Saturday, July 7, 2018

[Paleontology • 2018] Zhiwenia coronata • A Soft‐bodied Euarthropod from the early Cambrian Xiaoshiba Lagerstätte of China supports A New Clade, Protosutura nov., of Basal Artiopodans with Dorsal Ecdysial Sutures

 Zhiwenia coronata
Du, Ortega‐Hernández, Yang & Zhang, 2018

  DOI: 10.1111/cla.12344  

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.

Fig. 2. Completely articulated specimen of Zhiwenia coronata gen. et sp. nov. from the Cambrian Stage 3 Xiaoshiba Lagerst€atte. (a) YKLP 12370 Holotype, dorsal view of a complete individual. (b) Interpretative diagram.

Fig. 5. Morphological reconstruction of Zhiwenia coronata gen. et sp. nov. from the Xiaoshiba Lagerst€atte.

Euarthropoda Lankester, 1904 (see discussion in Ortega-Hernandez, 2016) 
Artiopoda Hou and Bergstrom, 1997 (see also Stein € and Selden, 2012). 

Protosutura nov. 

Diagnosis. Non-biomineralized artiopodan euarthropods characterized by a short semicircular cephalic shield with simple dorsal ecdysial sutures located on either side of the head (secondarily lost in some representatives). Trunk elongate and with homonomous construction, consisting exclusively of freely articulating tergites of subequal length that convey a subrectangular to suboval exoskeletal outline. Posterior trunk tergites strongly curved. Tailspine spinose and short—less than half the trunk length—occasionally bearing marginal spines of variable number and size. 

Etymology. Derived from the Greek prefix proto (first, primitive), and the Latin root sutura, referencing the presence of dorsal ecdysial sutures on the head shield. 

Included taxa. Acanthomeridion serratum Hou et al., 1989; Acanthomeridion anacanthus Hou et al., 2017; Australimicola spriggi Paterson et al., 2012; Zhiwenia coronata gen. et. sp. nov.

Zhiwenia coronata gen. et. sp. nov.

Type species, locality and stratigraphy. Zhiwenia coronata gen. et. sp. nov. from the Xiaoshiba section (Fig. 1), Kunming, Yunnan; Cambrian Stage 3 Hongjingshao Formation, YunnanocephalusChengjiangaspisHongshiyanaspis Biozone (Yang et al., 2013, 2014, 2015, 2016a, b, 2018).

Etymology. The new genus is named in memory of Professor Zhi-Wen Jiang for his contributions to microfossils and biostratigraphy of Yunnan Province; coron (Latin), crown, referring to the shape of the two-notch bearing cephalic shield. 

Fig. 6. Results of parsimony and Bayesian phylogenetic analyses. All trees depict a strict consensus. Asterisks indicate presence of dorsal ecdysial sutures on cephalic shield.
 (c) Implied weight parsimony, k = 5, 10 (1 MPT, CI = 0.41, RI = 0.73). 

Kun‐Sheng Du, Javier Ortega‐Hernández, Jie Yang and Xi‐Guang Zhang. 2018. A Soft‐bodied Euarthropod from the early Cambrian Xiaoshiba Lagerstätte of China supports A New Clade of Basal Artiopodans with Dorsal Ecdysial Sutures. Cladistics.  DOI: 10.1111/cla.12344  

No comments:

Post a Comment