The earliest ostracods: the geological evidence

Palaeobiodiversity and Palaeoenvironments 04/2008; 88(1):11-21. DOI: 10.1007/BF03043974

ABSTRACT The oldest assumed ostracods appear in the fossil record from the TremadocianPaltodus deltifer conodont Biozone. Although geographically widespread these early ostracods have no obvious Cambrian antecedents. Their first
appearance at ca. 485 Ma contrasts with molecular evidence that suggests a much earlier (latest Proterozoic or Cambrian) origin
for ostracods. Some Cambrian bivalved arthropods such asAltajanella andVojbokalina, conventionally referred to the Bradoriida, have carapace morphologies that resemble Ordovician palaeocopid ostracods, though
such a relationship is unproven without soft part anatomy. Evidence from preserved soft anatomy demonstrates that Bradoriida,
such asKunmingella, and Phosphatocopida, essentially the Cambrian ‘ostracod’ record of traditional usage, belong outside the Eucrustacea. Early
Ordovician ostracods appeared first in shallow marine, oxygenated environments on shelf margins, in a similar setting to other
elements of the ‘Paleozoic fauna’. Their biodiversity was low (3 named genera and ca. 12 species), though some taxa such asNanopsis andEopilla achieved widespread dispersal between major Ordovician palaeocontinents. As bradoriids were largely extinct by the Late Cambrian,
ostracods do not appear to have directly competed with them for shallow marine environments. The rapid colonisation of these
settings by ostracods may have been facilitated by the available ecospace vacated by Bradoriida.

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    ABSTRACT: A low-diversity early Middle Cambrian (Ordian) bradoriid fauna has been found in core samples of the Thorntonia Limestone (from drillholes BMR Hay River 11 and BHD9) and the Gum Ridge Formation (from NTGS02/1) in the Georgina Basin, Northern Territory. The described taxa include a new hipponicharionid genus Dictyocharion (type species D. eurys sp. nov.), and the comptalutids Phasoia armini sp. nov. and Quetopsis katarcha Hinz-Schallreuter, 1999. Other taxa are recorded as Anabarochilina? sp., Aristaluta? sp., Indota? sp., Monasterium oepiki Fleming, 1973? and Yaoyingella? sp. Their ages are determined in terms of associated agnostines and other trilobites. Additionally, the comptalutid species Zepaera rete Fleming, 1973 is recognised in a core sample of the Wonarah Formation (from NTGS00/1) of middle Middle Cambrian (late Templetonian to Floran) age. Palaeogeographically, the comptalutids show strong provincial relationships with genera from China. An updated census of Australian Bradoriida and Phosphatocopida is provided as an appendix.
    Memoirs of the Association of Australasian Palaeontologists. 01/2009; 37:55-86.
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    ABSTRACT: The study of ontogeny as an integral part of understanding the pattern of evolution dates back over 200 years, but only recently have ontogenetic data been explicitly incorporated into phylogenetic analyses. Pancrustaceans undergo radical ontogenetic changes. The spectacular upper Cambrian ‘Orsten’ fauna preserves phosphatized fossil larvae, including putative crown-group pancrustaceans with amazingly complete developmental sequences. The putative presence and nature of adult stages remains a source of debate, causing spurious placements in a traditional morphological analysis. We introduce a new coding method where each semaphoront (discrete larval or adult stage) is considered an OTU. This avoids a priori assumptions of heterochrony. Characters and their states are defined to identify changes in morphology throughout ontogeny. Phylogenetic analyses of semaphoronts produced relationships of each Orsten fossil to the crown-group clade expected from morphology shared with extant larvae. Bredocaris is a member of the stem lineage of Thecostraca or (Thecostraca + Copepoda), and Yicaris and Rehbachiella are likely members of the stem lineage of Cephalocarida. These placements rely directly on comparisons between extant and fossil larval character states. The position of Phosphatocopina remains unresolved. This method may have broader applications to other phylogenetic problems which may rely on ontogenetically variable homology statements.
    Cladistics 07/2014; 30(4):366-390. · 6.09 Impact Factor
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    ABSTRACT: The ostracod fauna from the Floian (Lower Ordovician) strata of the Cordillera Oriental, Argentina (Acoite Formation) are documented. One new genus Acoitella and four species are recognized, two of which are new (Nanopsis victoria sp. nov. and Conchoprimitia frequens sp. nov.). The diversity of the Early Ordovician ostracod faunas of the Central Andean Basin is evaluated. Compared with other regions, the ostracod diversity, at generic and specific level, of the Cordillera Oriental was comparatively high during the Tremadocian (nine species recorded) and comparatively low during the Floian (four species recorded). The taxonomic composition of the fauna is similar during the entire Early Ordovician of the Cordillera Oriental, where it displays a high percentage of soanellids. The Floian assemblages are characterized by the dominance of the eridostracan C. frequens sp. nov. with a high percentage of nondimorphic palaeocopids: Nanopsis and two genera of the Soanellidae family (Saltite and Acoitella gen nov.). An ostracod shell bed is described and interpreted to be a parautochthonous assemblage, as a result of transport within the same habitat. The composition of the fauna, with the presence of Saltite and Nanopsis, shows significant affinities with East Gondwana. Copyright © 2011 John Wiley & Sons, Ltd.
    Geological Journal 11/2011; 46(6). · 1.61 Impact Factor


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