Caryosyntrips : a radiodontan from the Cambrian of Spain, USA and Canada

Caryosyntrips appendages have previously been reported from the Burgess Shale (Cambrian, Stage 5), British Columbia, Canada. New specimens of the genus are here reported from the Wheeler Formation (Cambrian, Drumian) and Langston Formation, Spence Shale Member (Cambrian, Stage 5), Utah, USA. The original Burgess Shale specimens are re-examined alongside the new specimens. Caryosyntrips is shown to have paired ventral spines on each podomere. Three species of Caryosyntrips are recognised: C. serratus Daley and Budd, C. camurus nov. sp. and C. durus nov. sp., differentiated by the overall shape of their appendages and arrangement of dorsal and ventral spines. These differences have potential implications for the feeding methods employed by different species of Caryosyntrips. A specimen collected from the upper Valdemiedes Formation of Spain (Cambrian, Stage 4), previously described as the lobopodian Mureropodia apae Gámez Vintaned et al., is reinterpreted as a Caryosyntrips appendage. This identification is supported by the overall shape of the fossil, and the presence, orientation, and height:width ratio, of ventral spines. However the dorsal surface of the appendage is not well preserved, and the appendage and its ventral spines are larger than other known Caryosyntrips. Therefore it is left in open nomenclature as C. cf. camurus. These new finds increase the temporal range of Caryosyntrips (Cambrian Series 2, Stage 4 to Series 3, Drumian) and the geographic range to a new continent, Gondwana

The significance of Anomalocaris and other Radiodonta for understanding paleoecology and evolution during the Cambrian explosion

One of the most widespread and diverse animal groups of the Cambrian Explosion is a clade of stem lineage arthropods known as Radiodonta, which lived exclusively in the early Paleozoic. First reported in 1892 with Anomalocaris canadensis, radiodonts are now one of the best known early animal groups with excellent representation in the fossil record, and are ubiquitous components of <jats:italic>Konservat-Lagerstätten</jats:italic> from the Cambrian and the Early Ordovician. These large swimmers were characterised by a segmented body bearing laterally-oriented flaps, and a head with a distinct radial oral cone, a pair of large frontal appendages adapted for different feeding modes, compound eyes on stalks, and prominent head carapaces. Radiodonts inform on the paleoecology of early animal communities and the steps involved in euarthropod evolution. Four families within Radiodonta have been established. The raptorial predator families Anomalocarididae and Amplectobeluidae were dominant early in the evolutionary history of Radiodonta, but were later overtaken by the mega-diverse and widespread Hurdiidae, which has a more generalised sediment-sifting predatory mode. Suspension feeding, notably in the families Tamisiocarididae and Hurdiidae, also evolved at least twice in the history of the clade. The well-preserved anatomical features of the radiodont body and head have also provided insights into the evolution of characteristic features of Euarthropoda, such as the biramous limbs, compound eyes, and organisation of the head. With 37 species recovered from all major paleocontinents of the Cambrian and Early Ordovician, Radiodonta provides a unique opportunity for revealing evolutionary patterns during the Cambrian Explosion

Radiodont frontal appendages from the Fezouata Biota (Morocco) reveal high diversity and ecological adaptations to suspension-feeding during the Early Ordovician

Introduction: The Early Ordovician Fezouata Shale Formation (485–475Ma, Morocco) is a critical source of evidence for the unfolding Great Ordovician Biodiversification Event (GOBE), the largest radiation in animal diversity during the Paleozoic. The Fezouata Shale preserves abundant remains of ancient marine organisms, including hundreds of specimens of radiodonts, a diverse and globally distributed group of stem lineage arthropods that first appeared as raptorial predators during the Cambrian Explosion. Methods: In this work, we study 121 radiodont frontal appendages from the Fezouata Shale. Frontal appendages are the most commonly preserved body parts of radiodonts, and their well-preserved anatomical characters are crucial for describing taxonomic diversity at the species level, while also providing essential data on mode of life, paleoecology, and feeding behaviour. Results: Our data allow for a systematic review of suspension-feeding Hurdiidae radiodonts from Fezouata. The genus Pseudoangustidontus is recognised as a radiodont and ascribed to Hurdiidae, and a new second species of this genus is identified, Pseudoangustidontus izdigua sp. nov. Aegirocassis benmoulai is also reviewed and its diagnosis amended with new details of differentiated endites in this appendage. The morphological similarity between both genera allows us to erect Aegirocassisinae subfam. nov., which groups together the suspension-feeding hurdiids of the Fezouata Shale. Discussion: Suspension-feeding radiodont appendages are more abundant than those of sediment sifting or raptorial radiodonts, with the Fezouata Shale showing the highest diversity of suspension-feeding radiodonts in the history of the group. This dominance and diversity of frontal filter-feeding appendages follows the “Ordovician Plankton Revolution”, which started in the upper Cambrian and saw a huge radiation in plankton diversity

QUANTITATIVE ANALYSIS OF REPAIRED AND UNREPAIRED DAMAGE TO TRILOBITES FROM THE CAMBRIAN (STAGE 4, DRUMIAN) IBERIAN CHAINS, NE SPAIN

Repaired fossil skeletons provide the opportunity to study predation rates, repair mechanisms, and ecological interactions in deep time. Trilobites allow the study of repaired damage over long time periods and large geographic areas due to their longevity as a group, global distribution, and well-preserved mineralized exoskeletons. Repair frequencies on trilobites from three sites representing offshore marine environments in the Iberian Chains (Spain) show no injuries on 45 complete redlichiid thoraces from Minas Tierga (Huérmeda Formation, Cambrian Series 2, Stage 4), or 23 complete Eccaparadoxides pradoanus thoraces from Mesones de Isuela (Murero Formation, Cambrian Series 3, Drumian). Ten injuries on 69 E. pradoanus thoraces from Purujosa (Murero Formation, Cambrian Series 3, Drumian) were noted. There is no evidence for laterally asymmetric predation or size selection on the trilobites in this study. Weak evidence for selection for the rear of the thorax is documented. A series of injured trilobites illustrates four stages of the healing process. Analysis of injury locations and frequency suggests that injuries to these trilobites are predatory in origin. Semilandmark analysis of previously described exoskeletons with unrepaired damage assigned to the ichnotaxon Bicrescomanducator serratus alongside newly collected damaged exoskeletons from Purujosa (Mansilla and Murero Formations, Stage 5, Drumian), Mesones de Isuela (Murero Formation, Drumian), and Minas Tierga (Huérmeda Formation, Stage 4) found that shapes of biotic and abiotic breaks could not be distinguished.Department of Zoology, University of Oxford, Reino UnidoInstitute of Earth Sciences, University of Lausanne, SuizaPaleoscience Research Centre School of Environmental and Rural Science, University of New England, AustraliaUnidad de Zaragoza, Instituto Geológico y Minero de España, EspañaUnidad Asociada en Ciencias de la Tierra, Universidad de Zaragoza, Españ

Vertically migrating Isoxys and the early Cambrian biological pump.

The biological pump is crucial for transporting nutrients fixed by surface-dwelling primary producers to demersal animal communities. Indeed, the establishment of an efficient biological pump was likely a key factor enabling the diversification of animals over 500 Myr ago during the Cambrian explosion. The modern biological pump operates through two main vectors: the passive sinking of aggregates of organic matter, and the active vertical migration of animals. The coevolution of eukaryotes and sinking aggregates is well understood for the Proterozoic and Cambrian; however, little attention has been paid to the establishment of the vertical migration of animals. Here we investigate the morphological variation and hydrodynamic performance of the Cambrian euarthropod Isoxys. We combine elliptical Fourier analysis of carapace shape with computational fluid dynamics simulations to demonstrate that Isoxys species likely occupied a variety of niches in Cambrian oceans, including vertical migrants, providing the first quantitative evidence that some Cambrian animals were adapted for vertical movement in the water column. Vertical migration was one of several early Cambrian metazoan innovations that led to the biological pump taking on a modern-style architecture over 500 Myr ago

Biogenic Iron Preserves Structures during Fossilization: A Hypothesis

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First report of paired ventral endites in a hurdiid radiodont.

BACKGROUND: Radiodonta, large Palaeozoic nektonic predators, occupy a pivotal evolutionary position as stem-euarthropods and filled important ecological niches in early animal ecosystems. Analyses of the anatomy and phylogenetic affinity of these large nektonic animals have revealed the origins of the euarthropod compound eye and biramous limb, and interpretations of their diverse feeding styles have placed various radiodont taxa as primary consumers and apex predators. Critical to our understanding of both radiodont evolution and ecology are the paired frontal appendages; however, the vast differences in frontal appendage morphology between and within different radiodont families have made it difficult to identify the relative timings of character acquisitions for this body part. RESULTS: Here we describe a new genus of hurdiid, Ursulinacaris, from the middle Cambrian (Miaolingian, Wuliuan) Mount Cap Formation (Northwest Territories, Canada) and Jangle Limestone (Nevada, USA). Ursulinacaris has the same organisation as other hurdiid frontal appendages, with elongate endites on the first five podomeres in the distal articulated region and auxiliary spines on the distal margin of endites only. Unlike all other hurdiid genera, which possess a single row of elongated and blade-like ventral endites, this taxon uniquely bears paired slender endites. CONCLUSION: The blade-like endite morphology is shown to be a hurdiid autapomorphy. Two other frontal appendage characters known only in hurdiids, namely auxiliary spines on the distal margin of endites only, and elongate endites on the first five podomeres in the distal articulated region only, predate this innovation

Novel marrellomorph moulting behaviour preserved in the Lower Ordovician Fezouata Shale, Morocco

Exoskeleton moulting is the process of shedding the old exoskeleton to enable growth, development and repair, representing a crucial recurrent event in the life histories of all euarthropods. The fossil record of moulting allows us to interpret the evolution of this important behaviour and its impact on the evolutionary trajectories of extinct and extant euarthropods. Current knowledge of Palaeozoic euarthropod moulting relates largely to trilobites, with fewer examples known for non-mineralised extinct taxa from early in euarthropod evolutionary history. We describe exuviae from a marrellid marrellomorph found abundantly in the Early Ordovician Fezouata Shale Lagerstätte of Morocco, which allow a novel reconstruction, the second ever, of marrellid moulting behaviours. We identify the moulting suture location, describe preserved moulting assemblages, and suggest how its moulting behaviours are adaptive to its morphology. Several specimens represent complete and nearly complete assemblages and additional disarticulated specimens confirm the suture line location. The suture line is located between the mediolateral and posterolateral spine pairs, dividing the cephalic shield into anterior and posterior parts. The Fezouata marrellid likely exited the exoskeleton during exuviation using posterior and upwards movements, analogous in terms of movement to lobster-like extant arthropods. The suture line is comparable in the closely related marrellid Mimetaster, and distinctive from that of another marrellid, Marrella splendens, which has an exuvial opening at the anterior of the cephalic shield and exited the exoskeleton anteriorly. This difference in moulting behaviour as compared to Marrella is likely adaptive to the greater complexity of the Fezouata marrellid, with upwards rather than forwards movement presumably providing a more favourable angle for the extraction of complex spines. This description of the moulting behaviours and related morphological features of marrellomorphs expands our understanding of this crucial characteristic in extinct euarthropods