Exceptionally-preserved late Cambrian fossils from the McKay Group (British Columbia,Canada) and the evolution of tagmosis in aglaspidid arthropods |
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| Institution: | 1. Palaeoscience Research Centre, School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia;2. Department of Earth & Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada;1. Department of Geology, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden;2. 10 TONS ApS, Ved Slusen 34, 2300 København S. V., Denmark;1. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, 229 Taibai Road, Xi’an 710069, P.R. China;2. Chengdu Center, China Geological Survey, China;3. Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS 66045, USA;4. State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China;5. Early Life Evolution Laboratory, School of Earth Sciences and Resources, University of Geosciences, Beijing 100083, China;6. Seto Marine Biological Laboratory, Field Science Education and Research Center, Kyoto University, Shirahama, Nishimuro, Wakayama 649–2211, Japan;1. UMR CNRS 5276 Laboratoire de Géologie de Lyon, Terre, Planètes, Environnement (LGLTPE), Géode, campus de la Doua, Université Lyon 1, 2 rue Dubois, 69622 Villeurbanne cedex, France;2. Division of Earth Sciences, School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia |
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| Abstract: | Documentation of non- or weakly biomineralizing animals that lived during the Furongian is essential for a comprehensive understanding of the diversification dynamics of metazoans during the early Palaeozoic. However, the fossil record of ‘soft’-bodied metazoans is particularly scarce for this critical time interval, consisting of rare fossils found at a dozen or so localities worldwide. Here we report new occurrences of exceptional preservation in Furongian (Jiangshanian) strata of the McKay Group near Cranbrook, British Columbia, Canada. This locality had already yielded trilobites with phosphatised guts, with all specimens representing the same species and occurring within a 10-m-thick interval. Two stratigraphically higher horizons with soft-tissue preservation are reported herein; one has yielded a ctenophore and an aglaspidid arthropod, the other a trilobite with a phosphatised gut belonging to a different species than the previously described specimens. The ctenophore represents the first Furongian record of the phylum and the first reported occurrence of Burgess Shale-type preservation in the upper Cambrian of Laurentia. The aglaspidid belongs to a new species of Glypharthrus, and is atypical in having twelve trunk tergites and an anteriorly narrow ‘tailspine’. These features suggest that the tailspine of aglaspidids evolved from the fusion of a twelfth trunk segment with the telson. They also confirm the vicissicaudatan affinities of these extinct arthropods. Compositional analyses suggest that aglaspidid cuticle was essentially organic with a thin biomineralised (apatitic) outer layer. The trilobite reveals previously unknown gut features, such as medial fusion of digestive glands, possibly related to enhanced capabilities for digestion, storage, or the assimilation of food. The new fossils demonstrate that conditions conducive to soft-tissue preservation repeatedly developed in the outer shelf environment represented by the Furongian strata near Cranbrook. Future exploration of the c. 600-m-thick, mudstone-dominated upper part of the section may result in more abundant discoveries of exceptional fossils. |
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