On the half-shell

nine-banded armadillo
The nine-banded armadillo may not look like a typical mammal, but if you look carefully, you can see hair along the chin and between the protective plates (Photo: Rich Anderson, Creative Commons license)

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“Here’s a question for you… turtles and armadillos both have shells, so are they related?”

Whenever people gather for some kind of social event, the subject naturally turns to work. As in, “what do you do for a living?” In my case, what happens next is that the words “wildlife biologist” are out barely of my mouth before questions are spread before me like an appetizer tray.  It’s a pop quiz every time you meet someone new, with no idea what subject the test will cover. Just when I think I’ve heard every possible query, I’m reminded once again that the natural world is far too diverse to ever allow humans to run out of questions, much less find all the answers.

Turns out, this particular gentlemen had just returned from a trip to Texas, so naturally he had ‘dillos on his mind.

If you look at them from the right perspective, turtles and armadillos do have some surface similarities. But turtles, as most people know, are reptiles; armadillos are mammals.  Surprised? If so, you’re not alone. An armadillo just doesn’t fit the mammal profile. Where’s the hair… the teeth… the charisma?

Armadillos do have hair. It’s just that most of it isn’t in a form we recognize. The hard, shell-like covering is actually modified hair, with traditional strands between the jointed plates that allow the animal to curl up in a ball, protecting the vulnerable belly. Armadillo armor is similar to your fingernail, and at birth the shell is soft and pliable (a trait for which I’m sure Mom is grateful!), becoming harder as the young ones mature.  Armadillos have teeth, but like their close relatives, the sloths and anteaters, they are small and peg-like. As for personality… I’ll admit, they may not be as winsome as an otter or as sleek and athletic as a cougar. But I’ve found them to be inquisitive and surprisingly nimble for a creature who lives life on the half-shell.

turtle skeletonA turtle’s shell, on the other hand, is made of bony plates that have fused together and are connected to the ribs and spine. The shell is actually part of the skeleton, so that old Saturday morning cartoon trick, in which the turtle slips out of its shell, is possible only through the magic of animation. Of all the animals on Earth, only turtles and tortoises wear their hips and shoulders inside their ribcage. The shell continues to grow throughout the turtle’s life, and on some species you can actually see growth rings on each of the plates.

Even though they aren’t kin, armadillos and turtles do share one interesting characteristic: both are able to walk underwater along the bottoms of streams, ponds and lakes.

Why walk when you could swim?  Great question, but one that will have to wait until the next party. I’m going to stroll on over to the buffet table and dive into the dip.

Do you have questions about wildlife? Email NDN and the answer may turn up as a future blog post. And don’t forget to “Like” us on Facebook!

© 2011 Next-Door Nature— no reprints without written permission from the author.

2 Replies to “On the half-shell”

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