early palaeozoic rift related magmatism in variscan europe fragmentation of the armorican terrane assemblage early palaeozoic bimodal rift related magmatism is widespread throughout much of the variscides of europe it is traceable from the polish sudetes to nw iberia granitic plutonism generally predates cambro ordovician bimodal magmatism in the n bohemian massif this early palaeozoic granitic plutonism was generated by partial melting of cadomian basement whereas contemporaneous alkali granites with a mantle component are typical of the nw iberian massif silurian devonian mafic magmatism in the n bohemian massif massif central and nw iberian massif is partly preserved as obducted ophiolites compositional diversity displayed by cambro ordovician mafic magmatism can be accounted for by interaction between a spreading centre and an upwelling mantle plume this indicates that combined tensional forces and mantle plume convection assisted the early palaeozoic dispersal of terranes from the n gondwana margin continued fragmentation resulted in development of an archipelago of related terranes separated by a network of seaways and formation of oceanic crust

ordovician and silurian global geography presidential address delivered 3 may 2000 the main palaeocontinents during the early ordovician were gondwana laurentia baltica and siberia and a brief survey is made of their limits in the ordovician and silurian in particular gondwana by far the largest continent is analysed as including a core of south america antarctica africa australia and peninsular india and also the marginal terranes all of which show faunal links with but which may not have been attached to the core of avalonia ibero armorica and other european fragments turkey arabia and terranes from the far east including south china sibumasu and parts of australasia changes within the benthic faunas reveal that baltica whilst isolated in the early ordovician became united with avalonia by the end ordovician and the two with laurentia by the mid silurian to form the new supercontinent of laurussia island arcs had distinctive faunas during the ordovician in particular those in the iapetus between laurentia baltica and gondwana and the huge kipchak arc which ran from baltica to siberia as the period progressed the iapetus arcs became subducted beneath or accreted to their neighbouring cratons and the kipchak arc gradually collapsed to form the core of the new kazakhstania terrane gondwana drifted over the south pole and this movement is reflected in the cratonic benthic faunas particularly brachiopods and trilobites which in the early ordovician had formed a cline between the high latitude faunas of north africa and the equatorial faunas of the far east and australia but by the devonian lived in much warmer seas in southern europe and cooler waters in antarctica the faunas also reflect the global palaeoclimates which were warm in the early to mid ordovician and mid to late silurian but which were much colder in the half million year period of the late ordovician and early silurian particularly in the latest ordovician hirnantian ice age with its attendant widespread hirnantia brachiopod fauna the relative closeness of the chief palaeocontinents by the early silurian enabled brachiopod and trilobite larvae to cross the narrower oceans enabling a relatively cosmopolitan benthic fauna to be established over much of the globe apart from the cooler water higher latitude clarkeia fauna to the south and the tuvaella fauna to the north

a laboratory simulation of fibrous veins some first observations abstract following work by stephen taber 80 years ago we describe vein like arrays of parallel fibrous crystals that grow evaporatively between pairs of brine soaked porous ceramic substrates crystals of solute grow antitaxially from fixed sites on the substrate forcing older parts of the crystals away from the growth site without benefit of any long range cracking parallel to the substrate the nutrients for growth are fed to the growth site advectively or diffusively through the substrate blocks themselves not along the plane of the vein we call such crystallization taber growth and suggest as taber did that it might be an important mechanism for non evaporative fibrous vein development in nature the taber growth model provides a ready explanation for the ability of fibers to track vein opening directions and tracking is indeed the rule in our samples though exceptions are also seen our results lend support to ideas already in the literature that fibrous veins are not necessarily products of a crack seal process and that fibrous veins are not necessarily syntectonic our observations also raise questions about criteria for recognition of syntaxial fibrous veins and underscore the importance of finding new criteria for recognition of the younging direction along fibers

sedimentary patterns across the lower middle cambrian transition in the esla nappe cantabrian mountains northern spain in the carbonate platforms of the western gondwana margin the extinction recorded at the lower middle cambrian boundary is accompanied by a profound change in the style of carbonate deposition the lancara formation of the esla nappe cantabrian mountains northern spain contains a distinct sedimentary turnover due to a combination of tectonism eustatic fluctuations and immigration and colonization of new benthic communities such as the youngest archaeocyathan assemblage of the entire iberian peninsula during latest early cambrian times a regressive trend is recorded in the lancara formation this regression was recorded on a peritidal dominant homoclinal ramp that is topped by a tectonically induced discontinuity d1 the latter surface marks the beginning of a last prograding regressive tendency recorded on an intra shelf ramp with ooidal bioclastic shoals protecting archaeocyathan microbial patch reefs the overlying discontinuity d2 corresponds to a major erosive unconformity which coincides with the lower middle cambrian boundary in the cantabrian mountains the subsequent long term earliest middle cambrian rise in relative sea level allowed deposition of low relief bioclastic shoals bearing a diverse and cosmopolitan assemblage of benthic fauna finally the previous evolution is bounded by a third discontinuity d3 which marks the beginning of a rhythmic sedimentation indicative of a major phase of tectonic breakdown and drowning of platforms recognised throughout southwestern europe two associations of calcimicrobes occur in the latest early cambrian regressive trend of the lancara formation i proaulopora and subtiflora are identified in peritidal high energy settings lacking self supported structures whereas ii intergrowths of epiphyton renalcis and girvanella encrusted branching colonies and solitary archaeocyaths in protected back shoal patch reefs the latest early cambrian regression is correlated in southwestern europe in both siliciclastic iberian chains and ossa morena and carbonate dominant platforms cantabrian mountains montagne noire and sardinia its tops are recognised as diachronous unconformities ranging in age from early bilbilian to the bilbilian leonian or lower middle cambrian boundary

early palaeozoic palaeobiogeography and palaeoecology of stylophoran echinoderms abstract stylophorans cornutes mitrates represent one of the most diverse classes of cambro ordovician echinoderms they were free living benthic non radiate forms closely related to asterozoans and crinoids taphonomic sedimentological and palaeosynecological data provide useful information on key aspects of stylophoran palaeoecology such a combined approach suggests that the rarity of stylophorans in proximal environments above storm wave base was probably original and does not exclusively result from the possession of a loosely articulated polyplated calcitic test conversely stylophorans were relatively abundant in deeper settings below storm wave base where they frequently occur in low diversity dense beds several tens to hundreds of individuals per square metre such assemblages were either largely dominated by stylophorans only middle cambrian darriwilian or by the association of both stylophorans and ophiuroids latest darriwilian silurian comparison with ecological requirements of similar modern and fossil dense populations of ophiuroids suggests that stylophoran beds occurred in well oxygenated oligotrophic waters with low predatory pressure and that sea temperature played a key role in the palaeobiogeographic distribution of stylophorans seven main stylophoran biofacies are identified and described the associated environments and tropical distribution of primitive heavily plated forms suggest that the initial radiation of the class probably took place in warm to temperate shallow settings earliest middle cambrian late cambrian however from this primitive stock stylophorans radiated several times towards deeper and or colder environments possibly because of the lower predation pressure in such settings cothurnocystid cornutes in the middle cambrian mitrates in the late cambrian hanusiids in the tremadocian as a consequence the fact that most cambro ordovician cornutes and mitrates were psychrospheric i e cold water adapted probably explains their relatively wide palaeobiogeographic distribution in high palaeolatitudes cambro ordovician stylophorans were abundant and diverse in shallow to deep environments but they were generally restricted to deep settings in low palaeolatitudes the great caradocian transgression favoured the extension of stylophorans from circum polar regions e g western margin of gondwana towards external settings at lower palaeolatitudes avalonia baltica and eastern margin of laurentia where one group of mitrates underwent a major radiation anomalocystitids and extended towards shallower and warmer palaeoenvironments in contrast all silurian stylophoran assemblages known so far are rare poorly diversified and restricted to shallow warm to temperate environments in tropical regions this distribution partly results from 1 the probable eradication of psychrospheric forms e g cornutes because of the prolonged anoxia of deep environments in the late hirnantian early silurian of west gondwana 2 the radiation of some mitrates anomalocystitids in shallow tropical settings in the late ordovician and 3 of strong taphonomic and or sampling biases numerous ghost lineages

evolutionary paleoecology of the earliest echinoderms helicoplacoids and the cambrian substrate revolution bioturbation in neritic siliciclastic settings during the proterozoic phanerozoic transition increased in depth and intensity causing a change in substrates from the matgrounds characteristic of the proterozoic to the mixgrounds characteristic of the phanerozoic this change in bioturbation increased the water content of surficial layers of sediment and blurred the sediment water interface leading to the first appearance of a mixed layer development of a mixed layer throughout neritic environments would have had a strong impact on any benthic metazoans particularly sessile suspension feeders that were well adapted for survival on relatively unbioturbated proterozoic substrates the impact of this substrate transition on benthic metazoans has been termed the cambrian substrate revolution the unusual early cambrian helicoplacoid echinoderms were well adapted for survival on typical proterozoic style substrates the examination of new helicoplacoid specimens collected during this study combined with extensive study of the rocks in which they are preserved indicate that helicoplacoids lived as sediment stickers on a muddy substrate that underwent only low to moderate levels of strictly horizontal bioturbation and did not have a mixed layer the significant increase of bioturbation through the cambrian in neritic siliciclastic settings is likely to have led to the extinction of the helicoplacoids other similarly adapted sessile suspension feeding echinoderms may have also been driven to extinction by the effects of the cambrian substrate revolution the co existence during the cambrian of organisms adapted to the variety of substrates characteristic of this transitional period may also have contributed to the high degree of perceived morphological disparity during the cambrian explosion

the fezouata fossils of morocco an extraordinary record of marine life in the early ordovician the discovery of the fezouata biota in the latest tremadocian of southeastern morocco has significantly changed our understanding of the early phanerozoic radiation the shelly fossil record shows a well recognized pattern of macroevolutionary stasis between the cambrian explosion and the great ordovician biodiversification event but the rich soft bodied fezouata biota paints a different evolutionary picture the fezouata assemblage includes a considerable component of cambrian holdovers alongside a surprising number of crown group taxa previously unknown to have evolved by the early ordovician study of the fezouata biota is in its early stages and future discoveries will continue to enrich our view of the dynamics of the early phanerozoic radiation and of the nature of the fossil record supplementary material a complete faunal list is available at http www geolsoc org uk sup18843

evolutionary palaeoecology of early epifaunal echinoderms response to increasing bioturbation levels during the cambrian radiation abstract increasing bioturbation depth and intensity during the cambrian radiation created a transition in dominant subtidal soft substrates from firm proterozoic style soft substrates without a well developed mixed layer to soupier phanerozoic style soft substrates with a well developed mixed layer microbial mats were also relegated to settings with inhibited metazoan activity but made resurgences during later ecological crises previous work suggests that this substrate change strongly influenced the evolution of cambrian benthic suspension feeding echinoderms in order to test this previous work and reveal longer term evolutionary patterns the substrate adaptations of 93 genera in the three classes of benthic suspension feeding echinoderms with definitive cambrian origins edrioasteroids eocrinoids and helicoplacoids were examined throughout their fossil records this examination reveals that genera adapted to typical proterozoic style soft substrates were taxonomically dominant during and were almost entirely restricted to the early and middle cambrian thereafter from the late cambrian through the carboniferous genera adapted to typical phanerozoic style soft substrates were taxonomically dominant this trend supports previous studies and defines a fundamental evolutionary shift in echinoderm substrate interactions in response to increased mixed layer development during the cambrian radiation a notable exception to this trend is the late devonian edrioasteroid cooperidiscus which is morphologically convergent with the early and middle cambrian sediment attaching edrioasteroid stromatocystites this convergence is likely the result of cooperidiscus adapting as a sediment attacher to typical proterozoic style soft substrates that developed during or shortly after the late devonian mass extinction this study indicates for the first time that adaptation to non actualistic substrates during ecological crises can result in morphological convergence with forms adapted to similar substrates common during the cambrian radiation

effects of tropical weathering on quartz grain shape an example from northeastern australia abstract although previous work has provided qualitative evidence that the shapes of quartz sand grains can be modified significantly by postdepositional weathering and pedogenesis the magnitude and rate of such changes have not been quantified fourier shape analysis of quartz grains from two generations of stabilized parabolic dunes from north queensland australia has shown that the grains in the older dunes are significantly more angular than those from the younger dunes because the sands of both dune generations have a similar provenance and transport history the observed shape differences are attributed to postdepositional weathering in a humid tropical climate this interpretation is supported by scanning electron microscope examination of grain surface textures and by textural anal sis which revealed severe chemical etching and in situ silt production by disintegration of quartz grains the observed changes in grain shape have been brought about in less than 8000 years

palaeogeographical and palaeoecological aspects of the cambro ordovician radiation of echinoderms in gondwanan africa and peri gondwanan europe abstract ecology and tempo of the lower palaeozoic radiation of echinoderms are discussed in this paper based on comparison of the diversity patterns observed in cambro ordovician faunas from laurentia and the northern gondwana margin the cambrian agronomic revolution triggered a global radiation of echinoderms with the progressive disappearance of biomat related lifestyles and the colonisation of new environments both in laurentia and on the northern gondwana margin soft substrate echinoderm assemblages related to cold and or deep environments were dominated by blastozoans and stylophorans these assemblages show a pattern of continuous diversification from the middle cambrian to the middle ordovician the major radiation of crinoids in the lower to middle ordovician of laurentia is only a local diversification correlated with the development of hardgrounds in warm shallow environments no comparable major ordovician radiation event occurred in the cooler environments of the northern gondwana margin

sequence stratigraphy of the middle cambrian daegi formation korea and its bearing on the regional stratigraphic correlation abstract the sediments that comprise the middle cambrian daegi formation in eastern central korea are interpreted to have been deposited in a carbonate ramp setting the daegi formation consists of nine lithofacies argillaceous rock ribbon rock oolitic limestone skeletal limestone microbial limestone intraclastic limestone micritic limestone bioturbated limestone and crystalline limestone which are grouped into three facies associations presenting from base up outer ramp grain shoal and inner ramp facies associations two depositional sequences can be distinguished in the daegi formation sequence 1 in the lower part of the daegi formation comprises a lower transgressive systems tract tst and an upper highstand systems tract hst the tst consists of terrigenous deposits with subordinate limestones while the hst contains various types of limestone sequence 2 comprises the upper half of the daegi formation and was deposited during a tst the sequence stratigraphic analysis of the daegi formation suggests that the sediments were deposited during one 3rd order sea level change during the middle to late middle cambrian the sequence stratigraphic framework of the daegi formation can be excellently correlated with coeval deposits in north china the zhangxia and the lower part of the overlying gushan formations which belong to the same tectonic block as the korean peninsula the sino korean block skb the almost identical sequence stratigraphic frameworks in two separate basins suggest that the sequence stratigraphic development on the skb was mainly influenced by eustatic changes during the middle cambrian

the margins of avalonia during cambrian and earliest ordovician times avalonia was an area forming an integral part of the huge gondwanan continent probably along the northern margin of amazonia until in early ordovician late arenig or llanvirn time it split off from gondwana leaving a widening rheic ocean to its south today its southern margin with gondwana extends northeast from east of cape cod massachusetts through nova scotia north of the meguma terrane and thence below sea level to the south of newfoundland on the eastern side of the present atlantic the southern margin may separate southwest portugal from the rest of the iberian peninsula it can be traced eastwards with more certainty from the south cornwall nappes to a line separating the northern phyllite belt on the southern margin of the rhenohercynian terrane and the mid german crystalline high there is no certain evidence of avalonian crust to the northeast of the elbe line the northern margin of avalonia extends westwards from south of denmark to the british isles where it merges with the iapetus ocean suture between scotland and england traced westwards it crosses ireland and reappears in northern newfoundland to the east of new world island where it may follow the trace of the dog bay line and the cape ray fault recent work suggests that the northern margin of avalonia may clip the northern tip of cape breton island in nova scotia and then enter the north american mainland at the bay of chaleur it may then be traced from north and west of the popelogan and bronson hill arcs to long island sound near newhaven connecticut the cambrian to devonian faunas reflect the history of avalonia initially they were purely gondwanan but as ordovician time proceeded more genera crossed firstly the tornquist ocean as it narrowed between avalonia and baltica to close in latest ordovician and early silurian times and secondly the iapetus ocean so that by the early silurian most of the benthic shelly faunas apart from the ostracods were the same round the adjacent margins of all three palaeocontinents

the fezouata shale lower ordovician anti atlas morocco a historical review abstract exceptionally preserved fossils yield crucial information about the evolution of life on earth the fezouata biota from the lower ordovician of morocco is a konservat lagerstatte of major importance and it is today considered as an ordovician burgess shale this biota was discovered only some 15 years ago but geological studies of the area date back to the beginning of the 20th century pioneering geological investigations lead to the discovery of ordovician strata in the anti atlas 1929 and ultimately resulted in their formal subdivision into four main stratigraphic units 1942 in the agdz area the presence of fossiliferous tremadocian lower ordovician strata was suspected as early as 1939 but only definitively confirmed in 1955 in the 1960s 1990s jacques destombes provided the first detailed biostratigraphic framework for the lower ordovician of the anti atlas and collected thousands of fossils that were subsequently described in a series of monographs in the early 2000s exceptionally preserved fossils were discovered in the fezouata shale tremadocian late floian in the central anti atlas by mohamed ou said ben moula this biota now known as the fezouata biota is of utmost importance for it demonstrates the extent in the fossil record of non biomineralising animals typical of the cambrian explosion into the ordovician during the great ordovician biodiversification although most components are still in need of formal descriptions a fairly good picture of the composition and organisation of this biota and how it contributes to our understanding of the early evolution of metazoan communities can now be depicted moreover recent studies have substantially clarified the biostratigraphical and palaeoenvironmental context of the fezouata shale and are now being followed up by detailed investigations of the taphonomy geochemistry and micropalaeontology of this unique konservat lagerstatte these efforts will soon greatly benefit from the recovery of fresh unweathered samples from drill cores

origin of peritidal carbonate cycles early cambrian sardinia abstract cyclic shallow water carbonates of early cambrian age were investigated in sardinia they consist of muddy lagoonal deposits at the base followed by a thin bed of intertidal sediments they in turn are overlain by spillover oolites cycles are locally restricted and bordered laterally by non cyclic sequences these coeval sediments consist of platform margin oolites on one side and mostly terrigenous clastics of an intertidal regime on the other side sedimentary conditions within these environments were probably stable during deposition no proof of periods of emergence is given therefore sea level changes seem less likely as the driving mechanism of cycle formation instead cyclicity is supposed to be intrinsically controled the model developed is based on a changing sedimentation rate high accumulation and building up to sea level intertidal stage and drop of sedimentation rate lag time increasing water depth after that sedimentation recovered and a new cycle started

the great ordovician biodiversification event gobe the palaeoecological dimension abstract the great ordovician biodiversification event gobe saw a spectacular increase in marine biodiversity at all taxonomic levels largely within the phyla established much earlier during the so called cambrian explosion the diversification was probably the result of a combination of several geological and biological processes and the positive feedbacks resulting from them the present paper reviews the palaeoecological dimension of the gobe it involved major increases in s and biodiversity largely associated with the rise of the paleozoic evolutionary fauna dominated by suspension feeders and involving a greater occupation of ecospace and more complex ecological structures in the ecological evolutionary units p1 and p2 in the benthos these include more complex food webs than those of the cambrian greater tiering especially above the sediment water interface and the development of guild structures indicating increased competition between taxa for particular resources the ordovician is characterized by a profound change in reef composition with a switch from microbial dominated reefs in the early and middle ordovician to metazoan dominated reefs in the late ordovician increases in complexity of deep water trace fossil assemblages began in the early ordovician and mark the increasing exploitation in that environment and the development of hardgrounds permitted bioerosion and encrusting strategies together with the appearance of cryptic communities within the water column the gobe involved a significant increase in the diversity of the phytoplankton and the development of a diverse zooplankton including planktotrophic larvae from a range of invertebrate clades this revolution in the plankton enabled the establishment of a diverse fauna of pelagic vertebrates molluscs and arthropods and promoted the rise of suspension feeders in the benthos an escalation amongst predators and thus community evolution may also have been a major driver of biodiversification

a trilobite fauna from the highest shineton shales in shropshire and the correlation of the latest tremadoc a rich fauna dominated by trilobites and calcified chordates has been collected in shropshire from the arenaceous beds the highest member of the tremadoc shineton shale formation and hitherto regarded as poorly fossiliferous this fauna shows that shelf conditions persisted longer in shropshire than has been supposed it is likely that even younger tremadoc is cut out at the unconformity below the caradoc in the shineton inlier the correlation of the later tremadoc is reviewed and the nomenclature of british tremadoc biozones is revised the trilobites described here are a mixture of previously known and new forms the name shumardia conophrys salopiensis callaway is revived for british material traditionally assigned to the scandinavian species shumardia pusilla sars from which it is distinct the new taxa litagnostus meniscus sp nov apatokephalus sarculum sp nov and skljarella cracens sp nov are described the type species of asaphellus a homfrayi and leptoplastides l salteri are redescribed and geragnostus callavei pseudokainella impar and parapilekia sp are recorded new information on the ontogeny of s c salopiensis and a homfrayi is given litagnostus and skljarella are recorded from the british isles for the first time

unravelling extrinsic and intrinsic factors of the early palaeozoic diversification of blastozoan echinoderms abstract the subphylum blastozoa represents more than one third of the early palaeozoic echinoderm fauna a comprehensive database including all records of blastozoans was built to provide quantitative analyses of palaeogeography and diversity patterns and processes for the 10 classes currently included in this subphylum during the early palaeozoic the global pattern of taxonomic diversity shows two peaks during the cambrian series 3 and the late ordovician intervals in cambrian times the high taxonomic diversity seems to be related with a high turnover rate and a high endemicity of blastozoan genera whereas in ordovician times the rise in diversity is associated with a low endemicity and a low turnover rate the gradual increase of ordovician diversity can be explained by the progressive geographic extension of blastozoan genera onto most palaeocontinental margins associated to the long term gradual sea level rise this global pattern is subdivided into local trends to compare the relative influence of regional distributional patterns blastozoans occurred mainly on gondwanan and laurentian margins during the cambrian in both ordovician and silurian times blastozoans colonised different provinces characterised by varied latitudinal position and environmental conditions the laurentian province was mainly located in the equatorial latitudes temperate to warm waters mainly carbonate platforms and both the northwestern peri gondwanan and asian provinces in the intermediate to high latitudes temperate to cold water mainly siliciclastic environments after the hirnantian mass extinction blastozoans finally recovered chiefly on laurentian margins where climate and environmental conditions were probably more favourable the two diversification events recorded for blastozoans in the early palaeozoic concerned two distinct evolutionary faunas cambrian evolutionary fauna vs palaeozoic evolutionary fauna they were driven by distinct processes even if the ordovician diversification had indeed started during the middle furongian with a medium origination event difference in processes might be related to the evolution of global environmental climatic conditions coupled with the position of continental masses

earliest crinoids new evidence for the origin of the dominant paleozoic echinoderms the oldest crinoids have been discovered in early ordovician strata of the western united states a set of emergent crinoid traits based on these and other early crinoids enables reinterpretation of crinoid origins and early history the new fossils retain primitive echinoderm characteristics including ambulacral floor plates and largely unorganized cup plating a first for crinoids they lack shared derived characteristics linking them to other stalked echinoderms including blastozoans contrary to current widespread opinion crinoids originated as an independent group during the cambrian apparently from an edrioasteroid ancestor all four major paleozoic crinoid clades had evolved by the early ibexian tremadocian and this initial diversification slightly preceded those of most other paleozoic evolutionary fauna components these earliest crinoids attached to carbonate hardgrounds developed on sponge algal mounds intraformational conglomerates and grainstones

paleoecology of benthic metazoans in the early cambrian maotianshan shale biota and the middle cambrian burgess shale biota evidence for the cambrian substrate revolution abstract as the depth and intensity of bioturbation increased through the proterozoic phanerozoic transition the substrates on which marine benthos lived changed from being relatively firm with a sharp sediment water interface to having a high water content and blurry sediment water interface microbial mats once dominant on normal marine proterozoic seafloors were relegated to stressed settings lacking intense metazoan activity this change in substrates has been termed the agronomic revolution seilacher a pfluger f 1994 from biomats to benthic agriculture a biohistoric revolution in krumbein w e ed biostabilization of sediments bibliotheks and informationsystem del carl von ossietzky universitat oldenburg 97 105 and the impact of the subsequent development of the mixed layer on benthic metazoans has been termed the cambrian substrate revolution bottjer d j hagadorn j w dornbos s q 2000 the cambrian substrate revolution gsa today 10 9 1 7 because the early cambrian was a transitional time in this substrate revolution it is hypothesized that benthic metazoans adapted to typical proterozoic style soft substrates co existed with benthic metazoans adapted to more typical phanerozoic style soft substrates paleoecological examination of the benthic metazoans of the early cambrian maotianshan shale chengjiang biota and middle cambrian burgess shale biota combined with examination of core samples from the rocks in which the maotianshan shale biota is preserved was performed in order to test this hypothesis results of the core analysis reveal that the rocks in which the maotianshan shale biota was preserved and therefore the substrate on which it lived contains almost no evidence for bioturbation of any kind while the immediately underlying rocks of similar lithology are dominated by intermediate levels of horizontal bioturbation and contain some evidence for the beginning of mixed layer development these results suggest that benthic metazoans of the maotianshan shale biota lived on a typical proterozoic style soft substrate and that environmental conditions associated with the exceptional preservation of the maotianshan shale biota may have also suppressed bioturbation levels results of the paleoecological analysis indicate that the maotianshan shale and burgess shale biotas contain mobile and sessile benthic metazoans adapted to typical proterozoic style soft substrates and others adapted to typical phanerozoic style soft substrates in addition the maotianshan shale biota is dominated by benthic suspension feeding genera adapted to typical proterozoic style soft substrates indicating that this biota lived during the early stages of the cambrian substrate revolution the burgess shale biota however contains more benthic suspension feeding genera adapted to typical phanerozoic style soft substrates than the maotianshan shale biota which suggests that the soft substrate on which they lived had more advanced levels of mixed layer development this research suggests that the adaptive radiation of benthic metazoans during the cambrian explosion was driven in part by the cambrian substrate revolution as benthic metazoans were forced to adapt to the development of the mixed layer in subtidal siliciclastic soft substrate environments during the cambrian

rise of echinoderms in the paleozoic evolutionary fauna significance of paleoenvironmental controls echinoderms were a major enduring component of paleozoic marine faunas beginning with the rapid diversification of crinoids and other classes in the early ordovician this diversification was triggered by increased availability of habitable areas accompanying sea level rise and changed sedimentation styles newly collected early ordovician echinoderms facilitate determination in detail of life modes and important adaptations during this transition interval substrate consistency and stability were crucial spatial limiting factors that resulted in heterogeneous distribution patterns for echinoderm classes crinoids were overwhelmingly large food groove suspension feeders with relatively open filtration fans attached by small discs to hard ground surfaces in shallow water they were preadapted for this life mode rhombiferans were mobile small food groove suspension feeders they lived on soft substrates at various depths several important crinoid clades underwent a second phase of diversification during the middle ordovician by developing holdfasts adapted to soft substrates and densely pinnulate arms with small food grooves leading to dominance of this class among paleozoic echinoderms our findings are in basic agreement with the overall onshore diversification pattern of most paleozoic benthic invertebrates but we argue for an extrinsic environmental control substrate availability for the observed echinoderm distribution

taphonomy of cystoids echinodermata diploporita from the napoleon quarry of southeastern indiana usa the lower silurian massie formation as an atypical lagerstatte abstract diploporites like most pelmatozoan echinoderms are characterized by complex multi element skeletons prone to complete disarticulation if left exposed for extended periods of time consequently preservation of abundant articulated diploporite thecae is rare and generally restricted to environments where rapid burial events could catastrophically entomb individuals one such environment is represented by the lower portion of the wenlock age massie formation at the new point stone quarry near napoleon southeastern indiana which we recognize as a konservat lagerstatte yet taphonomic evidence does not support live burial diploporites holocystites spp are dominantly preserved as intact thecae without any portions of brachioles and with damage plate shifting and plate loss plate jumbling on one side post mortem encrustation is common but epibionts are typically present on the well preserved sides of thecae geopetal sediment fill of thecae shows that the well preserved side commonly faced upward following burial this taphonomic state is paradoxical as burial of live diploporites would have resulted in preservation of complete individuals with no encrusters and only compaction induced damage rapid burial of diploporites following a short interval of exposure would have resulted in preservation similar to observed patterns but with encrusters and geopetal infills indicating that the poorly preserved side faced up and burial after extended exposure would have resulted in thorough disarticulation of thecae rather a variable and in some cases complex taphonomic history is suggested for diploporites from the napoleon quarry with at least some individuals having experienced one or more brief episodes of exhumation prior to final burial early diagenetic cementation of initial theca filling sediment is the most likely mechanism for keeping thecae intact during subsequent exposure

palaeoecological aspects of the diversification of echinoderms in the lower ordovician of central anti atlas morocco abstract echinoderms are one of the major components of benthic faunas in the lower ordovician sequence near zagora central anti atlas morocco the fezouata shale tremadocian late floian has yielded numerous exquisitely preserved echinoderm assemblages ranging through several stratigraphic levels and palaeoenvironmental conditions these associations offer a unique opportunity to document both evolutionary and palaeoecological aspects of echinoderm diversification in high latitude siliciclastic dominated western gondwana sediments where rapid in situ burials facilitated excellent faunal census conditions lower shoreface deposits of the fezouata shale provide the most complete record of successive echinoderm faunas in late tremadocian times these relatively shallow shelf deposits show the progressive replacement of low diversity opportunistic cambrian like dwarfed communities dominated by cornute stylophorans in unhospitable dysoxic environmental conditions by higher diversity benthic assemblages more typical of the great ordovician biodiversification event and dominated by blastozoans on well oxygenated sea floors the turnover of the ordovician radiation was apparently slightly delayed in more proximal settings eocrinoid meadows persisted in shallower environmental conditions up to the middle floian in the late floian they were replaced by diploporite dominated communities typical of later ordovician high latitude peri gondwanan faunas from a palaeobiogeographic point of view low diversity assemblages display relatively strong affinities with cosmopolitan late cambrian echinoderm faunas whereas high diversity communities are dominated by peri gondwanan taxa

the cambrian substrate revolution and the early evolution of attachment in suspension feeding echinoderms abstract the cambrian characterized by the global appearance of diverse biomineralized metazoans in the fossil record for the first time represents a pivotal point in the history of life this period also documents a major change in the nature of the sea floor neoproterozoic type substrates stabilized by microbial mats were replaced by unconsolidated soft substrates with a well developed mixed layer the effect of this transition on the ecology and evolution of benthic metazoans is termed the cambrian substrate revolution csr and this is thought to have impacted greatly on early suspension feeding echinoderms in particular according to this paradigm most echinoderms rested directly on non bioturbated soft substrates as sediment attachers and stickers during the cambrian epoch 2 as the substrates became increasingly disturbed by burrowing forming a progressively thickening mixed layer echinoderms developed new strategies for attaching to firm and hard substrates to test this model we evaluated the mode of attachment of 83 cambrian suspension feeding echinoderm species attachment mode was inferred based on direct evidence in fossil specimens and interpretations of functional morphology these data were analyzed quantitatively to explore trends in attachment throughout the cambrian in contrast to previous studies the majority of cambrian clades eocrinoids helicoplacoids helicocystoids isorophid edrioasteroids and solutes are now interpreted as hard shelly substrate attachers only early edrioasteroids attached directly to firm substrates stabilized by microbially induced sedimentary structures contrary to the predictions of the csr paradigm our study demonstrates that cambrian echinoderms were morphologically pre adapted to the substrate changes that occurred during the cambrian allowing them to fully exploit the appearance of hardgrounds in the furongian we find no support for the claim that the csr explains the peak in echinoderm diversity during cambrian epochs 2 3 or that it caused the extinction of helicoplacoids

the absence of echinoderms from the lower cambrian chengjiang fauna of china palaeoecological and palaeogeographical implications abstract although deuterostome phylogeny has now achieved a good degree of consensus echinoderm emergence and early evolution remain highly enigmatic different phylogenetic scenarios have emerged based partially on early cambrian enigmatic animals of the chengjiang biota yuanshan formation cambrian series 2 yunnan china interpreted as primitive echinoderms they include cambrofengia yunnanensis hou et al 1999 cotyledion tylodes luo and hu 1999 and two vetulocystids dianchicystis jianshanensis and vetulocystis catenata shu et al 2004 their interpretation as echinoderms is here critically revised and c tylodes based on newly sampled specimens is tentatively re interpreted as a cnidarian polyp as a result it appears that the chengjiang biota one of the most diverse and earliest recorded communities is most probably devoid of echinoderm representatives this is not interpreted as a taphonomic artefact but as a palaeoecological signal of the radiation of echinoderm during the early cambrian on carbonate substrates up to ten exceptional biotas are described from the yangtze platform south china from cambrian stage 2 to early stage 5 in siliciclastic environments varying from shallow platform to basin slope the absence of echinoderms in those burgess shale type deposits from cambrian stages 2 and 3 along with their report from laterally coeval carbonate sediments argue for a proximal radiation of echinoderms during early cambrian times in carbonate environments they would have later colonized siliciclastic proximal and distal environments the same colonization sequence is generally observed at a global scale with the first appearance of echinoderms varying in time according to local palaeogeographical controls

laurentian origin of solutan echinoderms new evidence from the guzhangian cambrian series 3 weeks formation of utah usa a new solutan echinoderm pahvanticystis utahensi s gen et sp nov is described from the upper part of the weeks formation guzhangian the cambrian series 3 succession of the central house range in western utah documents the early diversification of the class soluta which is characterized by a major ecological transition from sessile pelmatozoan primitive taxa coleicarpus wheeler formation to more and more vagile temporarily attached castericystis marjum formation to mostly unattached homalozoan derived forms pahvanticystis weeks formation the morphology of pahvanticystis is remarkably intermediate between those of castericystis and minervaecystis its twisted flattened dististele possibly represents an adaptation for a more efficient crawling atop soft substrates this morphological feature also questions the phylogenetic relationships between syringocrinid and dendrocystitid solutans and the possible evolution of the latter from basal pahvanticystis or minervaecystis like syringocrinids by paedomorphosis

rifting during separation of eastern avalonia from gondwana evidence from subsidence analysis subsidence curves for cambrian ordovician sequences from the anglo welsh segment of the paleocontinent of avalonia reveal two periods of regionally enhanced basement subsidence early cambrian 545 518 ma and late cambrian to early tremadocian 505 490 ma the earlier event may record transtension following the avalonian cadomian orogeny the second event may be a transtensional precursor to the late tremadocian volcanic arc on eastern avalonia however paleomagnetic faunal volcanic and sedimentary evidence suggests that the main separation of eastern avalonia from gondwana occurred after middle arenigian time rifting during separation is probably recorded by localized middle arenigian to llanvirnian 480 462 ma subsidence along the welsh basin margin but rifting must have occurred mainly on the now obscured southern margin of the avalonian continent pronounced caradocian 462 449 ma subsidence is associated with back arc rifting after separation from gondwana