages. This biozonation allows inter-continental correlation of Silurian successions in Europe, Arctic Russia and Central Asia.Les ostracodes Myodocopes du Silurien britanniqueRÉSUMÉLa faune d’ostracodes myodocopes du Silurien de Grande-Bretagne, comprend six familles, 12 genres et 22 espèces, plus trois espèces en nomenclature ouverte. Le nouveau matériel comprend des représentants des familles Bolbozoidae, Entomozoidae, Cypridinidae et Seminovidae n. fam.; et sont décrit les nouveaux genres et espèces: Seminova gen. nov., Oculparva moncola gen. et sp. nov., Piscarista sagenata gen. et sp. nov., Nudator inflatus gen. et sp. nov., Nudator angiportatus gen. et sp. nov., Nudator artumatus gen. et sp. nov. et Bolbozoe psittaca sp. nov. Le fin contrôle biostratigraphique permet le développement d'une biozonation des ostracodes myodocopes pour le Wenlock et le Ludlow. Sept biozones à myodocopes peuvent être identifiés, du début de l’Homérien à la fin du Ludfordien. Cette biozonation permet une corrélation inter-continentale entre les successions siluriennes d’Europe, de Russie arctique et d’Asie centrale.Ostracoden der Ordnung Myodocopa aus dem Silur GroßbritanniensZUSAMMENFASSUNGDie silurischen myodocopen Ostrakoden aus Großbritannien umfassen sechs Familien, 12 Gattungen und 22 Arten, sowie drei Arten in offener Nomenklatur. Zu dem neuen Material gehören Vertreter der Familien Bolbozoidae, Entomozoidae, Cypridinidae und Seminovidae n. fam.; die folgende Gettungen und Arten werden beschrieben: Seminova gen. nov., Oculparva moncola gen. et sp. nov., Piscarista sagenata gen. et sp. nov., Nudator inflatus gen. et sp. nov., Nudator angiportatus gen. et sp. nov., Nudator artumatus gen. et sp. nov. und Bolbozoe psittaca sp. nov. Feinste biostratigraphische Auflösung ermöglicht die Entwicklung einer Biozonierung der myodocopen Ostrakoden für das Wenlock und das Ludlow. Sieben Biozonen können vom frühen Homerium (Wenlock) bis zum späten Ludfordium (Ludlow) bestimmt werden. Diese Biozonierung ermöglicht eine interkontinentale Korrelation silurischer Abfolgen innerhalb Europas, im arktischen Russland und in Zentralasien.Великобританские силурийские миoдокопидные oстркодыРЕЗЮМЕСилурийская фауна миодокопидных остракод Великобританий состоит из 22 видов, которые относятся к 12 родам, шести семействам, к ним добавляются 3 вида открытой номенклатуры. Новы материал относится к семействам Bolbozoidae, Entomozoidae, Cypridinidae, а также к Seminovidae n. fam. и Seminova gen. nov., Oculparva moncola gen. et sp. nov., Piscarista sagenata gen. et sp. nov., Nudator inflatus gen. et sp. nov., Nudator angiportatus gen. et sp. nov., Nudator artumatus gen. et sp. nov. и Bolbozoe psittaca sp. nov. Хороший биостратиграфический контроль способствовал разработку миодокоповой биозонаций для венлоксого и лудловского отделов силура. Семь биозонов устновлено для временного интервала от хомера (венлок) до позднего лудфорда (лудлов). Зональная шкала миодокопид пригодна для корреляций силурийских отложений в пределах Европы, арктической части России и Центральной Азии.

Silurian myodocope ostracods from Poland

Silurian myodocope ostracods from Poland

A pelagic myodocopid ostracod from the Silurian of Arctic Russia

Abstract. The Silurian myodocope ostracod Richteria migrans is reported from Arctic Russia, from Kotel’ny Island (New Siberian Islands) and the Taimyr Peninsula in strata of Ludfordian (late Ludlow, Late Silurian) age. These occurrences extend the biogeographical range of R. migrans from tropical to mid latitudes of the Early Palaeozoic Rheic Ocean in the palaeo-Southern Hemisphere, into subtropical regions of the palaeo-Northern Hemisphere on, or adjacent to, the Siberia Palaeocontinent. The new records reinforce the idea that R. migrans had wide dispersal capacity and probably possessed a pelagic lifestyle. It also endorses the use of R. migrans as a biostratigraphical marker fossil for the Ludfordian Stage, Ludlow Series, Upper Silurian.

Myodocope ostracods from the Silurian of Australia

The Silurian of Australia contains at least three genera (one new, Canalarta gen. nov.) and three species (two new, Canalarta papata sp. nov. and Bolbozoe beccata sp. nov.) of myodocope ostracods. These fossils were recovered from clastic sedimentary deposits in the lower Silurian (probably Homerian) Walker Volcanics unit of New South Wales that may represent mudflow deposits. In having the youngest occurrence of Entomozoe aff. tuberosa and the oldest known Bolbozoe species, the Australian myodocopes represent a chronologically intermediate assemblage between previously known early and late Silurian myodocope faunas. Several fossil groups from the Silurian of Australia, such as ostracods, trilobites, brachiopods and corals, apparently have a cosmopolitan distribution at generic level. The presence of many continental and micro-continental landmasses that existed along and within the tropical pan-Tethyan seaway, together with the prevailing ocean circulation, could explain this distributional pattern. The depositional setting, sedimentary deposits and faunal associates do not provide conclusive evidence concerning the lifestyle of the Australian myodocopes. They could represent nektobenthic species, as has been suggested for other early to mid Silurian myodocopes, or hyperbenthic/pelagic species, as was proposed for known late Silurian forms.http://zoobank.org/urn:lsid:zoobank.org:pub:D49A6C9C-13A8-443A-8BD4-73C34C1D0630

A Silurian myodocope with preserved soft-parts: cautioning the interpretation of the shell-based ostracod record

Ostracod crustaceans are the most abundant fossil arthropods. The Silurian Pauline avibella gen. et sp. nov., from the Herefordshire Lagerstätte, UK, is an extremely rare Palaeozoic example with soft-part preservation. Based on its soft-part morphology, especially the exceptionally preserved limbs and presence of lateral eyes, it is assigned to the myodocopid myodocopes. The ostracod is very large, with an epipod on the fifth limb pair, as well as gills implying the presence of a heart and an integrated respiratory-circulatory system as in living cylindroleberidid myodocopids. Features of its shell morphology, however, recall halocyprid myodocopes and palaeocopes, encouraging caution in classifying ostracods based on the carapace alone and querying the interpretation of their shell-based fossil record, especially for the Palaeozoic, where some 500 genera are presently assigned to the Palaeocopida.

An Atypical Silurian Myodocope Ostracod from the Armorican Massif, France

A new myodocope ostracod Sineruga insolita gen. et sp. nov. is herein described from the Armorican Massif (France). Sineruga resembles Silurian myodocopes (i.e., bolbozoids and cypridinids) in having anterior features (thinner carapace) possibly related to vision. On the other hand, it resembles entomozoid ostracods in having a bean-shaped outline along with a deep adductorial sulcus and a simple muscle spot, but lacks their characteristic ribbed ornament. The data available suggest that Sineruga insolita was probably an atypical, non-ribbed member of the entomozoids thus indicating that early entomozoids may have had smooth representatives. Comparisons with other Recent and fossils ostracods show that the presence of a rostrum and/or symmetrical vision related carapace features (i.e., indicating lateral eyes) can be used as diagnostic characters for myodocope ostracods. The position and shape of the dorsal connection and to a lesser extent that of the sulcus and the adductorial muscle scar can be used to...

Silurian bolbozoids and cypridinids (Myodocopa) from Europe: pioneer pelagic ostracods

Abstract: Bolbozoid and cypridinid myodocope ostracods from France, the Czech Republic and Sardinia consist of four genera (one new: Silurocypridina) and at least ten species (eight new: Bolbozoe acuta, B. rugosa, B. parvafraga, Parabolbozoe armoricana, Silurocypridina retroreticulata, S. variostriata, S. calva and Calocaria robusta). They have a functional design, palaeogeographical distribution, depositional setting and faunal associates that suggest that they were swimmers in the water column, living in dim light, relatively deep environments, above near bottom dysoxic/anoxic conditions. These myodocope faunas include some possible pelagic species sensu stricto, with widespread palaeogeographical (transoceanic) distribution, and some species that occupied hyperbenthic niches and were capable of making short incursions to the sediment to scavenge on carrion. These data support the model that Silurian myodocopes were pioneer pelagic ostracods.

The myodocope ostracode Entomozoe from an early Silurian (Telychian, Llandovery) carbonate mound of the Samuelsen Høj Formation, North Greenland

Entomozoe aff. Entomozoe tuberosa (Jones 1861), from carbonate mounds of the Samuelsen Høj Formation, represents one of the few ostracodes documented from the Silurian of Greenland and a rare occurrence of Entomozoe from outside Scotland. Like its coeval, congeneric Scottish counterparts, the Greenland Entomozoe lived on a shallow-water shelf dominated by epibenthonic fauna and probably had a benthonic, swimming(?) lifestyle. Its environmental, ecological and geographical setting is consistent with the idea that these earliest, Lower Silurian myodocopes were benthonic and, therefore, that Upper Silurian pelagic representatives must have resulted from an ecological shift in the group.

Silurian Myodocopes: Pioneer pelagic ostracods and the chronology of an ecological shift

Abstract. Analysis of all relevant palaeontological and global geological data strongly supports the notion that representatives of Silurian myodocope ostracods had pelagic lifestyles and habitats and that they may well be, within the Ostracoda, pioneer colonisers of such environments. Morphological evidence (from fossil and Recent myodocopes) combined with facies distributional and concomitant faunal evidence (from the Silurian of, for example, Britain, France, Czechoslovakia, Sardinia, Australia and China) endorses the idea that myodocope ostracods may have undergone a benthic to pelagic ecological shift during mid Silurian times.Lower Silurian myodocopes lived, with benthic associates, on well oxygenated shelves. Upper Silurian ostracods lived, typically with low diversity, largely pelagic faunas in outer shelf topographic lows or off-shelf basin slopes, and are characteristically associated with deposits which are in part suggestive of lowered oxygen levels or even anoxic conditions. A pre-adaptation for swimming may have allowed Silurian myodocopes to respond to environmental forcing (negative oxygen levels; positive trophic and nutrient incentives; rises in sea levels) by migrating, through time, up the water column.

The Silurian myodocope ostracodeEntomozoefrom the Pentland Hills, Scotland: its taxonomic, ecological and phylogenetic significance and the affinity of the bolbozoid myodocopes

ABSTRACTThe monotypic ostracodeEntomozoe(pro Entomis) (Superorder Myodocopa) from the Silurian of Scotland, type genus of the Entomozoidae, is revised for the first time since being established in 1861. Based on the type and new collections ofEntomozoe tuberosa(Jones, 1861), the genus shows affinity to bolbozoid myodocopes rather than to forms hitherto universally considered as ‘typical’ entomozoid myodocopes. The families Entomozoidae and Bolbozoidae are considered synonymous. In the interests of stability of nomenclature, in particular to preserve the traditionally understood usage of the taxon Entomozoidae, a case must be made to the International Commission on Zoological Nomenclature to set aside any previous designations and to establish a new type-species forEntomozoe.Entomozoe, from the Llandovery Series, is the earliest known myodocope in the fossil record. It occurs as part of a low diversity, shallow water, nearshore assemblage. In contrast to other, but younger, Silurian bolbozoid myodocopes, it is probably a benthic form. The differences in the anterior shell morphology of Silurian bolbozoid taxa possibly reflect changes both in soft-part morphology and from benthic to pelagic lifestyles within the group.Both bolbozoid and ‘entomozoid’ myodocopes are assigned to the Order Myodocopida rather than to the Order Halocypridida, though the taxonomic affinity of the ‘entomozoids’ is, at best, uncertain.