Macraucheniidae is a family in the Litopterna order of extinct South American ungulates. The recessed nasal bones of their skulls suggest that they may have had a small proboscis, or trunk. Their hooves were similar to those of rhinoceroses today, with a simple ankle joint and three digits on each foot. Thus, they may have been capable of rapid directional change when running away from predators, such as large Phorusrhacid terror birds and Smilodon saber-toothed cats. Macraucheniids probably lived in large herds to gain protection against these predators, as well as to facilitate finding mates for reproduction.