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

Abstract

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.

Occurrence of the hurdiid radiodontCambrorasterin the middle Cambrian (Wuliuan) Mantou Formation of North China

“…Although the new specimens are slightly different from the type specimen of C. falcatus in morphology, the Shandong specimens can still be assigned to a similar species to C. falcatus by comparison with other specimens of the type species in various taphonomic conditions. This extends the paleogeographical distribution of this genus beyond the Burgess Shale and even Laurentia, suggesting that although Cambroraster is considered a nektobenthic sediment-sifting feeder (Moysiuk and Caron, 2019), these animals had dispersed over a wide range. In addition, Cambroraster represents the first discovery of hurdiid radiodonts in North China.…”

“…Images were processed using Adobe Photoshop to adjust tone, contrast, and brightness. The morphological terminology about head sclerites used in this paper mainly follows Zeng et al (2017) and Moysiuk and Caron (2019), and the terms describing the frontal appendages are from Daley et al (2013). Measurement directions are expressed, respectively, as sagittal (sag.…”

Exploring abnormal Cambrian-aged trilobites in the Smithsonian collection

“…The slender and elongate auxiliary spines in some Anomalocaris species (Anomalocaris magnabasis Pates et al, in press and A. saron Hou, Bergström & Ahlberg, 1995) is not indicative of a purely durophagous feeding mode (Pates et al, in press). Furthermore, Radiodonta are now considered a group of arthropods with a diverse range of ecologies, from raptorial predation in Anomalocarididae and Amplectobeluidae (e.g., Daley & Edgecombe, 2014;Liu et al, 2018), to sediment sifting in Hurdiidae (e.g., Daley, Budd & Caron, 2013;Moysiuk & Caron, 2019), and filter feeding in Hurdiidae and Tamisiocarididae (Vinther et al, 2014;Van Roy, Daley & Briggs, 2015;Lerosey-Aubril & Pates, 2018). The diversity of feeding modes is supported by the discovery of multiple radiodonts with different inferred ecologies from the same site (Daley & Budd, 2010;Pates et al, in press).…”

A Cambrian fossil from the Chengjiang fauna sharing characters with gilled lobopodians and radiodontans

“…1A), exactly matching the count in Pambdelurion and Kerygmachela [9,16] and at least some radiodontans where the complete body is known [6,17]. Other radiodontans have been described with eight to ten pairs of trunk aps [3,8,18], while Opabinia has fteen. Additionally,Opabinia, Pambdelurion and Kerygmachela have all been interpreted as having both lateral aps and lobopod limbs [9,10]hence the name gilled lobopodians-although at least in Opabinia the lobopod limbs are less obvious and have not been universally accepted [19].…”

“…Some radiodontans achieved body lengths of more than two metres [6], rendering them among the largest Early Palaeozoic animals. Based on the armature of the frontal appendages and evolutionary trends from active predation through to suspension feeding has been proposed [7,8].…”