M. Stein
Arthroaspis n. gen., a common element of the Sirius Passet Lagerstätte (Cambrian, North Greenland), sheds light on trilobite ancestry
Stein, M.; Budd, G.E.; Peel, J.S.; Harper, D.A.T.
Abstract
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 Lagerstätte 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.
Citation
Stein, M., Budd, G., Peel, J., & Harper, D. (2013). Arthroaspis n. gen., a common element of the Sirius Passet Lagerstätte (Cambrian, North Greenland), sheds light on trilobite ancestry. BMC Evolutionary Biology, 13, Article 99. https://doi.org/10.1186/1471-2148-13-99
Journal Article Type | Article |
---|---|
Acceptance Date | Apr 29, 2013 |
Publication Date | May 11, 2013 |
Deposit Date | May 17, 2013 |
Publicly Available Date | Jul 27, 2015 |
Journal | BMC Evolutionary Biology |
Publisher | BioMed Central |
Peer Reviewed | Peer Reviewed |
Volume | 13 |
Article Number | 99 |
DOI | https://doi.org/10.1186/1471-2148-13-99 |
Keywords | Sirius Passet Lagerstätte, Arthropoda, Lamellipedia, Trilobita, Appendages, Pygidium, Functional morphology. |
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© 2013 Stein et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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