The scientific name for this species, Testudo chilensis, is misleading because it is not native to Chile. It occurs mainly in Argentina, Bolivia and neighboring Paraguay. When the species was first described by Gray in 1870, he mistakenly thought that Mendoza was in Chile instead of Argentina, thus the misnomer. Sclater corrected his mistake in the same year. However, the rules of nomenclature gave precedence to the name chilensis, even though it was based on an erroneous assumption, and the name persisted.
The carapace can measure up to 43.3 cm (but usually less than 25 cm) and may be either totally yellowish brown or have dark-brown to black annuli surrounding a tan center on each scute. Specimens found further south tend to be much larger than those found in further north populations. The rim of the shell is slightly serrated and has a dark wedge of pigment at the back edge of each scute. The plastron may be uniformly yellowish-brown or have a dark triangular wedge along the seams of each scute. The head, limbs and tail are greyish to yellowish-brown, with the front of each forelimb covered with large, angular scales and each thigh featuring several enlarged tubercles.
Like all tortoise species, the chaco tortoise is primarily herbivorous, consuming grasses, shrubs, fruits, and cactus pads.
As of right now, there is only one recognized species. However, some researchers believe G. chilensis should be divided into three species: G. chilensis, G. petersi, and G. donosobarrosi. Some feel that G. petersi is actually a juvenile G. chilensis. Others feel that they are male G. chilensis, the sexual dimorphism in these species having been little studied. Some support G. donosobarrosi as a subspecies (G. c. donosobarrosi), there is research to indicate that it may qualify as a separate species while G. petersi may just be a variant of G. chilensis, the variances being clinal variations in adjacent populations.
- Rhodin 2012, p. 000.276
- "Chaco tortoise videos, photos and facts - Chelonoidis chilensis". ARKive. Retrieved April 29, 2015.
- Melissa Kaplan. "Chaco Tortoises". Retrieved April 29, 2015.
- Rhodin, Anders G.J.; van Dijk, Peter Paul; Inverson, John B.; Shaffer, H. Bradley; Roger, Bour (2012-12-31). "Turtles of the world, 2012 update: Annotated checklist of taxonomy, synonymy, distribution and conservation status". Chelonian Research Monographs 5: 000.xx. doi:10.3854/crm.5.000.checklist.v5.2012. Archived from the original (PDF) on 2013-01-04.