The organization of the head provides critical data for resolving the phylogenetic relationships and evolutionary history of extinct and extant euarthropods1,2. The early Cambrian-period fuxianhuiids are regarded as basal representatives of stem-group Euarthropoda3,4,5,6,7, and their anterior morphology therefore offers key insights for reconstructing the ancestral condition of the euarthropod head1,2,3,8,9,10,11. However, the paired post-antennal structures in Fuxianhuia protensa remain controversial3,8,10; they have been interpreted as both ‘great appendages’1,2 and as gut diverticulae4,12,13. Here we describe Chengjiangocaris kunmingensis sp. nov. and Fuxianhuia xiaoshibaensis sp. nov. from a new early Cambrian (Stage 3) fossil Lagerstätte in Yunnan, China. Numerous specimens of both species show a unique ‘taphonomic dissection’ of the anterodorsal head shield, revealing the cephalic organization in detail. We demonstrate the presence of a pair of specialized post-antennal appendages (SPAs) in the fuxianhuiid head, which attach at either side of the posteriorly directed mouth, behind the hypostome. Preserved functional articulations indicate a well-defined but restricted range of limb movement, suggestive of a simple type of sweep feeding. The organization of the SPAs in fuxianhuiids is incompatible with the (deutocerebral) anterior raptorial appendages of megacheirans2,9,14,15, and argue against the presence of protocerebral limbs in the fuxianhuiids1,2,9. The positions of the fuxianhuiid antennae and SPAs indicate that they are segmentally homologous to the deutocerebral and tritocerebral appendages of crown-group Euarthropoda respectively2,11,16,17. These findings indicate that antenniform deutocerebral appendages with many podomeres are a plesiomorphic feature of the ancestral euarthropod head.
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This study is supported by the National Natural Science Foundation of China (41272027), and the PhD Fund of the Ministry of Education of China (20115301110005). J.O.-H. is funded by CONACYT (Consejo Nacional de Ciencia y Tecnología, México), the University of Cambridge Trusts and Darwin College, University of Cambridge. We thank C. Shen, T. Lan and J.-B Hou for assistance in the field.
This file contains Supplementary Figures 1-4, Supplementary Table 1 and Supplementary References.
About this article
Palaeogeography, Palaeoclimatology, Palaeoecology (2018)