Captive-raised tortoises may develop pyramidal-shaped plates in their carapaces (shells). This has been termed "pyramidal growth syndrome," or PGS. With very few exceptions (tortoises of the species Geochelone elegans and Psammobates sp., for example), this conical growth pattern is considered to be abnormal. This very common defect is believed to be an important indicator of the quality of the captive tortoise diet and management.
Several dietary factors may play important roles in pyramiding. These include:
Excessive protein: The normal diets of wild tortoises tend to be much lower in protein than what is often fed to captive tortoises. Diets high in protein are associated with pyramiding
Excessive food: Not only does excess protein appear to contribute to pyramiding, but simply feeding too much also may contribute to the condition by promoting too rapid growth.
Low calcium: Diets low in calcium or that have calcium that is not readily absorbed have been associated with pyramiding. Tortoises fed diets low in Vitamin D or who do not have access to UVB light also appear at higher risk of developing pyramiding.
Low fiber: Again, when we look at the normal diets of wild tortoises, the diets are very high in fiber. We need to duplicate those diets in pet tortoises by including plenty of grasses and grass hay in the diet.
In addition to diet, it has been suggested that insufficient exercise can also contribute to pyramiding. Humidity may also play a role, with lower humidity being associated with pyramidal growth. It has also been suggested that tortoises supplied insufficient water may be more prone to pyramiding.
It is clear that pyramidal growth syndrome is preventable through proper diet and management. Research the needs of your tortoise to be sure you are providing the appropriate nutrition and environment to keep him healthy and active.