Marine sloth. Illustration and photo-reconstruction of the South American water sloth Thalassocnus diving in search of seaweed. Thalassocnus is an extinct genus of apparently semiaquatic or fully aquatic marine sloth from the Miocene and Pliocene of South America. Fossils found to date have been from the coast of Peru and Chile. They were apparently grazers of sea grass and seaweed. The various species of this genus provide the best-documented case of gradual adaptation to a secondarily aquatic lifestyle. They may have used their powerful claws to anchor themselves to the sea floor to facilitate feeding, similar to the behaviour of the marine iguana.