Urokodia
{{Short description|Extinct genus of artiopod}}
{{automatic taxobox
| fossil_range = {{fossil range|518}}
| image = Liu et al. 2024 f01.jpg
| image_caption = Fossil specimen with preserved appendages
| image2 = Urokodia restoration.png
| image2_caption = Reconstruction of Urokodia
| taxon = Urokodia
| authority = Hou et al, 1989
| type_species = Urokodia aequalis
| type_species_authority = Hou et al, 1989
}}
Urokodia is an extinct genus of marine arthropod from the early Cambrian. The only known species is Urokodia aequalis from the Maotianshan Shales of China based on some 15 specimens.{{cite book |last1=Hou |first1=Xian-guang |last2=Siveter |first2=David J. |last3=Siveter |first3=Derek J. |last4=Aldridge |first4=Richard J. |last5=Cong |first5=Pei-yun |last6=Gabbott |first6=Sarah E. |last7=Ma |first7=Xiao-ya |last8=Purnell |first8=Mark A. |last9=Williams |first9=Mark |title=The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life |date=12 April 2017 |publisher=Wiley |location=Chichester, West Sussex, UK |isbn=978-1-118-89638-9 |edition=1 |doi=10.1002/9781118896372 |bibcode=2017cfcc.book.....H |url=https://onlinelibrary.wiley.com/doi/book/10.1002/9781118896372 |language=en}}
Description
Urokodia is an elongated arthropod measuring up to 3.5 cm. The dorsal exoskeleton (tergite) is composed of a cephalon (head) and a pygidium (tail shield) of subequal size. Both were initially thought to be nearly identical, possessing 4 pairs of large lateral spikes. However, subsequent studies revealed that the pygidium had a 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.{{Cite journal |last1=Zhang |first1=Xingliang |last2=Han |first2=Jian |last3=Shu |first3=Degan |date=2002 |title=New occurrence of the Burgess Shale arthropod Sidneyia in the Early Cambrian Chengjiang Lagerstätte (South China), and revision of the arthropod Urokodia |url=https://www.tandfonline.com/doi/abs/10.1080/03115510208619239 |journal=Alcheringa: An Australasian Journal of Palaeontology |language=en |volume=26 |issue=1 |pages=1–8 |doi=10.1080/03115510208619239 |bibcode=2002Alch...26....1Z |issn=0311-5518}} It possesses a pair of stalked eyes and stubby antennae below the front of its head. The remaining ventral region possesses 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 bore segmented, stenopodous (leg-like) inner branches.
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 is suggested to be stem-chelicerates.{{Cite journal|last1=Lerosey-Aubril|first1=Rudy|last2=Skabelund|first2=Jacob|last3=Ortega-Hernández|first3=Javier|date=2020-04-09|title=Revision of the mollisoniid chelicerate(?) Thelxiope, with a new species from the middle Cambrian Wheeler Formation of Utah|journal=PeerJ|volume=8|pages=e8879|doi=10.7717/peerj.8879|pmid=32296605|pmc=7151752|issn=2167-8359|doi-access=free}} However, a redescription published in July 2024 discovered the appendages of Urokodia differed markedly from those of mollisoniids or of any other chelicerates. Phylogenetic analysis based on the new discovery instead places Urokodia as the most basal member of Artiopoda, an extinct group which includes trilobites and their relatives.{{cite journal |last1=Liu |first1=Cong |last2=Fu |first2=Dongjing |last3=Wu |first3=Yu |last4=Zhang |first4=Xingliang |title=Cambrian euarthropod Urokodia aequalis sheds light on the origin of Artiopoda body plan |journal=iScience |date=July 2024 |volume=27 |issue=8 |pages=110443 |doi=10.1016/j.isci.2024.110443|doi-access=free |pmid=39148713 |pmc=11325232 |bibcode=2024iSci...27k0443L }}
References
{{Portal|Paleontology}}
{{Reflist}}
- [http://www.fossilmuseum.net/Fossil_Sites/Chengjiang/Urokodia/Urokodia.htm Urokodia aequalis Arthropod from Maotianshan Shales] - URL retrieved September 11, 2010
{{Taxonbar|from=Q4006491}}
Category:Maotianshan shales fossils
Category:Cambrian genus extinctions
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