Differentiating Geochelone denticulata and Geochelone carbonaria
by Jack W. Hagan
Quite often there is confusion in identifying two of the three tortoises which are native to continental South
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
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.
The range of G. denticulata is as follows: southern Colombia (absent from the north), Venezuela, Island of Trinidad, Guyana (formerly British Guiana), Surinam, French Guiana, Peru and Brazil, being absent from
G. carbonaria has much the same range, but includes Colombia, only the western portion of Peru and is
found in Paraguay.
*Gular shield even with posterior portion of carapace
*Gular shield short of posterior portion of carapace
Humeral median suture usually longer than femoral median suture
Femoral median suture usually longer than humeral median suture
*Inguinal quite inconspicuous
*Inguinal quite conspicuous
Prefrontals small and broken up
*First marginals denticulated in young
*First marginals not denticulated in young
Very little if any concentric grooving of scutes
Concentric grooving quite predominant
*Most constant characteristics
When the scientists compared DNA from all four species of gopher tortoise they confirmed the close link between X. agassizii and X. berlandieri, and between G. flavomarginatus and G. polyphemus. Their
results suggested that the Xerobates and Gopherus forms last shared a common female ancestor some 5-6
million years ago. The Texas tortoise, X. berlandieri, proved to be very closely related to the "eastern"
agassizii genotype. It is highly likely that berlandieri evolved from this eastern agassizii assemblage,
probably from Xerobates stock inhabiting the north central region of Sonora. Perhaps the closeness of the
relationship between the eastern agassizii assemblage and berlandieri explains the occasional occurrence
of hybrids from matings between captive Texas and desert tortoises.
Article reprinted with permission from International Turtle and Tortoise Society Journal 2:4-5, 1968.