Neuroanatomy in a middle Cambrian mollisoniid and the ancestral nervous system organization of chelicerates

• Published in: Nature communications 2022-01, Vol.13 (1), p.410-410, Article 410
• Main Authors: Ortega-Hernández, Javier, Lerosey-Aubril, Rudy, Losso, Sarah R., Weaver, James C.
• Format: Article
• Language: English
• Subjects: 147/135; 631/181/414; 631/181/757; 631/443/376; Anatomy; Animals; Arthropods - anatomy & histology; British Columbia; Cambrian; Central nervous system; Chelicerata; Evolution; Fossils; Gastrointestinal tract; Geologic Sediments; Humanities and Social Sciences; multidisciplinary; Nerves; Nervous system; Nervous System - anatomy & histology; Nervous tissues; Neuroanatomy; Phosphating (coating); Phylogeny; Science; Science (multidisciplinary); Shale; Shales; Time Factors; Ventral nerve cord
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-022-28054-9

Recent years have witnessed a steady increase in reports of fossilized nervous tissues among Cambrian total-group euarthropods, which allow reconstructing the early evolutionary history of these animals. Here, we describe the central nervous system of the stem-group chelicerate Mollisonia symmetrica from the mid-Cambrian Burgess Shale. The fossilized neurological anatomy of M . symmetrica includes optic nerves connected to a pair of lateral eyes, a putative condensed cephalic synganglion, and a metameric ventral nerve cord. Each trunk tergite is associated with a condensed ganglion bearing lateral segmental nerves, and linked by longitudinal connectives. The nervous system is preserved as reflective carbonaceous films underneath the phosphatized digestive tract. Our results suggest that M. symmetrica illustrates the ancestral organization of stem-group Chelicerata before the evolution of the derived neuroanatomical characters observed in Cambrian megacheirans and extant representatives. Our findings reveal a conflict between the phylogenetic signals provided by neuroanatomical and appendicular data, which we interpret as evidence of mosaic evolution in the chelicerate stem-lineage. Here, the authors report a preserved central nervous system in the soft-bodied stem-group chelicerate Mollisonia symmetrica from the mid-Cambrian Burgess Shale. The neuroanatomy described here is proposed to represent the ancestral state for the stem group Chelicerata.