Current Biology
Volume 25, Issue 22, 16 November 2015, Pages 2969-2975
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Report
Preservational Pathways of Corresponding Brains of a Cambrian Euarthropod

https://doi.org/10.1016/j.cub.2015.09.063Get rights and content
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Highlights

  • Brain organization of Cambrian arthropod fossils of Fuxianhuia protensa correspond

  • Fossils resolve tripartite brain organization, cephalic nerves, and optic neuropils

  • SEM and EDX demonstrate that brain traces are carbon films, variably overlaid with pyrite

  • Early diagenetic mineralization is not essential for preservation of labile tissues

Summary

The record of arthropod body fossils is traceable back to the “Cambrian explosion,” marked by the appearance of most major animal phyla. Exceptional preservation provides crucial evidence for panarthropod early radiation. However, due to limited representation in the fossil record of internal anatomy, particularly the CNS, studies usually rely on exoskeletal and appendicular morphology. Recent studies [1, 2, 3] show that despite extreme morphological disparities, euarthropod CNS evolution appears to have been remarkably conservative. This conclusion is supported by descriptions from Cambrian panarthropods of neural structures that contribute to understanding early evolution of nervous systems and resolving controversies about segmental homologies [4, 5, 6, 7, 8, 9, 10, 11, 12]. However, the rarity of fossilized CNSs, even when exoskeletons and appendages show high levels of integrity, brought into question data reproducibility because all but one of the aforementioned studies were based on single specimens [13]. Foremost among objections is the lack of taphonomic explanation for exceptional preservation of a tissue that some see as too prone to decay to be fossilized. Here we describe newly discovered specimens of the Chengjiang euarthropod Fuxianhuia protensa with fossilized brains revealing matching profiles, allowing rigorous testing of the reproducibility of cerebral structures. Their geochemical analyses provide crucial insights of taphonomic pathways for brain preservation, ranging from uniform carbon compressions to complete pyritization, revealing that neural tissue was initially preserved as carbonaceous film and subsequently pyritized. This mode of preservation is consistent with the taphonomic pathways of gross anatomy, indicating that no special mode is required for fossilization of labile neural tissue.

Keywords

Cambrian
Chengjiang biota
arthropod
brains
exceptional preservation
geochemistry

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This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).