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

  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},
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… 

Genomic insights of body plan transitions from bilateral to pentameral symmetry in Echinoderms

It is determined that the last common ancestor of echinoderms contained an organized Hox cluster and endoskeleton genes, and it is suggested that cooption of bilateral development genes was involved in evolution of the pentameric body plan.

Worms and gills, plates and spines: the evolutionary origins and incredible disparity of deuterostomes revealed by fossils, genes, and development.

The available morphological, palaeontological, developmental, and molecular data are reviewed to establish a framework for exploring the origins of Deuterostomia, and four characteristics most critical for understanding the form and function of the last common ancestor are considered.

Deciphering the early evolution of echinoderms with Cambrian fossils

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, which provides a clear narrative of the early evolution of the echinoderm body plan.

The Youngest Ctenocystoids from the Upper Ordovician of the United Kingdom and the Evolution of the Bilateral Body Plan in Echinoderms

During the early Palaeozoic, echinoderm body plans were much more diverse than they are today, displaying four distinct types of symmetry. This included the bilateral ctenocystoids, which were long

Oral Region Homologies in Paleozoic Crinoids and Other Plesiomorphic Pentaradial Echinoderms

Newly recognized oral region homologies are presented, based on the Universal Elemental Homology model for skeletal plates, in a wide range of fossil taxa for exploring branching order among stem groups on the echinoderm tree of life.

A hexamer origin of the echinoderms' five rays

It is proposed that the predominant five‐ray structure is derived from a hexamer structure that is grounded directly in the structure of the bilaterally symmetric larva, which implies that the adult echinoderm body can be derived directly from the larval bilateral symmetry and thus firmly ranks even the adults echinoderms among the bilaterians.

The oldest echinoderm faunas from Gondwana show that echinoderm body plan diversification was rapid.

The discovery of two new echinoderm faunas from the early part of the Cambrian of Morocco (West Gondwana) indicates that considerable diversification had already taken place by 510 Ma, and suggests that a rapid rate of morphological divergence took place during the initial stages of echinoderms evolution.

Testing for homologies in the axial skeleton of primitive echinoderms

  • C. Paul
  • Medicine
    Journal of Paleontology
  • 2017
The range of variation in echinoderms with fewer than five ambulacra implies that both the ‘branch’ and ‘stop’ instructions acted independently in all five rays, and terminal addition of plates, spacing of brachioles/pinnules, and lack of musculature to open cover plates all suggest that ‘cystoids’ had extensions of the water vascular system in their ambulanceacra.

Fixed, free, and fixed: the fickle phylogeny of extant Crinoidea (Echinodermata) and their Permian-Triassic origin.




Are homalozoans echinoderms? An answer from the extraxial-axial theory

The Extraxial-Axial Theory (EAT) identifies body-wall homologies, common ontogenetic patterns, and major events in bodyplan evolution and strongly suggests that the bizarre asymmetry of homalozoans is a derived characteristic, and not indicative of plesiomorphic morphology for either chordates or echinoderms.

Radical alterations in the roles of homeobox genes during echinoderm evolution

The expression domains in echinoderms of three important developmental regulatory genes ( distal-less, engrailed and orthodenticle ), all of which encode transcription factors that contain a homeodomain are reported, demonstrating the evolutionary lability of regulatory genes that are widely viewed as conservative.

The Early Phylogeny of Chordates and Echinoderms and the Origin of Chordate Left–Right Asymmetry and Bilateral Symmetry

The history of the echinoderm stem group is reconstructed and left–right asymmetry in Dexiothetica results mainly from dexiothetism—an episode in their ancestry when an animal resembling the Recent pterobranch Cephalodiscus lay right-side-downwards on the sea floor.

A critical reappraisal of the fossil record of the bilaterian phyla.

It is shown that the prospect of lineage diversification occurring early in the Proterozoic can be seen to be unlikely on grounds of both parsimony and functional morphology, and this analysis points to the requirement for a careful application of systematic methodology before explanations are sought for alleged patterns of constraint and flexibility.

The A/P axis in echinoderm ontogeny and evolution: evidence from fossils and molecules

SUMMARY Even though echinoderms are members of the Bilateria, the location of their anterior/posterior axis has remained enigmatic. Here we propose a novel solution to the problem employing three

A “rays-as-appendages” model for the origin of pentamerism in echinoderms

A new hypothesis concerning the evolutionary origin of pentameral symmetry in echinoderms is presented and it is proposed that a duplication of the uniray occurred and resulted in the addition of a pair of rays that followed Bateson's rules of symmetry to form a three-rayed 0-1-2, —A-BA, construction.

A phylogenetic test of the calcichordate scenario

The calcichordate scenario of Jefferies and colleagues purports to explain the origin and early evolution of the phyla Echinodermata and Chordata is tested, finding that it fails the erection of scenarios and fossils are unable to dictate the relationships among phyla.

Chapter 5 Evolution of Primitive Echinoderms

  • C. Paul
  • Geography, Environmental Science
  • 1977

Morphological diversity in the evolutionary radiation of Paleozoic and post-Paleozoic crinoids

  • M. Foote
  • Geography, Geology
  • 1999
Analysis of discrete-character data that cover the principal features of the crinoid skeleton shows that both Paleozoic and post-Paleozoic increases in morphological disparity were abrupt; this is consistent with rapid exploitation of open ecological opportunities in both cases.


Review of the functional morphology of Stephanocrinus suggests that these coronoid echinoderms were permanently attached by a column of moderate length and a cemented discoidal holdfast, and coronal canals probably served a respiratory function, gas exchange between sea water and coelomic fluids taking place through thin stereom of the coronal processes.