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Three-Dimensionally Preserved Appendages in an Early Cambrian Stem-Group Pancrustacean

2018; Elsevier BV; Volume: 29; Issue: 1 Linguagem: Inglês

10.1016/j.cub.2018.11.060

1879-0445

Dayou Zhai, Javier Ortega‐Hernández, Joanna M. Wolfe, Xianguang Hou, Chunjie Cao, Yu Liu,

Fossil Insects in Amber

Pancrustaceans boast impressive diversity, abundance, and ecological impact in the biosphere throughout the Phanerozoic [1Brusca R.C. Moore W. Shuster S.M. Invertebrates.Third Edition. Sinauer Associates, Inc. Publishers, Sunderland2016: 761-893Google Scholar]. Molecular clock estimates suggest an early Cambrian divergence for pancrustaceans [2Oakley T.H. Wolfe J.M. Lindgren A.R. Zaharoff A.K. Phylotranscriptomics to bring the understudied into the fold: monophyletic ostracoda, fossil placement, and pancrustacean phylogeny.Mol. Biol. Evol. 2013; 30: 215-233Crossref PubMed Scopus (190) Google Scholar, 3Schwentner M. Combosch D.J. Pakes Nelson J. Giribet G. A Phylogenomic Solution to the Origin of Insects by Resolving Crustacean-Hexapod Relationships.Curr. Biol. 2017; 27: 1818-1824.e5Abstract Full Text Full Text PDF PubMed Scopus (111) Google Scholar]. Despite the wealth of Palaeozoic exceptional fossiliferous deposits [4Zhang X.G. Siveter D.J. Waloszek D. Maas A. 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Exceptionally preserved crustaceans from western Canada reveal a cryptic Cambrian radiation.Proc. Natl. Acad. Sci. USA. 2012; 109: 1589-1594Crossref PubMed Scopus (94) Google Scholar]. Although these taphonomic windows capture minute morphology enabling detailed comparisons with extant representatives, these microfossils are limited to larval stages (Orsten) or recalcitrant fragmentary remains (SCFs) restricting their phylogenetic precision [5Edgecombe G.D. Legg D.A. The arthropod fossil record.Arthropod Biology and Evolution. Springer, Berlin, Heidelberg2013: 393-415Crossref Google Scholar, 12Edgecombe G.D. Legg D.A. Origins and early evolution of arthropods.Palaeontology. 2014; 57: 457-468Crossref Scopus (76) Google Scholar, 19Wolfe J.M. Hegna T.A. Testing the phylogenetic position of Cambrian pancrustacean larval fossils by coding ontogenetic stages.Cladistics. 2014; 30: 366-390Crossref Scopus (34) Google Scholar, 20Harvey T.H.P. Butterfield N.J. Sophisticated particle-feeding in a large Early Cambrian crustacean.Nature. 2008; 452: 868-871Crossref PubMed Scopus (67) Google Scholar, 22Wolfe J.M. Daley A.C. Legg D.A. Edgecombe G.D. Fossil calibrations for the arthropod Tree of Life.Earth Sci. Rev. 2016; 160: 43-110Crossref Scopus (118) Google Scholar, 23Edgecombe G.D. Inferring arthropod phylogeny: Fossils and their interaction with other data sources.Integr. Comp. Biol. 2017; 57: 467-476Crossref PubMed Scopus (10) Google Scholar]. We employed X-ray computed tomography [24Liu Y. Melzer R.R. Haug J.T. Haug C. Briggs D.E.G. Hörnig M.K. He Y.Y. Hou X.G. Three-dimensionally preserved minute larva of a great-appendage arthropod from the early Cambrian Chengjiang biota.Proc. Natl. Acad. Sci. USA. 2016; 113: 5542-5546Crossref PubMed Scopus (32) Google Scholar] to reveal the three-dimensionally appendage morphology of the Chengjiang bivalved euarthropod Ercaicunia multinodosa [25Luo H.L. Hu S.X. Chen L.Z. Zhang S.S. Tao Y.H. Early Cambrian Chengjiang Fauna from Kunming Region, China. Yunnan Sci. Technol. Press, Kunming1999Google Scholar] from the early Cambrian of China. E. multinodosa possesses characters uniquely shared with extant crustaceans, including differentiated tritocerebral antennae and epipodite-bearing biramous trunk appendages. Similarities between E. multinodosa with clypecaridids [9Hou X.-G. New rare bivalved arthropods from the Lower Cambrian Chengjiang fauna, Yunnan, China.J. Paleontol. 1999; 73: 102-116Crossref Google Scholar], waptiids [16Vannier J. Aria C. Taylor R.S. Caron J.-B. Waptia fieldensis Walcott, a mandibulate arthropod from the middle Cambrian Burgess Shale.R. Soc. Open Sci. 2018; 5: 172206Crossref PubMed Scopus (45) Google Scholar] and hymenocarines [11Briggs D.E.G. The arthropod 'Branchiocaris' n. gen., Middle Cambrian, Burgess Shale, British Columbia.Geol. Surv. Can. Bull. 1976; 264: 1-29Google Scholar, 14Aria C. Caron J.-B. Burgess Shale fossils illustrate the origin of the mandibulate body plan.Nature. 2017; 545: 89-92Crossref PubMed Scopus (53) Google Scholar] suggest that these euarthropods may also possess similarly differentiated appendages, but these details are obstructed by the limits of preservation of compacted macrofossils. E. multinodosa illuminates the early evolution of pancrustacean appendage differentiation and represents the oldest unequivocal crown-group mandibulate known from complete macrofossils [22Wolfe J.M. Daley A.C. Legg D.A. Edgecombe G.D. Fossil calibrations for the arthropod Tree of Life.Earth Sci. Rev. 2016; 160: 43-110Crossref Scopus (118) Google Scholar].