Quite often there is confusion in identifying two of the three tortoises which are native to continental South America.
The Argentine tortoise, Geochelone chilensis, is quite easily distinguished from the other two South American tortoises, looking at first glance much like one of the tortoises belonging to the genus Gopherus.
Geochelone denticulata and G. carbonaria are the two tortoises which are often misidentified, particularly by many of the animal dealers who supply these attractive tortoises. Geochelone denticulata is commonly called "yellow leg" tortoise and G. carbonaria is frequently known as "red leg" tortoise. Use of these common names causes confusion, due to the fact that the so-called "red legs" sometimes have red legs, sometimes yellow and very often, any shade in between the two. Many dealers use coloring as their only means of identification, listing a G.carbonaria with yellow legs as G. denticulata.
No one characteristic can be used to identify these two tortoises; it takes a combination of differences to properly identify them. It is hoped that the following text and diagrams will be helpful in identifying these two South American tortoises.
Some of the characteristics are more constant and will hold true in the majority of specimens examined. Others are not as stable and will vary from specimen to specimen of species being examined.
G. denticulata, which appears to be the species less often displayed in collections, is the larger of the two. Specimens sometimes reach a length of nearly 26 inches. Carapace of both young and adult is a uniform light brown, with lighter yellow-brown centers in each shield. The young denticulate tends to show some concentric grooving or ringing of the shields on the carapace, but larger specimens show very little, if any.
The concentric grooving is a very predominant characteristic of G. carbonaria in both old and young specimens. The adult male denticulate appears to be somewhat bell-shaped when viewed dorsally, tending to flare out at the posterior third of the carapace in the area directly above the intergular. Females retain the more rounded shape of the young. Both young and adult, male and female, have a quite highly domed carapace with a gentle rounding from central to marginals when viewed anteriorly or posteriorly, with females having a higher dome.
G. carbonaria retains much the same shape throughout its life, having sides of the carapace quite parallel, giving it the appearance of a loaf of bread. In older, adult specimens, the shell can be seen to be indented slightly at mid-body when viewed dorsally, thus giving it a slight hour-glass shape. Carbonaria does not appear to reach the size of denticulata, large adult specimens obtaining an average carapace length of about 19 inches.
There is very little information on actual habitat of these two species. They both range over much of the same area of South America, both being found in forested areas where adequate shade is available, as neither appears to like to bask in full sunlight. Carbonaria seems to prefer the damper habitat, being found in wet, muddy dens in the wild, showing a tendency to drink and soak more in captivity than denticulata.