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Arthroaspis n. gen., a common element of the Sirius Passet Lagerstatte (Cambrian, North Greenland), sheds light on trilobite ancestry
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
2013 (English)In: BMC Evolutionary Biology, ISSN 1471-2148, Vol. 13, 99- p.Article in journal (Refereed) Published
Abstract [en]

Background: Exceptionally preserved Palaeozoic faunas have yielded a plethora of trilobite-like arthropods, often referred to as lamellipedians. Among these, Artiopoda is supposed to contain taxa united by a distinctive appendage structure. This includes several well supported groups, Helmetiida, Nektaspida, and Trilobita, as well as a number of problematic taxa. Interrelationships remain unclear, and the position of the lamellipedian arthropods as a whole also remains the subject of debate. Results: Arthroaspis bergstroemi n. gen. n. sp., a new arthropod from the early Cambrian Sirius Passet Lagerstatte of North Greenland shows a striking combination of both dorsal and ventral characters of Helmetiida, Nektaspida, and Trilobita. Cladistic analysis with a broad taxon sampling of predominantly early Palaeozoic arthropods yields a monophyletic Lamellipedia as sister taxon to the Crustacea or Tetraconata. Artiopoda is resolved as paraphyletic, giving rise to the Marrellomorpha. Within Lamellipedia, a clade of pygidium bearing taxa is resolved that can be shown to have a broadly helmetiid-like tergite morphology in its ground pattern. This morphology is plesiomorphically retained in Helmetiida and in Arthroaspis, which falls basally into a clade containing Trilobita. The trilobite appendages, though similar to those of other lamellipedians in gross morphology, have a unique outward rotation of the anterior trunk appendages, resulting in a 'hard wired' lateral splay, different to that observed in other Lamellipedia. Conclusions: The combination of helmetiid, trilobite, and nektaspid characters in Arthroaspis gives important hints concerning character polarisation within the trilobite-like arthropods. The distinctive tergite morphology of trilobites, with its sophisticated articulating devices, is derived from flanged edge-to-edge articulating tergites forming a shield similar to the helmetiids, previously considered autapomorphic for that group. The stereotypical lateral splay of the appendages of lamellipedians is a homoplastic character shown to be achieved by several groups independently.

Place, publisher, year, edition, pages
2013. Vol. 13, 99- p.
Keyword [en]
Sirius Passet Lagerstatte, Arthropoda, Lamellipedia, Trilobita, Appendages, Pygidium, Functional morphology
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-203302DOI: 10.1186/1471-2148-13-99ISI: 000319425700001OAI: oai:DiVA.org:uu-203302DiVA: diva2:636114
Available from: 2013-07-08 Created: 2013-07-08 Last updated: 2013-07-08Bibliographically approved

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Budd, Graham E.Peel, John Stuart
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