Fossils from South China redefine the ancestral euarthropod body plan
Abstract Background Early Cambrian Lagerstätten from China have greatly enriched our perspective on the early evolution of animals, particularly arthropods. However, recent studies have shown that many of these early fossil arthropods were more derived than previously thought, casting uncertainty on...
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| Format: | Article |
| Language: | English |
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BMC
2020-01-01
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| Series: | BMC Evolutionary Biology |
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| Online Access: | https://doi.org/10.1186/s12862-019-1560-7 |
| _version_ | 1818574876985786368 |
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| author | Cédric Aria Fangchen Zhao Han Zeng Jin Guo Maoyan Zhu |
| author_facet | Cédric Aria Fangchen Zhao Han Zeng Jin Guo Maoyan Zhu |
| author_sort | Cédric Aria |
| collection | DOAJ |
| description | Abstract Background Early Cambrian Lagerstätten from China have greatly enriched our perspective on the early evolution of animals, particularly arthropods. However, recent studies have shown that many of these early fossil arthropods were more derived than previously thought, casting uncertainty on the ancestral euarthropod body plan. In addition, evidence from fossilized neural tissues conflicts with external morphology, in particular regarding the homology of the frontalmost appendage. Results Here we redescribe the multisegmented megacheirans Fortiforceps and Jianfengia and describe Sklerolibyon maomima gen. et sp. nov., which we place in Jianfengiidae, fam. nov. (in Megacheira, emended). We find that jianfengiids show high morphological diversity among megacheirans, both in trunk ornamentation and head anatomy, which encompasses from 2 to 4 post-frontal appendage pairs. These taxa are also characterized by elongate podomeres likely forming seven-segmented endopods, which were misinterpreted in their original descriptions. Plesiomorphic traits also clarify their connection with more ancestral taxa. The structure and position of the “great appendages” relative to likely sensory antero-medial protrusions, as well as the presence of optic peduncles and sclerites, point to an overall homology with the anterior head of radiodontans. This is confirmed by our Bayesian phylogeny, which places jianfengiids as the basalmost euarthropods, paraphyletic with other megacheirans, and in contiguity with isoxyids and radiodontans. Conclusions Sklerolibyon and other jianfengiids expand the disparity of megacheirans and suggest that the common euarthropod ancestor possessed a remarkable phenotypic variability associated with the externalized cephalon, as well as endopods that were already heptopodomerous, which differs from previous hypotheses and observations. These animals also demonstrate that the frontalmost pair of arthrodized appendage is homologous between radiodontans and megacheirans, refuting the claim that the radiodontan frontal appendages evolved into the euarthropod labrum, and questioning its protocerebral identity. This evidence based on external anatomy now constitutes a solid benchmark upon which we should address issues of homology, with the help of carefully examined palaeoneurological data. |
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| id | doaj.art-2c6d485f524046c3afcf9345c1960a19 |
| institution | Directory Open Access Journal |
| issn | 1471-2148 |
| language | English |
| last_indexed | 2024-12-15T00:32:07Z |
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| spelling | doaj.art-2c6d485f524046c3afcf9345c1960a192022-12-21T22:41:58ZengBMCBMC Evolutionary Biology1471-21482020-01-0120111710.1186/s12862-019-1560-7Fossils from South China redefine the ancestral euarthropod body planCédric Aria0Fangchen Zhao1Han Zeng2Jin Guo3Maoyan Zhu4State Key Laboratory of Palaeobiology and Stratigraphy & Center for Excellence in Life and Palaeoenvironment, Nanjing Institute of Geology and Palaeontology, Chinese Academy of SciencesState Key Laboratory of Palaeobiology and Stratigraphy & Center for Excellence in Life and Palaeoenvironment, Nanjing Institute of Geology and Palaeontology, Chinese Academy of SciencesState Key Laboratory of Palaeobiology and Stratigraphy & Center for Excellence in Life and Palaeoenvironment, Nanjing Institute of Geology and Palaeontology, Chinese Academy of SciencesManagement Committee of the Chengjiang Fossil Site World HeritageState Key Laboratory of Palaeobiology and Stratigraphy & Center for Excellence in Life and Palaeoenvironment, Nanjing Institute of Geology and Palaeontology, Chinese Academy of SciencesAbstract Background Early Cambrian Lagerstätten from China have greatly enriched our perspective on the early evolution of animals, particularly arthropods. However, recent studies have shown that many of these early fossil arthropods were more derived than previously thought, casting uncertainty on the ancestral euarthropod body plan. In addition, evidence from fossilized neural tissues conflicts with external morphology, in particular regarding the homology of the frontalmost appendage. Results Here we redescribe the multisegmented megacheirans Fortiforceps and Jianfengia and describe Sklerolibyon maomima gen. et sp. nov., which we place in Jianfengiidae, fam. nov. (in Megacheira, emended). We find that jianfengiids show high morphological diversity among megacheirans, both in trunk ornamentation and head anatomy, which encompasses from 2 to 4 post-frontal appendage pairs. These taxa are also characterized by elongate podomeres likely forming seven-segmented endopods, which were misinterpreted in their original descriptions. Plesiomorphic traits also clarify their connection with more ancestral taxa. The structure and position of the “great appendages” relative to likely sensory antero-medial protrusions, as well as the presence of optic peduncles and sclerites, point to an overall homology with the anterior head of radiodontans. This is confirmed by our Bayesian phylogeny, which places jianfengiids as the basalmost euarthropods, paraphyletic with other megacheirans, and in contiguity with isoxyids and radiodontans. Conclusions Sklerolibyon and other jianfengiids expand the disparity of megacheirans and suggest that the common euarthropod ancestor possessed a remarkable phenotypic variability associated with the externalized cephalon, as well as endopods that were already heptopodomerous, which differs from previous hypotheses and observations. These animals also demonstrate that the frontalmost pair of arthrodized appendage is homologous between radiodontans and megacheirans, refuting the claim that the radiodontan frontal appendages evolved into the euarthropod labrum, and questioning its protocerebral identity. This evidence based on external anatomy now constitutes a solid benchmark upon which we should address issues of homology, with the help of carefully examined palaeoneurological data.https://doi.org/10.1186/s12862-019-1560-7EuarthropodaBody planCambrianChengjiangMacroevolutionHomology |
| spellingShingle | Cédric Aria Fangchen Zhao Han Zeng Jin Guo Maoyan Zhu Fossils from South China redefine the ancestral euarthropod body plan BMC Evolutionary Biology Euarthropoda Body plan Cambrian Chengjiang Macroevolution Homology |
| title | Fossils from South China redefine the ancestral euarthropod body plan |
| title_full | Fossils from South China redefine the ancestral euarthropod body plan |
| title_fullStr | Fossils from South China redefine the ancestral euarthropod body plan |
| title_full_unstemmed | Fossils from South China redefine the ancestral euarthropod body plan |
| title_short | Fossils from South China redefine the ancestral euarthropod body plan |
| title_sort | fossils from south china redefine the ancestral euarthropod body plan |
| topic | Euarthropoda Body plan Cambrian Chengjiang Macroevolution Homology |
| url | https://doi.org/10.1186/s12862-019-1560-7 |
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