The main chinchilla species Chinchilla lanigera and Chinchilla brevicaudata are related to the viscachas. The large Plains Viscacha Lagostomus maximus does not bear much similarity to the main chinchilla species, while the smaller Mountain Viscacha Lagidium viscacia is similar to the main chinchilla species except for the elongated ears which make it more rabbit-like in appearance.
Mountain Viscachas have much in common with chinchillas, sharing similar habitat, diet, feeding methods and social structure. The main difference being that while chinchillas are nocturnal, Mountain Viscachas are active during the day.
The Plains Viscacha is nocturnal, feeding from dusk onwards through the night. It inhabits the steppe or grassland regions at lower altitude where it digs complex burrows and grazes on grassland vegetation.