The common Chaco tortoise, is mainly found in Argentina, but also in Bolivia and Paraguay, mainly within the Chaco and Monte ecoregions. Its distribution is mainly limited by temperature-related variables, and precipitation in the reproductive period.
The scientific name for this species, Chelonoidis 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 rings 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.
There is only one recognized species. However, some researchers believe C. chilensis should be divided into three species: C. chilensis, C. petersi, and C. donosobarrosi. Some support C. donosobarrosi as a subspecies (C. c. donosobarrosi). There is research to indicate that it may qualify as a separate species, while C. petersi may just be a variant of C. chilensis, the variances being clinal variations in adjacent populations. However, these taxa mentioned have all been formally synonymised and accepted. The morphological variation is explainable as a factor of elevation. Historically, these have been viewed as separate taxa, with little work done to confirm or deny it. Subsequent molecular analysis has found little to no genetic variation.
- Chelonoidis chilensis at the Reptarium.cz Reptile Database. Accessed 6 June 2015.
- Ruete, A.; Leynaud, G.C. (2015). "Identification of limiting climatic and geographical variables for the distribution of the tortoise Chelonoidis chilensis (Testudinidae): a baseline for conservation actions". PeerJ. 3: e1298. doi:10.7717/peerj.1298. PMC . PMID 26557430.
- Fritz, Uwe; et al. (2012). "Northern genetic richness and southern purity, but just one species in the Chelonoidis chilensis complex". Zoologica Scripta. 41 (3): 220–232. doi:10.1111/j.1463-6409.2012.00533.x.
- Melissa Kaplan. "Chaco Tortoises". Retrieved April 29, 2015.
- Fritz, U.; Alcalde, L.; Ramírez-Vargas, M.; Goode, E.V.; Fabius-Turoblin, D.U.; Praschag, P. (2012a). "Northern genetic richness and southern purity, but just one species in the Chelonoidis chilensis complex". Zoologica Scripta. 41: 220–232. doi:10.1111/j.1463-6409.2012.00533.x.
- Rhodin, Anders G.J.; van Dijk, Peter Paul; Inverson, John B.; Shaffer, H. Bradley; Roger, Bour (2012). "Turtles of the world, 2012 update: Annotated checklist of taxonomy, synonymy, distribution and conservation status". Chelonian Research Monographs. 5. doi:10.3854/crm.5.000.checklist.v5.2012.
- Turtle Taxonomy Working Group (van Dijk PP, Iverson JB, Rhodin AGJ, Shaffer HB, Bour R). 2014. Turtles of the world, 7th edition: annotated checklist of taxonomy, synonymy, distribution with maps, and conservation status.
- 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" (PDF). Chelonian Research Monographs. 5: 000.xx. doi:10.3854/crm.5.000.checklist.v5.2012. Archived from the original (PDF) on 2013-01-04.