Friday 21 February 2020

Why a turtle's shell is so important-It's delicate and beautiful, and it's not a suit of armor. - via Herp Digest

by Christian Cotroneo 2/4/20,

For a turtle, home isn't just where the heart is. It's where the brain, limbs, organs and the spinal cord reside, too.

In fact, one of the biggest myths still somehow circulating about a turtle's shell is that it's a mobile home — one that can be swapped out for another.

As wildlife technician Samantha Kennett writes in a blog for the Chattahoochee Nature Center, "A turtle's shell is as much a part of its body as our skeleton is to ours."
Think of it as a modified rib cage that a turtle can fully retreat inside of in case of trouble. (Unless, unfortunately, it's a sea turtle, which has long lost the ability to retract its limbs.)

That means turtles, like others members of the Testudines order — including tortoises and terrapins — have to take special care of those shells. It's the only home they've got.

And, of course, in spring — starting in May especially — humans have to be especially mindful of the slow stampede of turtles crossing roads as they head to their nesting grounds.

That's not to say a turtle's shell doesn't make for an enviable suit of medieval armor. It comes in two main pieces: the top, called the carapace and the bottom, the plastron. And, like forged armor, these pieces are linked together around the middle parts by the aptly called bridge.

The sturdy parts on the carapace are individual plates known as scutes, made from the same hardened protein as fingernails: keratin.

Yes, Mother Nature knows a thing or two about forging quality armor. The trouble is, no suit of armor is designed to withstand the 4,000-or-so pounds of pressure a modern automobile exerts. Nor is it a fortress against the sheer foolishness humans are capable — like, as Kennett points out, chaining two turtles together by piercing their shells.

The organization treated a couple of turtles in just such a predicament recently — turtles that are lucky to be alive thanks to a vigilant passerby who found them in a river.

Indeed, while a turtle's armor may seem like the ultimate in full-body protection, it's deceptively fragile. Predators may be rebuffed But the tiniest crack in that armor opens the door for infection.

"Because the shell is living bone, any puncture can lead to systemic bacterial, viral, and/or fungal infections," Kathryn Dudeck, wildlife director at the Chattahoochee Nature Center, explains in the blog. "Additionally, since the organs are not in a fixed position, but instead housed in a thin membrane called the coelom, the organs themselves can be damaged.”

Even a dab of paint could disrupt essential processes that occur on the surface of that shell. That's because the shell, like the leaf of a plant, does some pretty incredible things with sunlight. Specifically, it absorbs UV light and synthesizes the vitamin D needed to make bones grow big and strong. Paint, or anything that obscures the shell, throws a wrench into that process, resulting in stunted and misshapen shells.

In fact, the number of painted turtles showing up in Florida in recent years even prompted the state's wildlife authority to issue a plea to potential Picassos on its Facebook page.

"While to you it may seem harmless, painting the shells of turtles and tortoises can severely compromise their health — the paint can hinder their ability to absorb vitamins they need from the sun (and) cause respiratory problems," the Florida Fish and Wildlife Conservation Commission noted.

So, from an evolutionary perspective, a turtle's shell is a many splendored thing — from a lineage that harks back more than 200 million years. But in the modern age, it's too easily a many-splintered thing — vulnerable to everything from cars to errant paintbrushes to misguided pet owners.

Which is why it's even more essential to stop looking at a shell as armor that can be mended or swapped out entirely if it gets damaged.

For the turtle, this is no shell game. But a matter of life and death.

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