Fig 26. Fluke vertebral length as a proportion of total vertebral column length in cetaceans.

Modern species are shown in blue (21 species, N = 36 individuals). Fluke proportions are regressed on their denominators, showing that fluke proportions are independent of vertebral column length. Dorudon atrox has a fluke proportion of 0.041 (4.1%), and Basilosaurus isis has a fluke proportion of 0.031 (3.1%). Both are significantly smaller than the fluke proportion for any modern cetacean. Thus it is questionable whether Dorudon and Basilosaurus were tail-powered swimmers. A small fluke on a relatively long body may have served, initially, as a caudal stabilizer.