Stunted ribs gave turtles their shell

摘要

The mystery of the origin of the turtle's shell is a step closer to being solved.rnUnlike most vertebrates, turtles have ribs that are short and wide, and do not wrap around the body. Instead they fuse with vertebrae and bony plates in the skin of its back to form a shell.rnThe big question is whether the flattened ribs or the bony plates evolved first. Last year, a fossil was uncovered with a complete shell on its belly but an incomplete shell on its back. Its ribs were short and wide as in modern turtles, but the bony plates were absent - hinting that the ribs rather than the skin drove the evolution of the shell.