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Article: The post-embryonic ontogeny of the early Cambrian trilobite Estaingia bilobata from South Australia: trunk development and phylogenetic implications

Papers in Palaeontology - Volume 7 Issue 1 - Cover
Publication: Papers in Palaeontology
Volume: 7
Part: 2
Publication Date: May 2021
Page(s): 931 950
Author(s): James D. Holmes, John R. Paterson, and Diego C. García-Bellido
DOI: 10.1002/spp2.1323
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How to Cite

HOLMES, J.D., PATERSON, J.R., GARCíA-BELLIDO, D.C. 2021. . Papers in Palaeontology, 7, 2, 931-950. DOI: /doi/10.1002/spp2.1323

Author Information

  • James D. Holmes - School of Biological Sciences University of Adelaide North Terrace Adelaide SA 5005 Australia
  • John R. Paterson - Palaeoscience Research Centre School of Environmental & Rural Science University of New England Armidale NSW 2351 Australia
  • Diego C. García-Bellido - School of Biological Sciences University of Adelaide North Terrace Adelaide SA 5005 Australia
  • Diego C. García-Bellido - South Australian Museum North Terrace Adelaide SA 5000 Australia

Publication History

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    Trilobites are one of the most diverse and abundant fossil groups from the early Palaeozoic, and as such are useful for answering important questions about early animal evolution, including developmental processes. Ontogenetic information for a large number of trilobite species has been published, but cases where multiple articulated specimens are known across the full range of developmental stages are rare. The early Cambrian (Series 2, Stage 4) Emu Bay Shale biota from Kangaroo Island (South Australia) is numerically dominated by trilobites, particularly articulated specimens of the ellipsocephaloid Estaingia bilobata, which are present in densities of >600 individuals per square metre on certain bedding planes. Here we describe the essentially complete post-embryonic ontogenetic series of E. bilobata from the Emu Bay Shale, and investigate patterns of growth relating to articulation and segmentation in this early Cambrian arthropod. Estaingia bilobata exhibits the hypoprotomeric mode of growth, with the epimorphic phase (the cessation of trunk segment generation) reached prior to the onset of the holaspid period. The meraspid pygidium had an extended equilibrium period in which anterior segment release into the thorax was matched by subterminal segment generation. Previously undocumented morphological features of E. bilobata, including the hypostome and bispinose pleural tips in holaspides, are also described. The growth characteristics and morphological features of E. bilobata documented herein strengthen close phylogenetic relationships between the Estaingiidae, Ellipsocephalidae and Xystriduridae.

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