Thanks Frank.
I think my revised model is simplified a great deal now, but perhaps I can go further. The hippo does seem a tad simplified to me, but maybe some of the nuances are better handed with bump detail. I'm talking the nostrils, ears, and lips. I think I count 12 splines from the neck to the snout on the hippo, and about 9 from the lower jaw to the top of the head. By contrast, my desmostylus has about 20 and 14.
The desmostlyus is related to elephants and sea cows, but they may have lived more like a walrus. There are four genera in the order. The other main one I guess is paleoparadoxia. I am not a scientist so I'm no expert!
Your help has been invaluable.