title: Unlocking the early fossil record of the arthropod central nervous system.
abstract: Extant panarthropods (euarthropods, onychophorans and tardigrades) are hallmarked by stunning morphological and taxonomic diversity, but their central nervous systems (CNS) are relatively conserved. The timing of divergences of the ground pattern CNS organization of the major panarthropod clades has been poorly constrained because of a scarcity of data from their early fossil record. Although the CNS has been documented in three-dimensional detail in insects from Cenozoic ambers, it is widely assumed that these tissues are too prone to decay to withstand other styles of fossilization or geologically older preservation. However, Cambrian Burgess Shale-type compressions have emerged as sources of fossilized brains and nerve cords. CNS in these Cambrian fossils are preserved as carbon films or as iron oxides/hydroxides after pyrite in association with carbon. Experiments with carcasses compacted in fine-grained sediment depict preservation of neural tissue for a more prolonged temporal window than anticipated by decay experiments in other media. CNS and compound eye characters in exceptionally preserved Cambrian fossils predict divergences of the mandibulate and chelicerate ground patterns by Cambrian Stage 3 (ca 518 Ma), a dating that is compatible with molecular estimates for these splits.
authors.affiliation: Department of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK g.edgecombe@nhm.ac.uk.
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Edgecombe
authors.affiliation: Department of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK Yunnan Key Laboratory for Palaebiology, Yunnan University, Kunming 650091, People's Republic of China.
authors.forename: Xiaoya
authors.initials: X
authors.lastname: Ma
authors.affiliation: Department of Neuroscience and Center for Insect Science, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Nicholas J
authors.identifier: http://orcid.org/0000-0002-1115-1774
authors.initials: NJ
authors.lastname: Strausfeld
mesh_terms: D000818:Animals; D001181:Arthropods / Q000033:anatomy & histology* / Q000145:classification*; D002490:Central Nervous System / Q000033:anatomy & histology*; D005580:Fossils; D010802:Phylogeny
keywords: Arthropoda; Burgess Shale; Cambrian; Chengjiang; brains