Reptile & Amphibian Forums

I get lost when I can't read every day. Did anyone answer my question about why there a growth rings on box turtles but not painteds? If anyone answered, could you re-post? I should be able to get back on the computer tomorrow. apologies for falling behind.

Chrysemys sp. have growth rings, too. As in most aquatic turtles, they are noticeable for many years. They are less noticeable (or not evident at all) in adult painteds and adult box turtles, since growth may have ceased several years prior and any ridges would be worn down over the years. Perhaps box turtles have noticeable ridges for a longer period of their life as a result of how their shell grows over time (considerably more domed than a painted, yet hatchlings have the same general form). Also, there may be an adaptive advantage to painteds having less obvious ridges, as this would likely increase drag in a highly aquatic turtle. However, the aquatic nature may actually be the cause of the smoother shell, since there will inherently be more frictional forces acting on the shell.
Ryan

Ryan makes some good points.

Also, when it comes to Painteds...most who have kept Painteds know how often their shells peel as they grow. When a turtle grows, the new scute is formed underneath the old scute. The old scute will literally be sitting on top of the new scute. Painteds and some other aquatic turtles have a tendency to shed these older scutes. Box turtles tend to hold onto them. You can see the adaptive advantage...box turtles being more rigid and Painteds being more streamlined.

I have an excellent illustration of scute formation in an old book of mine. It is "Turtles, Tortoises, and Terrapins" 2nd edition (English translation) by Fritz Jurgen Obst, copyright 1988. My scanner is on the fritz(hahaha), but here's what it says...page 170, "Regular sloughing of skin from individual horny scutes is normal only in a few Pond terrapins such as Chrysemys and Cuora and in certain Side-necked turtles such as Emydura, Chelodina, and Elseya."

The illustration and key give a demonstration of this process in Painted turtles. Normally, I wouldn't reference such an old book (yikes, 1988 is old), but it's a great illustration. I'll try to remember to get this scanned at Office Depot whenever the flu releases its grip on my family.

If Fritz Jurgen Obst sounds familiar to some of you...he has a subspecies of Box turtle named after him. The Keeled Box turtle (Pyxidea mouhotii obsti).