Simplified phylogeny of cetaceans discussed here with evolutionary events indicated. Distribution pattern of the glomeruli on the coronal section of OB of a modern mysticete (modified from Thewissen et al. ; D, dorsal; M, medial; V, ventral; L, lateral) , and evolutionary changes of the speculated shapes of the coronal section of OB, are also shown. Our findings indicate that profound changes on olfactory systems occurred just before the modern whales-remingtonocetids split. Remingtonocetus are suggested to have been ambush predators that were one of the earliest whales living in seawater . They had well-established capabilities of underwater hearing, but their ecology remains largely elusive.