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

The position of graptolites within Lower Palaeozoic planktic ecosystems.

An integrated approach has been used to assess the palaeoecology of graptolites both as a discrete group and also as a part of the biota present within Ordovician and Silurian planktic realms. Study of the functional morphology of graptolites and comparisons with recent ecological analogues demonstrates that graptolites most probably filled a variety of niches as primary consumers, with modes of life related to the colony morphotype. Graptolite coloniality was extremely ordered, lacking any close morphological analogues in Recent faunas. To obtain maximum functional efficiency, graptolites would have needed varying degrees of coordinated automobility. A change in lifestyle related to ontogenetic changes was prevalent within many graptolite groups. Differing lifestyle was reflected by differing reproductive strategies, with synrhabdosomes most likely being a method for rapid asexual reproduction. Direct evidence in the form of graptolithophage 'coprolitic' bodies, as well as indirect evidence in the form of probable defensive adaptations, indicate that graptolites comprised a food item for a variety of predators. Graptolites were also hosts to a variety of parasitic organisms and provided an important nutrient source for scavenging organisms

A starfish with three-dimensionally preserved soft parts from the Silurian of England

Palaeozoic asteroids represent a stem-group to the monophyletic post-Palaeozoic Neoasteroidea, but many aspects of their anatomy are poorly known. Using serial grinding and computer reconstruction, we describe fully articulated Silurian (ca 425 Myr) specimens from the Herefordshire Lagerstätte, preserved in three dimensions complete with soft tissues. The material belongs to a species of Bdellacoma, a genus previously assigned to the ophiuroids, but has characters that suggest an asteroid affinity. These include a pyloric system in the gut, and the presence of large bivalved pedicellariae, the latter originally described under the name Bursulella from isolated valves. Ampullae are external and occur within podial basins; the radial canal is also external. Podia are elongate and lack terminal suckers. The peristome is large relative to the mouth. Aspects of the morphology are comparable to that of the extant Paxillosida, supporting phylogenetic schemes that place this order at the base of the asteroid crown group

A Carboniferous necrophagous myodocopid ostracod from Derbyshire, England

A monospecific population of cypridinid ostracods (Myodocopida) has been recovered from an ammonoid-bearing concretion of Namurian (Kindescoutian, R1a-b) age in the Bowland Shale Formation of Central England. These deposits represent sedimentation on the northern margin of a Carboniferous marine basin, the WNW-ESE orientated Widmerpool Gulf, where water depth probably exceeded 100 m. The ostracods occur in close association with the cranium of a shark (Orodus), on which they had most likely been scavenging. The sark carcass apparently formed a refuge to which the ostracods were restricted: they do not occur elsewhere within the concretion or surrounding strata. Adults and possibly as many as six moult stages are present so that the assemblage represents the original conspecific ostracod biocoenosis. The carapace morphology of this myodocopid ostracod. Eocypridina carsingtonensis sp. nov., is described and compared with related taxa. It is the oldest known myodocope to provide firm evidence of traces of an integumental circulatory system, present in positive relief on internal moulds as a series of anastomosing sinuses radiating away from the adductor muscle scar area, and comparable with modern cypridinids such as Vargula

Ostracods in the Palaeozoic?

The attribute traditionally used to recognise the occurrence of ostracods in the Palaeozoic stratigraphic record has in essence been the presence of a bivalved arthropod carapace of small size. Discoveries offering unparalleled insight into the soft part paleobiology of tiny bivalved Palaeozoic arthropods, when taken together with the notion that a bivalved carapace is a convergent phenomenon within the Arthropoda, have in the last decade revolutionised our understanding of the nature and stratigraphic record of the major groups of ostracod present in the Palaeozoic. Evidence from appendages and other soft parts is crucial in determining systematic affinity. Evidence from the soft part anatomy of bradoriids and phosphatocopids has undermined the record of ostracods in the Cambrian, but molecular and fossil evidence implies that they may be present at that time. In the absence of soft parts the case that leperditicopids (Ordovician-Devonian) are ostracods remains uncertain. Myodocopes certainly occur in the Palaeozoic, as determined on a wealth of new palaeobiological evidence. As yet, supposed Palaeozoic podocopes are represented in practical terms only by fossil shells. The systematic affinity of palaeocopes - a major group in the Palaeozoic and hitherto recognised as a coherent taxon - remains enigmatic, and they may turn out to represent an artificial grouping

Silurian myodocope ostracods from Poland

Newly collected material reveals that the Silurian myodocope ostracods from the Holy Cross Mountains, Poland comprise ten species (one new to science) belonging to four families: Bolbozoidae, Entomozoidae, Rhomboentomozoidae, and Cypridinidae. Biostratigraphic control using graptolites indicates that all three Polish outcrops investigated are of about the same chronostratigraphical level: middle Gorstian, lower Ludlow. The new occurrences in Poland extend the known distribution of several species and reinforce data that show many Silurian myodocope species with wide dispersal. Our new observations on the Holy Cross Mountains material confirm that the occurrences of Silurian myodocopes are mostly associated with pelagic animals and with rocks ranging from mudstone, siltstone or shale deposited in open- or deep-shelf marine settings. The cosmopolitan distribution of these ostracods, coupled with their facies and faunal associations, supports the notion of an ostracod (myodocope) ecological shift from benthic to planktonic habitats during the late Wenlock and Ludlow

A high-precision global biostratigraphy of myodocope ostracods for the Silurian upper Wenlock Series and Ludlow Series

The wide, trans-oceanic geographical distribution of myodocope ostracods during the Silurian (especially during the Ludlow and Pridoli epochs), and their widespread preservation in rocks of that age, permits the establishment of a transcontinental biostratigraphy of comparable resolution to coeval graptolite/chitinozoan/conodont biozones. Seven myodocope biozones, extending from the Homerian Stage, upper Wenlock Series Cyrtograptus lundgreni graptolite biozone to the middle part of the Ludfordian Stage of the Ludlow Series, enable a time-resolution for each biozone of circa 1 million years. These biozones can provide high-resolution correlation across Europe into Arctic Russia and Central Asia. There is also the potential for a myodocope biostratigraphy applicable from the uppermost Silurian (Pridoli) to the Carboniferous