Is a Turtle Shell Really Modified Ribs?

It’s thought that the evolution of turtles
A turtle shell is not a shell at all but is made up of specially evolved ribs.

How Did Turtles Get Their Shells? – Follow Your Legend

Turtles' solid shells first stemmed from robust ribs – A new anatomy, paleontology thing for curious kids – 2 New Things

Turtles in a nutshell - the Node

Shells Articles

Shelly Miscavige Articles

Species Spotlight - Woodland Box Turtle (U.S. National Park Service)

Extinct Reptile Eunotosaurus Reveals How Turtles Got Their Shells

Fact Checks Archive, Page 238

Curious about turtles? The shelled reptile is easy to observe. - The Washington Post

FILLING IN THE CRACKS-SHELL FRACTURES IN TURTLES

Research suggests turtle shells evolved for digging, not protection

It turns out, this fossil plant is really a fossil baby turtle - Field Museum