Hyoliths with pedicles illuminate the origin of the brachiopod body plan

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.

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“…The characters were partitioned into neomorphic and transformational character groups [15,16]. Model testing was conducted in IQ-Tree 1.6.9 [17].…”

Section: (B) Phylogenetic Analysesmentioning

confidence: 99%

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

2019

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“…In contrast, the high shell volume in Cambro-Ordovician nautiloids denotes a lower metabolic rate and a higher physiological efficiency (O'Dor et al, 1993;Boutilier et al, 1996). This metabolic trend mirrors that observed in the brachiopod total group through the Cambrian (Sun et al, 2018), suggesting that early neocoleoid-like organisms such as Nectocaris and Nectocotis were largely supplanted by metabolically conservative, externally shelled, passively buoyant nautiloids in response to declining oxygen and energy availability in the late Cambrian / early Ordovician.…”

Section: Discussionmentioning

confidence: 67%

An Ordovician nectocaridid hints at an endocochleate origin of Cephalopoda

Smith

2019

J. Paleontol.

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Nectocaridids are soft-bodied Cambrian organisms that have been controversially interpreted as primitive cephalopods, at odds with the long-held belief that these mollusks evolved from a shell-bearing ancestor. Here, I document a new nectocaridid from the Whetstone Gulf Formation, extending the group's range into the Late Ordovician. Nectocotis rusmithi n. gen. n. sp. possesses a robust internal element that resembles a non-mineralized phragmocone or gladius. Nectocaridids can be accommodated in the cephalopod total group if the earliest cephalopods (1) inherited a non-mineralized shell field from the ancestral mollusk; and (2) internalized this shell field. This evolutionary scenario would overturn the traditional ectocochleate, Nautilus-like reconstruction of the ancestral cephalopod, and indicate a trend towards increased metabolic efficiency through the course of Cambrian–Ordovician evolution.UUID: http://zoobank.org/ed594200-37b9-4642-bd8f-4fb72dc544eb

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“…; Sun et al . ). Together, these two lines of evidence suggest that decollation may have evolved multiple times in different clades.…”

Section: Discussionmentioning

confidence: 97%

Periodic shell decollation as an ecology‐driven strategy in the early Cambrian Cupitheca

Sun

Yin

et al. 2019

Palaeontology

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Shell decollation is a growth strategy that has been adopted by a number of invertebrate taxa to offset the metabolic and ecological disadvantages of shell growth. However, little is known about the origin and evolution of this process. We here describe well-preserved specimens of the hyolith Cupitheca decollata sp. nov. preserving the decollation process, from the early Cambrian Yu'anshan Formation (c. 518 Ma) of South China. Based on a large number of specimens collectively representing different developmental stages, we use high-resolution X-ray microtomography and scanning electronic microscopy to reconstruct the process of decollation in this taxon. Cupitheca is among the earliest known small shelly fossils, and thus our discovery confirms that periodic decollation had evolved by the onset of the Cambrian explosion, reflecting the high intensity of the predator-prey arms race in early Cambrian ecosystems. A comparison between the decollation processes of Cupitheca and other shelly invertebrates suggests that periodic decollation and the associated molecular mechanisms of calcium dissolution, uptake, allocation and deposition may have had multiple independent origins.

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Hyoliths with pedicles illuminate the origin of the brachiopod body plan

Cited by 36 publications

References 49 publications

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

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

An Ordovician nectocaridid hints at an endocochleate origin of Cephalopoda

Periodic shell decollation as an ecology‐driven strategy in the early Cambrian Cupitheca

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