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Article: A large new leanchoiliid from the Burgess Shale and the influence of inapplicable states on stem arthropod phylogeny

Palaeontology - Vol. 58 Part 4 - Cover Image
Publication: Palaeontology
Volume: 58
Part: 4
Publication Date: July 2015
Page(s): 629 660
Author(s): Cédric Aria, Jean‐Bernard Caron, and Robert Gaines
Addition Information

How to Cite

ARIA, C., CARON, J., GAINES, R. 2015. A large new leanchoiliid from the Burgess Shale and the influence of inapplicable states on stem arthropod phylogeny. Palaeontology, 58, 4, 629-660. DOI: 10.1111/pala.12161

Author Information

  • Cédric Aria - University of Toronto Department of Ecology and Evolutionary Biology Toronto Ontario Canada (Email: cedric.aria@outlook.com)
  • Cédric Aria - Palaeobiology Royal Ontario Museum Department of Natural History Toronto Ontario Canada
  • Jean‐Bernard Caron - University of Toronto Department of Ecology and Evolutionary Biology Toronto Ontario Canada (Email: jcaron@rom.on.ca)
  • Jean‐Bernard Caron - Palaeobiology Royal Ontario Museum Department of Natural History Toronto Ontario Canada
  • Robert Gaines - Pomona College Geology Department Claremont CA USA (Email: robert.gaines@pomona.edu)

Publication History

  • Issue published online: 30 June 2015
  • Article first published online: 01 January 1970
  • Manuscript Accepted: 17 February 2015
  • Manuscript Received: 10 August 2014

Funded By

University of Toronto (Department of Ecology and Evolution)
Natural Sciences and Engineering Research Council Discovery Grant. Grant Number: #341944
Royal Ontario Museum

Online Version Hosted By

Wiley Online Library
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Abstract

Characterized by atypical frontalmost appendages, leanchoiliids are early arthropods whose phylogenetic placement has been much debated. Morphological interpretations have differed, some of which concern critical characters such as the number of eyes and head appendages, but methodological approaches also have diverged. Here, we describe a new leanchoiliid, Yawunik kootenayi gen. et sp. nov., based on 42 specimens from the newly discovered Marble Canyon locality of the Burgess Shale (Kootenay National Park, British Columbia; middle Cambrian). This new morphotype demonstrates the presence of a four‐segmented head in leanchoiliids, along with two small antero‐median eyes in addition to lateral eyes. Yawunik is characterized by a 12‐segmented trunk and a carinate, lanceolate telson adorned with minute spines. The ‘great appendages’ of the animal bear teeth on their two distal rami, which would have enhanced their ability to grasp prey. Attitudes of specimens, resulting from burial at multiple aspects of bedding, suggest the ‘great appendages’ were flexible and capable of antero‐posterior rotation. We also discuss the nature of intersegmental tissues and filaments present within the ‘great appendages’. Our phylogenetic analyses extend the monophyly of leanchoiliids to include Haikoucaris and Yohoia in a new clade, the Cheiromorpha nom. nov. (within Heptopodomera nom. nov.). Other nodes are poorly resolved unless implied weights are used, and in this case, the topology is critically sensitive to the coding prerogative of inapplicable states (NAs). Both the traditional ‘Arachnomorpha’ hypothesis (NAs as additional states) and the more recently favoured ‘Artiopoda + Crustacea’ (NAs as uncertainties) were obtained using the same data set and outgroup. This result stresses, first, the historical importance of polarization over data content in scenarios of early arthropod evolution, and second, a pressing need to investigate the impacts of coding inapplicables, especially given the inflating effect of implied weights.

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