Bone question!

Bone question! Here are some domestic sheep skulls I found. Possibly Rambouillet breed. I recently saw some Bighorn sheep skulls and there was much more fusion between the bones in the skull. The nasal bones were completely fused to the maxilla, like you can see in the photo here. (I’ll get some of the ones here in Badlands NP in a day or two.) Why are they more fused in the bighorn than the domestic sheep? Possible reasons: 1. Different animals, different phenotypes. 2. The skulls selected for.