title: Preservational Pathways of Corresponding Brains of a Cambrian Euarthropod.
abstract: 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 studiesshow 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. 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. 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.
authors.affiliation: Yunnan Key Laboratory for Palaeobiology, Yunnan University, Kunming 650091, China; Department of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK. Electronic address: x.ma@nhm.ac.uk.
authors.forename: Xiaoya
authors.initials: X
authors.lastname: Ma
authors.affiliation: Department of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK.
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Edgecombe
authors.affiliation: Yunnan Key Laboratory for Palaeobiology, Yunnan University, Kunming 650091, China.
authors.forename: Xianguang
authors.initials: X
authors.lastname: Hou
authors.affiliation: Imaging and Analysis Centre, The Natural History Museum, Cromwell Road, London SW7 5BD, UK.
authors.forename: Tomasz
authors.initials: T
authors.lastname: Goral
authors.affiliation: Department of Neuroscience, University of Arizona, Tucson, AZ 85721, USA; Center for Insect Science, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Strausfeld
mesh_terms: D000818:Animals; D001181:Arthropods / Q000033:anatomy & histology*; D005075:Biological Evolution; D001921:Brain / Q000033:anatomy & histology; D005580:Fossils / Q000033:anatomy & histology*; D015203:Reproducibility of Results
keywords: Cambrian; Chengjiang biota; arthropod; brains; exceptional preservation; geochemistry