Journal of Mammalian Evolution

, Volume 7, Issue 2, pp 81–94

Endocranial Volume of Mid-Late Eocene Archaeocetes (Order: Cetacea) Revealed by Computed Tomography: Implications for Cetacean Brain Evolution


  • Lori Marino
    • Neuroscience and Behavioral Biology Program, Psychology BuildingEmory University
  • Mark D. Uhen
    • Department of Paleontology and ZoologyCranbrook Institute of Science
  • Bruno Frohlich
    • Department of AnthropologySmithsonian Institution
  • John Matthew Aldag
    • Neuroscience and Behavioral Biology Program, Psychology BuildingEmory University
  • Caroline Blane
    • Department of RadiologyUniversity of Michigan
  • David Bohaska
    • Department of PaleobiologySmithsonian Institution
  • Frank C. WhitmoreJr.
    • U.S. Geological Survey and Department of PaleobiologySmithsonian Institution

DOI: 10.1023/A:1009417831601

Cite this article as:
Marino, L., Uhen, M.D., Frohlich, B. et al. Journal of Mammalian Evolution (2000) 7: 81. doi:10.1023/A:1009417831601


The large brain of modern cetaceans has engendered much hypothesizing about both the intelligence of cetaceans (dolphins, whales, and porpoises) and the factors related to the evolution of such large brains. Despite much interest in cetacean brain evolution, until recently there have been few estimates of brain mass and/or brain–body weight ratios in fossil cetaceans. In the present study, computed tomography (CT) was used to visualize and estimate endocranial volume, as well as to calculate level of encephalization, for two fully aquatic mid-late Eocene archaeocete species, Dorudon atrox and Zygorhiza kochii. The specific objective was to address more accurately and more conclusively the question of whether relative brain size in fully aquatic archaeocetes was greater than that of their hypothesized sister taxon Mesonychia. The findings suggest that there was no increase in encephalization between Mesonychia and these archaeocete species.

archaeoceteendocranial volumeencephalizationcomputed tomographyCetacea

Copyright information

© Plenum Publishing Corporation 2000