Homology of the enigmatic nuchal bone reveals novel reorganization of the shoulder girdle in the evolution of the turtle shell

@article{Lyson2013HomologyOT,
  title={Homology of the enigmatic nuchal bone reveals novel reorganization of the shoulder girdle in the evolution of the turtle shell},
  author={Tyler R. Lyson and Bhart‐Anjan S. Bhullar and Gabriel S Bever and Walter G. Joyce and Kevin de Queiroz and Arhat Abzhanov and Jacques A. Gauthier},
  journal={Evolution \& Development},
  year={2013},
  volume={15}
}
The turtle shell represents a unique modification of the ancestral tetrapod body plan. The homologies of its approximately 50 bones have been the subject of debate for more than 200 years. Although most of those homologies are now firmly established, the evolutionary origin of the dorsal median nuchal bone of the carapace remains unresolved. We propose a novel hypothesis in which the nuchal is derived from the paired, laterally positioned cleithra—dorsal elements of the ancestral tetrapod… 

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References

SHOWING 1-10 OF 87 REFERENCES

The Origin of the Bony Shell of Turtles as a Unique Evolutionary Model in Reptiles

TLDR
Generally, the bony armor of reptiles consists of separate osteoderms which develop in the dermis independently from the internal skeleton, but Testudines progressed in a unique evolutionary direction.

Evolution of the turtle bauplan: the topological relationship of the scapula relative to the ribcage

TLDR
The topological relationship of the shoulder girdle relative to the ribcage is analysed within a broader phylogenetic context and it is determined that the condition found in turtles is also found in amphibians, monotreme mammals and lepidosaurs.

The ontogeny of the shell in side‐necked turtles, with emphasis on the homologies of costal and neural bones

TLDR
An alternative structural hypothesis for the neural reduction and, ultimately, the complete loss of the neural series is proposed and the complete reduction of neurals in Emydura spp.

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

TLDR
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.

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

TLDR
An anatomical investigations into plastron and carapace formation in the red‐eared slider, Trachemys scripta, and the snapping turtle, Chelydra serpentina suggest that the rib is organizing dermal ossification by secreting paracrine factors.

Growth of the pectoral girdle of the Leopard frog, Rana pipiens (Anura: Ranidae)

TLDR
Comparisons of anuran long bone and pectoral girdle growth suggest that different bones can have similar histology and development regardless of adult morphology.

An ancestral turtle from the Late Triassic of southwestern China

TLDR
A new 220-million-year-old turtle from China is described that documents an intermediate step in the evolution of the shell and associated structures and shows that the turtle shell is not derived from a fusion of osteoderms.

Evidence for the neural crest origin of turtle plastron bones

TLDR
It is shown that the bones of the plastron stain positively for HNK‐1 and PDGFRα and are therefore most likely of neural crest origin and extended the hypothesis of the neural crestorigin of the exoskeleton to include the turtle plastrons.

Skeletal development in the Chinese soft‐shelled turtle Pelodiscus sinensis (Testudines: Trionychidae)

TLDR
Investigation of the development of the whole skeleton of the soft‐shelled turtle Pelodiscus sinensis and an analysis of the sequence of skeletal ossification in cryptodirans reveals heterochronies, some of which reflect the hypothesized phylogeny considered taxa.
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