Ontogeny in the fossil record: diversification of body plans and the evolution of “aberrant” symmetry in Paleozoic echinoderms

@inproceedings{Sumrall2007OntogenyIT,
  title={Ontogeny in the fossil record: diversification of body plans and the evolution of “aberrant” symmetry in Paleozoic echinoderms},
  author={Colin D. Sumrall and Gregory A. Wray},
  booktitle={Paleobiology},
  year={2007}
}
Abstract Echinoderms have long been characterized by the presence of ambulacra that exhibit pentaradiate symmetry and define five primary body axes. In reality, truly pentaradial ambulacral symmetry is a condition derived only once in the evolutionary history of echinoderms and is restricted to eleutherozoans, the clade that contains most living echinoderm species. In contrast, early echinoderms have a bilaterally symmetrical 2–1–2 arrangement, with three ambulacra radiating from the mouth… 

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