During the late Miocene and Pliocene, the sloth genus Thalassocnus of the west coast of South America became adapted to a shallow-water marine lifestyle.

[8][9][10] However, the family placement of Thalassocnus has been disputed; while long considered a nothrotheriid, one 2017 analysis moves it to Megatheriidae,[1] while another retains it in a basal position within Nothrotheriidae.

[12] The last ground sloths in North America belonging to Nothrotheriidae, the Shasta ground sloth (Nothrotheriops shastensis), died so recently that their dried subfossilized dung has remained undisturbed in some caves – such as the Rampart Cave, located on the Arizona side of the Lake Mead National Recreation Area – as if it were just recently deposited.

A Shasta ground sloth skeleton, found in a lava tube at Aden Crater in New Mexico, still had skin and hair preserved, and is now at the Yale Peabody Museum.

[14] Pseudoglyptodon Bradypus Nematherium Analcitherium Neonematherium Sibyllotherium Proscelidodon Catonyx Scelidotherium Valgipes Pseudoprepotherium Brievabradys Octodontotherium Paroctodontotherium Octomylodon Urumacotherium Baraguatherium Octodontobradys Mylodon Thinobadistes Lestodon Lestobradys Bolivartherium Simomylodon Pleurolestodon Glossotherium Paramylodon Schismotherium Pelecyodon Hapalops Hyperleptus Eucholoeops Pseudortotherium Megalonychotherium Pliometanastes Megalonyx Australonyx Megistonyx Ahytherium Pliomorphus Megalocnus Parocnus Acratocnus Neocnus Choloepus Analcimorphus Thalassocnus Lakukullus Mionothropus Nothrotherium Nothrotheriops Pronothrotherium Aymaratherium Xyophorus Prepoplanops Planops Prepotherium Diabolotherium Megathericulus Anisodontherium Pyramiodontherium Proeremotherium Eremotherium Megatherium