Urokodia
| Urokodia Temporal range:
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|---|---|
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| Fossil specimen with preserved appendages | |
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| Reconstruction of Urokodia | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| (unranked): | †Artiopoda |
| Genus: | †Urokodia Hou et al, 1989 |
| Type species | |
| Urokodia aequalis Hou et al, 1989
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Urokodia is an extinct genus of arthropod from the early Cambrian. The only known species is Urokodia aequalis from the Maotianshan Shales of China based on some 15 specimens.[1]
Description
Urokodia is an elongated arthropod measured up to 3.5 cm. The dorsal exoskeleton (tergite) compose of a cephalon (head) and a pygidium (tail shield) of subequal size. Both were initially thought to be nearly identical, which possess 4 pairs of large lateral spikes. However, subsequent studies revealed the pygidium had distinct triangular shape and a parallel row of tiny posterior spikes. Between the cephalon and pygidium was an elongated thorax of 14 or 15 segments.[2] It possess a pair of stalked eyes and stubby antennae below the front of its head. The remaining ventral region possess subequal appendages with annulated bases and lamellar (lobe-like) outer branches, 3 pairs under both cephalon and pygidium and 1 pair under each thoracic segment. All but the pygidial appendages also bore segmented, stenopodous (leg-like) inner branches.[3]
Taxonomy
The ventral appendages of Urokodia had been unknown for a long time, and its dorsal features resemble Mollisoniidae (e.g. Mollisonia, Thelxiope, and Corcorania) at first glance. This lead to the previous classification of Urokodia as a member of the order Mollisoniida with other mollisoniids. Based on the discovery of Mollisonia appendages in 2019, the group are suggested to be stem-chelicerates.[4] However, a redescription published in July 2024 discovered the appendages of Urokodia unlike those of a mollisoniid or any other chelicerates. Phylogenetic analysis based on the new discovery instead placing Urokodia as the most basal member of Artiopoda, an extinct group which include trilobites and their relatives.[3]
References
- ^ Hou, Xian‐guang; Siveter, David J.; Siveter, Derek J.; Aldridge, Richard J.; Cong, Pei‐yun; Gabbott, Sarah E.; Ma, Xiao‐ya; Purnell, Mark A.; Williams, Mark (12 April 2017). The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life (1 ed.). Chichester, West Sussex, UK: Wiley. ISBN 978-1-118-89638-9.
- ^ Zhang, Xingliang; Han, Jian; Shu, Degan (2002). "New occurrence of the Burgess Shale arthropod Sidneyia in the Early Cambrian Chengjiang Lagerstätte (South China), and revision of the arthropod Urokodia". Alcheringa: An Australasian Journal of Palaeontology. 26 (1): 1–8. doi:10.1080/03115510208619239. ISSN 0311-5518.
- ^ a b Liu, Cong; Fu, Dongjing; Wu, Yu; Zhang, Xingliang (July 2024). "Cambrian euarthropod Urokodia aequalis sheds light on the origin of Artiopoda body plan". iScience: 110443. doi:10.1016/j.isci.2024.110443. PMC 11325232.
- ^ Lerosey-Aubril, Rudy; Skabelund, Jacob; Ortega-Hernández, Javier (2020-04-09). "Revision of the mollisoniid chelicerate(?) Thelxiope, with a new species from the middle Cambrian Wheeler Formation of Utah". PeerJ. 8: e8879. doi:10.7717/peerj.8879. ISSN 2167-8359. PMC 7151752. PMID 32296605.
- Urokodia aequalis Arthropod from Maotianshan Shales - URL retrieved September 11, 2010