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Article: Deciphering the early evolution of echinoderms with Cambrian fossils

Publication: Palaeontology
Volume: 57
Part: 6
Publication Date: November 2014
Page(s): 1105 1119
Author(s): Samuel Zamora and Imran A. Rahman
Addition Information

How to Cite

ZAMORA, S., RAHMAN, I. A. 2014. Deciphering the early evolution of echinoderms with Cambrian fossils. Palaeontology, 57, 6, 1105-1119.

Publication History

  • Samuel Zamora - Instituto Geológico y Minero de España, Zaragoza, Spain (email:
  • Samuel Zamora - Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA
  • Imran A. Rahman - School of Earth Sciences, University of Bristol, Bristol, UK (email:

Funded By

Ramón y Cajal. Grant Number: RYC-2012-10576
Spanish Ministry of Economy and Competitiveness. Grant Number: CGL2013-48877
1851 Royal Commission Research Fellowship

Online Version Hosted By

Wiley Online Library (Free Access)
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Echinoderms are a major group of invertebrate deuterostomes that have been an important component of marine ecosystems throughout the Phanerozoic. Their fossil record extends back to the Cambrian, when several disparate groups appear in different palaeocontinents at about the same time. Many of these early forms exhibit character combinations that differ radically from extant taxa, and thus their anatomy and phylogeny have long been controversial. Deciphering the earliest evolution of echinoderms therefore requires a detailed understanding of the morphology of Cambrian fossils, as well as the selection of an appropriate root and the identification of homologies for use in phylogenetic analysis. Based on the sister-group relationships and ontogeny of modern species and new fossil discoveries, we now know that the first echinoderms were bilaterally symmetrical, represented in the fossil record by Ctenoimbricata and some early ctenocystoids. The next branch in echinoderm phylogeny is represented by the asymmetrical cinctans and solutes, with an echinoderm-type ambulacral system originating in the more crownward of these groups (solutes). The first radial echinoderms are the helicoplacoids, which possess a triradial body plan with three ambulacra radiating from a lateral mouth. Helicocystoids represent the first pentaradial echinoderms and have the mouth facing upwards with five radiating recumbent ambulacra. Pentaradial echinoderms diversified rapidly from the beginning of their history, and the most significant differences between groups are recorded in the construction of the oral area and ambulacra, as well as the nature of their feeding appendages. Taken together, this provides a clear narrative of the early evolution of the echinoderm body plan.

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