I 3d-printed some skull-replicas of 3 sirenia genera: West Indian Manatee (Trichechus manatus) Padific Dugong (Dugong dugon) and Steller's Sea-cow (Hydrodamalis gigas). I was really amazed about the fact that, despite the immense disparity in body-size between the extinct sea-cow and its extant relatives, their heads/crania were remarkably similar to each other in overall dimensions.
The sea-cow skull was larger, but not by as much as one would think.