Many chelonian species have "hinges" in their shells. A hinge is simply a part or section of the shell that bends inward, as if hinged, to give further protection to the animal. Most have their hinge located on their plastron (bottom shell). The best known and also the one with the ability to close completely, are the box turtles.
The hingebacks however have their hinge on the carapace (the top shell). Their name, Kinixys comes from two Greek words: kineo (to move) and ixus (back or waist), thus meaning movable back. The hinge is located the carapace, between the seventh and eighth marginal scutes. The marginal scutes are the bottom edge scutes. It is also where the two shell halves are no longer joined (where the tortoise's legs are located).
This hinge does not allow them to close up completely like the box turtle, but does protect the tail area pretty well. It also may help when the female lays her eggs.
Hingebacks are not hatched with the hinge present, as shown by these Bell's hatchling.
Already you can see between these two Bell's hatchlings how the domed back is starting to happen.
At a little over a year, you can just barely start seeing the hinge appearing as shown in this Bell's. Notice the scute that has the light colored areas on both top corners? Can you see the slightest bit of flaring?
This two year old Bell's has a very pronounced start. See how the scute appears indented a little at the top, while starting to flare at the bottom? In the first picture, you can also see how it is starting to create a change between the two scutes above it.
Compare the difference between the two year old (the darker one at the top) and the one just a couple of months younger. See how the older one is able to keep his rear more tucked in? Gives it a more of a straight drop look at the rear.
In adults, the hinge looks like this.
The hingebacks however have their hinge on the carapace (the top shell). Their name, Kinixys comes from two Greek words: kineo (to move) and ixus (back or waist), thus meaning movable back. The hinge is located the carapace, between the seventh and eighth marginal scutes. The marginal scutes are the bottom edge scutes. It is also where the two shell halves are no longer joined (where the tortoise's legs are located).
This hinge does not allow them to close up completely like the box turtle, but does protect the tail area pretty well. It also may help when the female lays her eggs.
Hingebacks are not hatched with the hinge present, as shown by these Bell's hatchling.
Already you can see between these two Bell's hatchlings how the domed back is starting to happen.
At a little over a year, you can just barely start seeing the hinge appearing as shown in this Bell's. Notice the scute that has the light colored areas on both top corners? Can you see the slightest bit of flaring?
This two year old Bell's has a very pronounced start. See how the scute appears indented a little at the top, while starting to flare at the bottom? In the first picture, you can also see how it is starting to create a change between the two scutes above it.
Compare the difference between the two year old (the darker one at the top) and the one just a couple of months younger. See how the older one is able to keep his rear more tucked in? Gives it a more of a straight drop look at the rear.
In adults, the hinge looks like this.
