Biogeographical distributional patterns of cetaceans reflect dispersal events and colonization of the oceans from their ancestral area in the ancient Sea of Tethys ~53 Ma. Likewise, they shows several vicariance events throughout the evolutionary history of this group. However, our understanding of how these processes took place and what biogeographical scenarios occurred among the different groups of cetaceans through time, is limited. Consequently, this work focuses on explaining the distributional patterns of the well-known North Pacific toothed mysticetes, Aetiocetidae, through the power of retrodiction offered by track analysis (panbiogeography) and cladistic biogeography, using the approach of evolutionary biogeography. Our results show that the distributional patterns of Aetiocetidae explain their endemism in the North Pacific, as well as indicate that their hypothetical ancestor probably colonized the Pacific from the Atlantic Ocean by a dispersal event (founder effect) via the Central American Seaway. Furthermore, their biogeographic history shows the adaptive radiation (cladogenesis) of Aetiocetidae as result of peripatric speciation followed by sympatric speciation within a heterogeneous environment. Finally, the biogeographic framework of Aetiocetidae further supports the relevant role that the Pacific Ocean has played in the evolution of Oligocene cetaceans as a geographic area that promoted endemism, dispersal, and colonization. While at more local scales, environmental conditions further promoted increased diversity and disparity amongst Mysticeti.