A giant nektobenthic radiodont from the Burgess Shale and the significance of hurdiid carapace diversity

Caron, Jean‐Bernard; Moysiuk, Joseph

doi:10.1098/rsos.210664

Cited by 448 publications

(43 citation statements)

References 44 publications

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“…Most specimens were collected by the Royal Ontario Museum between 2018 and 2022 along Tokumm Creek in Kootenay National Park, British Columbia (figure 1a). The locality is approximately 6 km northwest of the Marble Canyon quarry [15][16][17][18][19] (figure 1a). At this new locality, Ursactis occurs in two stratigraphic intervals in the upper shale portion of the Burgess Shale Formation, approximately 13.0 and 25.8 m below the contact with the overlying Eldon Formation (figure 1b,c).…”

Section: Fossil Materials and Geological Settingmentioning

confidence: 99%

First record of growth patterns in a Cambrian annelid

2023

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Early annelid evolution is mostly known from 13 described species from Cambrian Burgess Shale-type Lagerstätten. We introduce a new exceptionally well-preserved polychaete, Ursactis comosa gen. et sp. nov., from the Burgess Shale (Wuliuan Stage). This small species (3–15 mm) is the most abundant Cambrian polychaete known to date. Most specimens come from Tokumm Creek, a new Burgess Shale locality in northern Kootenay National Park, British Columbia, Canada. Ursactis has a pair of large palps, thin peristomial neurochaetae and biramous parapodia bearing similarly sized capillary neurochaetae and notochaetae, except for segments six to nine, which also have longer notochaetae. The number of segments in this polychaete range between 8 and 10 with larger individuals having 10 segments. This number of segments in Ursactis is remarkably small compared with other polychaetes, including modern forms. Specimens with 10 segments show significant size variations, and the length of each segment increases with the body length, indicating that body growth was primarily achieved by increasing the size of existing segments rather than adding new ones. This contrasts with most modern polychaetes, which typically have a larger number of segments through additions of segments throughout life. The inferred growth pattern in Ursactis suggests that annelids had evolved control over segment addition by the mid-Cambrian.

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Section: Fossil Materials and Geological Settingmentioning

confidence: 99%

First record of growth patterns in a Cambrian annelid

2023

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“…Radiodontans also radiated based on a much broader diversity of specializations involving the cheirae (Moysiuk & Caron, 2021), which also possibly includes sediment sifting (Moysiuk & Caron, 2019a; Caron & Moysiuk, 2021; but see De Vivo et al ., 2021), that translated into a significantly greater disparity for these appendages (Aria & Caron, 2015; De Vivo et al ., 2021). Similar observations can be made about the variety of shapes realized by other arthrodized limbs and arthropod body segments, by comparison with the rather conservative morphology of lobopodians.…”

Section: The Panarthropod Cradle and A ‘Cambrian Planktonic Revolution’mentioning

confidence: 99%

The origin and early evolution of arthropods

Aria

2022

Biological Reviews

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The rise of arthropods is a decisive event in the history of life. Likely the first animals to have established themselves on land and in the air, arthropods have pervaded nearly all ecosystems and have become pillars of the planet's ecological networks. Forerunners of this saga, exceptionally well-preserved Palaeozoic fossils recently discovered or re-discovered using new approaches and techniques have elucidated the precocious appearance of extant lineages at the onset of the Cambrian explosion, and pointed to the critical role of the plankton and hard integuments in early arthropod diversification. The notion put forward at the beginning of the century that the acquisition of extant arthropod characters was stepwise and represented by the majority of Cambrian fossil taxa is being rewritten. Although some key traits leading to Euarthropoda are indeed well documented along a diversified phylogenetic stem, this stem led to several speciose and ecologically diverse radiations leaving descendants late into the Palaeozoic, and a large part, if not all of the Cambrian euarthropods can now be placed on either of the two extant lineages: Mandibulata and Chelicerata. These new observations and discoveries have altered our view on the nature and timing of the Cambrian explosion and clarified diagnostic characters at the origin of extant arthropods, but also raised new questions, especially with respect to cephalic plasticity. There is now strong evidence that early arthropods shared a homologous frontalmost appendage, coined here the cheira, which likely evolved into antennules and chelicerae, but other aspects, such as brain and labrum evolution, are still subject to active debate. The early evolution of panarthropods was generally driven by increased mastication and predation efficiency and sophistication, but a wealth of recent studies have also highlighted the prevalent role of suspension-feeding, for which early panarthropods developed their own adaptive feedback through both specialized appendages and the diversification of small, morphologically differentiated larvae. In a context of general integumental differentiation and hardening across Cambrian metazoans, arthrodization of body and limbs notably prompted two diverging strategies of basipod differentiation, which arguably became founding criteria in the divergence of total-groups Mandibulata and Chelicerata. The kinship of trilobites and their relatives remains a source of disagreement, but a recent topological solution, termed the 'deep split', could embed Artiopoda as sister taxa to chelicerates and constitute definitive support for Arachnomorpha. Although Cambrian fossils have been critical to all these findings, data of exceptional quality have also been accumulating from other Palaeozoic Konservat-Lagerstätten, and a better integration of this information promises a much more complete and elaborate picture of early arthropod evolution in the near future. From the broader perspective of a total-evidence approach to the understanding of life's history, and ...

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“…The prolate, box-like shape of the bell provides indirect evidence of rowing propulsion and predatory habit based on cubozoan analogues. Burgessomedusa shows that pelagic Cambrian ecosystems were not uniquely dominated by large arthropod predators such as Anomalocaris [30] and Titanokorys [50], but that they also harboured a diversity of other predators including chaetognaths [44,51], ctenophores [47] and jellyfish.…”

Section: Discussionmentioning

confidence: 99%

A macroscopic free-swimming medusa from the middle Cambrian Burgess Shale

Moon,

Caron,

Moysiuk

2023

Proc. R. Soc. B.

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Cnidarians are regarded as one of the earliest-diverging animal phyla. One of the hallmarks of the cnidarian body plan is the evolution of a free-swimming medusa in some medusozoan classes, but the origin of this innovation remains poorly constrained by the fossil record and molecular data. Previously described macrofossils, putatively representing medusa stages of crown-group medusozoans from the Cambrian of Utah and South China, are here reinterpreted as ctenophore-grade organisms. Other putative Ediacaran to Cambrian medusozoan fossils consist mainly of microfossils and tubular forms. Here we describe Burgessomedusa phasmiformis gen. et sp. nov., the oldest unequivocal macroscopic free-swimming medusa in the fossil record. Our study is based on 182 exceptionally preserved body fossils from the middle Cambrian Burgess Shale (Raymond Quarry, British Columbia, Canada). Burgessomedusa possesses a cuboidal umbrella up to 20 cm high and over 90 short, finger-like tentacles. Phylogenetic analysis supports a medusozoan affinity, most likely as a stem group to Cubozoa or Acraspeda (a group including Staurozoa, Cubozoa and Scyphozoa). Burgessomedusa demonstrates an ancient origin for the free-swimming medusa life stage and supports a growing number of studies showing an early evolutionary diversification of Medusozoa, including of the crown group, during the late Precambrian–Cambrian transition.

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A giant nektobenthic radiodont from the Burgess Shale and the significance of hurdiid carapace diversity

Cited by 448 publications

References 44 publications

First record of growth patterns in a Cambrian annelid

First record of growth patterns in a Cambrian annelid

The origin and early evolution of arthropods

A macroscopic free-swimming medusa from the middle Cambrian Burgess Shale

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