Really the only way to believably render Coryphodons is to look closely at similar animals of today.  Their anatomical contemporaries/analogues give some suggestion, but compared to a hippopotamus, for example, their skeleton and (therefore) distribution of muscle mass are quite different.  They aren’t even closely related to hippos or any living mammal.  The legs on a Coryphodon are relatively longer, but they have a much shorter foot than a hippo.  And of course their skulls are quite different in where features like eyes and brain lie.  Here are some of my layers of tracing paper anatomical reference sketches that I will digitally paint overtop, and adjust as I go…