The turtle shell isn't like any other protective element of any living animal: it's not an exoskeleton, like some invertebrates have, nor is it made of ossified scales like armadillos, pangolins, or some snake and reptile species. It's not made of skin. It can't be removed--to do so would kill the turtle, and all that's underneath is internal organs. So how did this very common animal end up so unique?
New research from Tyler Lyson at Yale University furthers an existing theory: that turtles stem from a 200-million-year-old dinosaur called Eunotosaurus. Eunotosaurus looks sort of like a cross between a turtle and a lizard, or like a lizard that's somehow swallowed a cannonball:
The turtle shell is actually a peculiar evolution of a turtle's bone structure. Its vertebrae, pelvis, ribcage--it has no muscles between its ribs, which makes this easier--and other bones fuse together to form a sort of reptilian exoskeleton. The scale-like pieces which make the turtle shell look like a soccer ball are called scutes, and they have individual names, often based on location, after what they'd be called in a less bizarre animal (anal scute, pectoral scute, that kind of thing).
Turtles are very old, appearing in the fossil record about 210 million years ago. But the shell was already full formed in those fossils. Where the hell did the turtle come from?
Lyson analyzed more than 45 Eunotosaurus fossils, as Eunotosaurus has a sort of proto-shell in which its ribs are touching, like the turtle and unlike any other reptile. Then he put together this animation, which shows the organic and natural way that Eunotosaurus could have led to the turtle:
You can see the bones of the more typically reptilian early relatives broadening, joining together, and moving to the top and bottom of the animal, forming a protective barrier. And, interestingly, this process is mirrored in the development of turtle embryos. "The first thing we see in a developing turtle embryo is the broadening of its ribs, followed by the broadening of its vertebrae, and finally by the acquisition of the osteoderms along the perimeter of the shell," Lyson says.
The paper appears in the latest issue of Current Biology.
While I appreciate and am well-informed by many of the publications of PopSci,
I registered just to protest, just once, all this 200-million year old bunk and similar foolishness. The most improbable and statistically indefensible of any human intellectual notion is the THEORY of evolution.
God, the Intelligent Creator, created a turtle with its shell, just like He created you without one... not by chance, but with a word!
I fully expect disdain for this perspective and I won't engage in an online debate, but on the last day the faith of every Christian who holds to a literal understanding of the creation account in Genesis 1 will be vindicated.
Interested in a reality check? --> creation.com
You are forgetting PoPSCi theory or statement that "... like a lizard that's somehow swallowed a cannonball...".
Fasinating, after seeing the insides of many box turtles.(lawn mowing accidents) I wondered how their amazing structure came about.
"But the shell was already full formed in those fossils. Where the hell did the turtle come from?"
Do you want the easy sensible answer? Or the one that the naturalists will do all sorts of gymnastics to contrive with out any ability to support it with observation?
"the shell was already full formed" You're half way there Dan, just think about it a little longer.
Fascinating! Thanks Dan!
Your stock photo shows signs of pyramiding which is typically found in unhealthy turtles.
The YouTube video alone was worth the read. Awesome stuff.