A three-eyed radiodont with fossilized neuroanatomy informs the origin of the arthropod head and segmentation

Moysiuk, Joseph; Caron, Jean‐Bernard

doi:10.1016/j.cub.2022.06.027

Cited by 29 publications

(51 citation statements)

References 58 publications

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“…Multiple lines of evidence support this interpretation. Firstly, while no palaeoneurological tissues have been reported from an opabiniid, neural tissues are known from taxa which phylogenetically bracket opabiniids and the Castle Bank specimens: Kerygmachela and the radiodont Lyrarapax 3 , 25 , which support a protocerebral affinity (note that fossilised neural tissues in a second radiodont taxon, Stanleycaris , argued to support a deutocerebral affinity for radiodont appendages 51 can also be interpreted as innervated by the protocerebrum 52 ). Secondly all members of the euarthropod lower stem group are widely thought to have a head composed of a single segment that bears one pair of appendages 11 , 14 (though see Ref.…”

Section: Discussionmentioning

confidence: 99%

“…Secondly all members of the euarthropod lower stem group are widely thought to have a head composed of a single segment that bears one pair of appendages 11 , 14 (though see Ref. 51 for an alternative view that is itself open to reinterpretation 52 ). In opabiniids and the Castle Bank specimens, only a single proboscis is present in the head region, and no other appendage-like structures.…”

Section: Discussionmentioning

confidence: 99%

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Ordovician opabiniid-like animals and the role of the proboscis in euarthropod head evolution

et al. 2022

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A crucial step in the evolution of Euarthropoda (chelicerates, myriapods, pancrustaceans) was the transition between fossil groups that possessed frontal appendages innervated by the first segment of the brain (protocerebrum), and living groups with a protocerebral labrum and paired appendages innervated by the second brain segment (deutocerebrum). Appendage homologies between the groups are controversial. Here we describe two specimens of opabiniid-like euarthropods, each bearing an anterior proboscis (a fused protocerebral appendage), from the Middle Ordovician Castle Bank Biota, Wales, UK. Phylogenetic analyses support a paraphyletic grade of stem-group euarthropods with fused protocerebral appendages and a posterior-facing mouth, as in the iconic Cambrian panarthropod Opabinia. These results suggest that the labrum may have reduced from an already-fused proboscis, rather than a pair of arthropodized appendages. If some shared features between the Castle Bank specimens and radiodonts are considered convergent rather than homologous, phylogenetic analyses retrieve them as opabiniids, substantially extending the geographic and temporal range of Opabiniidae.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Ordovician opabiniid-like animals and the role of the proboscis in euarthropod head evolution

et al. 2022

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“…This dataset, referred to as dataset 1, was pruned to include only euarthropod and stem-euarthropod species and applicable characters. New hymenocarine characters and taxa were included from previous publications [ 37 ], as well as characters related to the frontal appendages from a different dataset [ 38 ], to a total of 113 taxa (electronic supplementary material, table S5) and 300 characters. All characters were discrete, binary or multi-state, and equally weighted.…”

Section: Methodsmentioning

confidence: 99%

The problematic Cambrian arthropod Tuzoia and the origin of mandibulates revisited

Izquierdo-López

Caron

2022

R. Soc. open sci.

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The origin of mandibulates, the hyperdiverse arthropod group that includes pancrustaceans and myriapods, dates back to the Cambrian. Bivalved arthropod groups such as hymenocarines have been argued to be early mandibulates, but many species are still poorly known, and their affinities remain uncertain. One of the most common and globally distributed Cambrian bivalved arthropods is Tuzoia . Originally described in 1912 from the Burgess Shale based on isolated carapaces, its full anatomy has remained largely unknown. Here, we describe new specimens of Tuzoia from the Canadian Burgess Shale (Wuliuan, Cambrian) showcasing exceptionally preserved soft tissues, allowing for the first comprehensive reconstruction of its anatomy, ecology and evolutionary affinities. The head bears antennae and differentiated cephalic appendages. The body is divided into a cephalothorax, a homonomous trunk bearing ca 10 pairs of legs with heptopodomerous endopods and enlarged basipods, and a tail fan with two pairs of caudal rami. These traits suggest that Tuzoia swam along the seafloor and used its spinose legs for predation or scavenging. Tuzoia is retrieved by a Bayesian phylogenetic analysis as an early mandibulate hymenocarine lineage, exemplifying the rapid diversification of this group in open marine environments during the Cambrian Explosion.

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“…This reexamination aligns with the recent description of similar structures in another radiodontan, Stanleycaris hirpex . [ 43 ] This taxon satisfies the best scenario criteria for the identification of a fossilized brain for similar reasons as Lyrarapax unguispinus does, with the help of multiple, particularly well‐preserved specimens. Although it is not entirely clear whether part of the foregut or esophagus could be associated with the remains described as the CNS, the structures identified as brain, optic tracts and appendicular nerves form a coherent ensemble characterized by dense kerogen remains.…”

Section: Case Analysesmentioning

confidence: 99%

“…This would therefore support an optic neuropil identity for the radiodontan ‘frontal lobes,’ with the base and first neuropil possibly lying on a slightly different plane than the distal neuropils. Based on Stanleycaris , it was recently proposed that these lobes could be related to a large ancestral median eye, [ 43 ] but the connection between the median eye and the rest of the protocerebrum in this taxon is not clearly preserved as it is in the anterior lobes of Lyrarapax or the proximal optic neuropils of Fuxianhuia .…”

Section: What Do We Really Know About Nervous Systems In Early Arthro...mentioning

confidence: 99%

Interpreting fossilized nervous tissues

et al. 2023

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Paleoneuranatomy is an emerging subfield of paleontological research with great potential for the study of evolution. However, the interpretation of fossilized nervous tissues is a difficult task and presently lacks a rigorous methodology. We critically review here cases of neural tissue preservation reported in Cambrian arthropods, following a set of fundamental paleontological criteria for their recognition. These criteria are based on a variety of taphonomic parameters and account for morphoanatomical complexity. Application of these criteria shows that firm evidence for fossilized nervous tissues is less abundant and detailed than previously reported, and we synthesize here evidence that has stronger support. We argue that the vascular system, and in particular its lacunae, may be central to the understanding of many of the fossilized peri‐intestinal features known across Cambrian arthropods. In conclusion, our results suggest the need for caution in the interpretation of evidence for fossilized neural tissue, which will increase the accuracy of evolutionary scenarios. Also see the video abstract here: https://youtu.be/2_JlQepRTb0

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A three-eyed radiodont with fossilized neuroanatomy informs the origin of the arthropod head and segmentation

Cited by 29 publications

References 58 publications

Ordovician opabiniid-like animals and the role of the proboscis in euarthropod head evolution

Ordovician opabiniid-like animals and the role of the proboscis in euarthropod head evolution

The problematic Cambrian arthropod Tuzoia and the origin of mandibulates revisited

Interpreting fossilized nervous tissues

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