There are three North American species of Sphenocoeuls: S. uintensis, S. intermedius, and S. hyognathus. S. uintensis is the most primitive, S. hyognathus is the most advanced, and S. intermedius is in the middle. This skull is of S. uintensis. Found by my friend Garrett, it was in some very soft (poorly cemented) sandstone matrix. So I was able to finish it in three days, hence so few progress photos.
As you can see, a lot of the teeth are missing. It was a fairly old individual because the wear on the remaining molars is very extensive. Here are the sagittal (top) and right side views of the same skull. When you compare it to the two S. intermedius skulls I prepared earlier this year (1 and 2), you can see that while those ones have more teeth, this one has more of the entire skull.