The Devonian nekton revolution

Klug, C., Kröger, B., Kiessling, W., Mullins, G.L., Servais, T., Frýda, J., Korn, D. & Turner, S. 2009: The Devonian nekton revolution. Lethaia, 10.1111/j.1502‐3931.2009.00206.x Traditional analyses of Early Phanerozoic marine diversity at the genus level show an explosive radiation of marine life until the Late Ordovician, followed by a phase of erratic decline continuing until the end of the Palaeozoic, whereas a more recent analysis extends the duration of this early radiation into the Devonian. This catch‐all approach hides an evolutionary and ecological key event long after the Ordovician radiation: the rapid occupation of the free water column by animals during the Devonian. Here, we explore the timing of the occupation of the water column in the Palaeozoic and test the hypothesis that ecological escalation led to fundamental evolutionary changes in the mid‐Palaeozoic marine water column. According to our analyses, demersal and nektonic modes of life were probably initially driven by competition in the diversity‐saturated benthic habitats together with the availability of abundant planktonic food. Escalatory feedback then promoted the rapid rise of nekton in the Devonian as suggested by the sequence and tempo of water‐column occupation. □Devonian, diversity, ecology, food webs, nekton, plankton, radiation.     

Rings without a lord? Enigmatic fossils from the lower Palaeozoic of Bohemia and the Carnic Alps

Fossilized ring‐like structures with enigmatic function and taxonomic affiliation were recovered for the first time from the Upper Ordovician of the Carnic Alps and the Silurian of Bohemia. These rings, already mentioned as minor constituents in previous conodont studies (e.g. Webers 1966, p. 1; Bischoff 1973, p. 147), were reported from the Palaeozoic of several regions in Europe and North America. Originally considered as inwardly accreted adhering discs of a benthic hyolithelminth worm with a phosphatic tubular projection, they were later reinterpreted in relation to a putative crinoid epibiont or even as possible scyphozoans. Despite a long debate, neither the function of the enigmatic Palaeozoic rings nor their taxonomic affiliation has been fully clarified. The studied material, extracted by a standard technique in use for conodonts, consists of 235 elements from 16 stratigraphic levels in the Plöcken Formation (Carnic Alps, Cellon Section; Amorphognathus ordovicicus Biozone, Hirnantian, Ordovician) and in the Kopanina Formation (Bohemia, Mu?lovka Quarry; Polygnathoides siluricus Biozone, Ludfordian, Silurian). To explore whether ring size and shape changed over time, we employed a novel combination of geometric morphometric approaches for outlines with no ‘homologous’ landmarks and showed that only size appreciably varied with an increase of ca. 20%. The emerging data from this study are consistent with the interpretation of the rings as an adhering structure of a benthic organism living on a relatively uniform hard substrate.     

Marine ostracod provinciality in the late ordovician of palaeocontinental laurentia and its environmental and geographical expression

Background

We examine the environmental, climatic and geographical controls on tropical ostracod distribution in the marine Ordovician of North America.

Methodology/Principal Findings

Analysis of the inter-regional distribution patterns of Ordovician Laurentian ostracods, focussing particularly on the diverse Late Ordovician Sandbian (ca 461 to 456 Ma) faunas, demonstrates strong endemicity at the species-level. Local endemism is very pronounced, ranging from 25% (e.g. Foxe basin) to 75% (e.g. Michigan basin) in each basin, a pattern that is also reflected in other benthic faunas such as brachiopods. Multivariate (ordination) analyses of the ostracod faunas allow demarcation of a Midcontinent Province and a southern Marginal Province in Laurentia. While these are most clearly differentiated at the stratigraphical level of the bicornis graptolite biozone, analyses of the entire dataset suggest that these provinces remain distinct throughout the Sandbian interval. Differences in species composition between the provinces appear to have been controlled by changes in physical parameters (e.g. temperature and salinity) related to water depth and latitude and a possible regional geographic barrier, and these differences persist into the Katian and possibly the Hirnantian. Local environmental parameters, perhaps operating at the microhabitat scale, may have been significant in driving local speciation events from ancestor species in each region.

Conclusions/Significance

Our work establishes a refined methodology for assessing marine benthic arthropod micro-benthos provinciality for the Early Palaeozoic.     

Trilobites in Paleozoic carbonate buildups

The trilobite faunas found in carbonate buildups throughout much of the Paleozoic are remarkably similar in both composition and general morphological characteristics. This is primarily the result of the domination of these faunas by a limited number of trilobite families which are long-ranging in the buildup environment. Illaenids are the dominant trilobites in Ordovician-Devonian buildups and are generally accompanied by members of the Lichidae and Cheiruridae. Proetid trilobites are characteristic of Ordovician-Permian buildups but are seldom common. The number of trilobite families found in carbonate buildups is highest in the late Ordovician, with most of the important families persisting into the Devonian. After the Devonian only proetids are found in this environment. The conservative nature of these trilobite faunas suggests that the environmental characteristics of normal-marine Paleozoic carbonate buildups are similar. Trilobita, palaeoecology, faunistics, morphology. carbonate buildups. Palaeozoic .     

SCAPHOPODIZATION IN PALAEOZOIC MOLLUSCS

Abstract:  The relationship of a variety of problematic Early Palaeozoic fossils to the true scaphopods (Late Palaeozoic–Recent) is clarified by the recognition that a trend towards the development of a tubular shell is a recurrent theme within Palaeozoic benthic molluscs. This trend is here termed scaphopodization and can be recognized already in the Cambrian in helcionelloids such as Yochelcionella and Eotebenna . The problematic Early Palaeozoic tubular fossils Janospira , Jinonicella and Rhytiodentalium are interpreted as pseudo-scaphopod derivatives of the apparently exogastric ribeirioid rostroconchs. The direction of coiling of the protoconch indicates that they are not closely related to the true scaphopods, which were derived from endogastric concocardioidean rostroconchs in the Devonian or Carboniferous. Scaphopods show a comparable underlying morphological blueprint to these conocardioideans, but they represent a distinct stream-lining to the infaunal habitat.     

Phylogenetic relationships of Early–Middle Ordovician ostracods of Baltoscandia

Phylogenetic analysis of the Early and early Middle Ordovician (Tremadoc and Arenig) ostracod species of Baltoscandia suggests a polyphyletic origin for the suborder Beyrichiocopa. Binodicopes, leiocopes and eridostracans are excluded from the beyrichiocopide clade. An independent origin from the basal ostracods is suggested for the binodicopes and eridostracans. The palaeocopes form a strongly supported monophyletic clade. Within this suborder, the ctenonotellid and the tetradellid families together form a monophyletic clade. The tetradellids are paraphyletic, being a stem-group for the ctenonotellids. Nanopsis nanella , the earliest known ostracod from the Tremadoc, is a basal palaeocope. The early eridostracans Conchoprimitia and Incisua , with their uncomplicated carapace morphology, might be the most primitive ostracods.     

Conodont affinity of the enigmatic Carboniferous chordate Conopiscius

Conopiscius shares V-shaped myomeres with the co-occurring conodont Clydagnathus but instead of a complex oral apparatus it has only a single pair of conical elements, and structures resembling scales are associated with its myomeres. Moreover, the coarsely crystalline crown tissue typical for conodonts has not been identified in the Conopiscius elements, which show only a finely lamellar skeletal tissue. The gap between conodonts and Conopiscius may be filled by isolated elements of similar morphology and structure occurring in the Late Devonian. They reveal a very thin external layer developed mostly at the tooth tip and resembling conodont crown tissue. The pulp cavity is partially filled with layered or spherulitic phosphatic tissue of the kind known also in conodonts (basal filling tissue) and early vertebrates (lamellin). Conodont elements of similar morphology and representing uni-membrate oral apparatuses have not been previously reported from the Devonian or Carboniferous but occur near the Cambrian–Ordovician transition ( Proconodontus ) and in the Late Permian ( Caenodontus ). It is proposed that Conopiscius represents a mostly cryptic conodont lineage extending from the Early Ordovician to the Permian, instead of being directly related to the agnathans.     

Traces of microboring organisms in Palaeozoic conodont elements

Conodont elements from Palaeozoic strata (Ordovician, Devonian and Carboniferous) contain abundant evidence for presumed post-mortem colonisation by endolithic organisms. It is possible to distinguish several morphotypes of microcavities in conodont apatite, which show some morphological similarities to microborings in calcareous substrates. Some of them are believed to be produced by microendoliths, some others are yet unknown from calcareous substrates. The present report deals with the various kinds of microendolithic traces in conodont apatite. The significance of microborings in conodont elements is discussed.     

The cuticular structure of the 495-Myr-old type species of the fossil worm Palaeoscolex,P. piscatorum (?Priapulida)

Latex impressions of the cuticle of a compression fossil of the ? priapulid Palaeoscolex piscatorum, from the Lower Ordovician of Shropshire, demonstrate a complex ornamentation of sclerites similar to isolated material, e.g. Hadimopanella and phosphatized arrays. Each ‘segment‘is defined by an intercalary zone and bears two rows of sub-circular plates with prominent nodes on the upper surface. The intercalary zone bears two narrow grooves and a series of platelets, similar to but smaller than the plates. The remainder of each segment is occupied by microplates. Palaeoscolex piscatorum is fairly similar to a number of other species, including Gamoscolex herodes and Milaculum elongatum. Present evidence suggests the palaeoscolecidans are priapulid worms (or near relatives). Their abundance, combined with records from Burgess Shale-like occurrences, suggest priapulids were a major component of many Lower Palaeozoic benthic communities.     

Palaeozoic oolitic ironstones on the North American Craton

More than 40 mostly minor Palaeozoic oolitic ironstones (OI) accumulated on low-latitude cratonic North America, almost entirely in USA. A few Middle Cambrian OI, among the oldest anywhere, were deposited on the western cratonic shelf of USA. Widely scattered Late Cambrian ones developed on the southwestern, southeastern and northeastern flanks of the Transcontinental Arch. Middle Ordovician OI were deposited on the cratonic interior and on the southern and southeastern cratonic margins. In latest Ordovician time Neda OI spread across north-central USA east of the Arch and south of the Laurentian upland. Minor ones developed in the southern part of the Taconian foreland basin after major orogeny. Early and Middle Silurian Clinton OI flourished throughout the foreland basin in eastern USA, producing the largest OI deposit on the North American craton. Minor early Late Silurian OI accumulated in the central part of the basin. Middle and Late Devonian OI in the Acadian foreland basin in northeastern cratonic USA developed progressively westward of the encroaching Catskill delta. An isolated Middle Devonian one accumulated in southwestern cratonic USA, and latest Devonian ones in north-central USA east of the Arch.

During this Palaeozoic episode sites of OI deposition shifted eastward across the craton. Most of the OI were deposited during a hiatus in normal sedimentation, accumulating in the upper part of shoaling-upward sequences. Some early Palaeozoic ones occur in glauconitic siliciclastic-carbonate facies and contain mostly spherical hematitic ooids. These suggest derivation from iron-rich soils developed on glauconitic deposits. OI in wholly siliciclastic facies, containing distorted chamositic ooids with cores of mud peloids, were common in later Palaeozoic time. These OI, like many other Phanerozoic ones, suggest a synsedimentary to early diagenetic origin.     

Palaeoenvironmental setting (glaciations,sea level,and plate tectonics) of Palaeozoic major biotic radiations in the marine realm

The life on the Earth experienced periodically not only significant impoverishments (mass extinctions), but also remarkable rises in diversity. Two recent biodiversity curves and new information on glaciations, sea- level, and plate tectonics, permit to extend our knowledge on the latters. Four Palaeozoic major radiations in the marine realm are identified. They include the early Cambrian (PZMR1), Ordovician (PZMR2), Early Devonian (PZMR3), and mid-Permian (PZMR4) events. PZMR1 occurred immediately after the major end-Proterozoic glaciations, when global sea-level rose with low-magnitude fluctuations and huge well-connected oceans provided a peculiar space for biological innovations. PZMR2 happened at a time of unique sea-level highstand and well-connected watermasses. PZMR3 coincided with a relative sea-level lowstand, which, together with the presence of elongated island chains, might have enhanced the radiation by a rapid dispersal of organisms across shallow oceans and along connected shorelines. PZMR4 occurred at the end of the outstanding planetary-scale Late Palaeozoic glaciation. Generally, the Palaeozoic major radiations in the marine realm did not have an ultimate cause and did not occur in a similar palaeoenvironmental setting. The molecular clock approach suggests a possible link between the DNA-dated divergences of marine invertebrates and the identified major radiations.     

The Ordovician Biodiversification: revolution in the oceanic trophic chain

The Early Palaeozoic phytoplankton (acritarch) radiation paralleled a long-term increase in sea level between the Early Cambrian and the Late Ordovician. In the Late Cambrian, after the SPICE δ¹³C_carb excursion, acritarchs underwent a major change in morphological disparity and their taxonomical diversity increased to reach highest values during the Middle Ordovician (Darriwilian). This highest phytoplankton diversity of the Palaeozoic was possibly the result of palaeogeography (greatest continental dispersal) and major orogenic and volcanic activity, which provided maximum ecospace and large amounts of nutrients. With its warm climate and high atmospheric CO₂ levels, the Ordovician was similar to the Cretaceous: a period when phytoplankton diversity was at its maximum during the Mesozoic. With increased phytoplankton availability in the Late Cambrian and Ordovician a radiation of zooplanktonic organisms took place at the same time as a major diversification of suspension feeders. In addition, planktotrophy originated in invertebrate larvae during the Late Cambrian–Early Ordovician. These important changes in the trophic chain can be considered as a major palaeoecological revolution (part of the rise of the Palaeozoic Evolutionary Fauna of Sepkoski). There is now sufficient evidence that this trophic chain revolution was related to the diversification of the phytoplankton, of which the organic-walled fraction is partly preserved.     

Palaeoecology and diversity of endosymbionts in Palaeozoic marine invertebrates: Trace fossil evidence

Endosymbionts are organisms that live within the growing skeleton of a live host organism, producing a cavity called a bioclaustration. The endosymbiont lives inside the bioclaustration, which it forms by locally inhibiting the normal skeletal growth of the host, a behaviour given the new ethological category, impedichnia. As trace fossils, bioclaustrations are direct evidence of past symbioses and are first recognized from the Late Ordovician (Caradoc). Bioclaustrations have a wide geographic distribution and occur in various skeletal marine invertebrates, including tabulate and rugose corals, calcareous sponges, bryozoans, brachiopods, and crinoids. Ten bioclaustration ichnogenera are recognized and occur preferentially in particular host taxa, suggesting host-specificity among Palaeozoic endosymbionts. The diversity of bioclaustrations increased during the Silurian and reached a climax by the late Middle Devonian (Givetian). A collapse in bioclaustration diversity and abundance during the Late Devonian is most significant among endosymbionts of host coral and calcareous sponge taxa that were in decline leading up to the Frasnian-Famennian mass extinction.     

Predatory asteroids and the decline of the articulate brachiopods

Various causes, such as increased predation pressure, the lack of planktotrophic larvae, a 'resetting' of diversity, increased competition from benthic molluscs and the decline of the Palaeozoic fauna, have been suggested to explain the failure of the brachiopods to reradiate following the Permo-Triassic mass extinction. Increased predation pressure has hitherto appeared improbable, because typical predators of brachiopods, such as teleostean fish, brachyuran crabs and predatory gastropods, did not undergo major radiation until the late Mesozoic and early Cenozoic. However, new evidence strongly suggests that one important group of predators of shelly benthic organisms, the asteroids, underwent a major radiation at the beginning of the Mesozoic. Although asteroids appeared in the early Ordovician, they remained a minor element of the marine benthos during the Palaeozoic acme of the brachiopods. However, these early asteroids lacked four important requirements for active predation on a bivalved epifauna: muscular arms (evolved in the early Carboniferous); suckered tube feet, a flexible mouth frame and an eversible stomach (all evolved in the early Triassic). Thus radiation of the Subclass Neoasteroidea coincided with both their improved feeding capability and the decline of the articulates. The asteroids were the only group of predators of brachiopods that underwent a major adaptive radiation in the earliest Mesozoic. The asteroids may therefore have contributed to inhibiting a Mesozoic reradiation of the brachiopods. Epifaunal species lacking a muscular pedicle may have been particularly vulnerable. Unlike bivalve molluscs, modern brachiopods show only a limited range of adaptations to discourage asteroid predation. □ Asteroidea, Brachiopoda, evolution, predation, functional morphology.     

The oldest Devonian circumpolar ray-finned fish?

Actinopterygians (ray-finned fishes) are the most diverse group of living fishes, but have a sparse Devonian fossil record restricted to low palaeolatitudes. Here we report a new actinopterygian from the Paraná Basin of Brazil, which occupied a circumpolar position in the Palaeozoic. Available geological evidence supports a Middle Devonian or older age for this taxon, which shares features of the mandibular symphysis with the latest Devonian Tegeolepis. A phylogenetic analysis resolves these two as sister taxa. This new record expands the palaeogeographic distribution of Devonian ray-fins and suggests that gaps in their fossil record might be filled by exploring poorly sampled high-latitude localities within the Malvinokaffric Realm.     

Larval ecology and morphology in fossil gastropods

The shell of marine gastropods conserves and reflects early ontogeny, including embryonic and larval stages, to a high degree when compared with other marine invertebrates. Planktotrophic larval development is indicated by a small embryonic shell (size is also related to systematic placement) with little yolk followed by a multiwhorled shell formed by a free‐swimming veliger larva. Basal gastropod clades (e.g. Vetigastropoda) lack planktotrophic larval development. The great majority of Late Palaeozoic and Mesozoic ‘derived’ marine gastropods (Neritimorpha, Caenogastropoda and Heterobranchia) with known protoconch had planktotrophic larval development. Dimensions of internal moulds of protoconchs suggest that planktotrophic larval development was largely absent in the Cambrian and evolved at the Cambrian–Ordovician transition, mainly due to increasing benthic predation. The evolution of planktotrophic larval development offered advantages and opportunities such as more effective dispersal, enhanced gene flow between populations and prevention of inbreeding. Early gastropod larval shells were openly coiled and weakly sculptured. During the Mid‐ and Late Palaeozoic, modern tightly coiled larval shells (commonly with strong sculpture) evolved due to increasing predation pressure in the plankton. The presence of numerous Late Palaeozoic and Triassic gastropod species with planktotrophic larval development suggests sufficient primary production although direct evidence for phytoplankton is scarce in this period. Contrary to previous suggestions, it seems unlikely that the end‐Permian mass extinction selected against species with planktotrophic larval development. The molluscan classes with highest species diversity (Gastropoda and Bivalvia) are those which may have planktotrophic larval development. Extremely high diversity in such groups as Caenogastropoda or eulamellibranch bivalves is the result of high phylogenetic activity and is associated with the presence of planktotrophic veliger larvae in many members of these groups, although causality has not been shown yet. A new gastropod species and genus, Anachronistella peterwagneri, is described from the Late Triassic Cassian Formation; it is the first known Triassic gastropod with an openly coiled larval shell.     

The Cambro - Ordovician boundary

Henningsmoen, G.: The Cambro-Ordovician boundary.
The Cambrian and Ordovician Systems were established in Britain, and it seems appropriate to define the Cambro-Ordovician boundary in Britain or where there is a closely related faunal succession at the junction. When Lapworth erected the Ordovician System in 1879, his intention was that its lower boundary should separate the so-called primordial (or first) and second Palaeozoic faunas. He drew this boundary at the base of the Lower Arenig, but apparently included the Upper Tremadoc in the Lower Arenig. It seems problematic to base the Cambro-Ordovician boundary on grounds of historical priority, and we seem to be free to decide whether to have the boundary at the base of the Tremadocian, at the base of the Arenigian, or within the Tremadocian (e.g. at the base of the Upper Tremadoc). The alternatives are shortly discussed. Arguments are put forward for placing the boundary not at a break, but preferably in a sequence with cosmopolitan fossils, either in a sequence of uniform facies or perhaps rather in a sequence with frequently alternating facies.     

Locomotion in Nebalia bipes: a possible model for Palaeozoic phyllocarid crustaceans

The morphofunctional aspects of locomotion in Recent phyllocarid crustaceans are presented, based on combined video observations of living specimens of the cosmopolitan nektobenthic Nebalia (Leptostraca, Nebaliidae) and scanning electron microscopy of fixed material. N. bipes is infaunal by day, showing a preference for organic-rich black muds and dim light conditions. Under natural conditions, emergence from sediment and nocturnal swimming activities are controlled by a circadian rhythm. The 1st and 2nd antennae perform the major role in digging. The carapace rostral plate acts as a ram diverting particles and preventing inputs of sediment into the carapace. Superficial burrowing may provide camouflaged shelter against predation. Swimming is accomplished by the combined action of the first four pairs of pleopods (backward metachronal flexion during the power stroke) and the well-articulated abdominal shaft (downward flap). Plumose setae present on both the pleopods and furcal rami (governed by low Reynolds numbers) behave like paddles maximizing the resistance to the water. Clusters of cuticular microscales (3-5 μm) and microdenticles are present on the external surface of the carapace and the trunk segments, respectively. Both show a uniform directional arrangement suggesting functional interpretations in relation to locomotion (e.g., to prevent back slippage during digging, to reduce turbulence in the flow layer close to the body, and/or to serve as mechanoreceptors for the detection of variation in water flow). Key features of functional importance in the locomotion of living leptostracans (natatory pleopods, a highly flexible abdomen, setulate or paddle-like furcal rami) are also recognized in Palaeozoic archaeostracan phyllocarids, suggesting that swimming was accomplished by the same pleopodal movements as described for N. bipes. Comparisons with Recent analogues (Nebaliopsis) suggest that phyllocarids with a free swimming life-style existed among the lower Palaeozoic archaeostracans (e.g., Caryocaris; Ordovician). Asymmetrical cuticular ornament in some archaeostracans indicates burrowing habits. Some Palaeozoic phyllocarids may have been occasional (possibly diurnal) mud dwellers comparable to modern nebaliids.     

Phanerozoic changes in the high-rank suprageneric diversity structure of brachiopods: Linear and non-linear effects

Phanerozoic evolution of brachiopods produced many linear (established by a comparison of successive geologic time units) and non-linear (established by a comparison of non-successive geologic time units) effects, which can be examined quantitatively by using the similarity coefficients (Czekanowski's Quantified Coefficient and Gower Index) and correlation tools. The high-rank suprageneric diversity structure accounts for a number of superfamilies in each of 26 orders for every epoch of geological time. The intensity of turnovers in this structure was generally low during the entire Phanerozoic. It was slightly stronger during the Early Paleozoic, but close to zero during the Cenozoic, when the high-rank suprageneric diversity structure of brachiopods stabilized finally. Significant turnovers took place at the Middle Cambrian–Early Ordovician, the Late Ordovician–Early Silurian, the Late Silurian–Early Devonian, the Middle Devonian–Mississippian, and the Permian–Triassic transitions. Influences of mass extinctions, both major like those End Ordovician or Permian/Triassic and minor like Early Jurassic or Jurassic/Cretaceous, on the high-rank suprageneric diversity structure of brachiopods is registered. The strongest was the consequences of the Permian/Triassic catastrophe, which perhaps even reset the brachiopod evolution. No evident direct relationships are established between intensity of turnovers and eustatic fluctuations. However, the changes in the diversity structure recorded with the Gower Index provide evidence that eustatic lowstands were more favorable for intensification in these changes.     

New insights into early land ecosystems: a glimpse of a lilliputian world

Small, relatively uncompressed, very fragmentary plant remains (mesofossils) are described from a Silurian (P ídolí) and a Lower Devonian (Lochkovian) locality in the Welsh Borderland. Excellent cellular preservation provides characters leading to the demonstration of diversity in plants of simple gross morphology and allows deliberations on functional anatomy (e.g. of stomata), and reproductive biology (including development and dehiscence of sporangia). A survey of in-situ spores is presented, and preliminary comparisons made with dispersed spore assemblages especially in relation to reconstruction of vegetation on local and regional scales. The earliest body fossils of unequivocal terrestrial arthropods isolated from the same locality as the P ídolí plants suggest that the decomposer/microherbivore/predator soil and litter communities found in the Lower and Middle Devonian extend back at least into the Silurian. Evidence for plant—animal interaction in the Lower Devonian comes from spore-dominated coprolites believed to have been produced by litter-feeding myriapods.