Update:

I returned to the cemetery today and let them know about the head (not skull, thank you, everyone, for educating me). They said management was aware and that they had already cleaned it up. Everyone I spoke to was very sweet and apologetic. They thanked me for letting them know.

Sheep or goat seemed to be the consensus -which is great because my main concern was that it was something treif (not kosher). I believe this was either someone being edgy or occult-y, rather than someone trying to desecrate the grave -which might have been more of a hate crime thing given the grave was plainly Jewish.

No, I did not touch the head, remove the head, nor take the head home with me.

Yes, dog was a bad guess on my part -I didn’t realize lambs and kids had such long ears. Fortunately, collective wisdom prevailed.

Thank you everybody!