The early Cambrian Kylinxia zhangi and evolution of the arthropod head

Robert J O'Flynn; Yu Liu; Xianguang Hou; Huijuan Mai; Mengxiao Yu; Songling Zhuang; Mark Williams; Jin Guo; Gregory D Edgecombe

doi:10.1016/j.cub.2023.08.022

The early Cambrian Kylinxia zhangi and evolution of the arthropod head

Curr Biol. 2023 Sep 25;33(18):4006-4013.e2. doi: 10.1016/j.cub.2023.08.022. Epub 2023 Aug 28.

Authors

Robert J O'Flynn¹, Yu Liu², Xianguang Hou³, Huijuan Mai³, Mengxiao Yu³, Songling Zhuang³, Mark Williams⁴, Jin Guo⁵, Gregory D Edgecombe⁶

Affiliations

¹ Yunnan Key Laboratory for Palaeobiology, Yunnan University, 650500 Kunming, China and School of Geography, Geology and the Environment, University of Leicester, University Road, Leicester, LE1 7RH, UK; Institute of Palaeontology, Yunnan University, 650500 Kunming, China; MEC International Joint Laboratory for Palaeobiology and Palaeoenvironment, Yunnan University, 650500 Kunming, China.
² Institute of Palaeontology, Yunnan University, 650500 Kunming, China; MEC International Joint Laboratory for Palaeobiology and Palaeoenvironment, Yunnan University, 650500 Kunming, China; Chengjiang Fossil Museum of the Management Committee of the Chengjiang World Heritage Fossil Site, Chengjiang 652599, China. Electronic address: yu.liu@ynu.edu.cn.
³ Institute of Palaeontology, Yunnan University, 650500 Kunming, China; MEC International Joint Laboratory for Palaeobiology and Palaeoenvironment, Yunnan University, 650500 Kunming, China.
⁴ MEC International Joint Laboratory for Palaeobiology and Palaeoenvironment, Yunnan University, 650500 Kunming, China; School of Geography, Geology and the Environment, University of Leicester, University Road, Leicester, LE1 7RH, UK.
⁵ Institute of Palaeontology, Yunnan University, 650500 Kunming, China; MEC International Joint Laboratory for Palaeobiology and Palaeoenvironment, Yunnan University, 650500 Kunming, China; Chengjiang Fossil Museum of the Management Committee of the Chengjiang World Heritage Fossil Site, Chengjiang 652599, China.
⁶ MEC International Joint Laboratory for Palaeobiology and Palaeoenvironment, Yunnan University, 650500 Kunming, China; The Natural History Museum, London SW7 5BD, UK. Electronic address: g.edgecombe@nhm.ac.uk.

PMID: 37643622
DOI: 10.1016/j.cub.2023.08.022

Abstract

The early Cambrian Kylinxia zhangi occupies a pivotal position in arthropod evolution, branching from the euarthropod stem lineage between radiodonts (Anomalocaris and relatives) and "great-appendage" arthropods.¹^,² Its combination of appendage and exoskeletal features is viewed as uniquely bridging the morphologies of so-called "lower" and "upper" stem-group euarthropods.³^,⁴ Microtomographic study of new specimens of Kylinxia refines and corrects previous interpretation of head structures in this species. Phylogenetic analyses incorporating new data reinforce the placement of Kylinxia in the euarthropod stem group but support new hypotheses of head evolution. The head of Kylinxia is composed of six segments, as in extant mandibulates, e.g., insects.⁵ In Kylinxia, these are an anterior sclerite associated with an unpaired median eye and paired lateral eyes (thus three rather than five eyes as was previously described¹), deutocerebral frontal-most appendages, and four pairs of biramous appendages (rather than two pairs of uniramous appendages). Phylogenetic trees suggest that a six-segmented head in the euarthropod crown group was already acquired by a common ancestor with Kylinxia. The segmental alignment and homology of spinose frontal-most appendages between radiodonts and upper stem-group euarthropods⁶^,⁷^,⁸^,⁹^,¹⁰ is bolstered by morphological similarities and inferred phylogenetic continuity between Kylinxia and other stem-group euarthropods.

Keywords: anterior sclerite; computed tomography; euarthropod head; median eye.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Arthropods* / anatomy & histology
Biological Evolution
Extremities / anatomy & histology
Fossils
Head / anatomy & histology
Phylogeny