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: Thesis submitted for the degree of Doctor of Philosophy at the University of Leicester, September 2009. Awarded 24 March 2010. Ostracods are a diverse group of arthropod crustaceans with a geological record from the Ordovician. Their radiation from marine to non-marine environments is a key step in the evolution of the group. The nature and chronology of this transition is examined, and proxies for non-marine environments determined. The Mississippian of the Midland Valley of Scotland contains a wide range of marine to non-marine ostracods, macrofauna and sediments that make it an ideal study area. This study documents the evidence for early Mississippian freshwater ostracods, 20 million years older than previously recorded. Twentyfive ostracod species from the orders Myodocopida, Palaeocopida and Podocopida are described, four of which are new species. Macrofossils are used to interpret the environmental tolerance of the ostracods. Important brackish to freshwater macrofauna are the bivalves Carbonicola, Curvirimula and Naiadites, the vermiform microconchid “Spirorbis”, conchostracans and fish. Eurytopic ostracods are species of Cavellina, palaeocopes and Shemonaella siveteri n. sp. Key brackish to freshwater ostracods are species of Geisina arcuata, and Paraparchites circularis n. sp. Freshwater ostracods are species of Carbonita. Non-marine sediments contain three new types of algal palynomorph, Botryococcus sp., and arthropod fragments. The algal palynomorphs are interpreted as freshwater. Brackish to freshwater habitats identified include estuaries, lakes, temporary pools and swamps. A protocol for the examination of diagenetic alteration of ostracods and macrofossils is proposed, which is essential prior to any isotope analysis. Diagenetically altered ostracods may be mistaken as pristine specimens, without a study of the carapace ultrastructure. This is assessed by comparing Carboniferous and Recent specimens. The Carboniferous ostracods have undergone seven diagenetic stages: 1. neomorphic calcite; 2. dissolution and pitting; 3. euhedral pyrite; 4. ferroan calcite; 5. ferroan dolomite; 6. iron oxide; 7. sphalerite and barite. The carbon and oxygen stable isotope data from the ostracods reflect these stages of diagenesis. The Natural Environment Research Council (NERC) funded the project, grant number NER/S/A/2005/13368. The British Geological Survey (BGS) provided additional CASE award funding, and BUFI (British Universities Funding Initiative) studentship financial support.
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    ABSTRACT: An ambitious, yet fundamental goal for comparative biology is to understand the evolutionary relationships for all of life. However, many important taxonomic groups have remained recalcitrant to inclusion into broader scale studies. Here, we focus on collection of 9 new 454 transcriptome data sets from Ostracoda, an ancient and diverse group with a dense fossil record, which is often undersampled in broader studies. We combine the new transcriptomes with a new morphological matrix (including fossils) and existing expressed sequence tag, mitochondrial genome, nuclear genome, and ribosomal DNA data. Our analyses lead to new insights into ostracod and pancrustacean phylogeny. We obtained support for three epic pancrustacean clades that likely originated in the Cambrian: Oligostraca (Ostracoda, Mystacocarida, Branchiura, and Pentastomida); Multicrustacea (Copepoda, Malacostraca, and Thecostraca); and a clade we refer to as Allotriocarida (Hexapoda, Remipedia, Cephalocarida, and Branchiopoda). Within the Oligostraca clade, our results support the unresolved question of ostracod monophyly. Within Multicrustacea, we find support for Thecostraca plus Copepoda, for which we suggest the name Hexanauplia. Within Allotriocarida, some analyses support the hypothesis that Remipedia is the sister taxon to Hexapoda, but others support Branchiopoda + Cephalocarida as the sister group of hexapods. In multiple different analyses, we see better support for equivocal nodes using slow-evolving genes or when excluding distant outgroups, highlighting the increased importance of conditional data combination in this age of abundant, often anonymous data. However, when we analyze the same set of species and ignore rate of gene evolution, we find higher support when including all data, more in line with a "total evidence" philosophy. By concatenating molecular and morphological data, we place pancrustacean fossils in the phylogeny, which can be used for studies of divergence times in Pancrustacea, Arthropoda, or Metazoa. Our results and new data will allow for attributes of Ostracoda, such as its amazing fossil record and diverse biology, to be leveraged in broader scale comparative studies. Further, we illustrate how adding extensive next-generation sequence data from understudied groups can yield important new phylogenetic insights into long-standing questions, especially when carefully analyzed in combination with other data.
    Molecular Biology and Evolution 09/2012; · 10.35 Impact Factor
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    ABSTRACT: Early Silurian (Aeronian) carbonate platform deposits of the lower Niur Formation of east central Iran yield an ostracod fauna of fourteen species dominated by podocopes with rare palaeocopes and binodicopes. The podocope-rich fauna is unusual in that Early Palaeozoic carbonate platforms are typically dominated by palaeocopes. Despite its mid-palaeolatitude peri-Gondwanan setting and isolation from low palaeolatitudes, the ostracod assemblage of the lower Niur Formation shows striking affinities to species-level with Late Ordovician and Early Silurian ostracod faunas of palaeo-equatorial Laurentia. Biogeographically the lower Niur Formation ostracod fauna also shows species- and genus-links with Late Ordovician and Early Silurian faunas of low-palaeolatitude (0°–30°S) Baltica and mid palaeolatitude peri-Gondwanan Uzbekistan, dispelling the notion of strict endemism for Early Silurian ostracods. Two new species Bulbosclerites jamshidis sp. nov. and Steusloffina fravashi sp. nov. are described.
    Gondwana Research 01/2011; 20(2):645-653. · 7.40 Impact Factor


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