Furongian (Jiangshanian) occurrences of radiodonts in Poland and South China and the fossil record of the Hurdiidae

The Furongian period represents an important gap in the fossil record of most groups of non-biomineralizing organisms, owing to a scarcity of Konservat-Lagerstätten of that age. The most significant of these deposits, the Jiangshanian strata of the Sandu Formation near Guole Township (Guangxi, South China), have yielded a moderately abundant, but taxonomically diverse soft-bodied fossil assemblage, which provides rare insights into the evolution of marine life at that time. In this contribution, we report the first discovery of a radiodont fossil from the Guole Konservat-Lagerstätte. The specimen is an incomplete frontal appendage of a possibly new representative of the family Hurdiidae. It is tentatively interpreted as composed of seven podomeres, six of which bearing laminiform endites. The best preserved of these endites is especially long, and it bears short auxiliary spines that greatly vary in size. This is the second occurrence of hurdiids and more generally radiodonts in the Furongian, the first being the external mould of an oral cone from Jiangshanian strata of the Wiśniówka Sandstone Formation in Poland. Restudy of this Polish specimen confirms that it belongs to a hurdiid radiodont and best compares to Peytoia. The family Hurdiidae includes the oldest (basal Cambrian Epoch 2) and youngest (Early Ordovician, possibly Early Devonian) representatives of the Radiodonta and as such, has the longest stratigraphical range of the group. Yet, hurdiids only became prominent components of marine ecosystems during the middle Cambrian (Miaolingian), and their fossil record in younger strata remains limited.

The diverse radiodont fauna from the Marjum Formation of Utah, USA (Cambrian: Drumian)

Radiodonts have long been known from Cambrian deposits preserving non-biomineralizing organisms. In Utah, the presence of these panarthropods in the Spence and Wheeler (House Range and Drum Mountains) biotas is now well-documented. Conversely, radiodont occurrences in the Marjum Formation have remained scarce. Despite the large amount of work undertaken on its diverse fauna, only one radiodont (Peytoia) has been reported from the Marjum Biota. In this contribution we quadruple the known radiodont diversity of the Marjum fauna, with the description of the youngest members of two genera, Caryosyntrips and Pahvantia, and that of a new taxon Buccaspinea cooperi gen. et sp. nov. This new taxon can be identified from its large oral cone bearing robust hooked teeth with one, two, or three cusps, and by the unique endite morphology and organisation of its frontal appendages. Appendages of at least 12 podomeres bear six recurved plate-like endites proximal to up to four spiniform distal endites. Pahvantia hastata specimens from the Marjum Formation are particularly large, but otherwise morphologically indistinguishable from the carapace elements of this species found in the Wheeler Formation. One of the two new Caryosyntrips specimens can be confidently assigned to C. camurus. The other bears the largest spines relative to appendage length recorded for this genus, and possesses endites of variable size and unequal spacing, making its taxonomic assignment uncertain. Caryosyntrips, Pahvantia, and Peytoia are all known from the underlying Wheeler Formation, whereas isolated appendages from the Spence Shale and the Wheeler Formation, previously assigned to Hurdia, are tentatively reidentified as Buccaspinea. Notably, none of these four genera occurs in the overlying Weeks Formation, providing supporting evidence of a faunal restructuring around the Drumian-Guzhangian boundary. The description of three additional nektonic taxa from the Marjum Formation further documents the higher relative proportion of free-swimming species in this biota compared to those of the Wheeler and Weeks Lagerstätten. This could be related to a moderate deepening of the basin and/or changing regional ocean circulation at this time.

A new hurdiid radiodont from the Burgess Shale evinces the exploitation of Cambrian infaunal food sources

Radiodonts, a clade of Cambro-Devonian stem group euarthropods, have classically been regarded as nektonic apex predators. However, many aspects of radiodont morphology and ecology have remained unclear because of the typically fragmentary nature of fossil material. Here, we describe a new hurdiid radiodont based on abundant and exceptionally well-preserved fossils from the Burgess Shale (Marble Canyon area, British Columbia, Canada). Cambroraster falcatus gen. et sp. nov . is characterized by an extra-large horseshoe-shaped head carapace, bearing conspicuous posterolateral spinous processes, and partially covering a short trunk with eight pairs of lateral flaps. Each of the pair of frontal appendages possess five mesially curving rake-like endites equipped with a series of anteriorly directed hooked spines, altogether surrounding the oral cone. This feeding apparatus suggests a micro to macrophagous sediment-sifting feeding ecology. Cambroraster illuminates the evolution of Hurdiidae and evinces the exploitation of the diversifying infauna by these large and specialized nektobenthic carnivores in the aftermath of the Cambrian explosion.

A new radiodontan oral cone with a unique combination of anatomical features from the early Cambrian Guanshan Lagerstätte, eastern Yunnan, South China

The radiodontans, including anomalocaridids and their allies, are enigmatic stem-group euarthropods and are the most ancient apex giant predators known from the fossil record. Most studies on their feeding behaviors have emphasized their diverse and abundant raptorial frontal appendages, while the oral cone surrounding the mouth opening in these animals has attracted less attention. At present, three oral cone morphotypes are known, from Anomalocaris Whiteaves, 1892, Peytoia Walcott, 1911, and Hurdia Walcott, 1912, respectively. In this paper, we report on a novel form of radiodontan oral cone from the Guanshan Lagerstätte (Cambrian Series 2, Stage 4) in the Wulongqing Formation, eastern Yunnan, South China. This oral cone is unique in combining features seen in Peytoia/Hurdia and Anomalocaris. It possesses a Peytoia/Hurdia-type ‘tetraradial’ configuration comprising a 32-plate outer ring that consists of four perpendicularly arranged large plates and 28 small plates, in addition to furrowed folds and scale-like nodes on plate surfaces otherwise seen only in Anomalocaris. As an intermediate morphotype, the Guanshan oral cone improves our understanding of the occurrence and morphological disparity of radiodontan oral cones, illuminates future investigations on potentially variable radiodontan feeding mechanisms, and reveals possible evolutionary transformations of these peculiar feeding structures. The resolution of current radiodontan phylogeny would be potentially improved by new knowledge on other body parts apart from frontal appendages in future studies.

Morphology of Anomalocaris canadensis from the Burgess Shale

Recent description of the oral cone of Anomalocaris canadensis from the Burgess Shale (Cambrian Series 3, Stage 5) highlighted significant differences from published accounts of this iconic species, and prompts a new evaluation of its morphology as a whole. All known specimens of A. canadensis, including previously unpublished material, were examined with the aim of providing a cohesive morphological description of this stem lineage arthropod. In contrast to previous descriptions, the dorsal surface of the head is shown to be covered by a small, oval carapace in close association with paired stalked eyes, and the ventral surface bears only the triradial oral cone, with no evidence of a hypostome or an anterior sclerite. The frontal appendages reveal new details of the arthrodial membranes and a narrower cross-section in dorsal view than previously reconstructed. The posterior body region reveals a complex suite of digestive, respiratory, and locomotory characters that include a differentiated foregut and hindgut, a midgut with paired glands, gill-like setal blades, and evidence of muscle bundles and struts that presumably supported the swimming movement of the body flaps. The tail fan includes a central blade in addition to the previously described three pairs of lateral blades. Some of these structures have not been identified in other anomalocaridids, making Anomalocaris critical for understanding the functional morphology of the group as a whole and corroborating its arthropod affinities.

Copepoda (Siphonostomatoida) from Pacific hydrothermal vents and cold seeps, including Dirivultus spinigulatus sp. nov. in Papua New Guinea

Dirivultus spinigulatus sp. nov. (Copepoda: Siphonostomatoida) is described from vestimentiferans at a deep-water hydrothermal site near Lihir Island in the South Pacific. The species is characterized by several features: sexual dimorphism in the second segment of the antennule, the rostrum with lateral spines, the oral cone with four conspicuous spines, the mandible without palp, the maxilla without an axillary seta, the endopod of leg 1 with segments 1 and 2 partly fused, and leg 5 in the female represented by a conspicuous ventrally located spine but in the male by a free segment having setae. A key is included to the 11 genera of the family Dirivultidae, whose members are endemic to hydrothermal vents and cold seeps.