It is a spaniel type dog that is closely related to the English Cocker Spaniel; the two breeds diverged during the 20th century due to differing breed standards in America and the UK.
They were eventually successful; a litter produced in 1981 provided the foundation stock of the breed.
It is important to note that many modern American Bulldogs are a combination of the two types usually termed "hybrid." In general, American Bulldogs weigh between 27 to 54 kg (60 to 120 lb) and are 52 to 70 cm (20 to 28 in) at the withers, but have been known to greatly exceed these dimensions, especially in the "out of standard," nonworking stock.
This comes from poorly functioning blood platelets and can result in excessive bleeding from minor bumps or cuts.