Retifacies abnormalis is an extinct arthropod that lived in the lower Cambrian (about 518 million years ago). Its fossil remains have been found in the Maotianshan Shales of Yunnan, China. It is a member of the Artiopoda, and closely related to Pygmaclypeatus.
Reconstruction in various views. E=uniramous cephalic appendages F=biramous appendages Key: exopod (exo) exite (exi) protopodite (pt) podomere (pd) spine/setae (s) terminal claw (tc)Two life restorations showing variation in carapace ornamentation
Retifacies was relatively large sized, reaching a carapace length of 35 centimetres (1.15 ft), and a total length of 55 centimetres (1.80 ft), including the extended antennae and tailspine. The head shield was broad and short , and appears to have lacked eyes. The antennae had 17 segments, which telescoped into each other, with spines present on the underside of the antennae at the boundary between the segments. Also present on the head were four closely spaced pairs of appendages, the first three of which were uniramous, while the last was biramous. The three uniramous appendages had six segments (podomeres), each ending with a terminal claw, with the endopod of the fourth limb having a similar morphology. The trunk was divided up into 10 segments (tergites), all of approximately equal length and width, each of which were associated with pairs of biramous appendages. The endopods of these limbs had 5/6 podomeres with terminal claws, while the exopod comprised a semicircular lobe that bore over 12 paddle-shaped lamellae, the last of which bore setae at its edge. These limbs also bore exites, consting of lamellae borne from the basal segment (basipod) of the appendage. The pygidium segment at the end of the body was proportionally large, and bore 5-6 pairs of biramous appendages. The segmented tailspine emerged from the underside of the pygidium.[2] The carapace was covered in polygonal reticulated (net-like) ornamentation, which varied between specimens, corresponding to two morphotypes. Due to one morphotype only being found among the largest specimens the differences may be due to ontogeny.[3]
Classificationedit
The vaguely similar appearance to that of a trilobite originally led scholars to think that Retifacies was a possible relative of Helmetia or Naraoia , two other primitive arthropods related to trilobites (Delle Cave and Simonetta 1991, Hou and Bergstrom 1997). Subsequently, another study on showed how Retifacies was related to other basal arthropods, as Emeraldella and Sidneyia, from the Burgess Shale in Canada, as part of Artiopoda, a placement that has been confirmed in subsequent studies. Hou and Bergstrom suggested a close relationship to the genus Squamacula. However, after a redescription of both Retifacies and Pygmaclypeatus from the same deposit in 2022, the latter is considered to be Retifacies closest known relative, based on the fact that both taxa share a multi-segmented tailspine, among other morphological similarities, with a close relation to Squamacula being rejected. The clade containing Retifacies+Pygmaclypeatus was either classified in Trilobitomorpha, or in a more basal position within Artiopoda.[4][2]
Lifestyleedit
Life restoration
Due to a lack of information about the gut morphology or contents, the reconstruction of the ecology of Retifacies is speculative. The authors of the 2022 redescription suggested that Retifacies was a benthic organism (living on the seafloor) that scavenged on the remains of soft-bodied organisms or organic matter.[2]
Referencesedit
^Yang, C.; Li, X.-H.; Zhu, M.; Condon, D. J.; Chen, J. (2018). "Geochronological constraint on the Cambrian Chengjiang biota, South China" (PDF). Journal of the Geological Society. 175 (4): 659–666. Bibcode:2018JGSoc.175..659Y. doi:10.1144/jgs2017-103. ISSN 0016-7649. S2CID 135091168.
^ abcZhang, Maoyin; Liu, Yu; Hou, Xianguang; Ortega-Hernández, Javier; Mai, Huijuan; Schmidt, Michel; Melzer, Roland R.; Guo, Jin (2022-08-19). "Ventral Morphology of the Non-Trilobite Artiopod Retifacies abnormalis Hou, Chen & Lu, 1989, from the Early Cambrian Chengjiang Biota, China". Biology. 11 (8): 1235. doi:10.3390/biology11081235. ISSN 2079-7737. PMC9405172. PMID 36009864.
^Lin, Weiliang; Pates, Stephen; Losso, Sarah R.; Fu, Dongjing (2024-02-19). "Intraspecific variation of early Cambrian (stage 3) arthropod Retifacies abnormalis revealed by morphometric analyses". Frontiers in Ecology and Evolution. 12. doi:10.3389/fevo.2024.1336365. ISSN 2296-701X.
^Schmidt, Michel; Hou, Xianguang; Zhai, Dayou; Mai, Huijuan; Belojević, Jelena; Chen, Xiaohan; Melzer, Roland R.; Ortega-Hernández, Javier; Liu, Yu (2022-03-28). "Before trilobite legs: Pygmaclypeatus daziensis reconsidered and the ancestral appendicular organization of Cambrian artiopods". Philosophical Transactions of the Royal Society B: Biological Sciences. 377 (1847): 20210030. doi:10.1098/rstb.2021.0030. PMC8819370. PMID 35125003.
Sourcesedit
Hou, Chen & Lu, 1989. Early Cambrian new arthropods from Chengjiang, Yunnan. Acta Palaeontologica Sinica, 28, 42–57.
Chen & Zhou, 1997. Biology of the Chengjiang fauna. Bulletin of the Natural Museum of Natural Science, 10, 11 – 106.
Hou & Bergstrom, 1997. Arthropods of the Lower Cambrian Chengjiang fauna, southwest China. Fossils and strata, 45, 116 pp.
Edgecombe & Ramskold, 1999b. Relationships of Cambrian Arachnata and the systematic position of Trilobita. Journal of Paleontology, 73, 263 – 287.
Hou, Bergstrom, Wang, Feng & Chen, 1999. The Chengjiang fauna. Exceptionally well-preserved animals from 530 million years ago. 170 pp. Yunnan Science and Technology Press, Kunming, Yunnan Province, China.
May 03, 2024
retifacies, abnormalis, extinct, arthropod, that, lived, lower, cambrian, about, million, years, fossil, remains, have, been, found, maotianshan, shales, yunnan, china, member, artiopoda, closely, related, pygmaclypeatus, temporal, range, cambrian, stage, preꞒ. Retifacies abnormalis is an extinct arthropod that lived in the lower Cambrian about 518 million years ago Its fossil remains have been found in the Maotianshan Shales of Yunnan China It is a member of the Artiopoda and closely related to Pygmaclypeatus RetifaciesTemporal range Cambrian Stage 3 518 Ma 1 PreꞒ Ꞓ O S D C P T J K Pg N Fossil of the dorsal carapace Scientific classification Domain Eukaryota Kingdom Animalia Phylum Arthropoda unranked Artiopoda Subphylum Trilobitomorpha Genus RetifaciesHou et al 1989 Species R abnormalis Binomial name Retifacies abnormalisHou et al 1989 Contents 1 Description 2 Classification 3 Lifestyle 4 References 5 SourcesDescription edit nbsp Reconstruction in various views E uniramous cephalic appendages F biramous appendages Key exopod exo exite exi protopodite pt podomere pd spine setae s terminal claw tc nbsp Two life restorations showing variation in carapace ornamentation Retifacies was relatively large sized reaching a carapace length of 35 centimetres 1 15 ft and a total length of 55 centimetres 1 80 ft including the extended antennae and tailspine The head shield was broad and short and appears to have lacked eyes The antennae had 17 segments which telescoped into each other with spines present on the underside of the antennae at the boundary between the segments Also present on the head were four closely spaced pairs of appendages the first three of which were uniramous while the last was biramous The three uniramous appendages had six segments podomeres each ending with a terminal claw with the endopod of the fourth limb having a similar morphology The trunk was divided up into 10 segments tergites all of approximately equal length and width each of which were associated with pairs of biramous appendages The endopods of these limbs had 5 6 podomeres with terminal claws while the exopod comprised a semicircular lobe that bore over 12 paddle shaped lamellae the last of which bore setae at its edge These limbs also bore exites consting of lamellae borne from the basal segment basipod of the appendage The pygidium segment at the end of the body was proportionally large and bore 5 6 pairs of biramous appendages The segmented tailspine emerged from the underside of the pygidium 2 The carapace was covered in polygonal reticulated net like ornamentation which varied between specimens corresponding to two morphotypes Due to one morphotype only being found among the largest specimens the differences may be due to ontogeny 3 Classification editThe vaguely similar appearance to that of a trilobite originally led scholars to think that Retifacies was a possible relative of Helmetia or Naraoia two other primitive arthropods related to trilobites Delle Cave and Simonetta 1991 Hou and Bergstrom 1997 Subsequently another study on showed how Retifacies was related to other basal arthropods as Emeraldella and Sidneyia from the Burgess Shale in Canada as part of Artiopoda a placement that has been confirmed in subsequent studies Hou and Bergstrom suggested a close relationship to the genus Squamacula However after a redescription of both Retifacies and Pygmaclypeatus from the same deposit in 2022 the latter is considered to be Retifacies closest known relative based on the fact that both taxa share a multi segmented tailspine among other morphological similarities with a close relation to Squamacula being rejected The clade containing Retifacies Pygmaclypeatus was either classified in Trilobitomorpha or in a more basal position within Artiopoda 4 2 Lifestyle edit nbsp Life restoration Due to a lack of information about the gut morphology or contents the reconstruction of the ecology of Retifacies is speculative The authors of the 2022 redescription suggested that Retifacies was a benthic organism living on the seafloor that scavenged on the remains of soft bodied organisms or organic matter 2 References edit Yang C Li X H Zhu M Condon D J Chen J 2018 Geochronological constraint on the Cambrian Chengjiang biota South China PDF Journal of the Geological Society 175 4 659 666 Bibcode 2018JGSoc 175 659Y doi 10 1144 jgs2017 103 ISSN 0016 7649 S2CID 135091168 a b c Zhang Maoyin Liu Yu Hou Xianguang Ortega Hernandez Javier Mai Huijuan Schmidt Michel Melzer Roland R Guo Jin 2022 08 19 Ventral Morphology of the Non Trilobite Artiopod Retifacies abnormalis Hou Chen amp Lu 1989 from the Early Cambrian Chengjiang Biota China Biology 11 8 1235 doi 10 3390 biology11081235 ISSN 2079 7737 PMC 9405172 PMID 36009864 Lin Weiliang Pates Stephen Losso Sarah R Fu Dongjing 2024 02 19 Intraspecific variation of early Cambrian stage 3 arthropod Retifacies abnormalis revealed by morphometric analyses Frontiers in Ecology and Evolution 12 doi 10 3389 fevo 2024 1336365 ISSN 2296 701X Schmidt Michel Hou Xianguang Zhai Dayou Mai Huijuan Belojevic Jelena Chen Xiaohan Melzer Roland R Ortega Hernandez Javier Liu Yu 2022 03 28 Before trilobite legs Pygmaclypeatus daziensis reconsidered and the ancestral appendicular organization of Cambrian artiopods Philosophical Transactions of the Royal Society B Biological Sciences 377 1847 20210030 doi 10 1098 rstb 2021 0030 PMC 8819370 PMID 35125003 Sources editHou Chen amp Lu 1989 Early Cambrian new arthropods from Chengjiang Yunnan Acta Palaeontologica Sinica 28 42 57 Chen amp Zhou 1997 Biology of the Chengjiang fauna Bulletin of the Natural Museum of Natural Science 10 11 106 Hou amp Bergstrom 1997 Arthropods of the Lower Cambrian Chengjiang fauna southwest China Fossils and strata 45 116 pp Edgecombe amp Ramskold 1999b Relationships of Cambrian Arachnata and the systematic position of Trilobita Journal of Paleontology 73 263 287 Hou Bergstrom Wang Feng amp Chen 1999 The Chengjiang fauna Exceptionally well preserved animals from 530 million years ago 170 pp Yunnan Science and Technology Press Kunming Yunnan Province China Retrieved from https en wikipedia org w index php title Retifacies amp oldid 1210104710, wikipedia, wiki, book, books, library,
