Morphogenesis of the turtle shell: the development of a novel structure in tetrapod evolution

  title={Morphogenesis of the turtle shell: the development of a novel structure in tetrapod evolution},
  author={Scott F. Gilbert and Grace A. Loredo and Alla Brukman and Ann C. Burke},
  journal={Evolution \& Development},
SUMMARY The turtle shell is an evolutionary novelty that is synapomorphic for chelonians. The carapace is initiated by the entrapment of the ribs by the carapacial ridge (CR), a lateral bulge of the dorsal ectoderm and dermal mesoderm. The mechanisms by which the CR is initiated, the ribs entrapped and the dorsal dermis ossified, remains unknown. Similarly, the formation of the plastron remains unexplained. Here, we present a series of anatomical investigations into plastron and carapace… 

Origin of the Turtle Body Plan: The Folding Theory to Illustrate Turtle-Specific Developmental Repatterning

This developmental sequence of the modern turtles aligns with a stepwise evolutionary process in the group, which is supported by the anatomy of a recently discovered fossil species, Odontochelys.

The evolutionary origin of the turtle shell and its dependence on the axial arrest of the embryonic rib cage.

Both paleontological and genomic evidence suggest that the axial arrest is the first step toward acquisition of the turtle body plan, which is estimated to have taken place after the divergence of a clade including turtles from archosaurs.

On the carapacial ridge in turtle embryos: its developmental origin, function and the chelonian body plan

It is concluded that the CR is a true embryonic novelty among amniotes and, because of the specific expression of regulatory genes, it functions in the marginal growth of the carapacial primordium, thereby inducing the fan-shaped arrangement of the ribs.

How the turtle forms its shell: a paracrine hypothesis of carapace formation.

It is shown here that the carapacial ridge (CR) is critical for the entry of the ribs into the dorsal dermis, and that the maintenance of the CR and its ability to attract the migrating rib precursor cells depend upon fibroblast growth factor (FGF) signaling.

Evolution of the Turtle Body Plan by the Folding and Creation of New Muscle Connections

This work proposes that the evolutionary origin of the turtle body plan results from heterotopy based on folding and novel connectivities, and suggests that some limb muscles establish new turtle-specific attachments associated with carapace formation.

Body plan of turtles: an anatomical, developmental and evolutionary perspective

Comparative developmental data allow us to hypothesize the gradual evolution of turtles, which is consistent with the recent finding of a transitional fossil animal, Odontochelys, which did not have the carapace but already possessed the plastron.

Evolutionary developmental perspective for the origin of turtles: the folding theory for the shell based on the developmental nature of the carapacial ridge

The turtle body plan can be explained with knowledge of vertebrate anatomy and developmental biology, consistent with the evolutionary origin of the turtle suggested by the recently discovered fossil species, Odontochelys.

Development of an evolutionarily novel structure: fibroblast growth factor expression in the carapacial ridge of turtle embryos.

Data is presented suggesting that carapace formation is initiated by co-opting genes that had other functions in the ancestral embryo, specifically those of limb outgrowth, and there is divergence in the signaling repertoire from that involved in limb initiation and outgrowth.

Evolutionary Origin of the Turtle Shell

Emerging from the rib: resolving the turtle controversies.

Two of the major controversies in the present study of turtle shell development involve the mechanism by which the carapacial ridge initiates shell formation and the mechanism by which each rib forms



Development of the turtle carapace: Implications for the evolution of a novel bauplan

  • A. Burke
  • Biology
    Journal of morphology
  • 1989
Embryos of Chelydra serpentina were studied during stages of carapace development and tissue morphology, autoradiography, and indirect immunofluorescent localization of adhesion molecules indicate that the outgrowth of the embryonic carapACE occurs as the result of an epithelial–mesenchymal interaction in the body wall.

The Development and Evolution of the Turtle Body Plan: Inferring Intrinsic Aspects of the Evolutionary Process from Experimental Embryology

Surgical perturbations were designed to test the causal connection between the epithelial-mesenchymal interaction in the body wall and the unusual placement of the ribs in turtles.

Morphogenesis of shell and scutes in the turtle Emydura macquarii

Formation of the scutes and dermis of the embryonic shell of the turtle Emydura macquarii was studied using light and electron microscopy. Shell morphogenesis begins at embryonic stage 15 and the

Correlated progression and the origin of turtles

It is shown that certain pareiasaurs—dwarf, heavily armoured forms such a Nanoparia—approach the chelonian morphology even more closely than previously thought, suggesting that the rigid armoured body of turtles evolved gradually, through 'correlated progression'.

Epidermal differentiation during carapace and plastron formation in the embryonic turtle Emydura macquarii

This work provides the first ultrastructural description of differentiation of the epidermis of the carapace and plastron in the Chelonia, using the Australian pleurodiran turtle Emydura macquarii as a model to demonstrate the role of calcium in the development of reptilian skin.


  • Howard K. Suzuki
  • Environmental Science, Biology
    Annals of the New York Academy of Sciences
  • 1963
Phylogenetically the turtles are considered to be an early offshoot of the primitive stem reptiles (e.g., Seymouriu) and have retained their primitive characteristics (Romer, 1955), and their normal histology is not widely known.

XI. On the development and homologies of the carapace and plastron of the chelonian reptiles

  • R. Owen
  • Biology
    Philosophical Transactions of the Royal Society of London
  • 1849
To ascertain the precise nature and extent of modifications, in other words, to determine the homologies of the bony framework of the case in question, is the aim of the present communication.


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An exoskeleton is extensive in the head, trunk, and tail of agnathan and gnathostome fishes, where it forms a thick, rigid armor in most fossil fishes, although many only have a covering of separate

Complete mitochondrial genome suggests diapsid affinities of turtles.

  • R. ZardoyaA. Meyer
  • Biology
    Proceedings of the National Academy of Sciences of the United States of America
  • 1998
The results challenge the classic view of turtles as the only survivors of primary anapsid reptiles and imply that turtles might have secondarily lost their skull fenestration.