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ABSTRACT Preservation of neural tissue in early Cambrian arthropods has recently been demonstrated1, to a degree that segmental structures of the head can be associated with individual brain

neuromeres. This association provides novel data for addressing long-standing controversies about the segmental identities of specialized head appendages in fossil taxa2,3. Here we document

neuroanatomy in the head and trunk of a ‘great appendage’ arthropod, _Alalcomenaeus_ sp., from the Chengjiang biota, southwest China, providing the most complete neuroanatomical profile

known from a Cambrian animal. Micro-computed tomography reveals a configuration of one optic neuropil separate from a protocerebrum contiguous with four head ganglia, succeeded by eight

contiguous ganglia in an eleven-segment trunk. Arrangements of optic neuropils, the brain and ganglia correspond most closely to the nervous system of Chelicerata of all extant arthropods,

supporting the assignment of ‘great appendage’ arthropods to the chelicerate total group4,5. The position of the deutocerebral neuromere aligns with the insertion of the great appendage,

indicating its deutocerebral innervation and corroborating a homology between the ‘great appendage’ and chelicera indicated by morphological similarities4,6,7. _Alalcomenaeus_ and

_Fuxianhuia protensa_1 demonstrate that the two main configurations of the brain observed in modern arthropods, those of Chelicerata and Mandibulata, respectively8, had evolved by the early

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support SIMILAR CONTENT BEING VIEWED BY OTHERS NEUROANATOMY IN A MIDDLE CAMBRIAN MOLLISONIID AND THE ANCESTRAL NERVOUS SYSTEM ORGANIZATION OF CHELICERATES Article Open access 20 January

2022 ORDOVICIAN OPABINIID-LIKE ANIMALS AND THE ROLE OF THE PROBOSCIS IN EUARTHROPOD HEAD EVOLUTION Article Open access 15 November 2022 ORGAN SYSTEMS OF A CAMBRIAN EUARTHROPOD LARVA Article

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references ACKNOWLEDGEMENTS We thank N. Shimobayashi, H. Maeda, and T. Kogiso for arranging and performing EDXRF analyses, and D. Andrew for advice on cladistics. This work was supported by

grants from the Natural Science Foundation of China (no. 40730211), Research in Education and Science from the Government of Japan (no. 21740370), a Leverhulme Trust Research Project Grant

(F/00 696/T), by the Center for Insect Science, University of Arizona, and a grant from the Air Force Research Laboratories (FA8651-10-1-0001) to N.J.S. AUTHOR INFORMATION AUTHORS AND

AFFILIATIONS * Japan Agency for Marine-Earth Science and Technology, Yokosuka 2370061, Japan, Gengo Tanaka * Yunnan Key Laboratory for Palaeobiology, Yunnan University, Kunming 650091,

China, Xianguang Hou & Xiaoya Ma * Department of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK, Xiaoya Ma & Gregory D. Edgecombe * Department of

Neuroscience and Center for Insect Science, University of Arizona, Tucson, 85721, Arizona, USA Nicholas J. Strausfeld Authors * Gengo Tanaka View author publications You can also search for

this author inPubMed Google Scholar * Xianguang Hou View author publications You can also search for this author inPubMed Google Scholar * Xiaoya Ma View author publications You can also

search for this author inPubMed Google Scholar * Gregory D. Edgecombe View author publications You can also search for this author inPubMed Google Scholar * Nicholas J. Strausfeld View

author publications You can also search for this author inPubMed Google Scholar CONTRIBUTIONS The project was conceived by G.T. Fossil data were analysed by all authors. G.D.E., N.J.S. and

X.M. composed the text. CORRESPONDING AUTHORS Correspondence to Xianguang Hou or Nicholas J. Strausfeld. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing financial

interests. EXTENDED DATA FIGURES AND TABLES EXTENDED DATA FIGURE 1 CEPHALIC REGION OF _ALALCOMENAEUS_ SP. YKLP 11075 All in dorsal view, composites of part and counterpart (upper left).

Second left to right: CT scan (green); EDXRF Fe (red); superimposition of CT and EDXRF Fe. Lower row, left to right: EDXRF Cu (blue); superimposition of CT and EDXRF Cu; superimposition of

EDXRF Fe and EDXRF Cu; superimposition of all scans. C1, first post-GA neuropil = tritocerebrum (tri); C2, second post-GA neuropil; GA, great appendage neuropil = deutocerebrum (deu); on1,

first optic neuropil; pr, protocerebrum. EXTENDED DATA FIGURE 2 ARTHROPOD RELATIONSHIPS BASED ON NEUROANATOMICAL CHARACTERS. Strict consensus of 34 shortest cladograms based on 145

characters in Supplementary Information Table 2. SUPPLEMENTARY INFORMATION SUPPLEMENTARY INFORMATION This file contains Supplementary Tables 1-2, Phylogenetic Methods and Supplementary

References. (PDF 249 kb) SUPPLEMENTARY DATA This zipped file contains characters coded in phylogenetic analysis (in nexus format, it can be opened in freeware such as Mesquite and Nexus Data

Editor). (ZIP 3 kb) POWERPOINT SLIDES POWERPOINT SLIDE FOR FIG. 1 POWERPOINT SLIDE FOR FIG. 2 POWERPOINT SLIDE FOR FIG. 3 POWERPOINT SLIDE FOR FIG. 4 RIGHTS AND PERMISSIONS Reprints and

permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Tanaka, G., Hou, X., Ma, X. _et al._ Chelicerate neural ground pattern in a Cambrian great appendage arthropod. _Nature_ 502, 364–367 (2013).

https://doi.org/10.1038/nature12520 Download citation * Received: 10 June 2013 * Accepted: 01 August 2013 * Published: 16 October 2013 * Issue Date: 17 October 2013 * DOI:

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