While both breeds are considered molosser-type dogs, they have different origins and lineage.
* American Bulldogs are descendants of Old English Bulldogs brought to the United States in the 18th century. They were originally bred for bull-baiting and farm work.
* Bullmastiffs were developed in the 19th century in England by crossing Bulldogs with Mastiffs. They were bred for guarding and protecting property.
They share a common ancestor in the Old English Bulldog, but they have been selectively bred for different purposes, leading to significant differences in appearance, temperament, and characteristics.