All chinchillas currently being bred in domestic populations are long-tailed chinchillas, including our own herd. Animals that have visibly shorter tails than other chinchillas may have had an injury, birth defect, or may just have a smaller bone structure. This does not mean they can be classified as a "short-tailed" chinchilla as they are not genetically related to this species. Just like people, all animals are unique and can be born in all different sizes with different features. Originally, there were two species of chinchillas. One was the Chinchilla brevicaudata and the other was Chinchilla chinchilla/Chinchilla lanigera. Short-tailed chinchillas typically refer to the Chinchilla brevicaudata as there were less caudal bones than Chinchilla lanigera, leading to a shorter tail. Currently, there are no Chinchilla brevicaudata animals in our domestic chinchilla populations.
Chinchilla lanigera typically have a five inch bushy tail, are around 12-14 inches in length and can vary in weight depending on breeding quality. These animals have a gestation period of around 111 days, while the brevicaudata animals produce young around 128 days. Brevi animals had longer fur, giving them a larger appearance with deeper set eyes due to the furs depth. These animals were blockier with shorter extremities and denser fur, however their clarity of color was lacking. Attempts were made to introduce the brevi into lanigera populations to improve the brevi color while simultaneously giving size to the lanigera. However, these were not successful. Some animals with smaller size and thinner fur were classified as the Costina. These animals typically had a more "rat-like" appearance. These were sometimes crossed with the lanigera to attempt to fix their coarse, woolly fur.