Something crossed with a jack russel, lol. The head looks identical to my parents JR.
How about my bigger girl Dairy, she is about 5 and I just got her 6 months ago [given to me as a boxer] but I think she has some american bull, or at least something in her.
The reason I say american bull is because when she gets playful she has this big grin and looks exactly like an american bull. [of course I dont have a pic of her excited, but here's a couple.