How the turtle got its shell — clues revealed by a new discovery

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Through careful study of an ancient ancestor of modern turtles, researchers now have a clearer picture of how the turtles’ unusual shell came to be. The findings, reported today in Current Biology, a publication of Elsevier’s Cell Press, help fill a 30- to 55-million-year gap in the turtle fossil record through study of an extinct South African reptile known as Eunotosaurus.


“The turtle shell is a complex structure whose initial transformations started over 260 million years ago in the Permian period,” said lead author Dr. Tyler Lyson of Yale University and the Smithsonian Institution, who traveled to the Karoo Basin in South Africa to examine specimens in the field and in museums with Dr. Gaberiel Bever, an anatomy professor at the New York Institute of Technology College of Osteopathic Medicine. “Like other complex structures, the shell evolved over millions of years and was gradually modified into its present-day shape.”

The turtle shell isn’t really just one thing — it is made up of approximately 50 bones. Turtles are the only animals that form a shell through the fusion of ribs and vertebrae. In all other animals, shells are formed from bony scales on the surface; they don’t stick their bones on the outsides of their bodies.

“The reason, I think, that more animals don’t form a shell via the broadening and eventually suturing together of the ribs is that the ribs of mammals and lizards are used to help ventilate the lungs,” Lyson said. “If you incorporate your ribs into a protective shell, then you have to find a new way to breathe.” Turtles have done just that, with the help of a muscular sling.

Written By: Mary Beth O’Leary and Elaine Iandoli
continue to source article at elsevierconnect.com

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  1. This is somewhat off topic. I learned the other day that turtles are unfortunate omens in Chinese culture. They even rejected streamlined cars on the grounds they looked like turtles. They apparently believe that turtles have unusually degenerate sex lives. I have never heard of this. Has anyone?

    It seems to me that in other mythologies, turtles are considered unusually wholesome animals.

  2. Perhaps the breathing arrangement that evolved was relatively inefficient hence the slow movement of turtles and tortoises. The benefit of developing a hard protective outer shell may have outweighed a consequent loss of agility and speed?

    • In reply to #4 by Richard01:

      Perhaps the breathing arrangement that evolved was relatively inefficient hence the slow movement of turtles and tortoises. The benefit of developing a hard protective outer shell may have outweighed a consequent loss of agility and speed?

      In water, however, the turtle is a graceful and efficient mover. I suppose, if a tortoise fell into a pond, it would be able to swim and might be able to do so quite well too, at least to get itself out of the water again. But watching turtles swim is a pleasure in itself.

  3. I heard an interview on the Quirks and Quarks radio show about this discovery. Apparently there were two hypothesis. The paleontologists figured plates formed on the outside. The embryologists figured ribs and vertebrae had thickened. The clincher was finding some quasi-turtle fossils. Ontology recapitulates phylogeny when I was taught back in the 60 was a sort of strange quirk of nature. Now I think we would explain it as a necessary consequence of how genes evolve. I would have thought it would have resolved this controversy earlier.

  4. This raises an obvious question to my mind: the development of the shell depends clearly upon also developing the new way to breathe – how is such a dual dependency of effect achieved in terms of the orthodox understanding without a fatal mismatch of timing?

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