How Does a Turtle Develop Its Shell?
As an undergraduate student, I worked in Scott Gilbert's developmental biology lab, studying embryonic cues that drive turtle shell (carapce) development from an evolutionary perspective. The turtle shell is an evolutionarily novel adaptation that co-opts typical vertebrate rib development to induce shell formation.
Cebra-Thomas J., F. Tan, S. Sistla, E. Estes, G. Bender, C. Kim, P. Riccio, S. Gilbert. How the turtle forms its shell: A paracrine hypothesis of carapace formation. J. Experimental Zoology B: 558 – 569.