Fig 9. Internal architecture distinguishing the elongated lumbar vertebrae of Pachycetinae and Basilosaurinae.

A, diagrammatic midsagittal section of the pachycetine Antaecetus aithai showing anterior and posterior cones of cancellous bone surrounded by dense cortical bone. B, diagrammatic midsagittal section of the basilosaurine Eocetus schweinfurthi showing anterior and posterior cylinders of cancellous bone surrounded by dense cortical bone. The proportion of dense cortical bone is much greater in pachycetines than it is in basilosaurines. Drawings are based on midsagittal sections of broken vertebrae observed in the field.