Paleontological classifications previously used Hydrochoeridae for all capybaras, while using Hydrochoerinae for the living genus and its closest fossil relatives, such as "Neochoerus", but more recently have adopted the classification of Hydrochoerinae within Caviidae. The taxonomy of fossil hydrochoerines is also in a state of flux. In recent years, the diversity of fossil hydrochoerines has been substantially reduced. This is largely due to the recognition that capybara molar teeth show strong variation in shape over the life of an individual. In one instance, material once referred to four genera and seven species on the basis of differences in molar shape is now thought to represent differently aged individuals of a single species, "Cardiatherium paranense".