Early Cambrian deuteropods from the Chengjiang Konservat-Lagerstätte: anatomy, taxonomy and phylogenetic significance

This thesis presents detailed systematic palaeontology of four early Cambrian (Series 2, Stage 3) euarthropods from the Chengjiang biota of Yunnan Province, China. These are: Kylinxia zhangi Zeng, Zhao & Huang, Fengzhengia mamingae O’Flynn et al., Bushizheia yangi O’Flynn & Liu and Kuamaia lata Hou. These are deuteropods (i.e. upper stem- and crown-group euarthropods), being characterized by complete dorsal arthrodization, a multi-segmented head, deutocerebral first appendages and appendage arthropodization, which distinguish them from lower stem-group euarthropods. The taxa have been selected for analysis to address some fundamental questions bearing on the number of segments in the euarthropod head, and the homology of raptorial frontal appendages (A1) across the euarthropod stem and crown-groups. Of these taxa, K. lata nests robustly within Artiopoda Hou & Bergström, whereas earlier-branching K. zhangi, F. mamingae and B. yangi have uncertain placements within Deuteropoda Ortega-Hernández at class, order and family levels.The presence of a six-segmented head in Kylinxia zhangi and, for example, Jianfengia multisegmentalis Hou (a megacheiran euarthropod), attests to an early acquisition of this character within the euarthropod upper stem-group and its retention in the crown-group. The ‘great appendage’-like A1 is retained across a large region of tree space from lower to upper stem- and crown-group Euarthropoda, indicating that a raptorial A1 is symplesiomorphic for Deuteropoda, and indicates homology of these limbs between stem and crown euarthropods. Conjoined segments posterior to the last trunk articulation, present in comparatively early- (K. zhangi and Fengzhengia mamingae) and late-branching (Kuamaia lata) deuteropods (and Bushizheia yangi that bridges between), are interpreted as pygidia. However, there is incomplete developmental (ontogenetic) evidence in these and other non-artiopodan euarthropods to show whether these represent homologous structures across a range of deuteropods — and congruence tests of homology imply multiple origins.