Cerro Ballena is a fossiliferous locality of the Bahía Inglesa Formation, located in the Atacama Desert along the Pan-American Highway a few kilometers north of the port of Caldera, Chile. It has been dated back to the Late Miocene epoch, during the Neogene period. The locality was first noted in 1965 during military work and fully excavated and studied between 2011 and 2012, and is protected by law since the latter year.

Thalassocnus is an extinct genus of semiaquatic ground sloths from the Miocene and Pliocene of the Pacific South American coast. It is monotypic within the subfamily Thalassocninae. The five species—T. antiquus, T. natans, T. littoralis, T. carolomartini, and T. yuacensis—represent a chronospecies, a population gradually adapting to marine life in one direct lineage. They are the only known aquatic sloths, but they may have also been adapted to a terrestrial lifestyle. They have been found in the Pisco Formation of Peru, the Tafna Formation of Argentina, and the Bahía Inglesa, Coquimbo, and Horcón formations of Chile. Thalassocninae has been placed in both the families Megatheriidae and Nothrotheriidae.