, Volume 132, Issue 1, pp 95–110 | Cite as

Evolution and development of the synarcual in early vertebrates

  • Zerina JohansonEmail author
  • Kate Trinajstic
  • Robert Carr
  • Alex Ritchie
Original Paper


The synarcual is a structure incorporating the anterior vertebrae of the axial skeleton and occurs in vertebrate taxa such as the fossil group Placodermi and the Chondrichthyes (Holocephali, Batoidea). Although the synarcual varies morphologically in these groups, it represents the first indication, phylogenetically, of a differentiation of the vertebral column into separate regions. Among the placoderms, the synarcual of Cowralepis mclachlani Ritchie, 2005 (Arthrodira) shows substantial changes during ontogeny to produce an elongate, spool-shaped structure with a well-developed dorsal keel. Because the placoderm synarcual is covered in perichondral bone, the ontogenetic history of this Cowralepis specimen is preserved as it developed anteroposteriorly, dorsally and ventrally. As well, in the placoderm Materpiscis attenboroughi Long et al., 2008 (Ptyctodontida), incomplete fusion at the posterior synarcual margin indicates that both neural and haemal arch vertebral elements are added to the synarcual. A survey of placoderm synarcuals shows that taxa such as Materpiscis and Cowralepis are particularly informative because perichondral ossification occurs prior to synarcual fusion such that individual vertebral elements can be identified. In other placoderm synarcuals (e.g. Nefudina qalibahensis Lelièvre et al., 1995; Rhenanida), cartilaginous vertebral elements fuse prior to perichondral ossification so that individual elements are more difficult to recognize. This ontogenetic development in placoderms can be compared to synarcual development in Recent chondrichthyans; the incorporation of neural and haemal elements is more similar to the holocephalans, but differs from the batoid chondrichthyans.


Vertebral fusion Synarcual Placodermi Chondrichthyes Holocephali Batoidea Vertebral column 



KT would like to acknowledge the receipt of a QEII Fellowship and KT and ZJ acknowledge DP110101127 awarded by the Australian Research Council. We also thank Mikael Siversson Western Australian Museum for access to the collections. AR would like to thank Mr. Alex McLachlan, owner of the quarry from which Cowralepis mclachlani has been collected. Mr. McLachlan has provided unlimited access to the quarry and substantial financial support. We would also like to thank Mr. Bruce Loomes, Canowindra, for discovering the specimen of C. mclachlani described in this paper, and for recognizing its importance. RC thanks Scott Schaefer for access to AMNH Ichthyology Collections. Finally, we would like to thank an anonymous reviewer and Kerin Claeson for their comments, which were very helpful in improving this paper.


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Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  • Zerina Johanson
    • 1
    Email author
  • Kate Trinajstic
    • 2
    • 3
  • Robert Carr
    • 4
  • Alex Ritchie
    • 5
  1. 1.Earth Sciences, Natural History MuseumLondonUK
  2. 2.Western Australian Organic and Isotope Geochemistry Centre, Department of ChemistryCurtin UniversityBentleyAustralia
  3. 3.Department of Earth and Planetary SciencesWestern Australian MuseumWelshpoolAustralia
  4. 4.Department of Natural Sciences and GeographyConcordia University ChicagoRiver ForestUSA
  5. 5.PalaeontologyAustralian MuseumSydneyAustralia

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