 This genus's lineage dates back to the Miocene.The ancestors of "Nothrotheriops" migrated to North America from South America as part of the Great American Interchange during the Blancan, about 2.6 MYA.Although "N. shastensis" was one of the smallest ground sloth species, it still reached from snout to tail tip and weighed  (one-quarter of a tonne) - much smaller than some of its contemporary species such as the "Eremotherium", which could easily weigh over two tonnes and be long.