| Xandarellida Temporal range:
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|---|---|
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| Fossils of Zhugeia | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| (unranked): | †Artiopoda |
| Subphylum: | †Trilobitomorpha |
| (unranked): | †Xandarellida Chen, Ramsköld, Edgecombe & Zhou in Chen et al, 1996[1] |
| Type species | |
| †Xandarella spectaculum Hou, Ramsköld & Bergström, 1991[2]
| |
| Genera | |
Xandarellida is an extinct order of artiopods known exclusively from the middle Cambrian.
Xandarellida contains numerous species, most from the Maotianshan Shales of China. The only exception to this is Phytophilaspis, which is instead from the Sinsk Formation. In terms of anatomy, xandarellids share numerous characteristics such as a natant hypostome, alongside a unique feature known as “segment decoupling” where the amount of limbs exceeds the amount of tergites.[3] They also share a posteriorly extended semicircular head shield and ventral stalked eyes. The genus Cindarella in particular has complex eyes, with over 2000 ommatidia in each.[4] Cindarella also has a large anterior spine on the fifteenth tergite. Xandarella has an unusual tripartite head shield, with ventral eye slits likely retained from the ancestral stalked eyes, alongside possibly lacking the anterior spine.[3] Phytophilaspis has an especially intricate head shield, sharing its tripartite nature with Xandarella alongside bearing several sutures all over its body and seemingly having almost completely fused tergites. [5] Luohuilinella has a large amount of tergites (with the type species having 27) but otherwise resembles other xandarellids save for an unfused three-segmented pygidium.[6] Sinoburius resembles Xandarella in having an elongate posterior spine and Phytophilaspis in having all but a few tergites fused, although it exhibits secondary loss of eye slits. Unusually, Sinoburius also has two small lateral spines near its posterior.[3] Zhugeia is relatively usual for the clade, however its median spine is very long and needle-like, in addition to having a relatively large pygidium.[7]
References
[edit]- ^ Ramsköld, Lars; Junyuan, Chen; Edgecombe, Gregory D.; Guiqing, Zhou (1997). "Cindarella and the arachnate clade Xandarellida (Arthropoda, Early Cambrian) from China". Transactions of the Royal Society of Edinburgh: Earth Sciences. 88 (1): 19–38. doi:10.1017/S0263593300002297.
- ^ Xianguang, Hou; Ramsköld, Lars; Bergström, Jan (October 1991). "Composition and preservation of the Chengjiang fauna –a Lower Cambrian soft-bodied biota". Zoologica Scripta. 20 (4): 395–411. doi:10.1111/j.1463-6409.1991.tb00303.x.
- ^ a b c Chen, Xiaohan; Ortega-Hernández, Javier; Wolfe, Joanna M.; Zhai, Dayou; Hou, Xianguang; Chen, Ailin; Mai, Huijuan; Liu, Yu (December 2019). "The appendicular morphology of Sinoburius lunaris and the evolution of the artiopodan clade Xandarellida (Euarthropoda, early Cambrian) from South China". BMC Evolutionary Biology. 19 (1): 165. Bibcode:2019BMCEE..19..165C. doi:10.1186/s12862-019-1491-3.
- ^ Zhao, Fangchen; Bottjer, David J.; Hu, Shixue; Yin, Zongjun; Zhu, Maoyan (25 September 2013). "Complexity and diversity of eyes in Early Cambrian ecosystems". Scientific Reports. 3 (1): 2751. Bibcode:2013NatSR...3.2751Z. doi:10.1038/srep02751. PMID 24067397.
- ^ Ivantsov, A. Yu. (1999). "Trilobite-like arthropod from the Lower Cambrian of the Siberian Platform" (PDF). Acta Palaeontologica Polonica. 44 (4): 455–466.
- ^ Hou, Xianguang; Williams, Mark; Sansom, Robert; Siveter, Derek J.; Siveter, David J.; Gabbott, Sarah; Harvey, Thomas H. P.; Cong, Peiyun; Liu, Yu (August 2019). "A new xandarellid euarthropod from the Cambrian Chengjiang biota, Yunnan Province, China". Geological Magazine. 156 (8): 1375–1384. Bibcode:2019GeoM..156.1375H. doi:10.1017/s0016756818000730.
- ^ Zhu, Yuyan; Zeng, Han; Liu, Yao; Zhao, Fangchen (2023). "New artiopodan euarthropods from the Chengjiang fauna (Cambrian Stage 3) at Malong, Yunnan, China". Acta Palaeontologica Polonica. 68. doi:10.4202/app.01080.2023.