A soft‐bodied euarthropod from the early Cambrian Xiaoshiba Lagerstätte of China supports a new clade of basal artiopodans with dorsal ecdysial sutures

Abstract

We describe the exceptionally well‐preserved non‐trilobite artiopodan Zhiwenia coronata gen. et sp. nov. from the Cambrian Stage 3 Xiaoshiba Lagerstätte in Yunnan, China. The exoskeleton consists of a cephalic shield with dorsal sutures expressed as lateral notches that accommodate stalked lateral eyes, an elongate trunk composed of 20 tergites—the first of which is reduced—and a short tailspine with marginal spines. Appendicular data include a pair of multi‐segmented antennae, and homonomous biramous trunk limbs consisting of an endopod with at least seven podomeres and a flattened exopod with lamellae. Although the presence of cephalic notches and a reduced first trunk tergite invites comparisons with the petalopleurans Xandarella, Luohiniella and Cindarella, the proportions and exoskeletal tagmosis of Zhiwenia do not closely resemble those of any major group within Trilobitomorpha. Parsimony and Bayesian phylogenetic analyses consistently support Zhiwenia as sister‐taxon to the Emu Bay Shale artiopodan Australimicola spriggi, and both of them as closely related to Acanthomeridion from the Chengjiang. This new monophyletic clade, Protosutura nov., occupies a basal phylogenetic position within Artiopoda as sister‐group to Trilobitomorpha and Vicissicaudata, illuminates the ancestral organization of these successful euarthropods, and leads to a re‐evaluation of the evolution of ecdysial dorsal sutures within the group.

The appendicular morphology of Sinoburius lunaris and the evolution of the artiopodan clade Xandarellida (Euarthropoda, early Cambrian) from South China

“…3a, 4d, e). The antennae do not face forwards as typically observed in artiopodans [1, 6, 10, 24, 27, 30, 39], but rather are splayed at either side due to the strong lateral flexure of the third to fifth podomeres. We regard the preserved orientation of the antennae in YRCP 0011 as close to life position (Fig.…”

“…For example, the posterior articulation of the head shield with a reduced thoracic tergite appears to be synapomorphic and the only character observable in all representatives of Xandarellida, even if this feature is also found in taxa outside this group (e.g. Zhiwenia coronata [30], Tremaglaspis vanroyi [31]. The occurrence of dorsoventral segmental mismatch between tergites and biramous limb pairs is also expressed in all members of Xandarellida that feature both appendicular and exoskeletal preservation, namely Cindarella, Sinoburius, and Xandarella [1, 6, 28].…”

“…Du et al [30] recently addressed the evolution of ecdysial sutures in Artiopoda based on the perceived similarity between the lateral notches in the head shield of Zhiwenia coronata and Luohuilinella rarus [25]. The preservation of the type material of Luohuilinella rarus gives the impression that this taxon may have possessed a similar cephalic organization to that of Xandarella spectaculum [1], including the possible presence of eye slits and dorsal exoskeletal bulges.…”

A new euarthropod with ‘great appendage’-like frontal head limbs from the Chengjiang Lagerstätte, Southwest China

“…A single specimen of Bushizheia yangi gen. et sp. nov. was recovered from the Yu'anshan Member, Chiungchussu Formation at Jiucun Town (24°41'33" N, 102°59'26" E) (see Du et al, 2018, figure 1), Chengjiang County. The Yu'anshan Member is informally divided stratigraphically into four lithologically and palaeontologically distinctive parts (Zhu et al, 2001).…”

The trouble with trilobites: classification, phylogeny and the cryptogenesis problem

“…The phylogenetic relationship between trilobites and their artiopodan relatives has received considerable attention over the past 20 years (e.g. Edgecombe & Ramsköld, 1999;Caron et al 2004;Cotton & Braddy, 2004;Hendricks & Lieberman, 2008;Paterson et al 2010Paterson et al , 2012Budd, 2011;Stein & Selden, 2012;Ortega-Hernández et al 2013;Stein et al 2013;Edgecombe et al 2017;Hou et al 2017Hou et al , 2018Lerosey-Aubril et al 2017b;Zeng et al 2017;Du et al 2018;Mayers et al 2019). Unfortunately, the results of these analyses are ambiguous, in that trilobites are resolved either in a polytomy with other artiopodan clades, or their position jumps around depending on taxon sampling, character selection and coding, and the analytical methods used.…”