Carys E. Bennett

A review of the Carboniferous colonisation of non-marine environments by ostracods

This review examines the nature and chronology of the transition of ostracods from marine to non-marine aquatic environments in the Devonian and Carboniferous. There is putative evidence of ostracods in brackish waters from the middle Silurian, but more robust evidence from the Devonian. The first putative freshwater ostracods are species of the generaCarbonita andGeisina which are found in the early to middle Carboniferous Coal Measures. Freshwater ostracods are common in the middle Pennsylvanian Coal Measures of late Carboniferous age, with species of genera such asDarwinula, Carbonita, Candona andCypridopsis. The Lower Carboniferous Visean succession from the Midland Valley of Scotland provides a unique range of sedimentary environments from marine to non-marine, and a diverse range of ostracods and macrofauna. It is an ideal sequence to study the radiation of the Ostracoda from marine to non-marine realms. Non-marine species ofCarbonita are found in the lower Viséan, associated with spirorbids,Naiadites, Estheria, plant and fish fragments. Marginal marine species include the generaGeisina, Parapar-chites, Sbemonaella andCapellina, all of which are eurytopic. The first non-marine environments occupied by ostracods were near the shoreline, and influenced by marine transgressions. The adaptations needed to survive in freshwater or low salinities would have included changes in osmoregulation, feeding, and reproductive strategies such as parthenogenesis, to enable opportunistic colonisation of temporary freshwater habitats such as seasonal pools.

Phylogenetic and environmental context of a Tournaisian tetrapod fauna

The end-Devonian to mid-Mississippian time interval has long been known for its depauperate palaeontological record, especially for tetrapods. This interval encapsulates the time of increasing terrestriality among tetrapods, but only two Tournaisian localities previously produced tetrapod fossils. Here we describe five new Tournaisian tetrapods (Perittodus apsconditus, Koilops herma, Ossirarus kierani, Diploradus austiumensis and Aytonerpeton microps) from two localities in their environmental context. A phylogenetic analysis retrieved three taxa as stem tetrapods, interspersed among Devonian and Carboniferous forms, and two as stem amphibians, suggesting a deep split among crown tetrapods. We also illustrate new tetrapod specimens from these and additional localities in the Scottish Borders region. The new taxa and specimens suggest that tetrapod diversification was well established by the Tournaisian. Sedimentary evidence indicates that the tetrapod fossils are usually associated with sandy siltstones overlying wetland palaeosols. Tetrapods were probably living on vegetated surfaces that were subsequently flooded. We show that atmospheric oxygen levels were stable across the Devonian/Carboniferous boundary, and did not inhibit the evolution of terrestriality. This wealth of tetrapods from Tournaisian localities highlights the potential for discoveries elsewhere.

Ostracods from freshwater and brackish environments of the Carboniferous of the Midland Valley of Scotland: the early colonization of terrestrial water bodies

The Mississippian Strathclyde Group of the Midland Valley of Scotland yields some of the earliest non-marine ostracods. The succession records shallow marine, deltaic, estuarine, lagoonal, lacustrine, fluvial and swamp environments representing a series of staging-posts between fully marine and limnetic settings. Macrofossils and ostracods are assigned to marine, marginal marine, brackish and freshwater environments based on their faunal assemblage patterns. Key brackish to freshwater ostracods are Geisina arcuata , Paraparchites circularis n. sp., Shemonaella ornata n. sp. and Silenites sp. A, associated with the bivalves Anthraconaia , Carbonicola , Cardiopteridium , Curvirimula , Naiadites , the microconchid ‘ Spirorbis ’, Spinicaudata and fish. Many Platycopina and Paraparchiticopina ostracods are interpreted as euryhaline, which corresponds with their occurrence in marine to coastal plain water bodies, and supports the ‘estuary effect’ hypothesis of non-marine colonization. The success of non-marine colonization by ostracods was dependent on the intrinsic adaptations of ostracod species to lower salinities, such as new reproductive strategies and the timing of extrinsic mechanisms to drive non-marine colonization, such as sea-level change. The genus Carbonita is the oldest and most common freshwater ostracod, and went on to dominate freshwater environments in the Late Palaeozoic.

Carboniferous ostracods from central Honshu, JapanC. P. STOCKER AND OTHERSCarboniferous ostracods from Japan

Silicified beyrichiocopid and podocopid ostracods from limestone nodules derived from the middle part of the Ichinotani Formation within the Hida Gaien Terrane of central Honshu Island, Japan, are associated with fusulinid foraminifera that indicate strata of the middle Moscovian (Pennsylvanian, Carboniferous). This is a rare record of ostracods from the Palaeozoic of Japan and the first systematic description of ostracods from the Carboniferous of the Hida Gaien Terrane. The fauna comprises six ostracod species (two new) assigned to the genera Amphissites , Kirkbya , Bairdia , Aechmina and Healdia , and additional material of possible cavellinids. The numerical dominance of ornamented beyrichiocopids such as Kirkbya and Amphissites , along with smaller numbers of smooth podocopids such as Bairdia , indicates an ‘Eifelian mega-assemblage’ ecotype ( sensu G. Becker), that is typical of mid Palaeozoic shallow marine, high-energy environments in a fore-reef ecosystem.